MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Cardiovascular Engineering' source. Sun, 20 Feb 2011 16:25:02 +0100 http://www.springerlink.com/content/f1502k1150qh6351/ Abstract  The aim of this study is to describe a robust unified framework for segmentation of the phonocardiogram (PCG) signal sounds based on the false-alarm probability (FAP) bounded segmentation of a properly calculated detection measure. To this end, first the original PCG signal is appropriately pre-processed and then, a fixed sample size sliding window is moved on the pre-processed signal. In each slid, the area under the excerpted segment is multiplied by its curve-length to generate the Area Curve Length (ACL) metric to be used as the segmentation decision statistic (DS). Afterwards, histogram parameters of the nonlinearly enhanced DS metric are used for regulation of the α-level Neyman-Pearson classifier for FAP-bounded delineation of the PCG events. The proposed ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4289148 Wed, 22 Dec 2010 20:19:32 +0100 4289148 http://www.springerlink.com/content/xx666509452j57n4/ Content Type Journal ArticleDOI 10.1007/s10558-010-9115-yAuthors John K-J. Li, Cardiovascular Engineering Lab, Department of Biomedical Engineering, Rutgers University, 599 Taylor Rd, Piscataway, NJ 08854, USA Journal Cardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4272823 Fri, 17 Dec 2010 17:40:51 +0100 4272823 http://www.springerlink.com/content/281362653383976p/ Content Type Journal ArticleDOI 10.1007/s10558-010-9114-z Journal Cardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4272824 Fri, 17 Dec 2010 06:52:44 +0100 4272824 http://www.springerlink.com/content/876487201q005922/ Abstract  A clinical comparison, of two methods of afterload assessment, has been made. The first method, systemic vascular resistance index (SVR i ), is based upon the traditional formula for afterload which utilizes central venous pressure (CVP), as well as cardiac index (C i ), and mean arterial blood pressure (MAP). The second method, total systemic vascular resistance index (TSVR i ), also uses MAP and C i . However, TSVR i ignores the contribution of CVP. This preliminary examination, of 10 randomly-selected ICU patients, has shown a high degree of correlation (ranging from 90 to 100%) between SVR i and TSVR i (P < 0.0001). Furthermore, there was also a high degree of correlation (ranging from 94 to 100%) noted between the hour-to-hour cha... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4272825 Thu, 16 Dec 2010 18:26:19 +0100 4272825 http://www.springerlink.com/content/pv74884674044031/ Abstract  Several works have separated the pressure waveform p in systemic arteries into reservoir p r and excess p exc components, p = p r  + p exc , to improve pulse wave analysis, using windkessel models to calculate the reservoir pressure. However, the mechanics underlying this separation and the physical meaning of p r and p exc have not yet been established. They are studied here using the time-domain, inviscid and linear one-dimensional (1-D) equations of blood flow in elastic vessels. Solution of these equations in a distributed model of the 55 larger human arteries shows that p r calculated using a two-element windkessel model is space-independent and well approximated by the compliance-weighted space-average pressure o... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4272827 Thu, 16 Dec 2010 18:26:18 +0100 4272827 http://www.springerlink.com/content/y0m840247v8q044t/ Abstract  The brain is most sensitively dependent on oxygen to maintain its normal function. Methods to assess the degree of its oxygenation have generally been invasive and indirect. Rapid assessment of brain oxygenation is particularly vital during cerebrospinal ischemia and hypoxia. We have developed a noninvasive electro-optical method using pulsed near-infrared (NIR) light to quantify brain oxygenation during ischemia and hypoxia in anesthetized rabbits. Cerebral ischemia was induced through 30–40 s of bi-lateral carotid artery occlusion. Cerebral hypoxia was induced by varying inspired oxygen levels. The NIR light response to the interventions was expressed in terms of relative absorption (RA). Results showed that our pulsed NIR system could rapidly detect sudde... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4272826 Thu, 16 Dec 2010 18:26:18 +0100 4272826 http://www.springerlink.com/content/r4r5414753003607/ Abstract  Similar pulse pressure increases and flow reductions have been reported by many investigators, despite dissimilar forms of arterial loading applied. Increased vascular load is most commonly observed due to mechanical and vasoactive interventions. The present study intended to differentiate the hemodynamic contributions of these two forms of arterial loading at closely matched blood pressure levels. To accomplish this, proximal aortic characteristic impedance (Z o ), total arterial compliance (C), peripheral vascular resistance (R s ) and time-domain resolved forward (P f ) and reflected (P r ) waves were obtained in six anesthetized, thoracotomized and ventilated dogs. Acute loading was accomplished by brief descending thoracic aorta (DTA) occlusion ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4253791 Thu, 09 Dec 2010 17:52:41 +0100 4253791 http://www.springerlink.com/content/v052233gh9078614/ Abstract  T-wave abnormalities are gaining significance in the realm of electrocardiogram diagnostics. In particular, T-wave alternans are proving to be powerful predictive indicators of potentially fatal arrhythmias. T-wave morphology monitoring and analysis are the means by which alternans and other abnormalities are detected. We have presented a preliminary design of an analog T-wave monitor to provide a characteristic description of the beat-to-beat T-wave morphology in terms of its maximum leading edge and trailing edge slopes, and its area. Experimental results showed that data from the analog T-wave monitor compared well with those predicted theoretically. Current design of the T-wave monitor, once improved, can find use in the screening, diagnosis, and early detecti... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4246326 Tue, 07 Dec 2010 13:47:26 +0100 4246326 http://www.springerlink.com/content/96517218805p1172/ The objective of this study was therefore to determine timing of onset of mechanical systole and diastole in reference to the QRS-T Complex. One hundred and twenty-three adult echocardiographic studies were assessed for the point of mitral and aortic valve closure in relation to the QRS complex and T wave in a representative population. We found that onset of mechanical systole occurred on and usually shortly after the peak of a first dominant QRS complex deflection, and onset of diastole occurred at the earliest on and most commonly beyond the peak or midpoint of the T wave. A DTV should ideally be able to stop vibrating on or before the peak of the first dominant deflection of a QRS complex, and begin vibrating near the peak of the T wave. Given early detection of ventricular depol... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4214923 Sat, 27 Nov 2010 17:04:04 +0100 4214923 http://www.springerlink.com/content/vu6327270n23022g/ Abstract  Current density threshold and liminal area are subthreshold parameters of the cardiac tissue that indicate its susceptibility to external and internal stimulations. Extensive experimental and theoretical research has been conducted to quantify these two parameters in normal conditions for both animal and human models. Here we employed a 2D numerical model of human cardiac tissue to assess these subthreshold parameters under the pathological conditions of heart failure and fibrosis. Stimuli were applied over an area ranging from 0.04 to 1 mm2 using various pulse durations. The current density threshold decreased with increasing stimulation area or pulse duration. No significant changes were found in both parameters between control conditions and heart failure i... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4179923 Tue, 16 Nov 2010 19:28:24 +0100 4179923 http://www.springerlink.com/content/c05u4683377p3263/ In this study we discuss some relations that connect ejection fraction EF to the parameters describing the end-systolic pressure–volume relation (ESPVR). It is shown that the study of the relation between EF and ESPVR can give some understanding of the problem of HFpEF. An important feature of the present approach is the introduction of the active force of the myocardium (also called isovolumic pressure) in the formalism describing the ESPVR. Content Type Journal ArticleDOI 10.1007/s10558-010-9105-0Authors Rachad M. Shoucri, Department of Mathematics & Computer Science, Royal Military College of Canada, Kingston, ON K7K 7B4, Canada Journal Cardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=4179924 Tue, 16 Nov 2010 19:28:12 +0100 4179924 http://www.springerlink.com/content/h1662w7023020462/ Abstract  The aim of this study is to develop and describe a new ambulatory holter electrocardiogram (ECG) events detection-delineation algorithm with the major focus on the bounded false-alarm probability (FAP) segmentation of an information-optimized decision statistic. After implementation of appropriate preprocessing methods to the discrete wavelet transform (DWT) of the original ECG data, a uniform length sliding window is applied to the obtained signal and in each slid, six feature vectors namely as summation of the nonlinearly amplified Hilbert transform, summation of absolute first order differentiation, summation of absolute second order differentiation, curve length, area and variance of the excerpted segment are calculated to construct a newly proposed principal ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3947850 Wed, 08 Sep 2010 05:21:19 +0100 3947850 http://www.springerlink.com/content/g32849306645124m/ Abstract  Quantitative evaluation of cardiac function from cardiac magnetic resonance (CMR) images requires the identification of the myocardial walls. This generally requires the clinician to view the image and interactively trace the contours. Especially, detection of myocardial walls of left ventricle is a difficult task in CMR images that are obtained from subjects having serious diseases. An approach to automated outlining the left ventricular contour is proposed. In order to segment the left ventricle, in this paper, a combination of two approaches is suggested. Difference of Gaussian weighting function (DoG) is newly introduced in random walk approach for blood pool (inner contour) extraction. The myocardial wall (outer contour) is segmented out by a modified active ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3930078 Thu, 02 Sep 2010 06:59:34 +0100 3930078 http://www.springerlink.com/content/g078795401077083/ Abstract  Analysis of digital volume pulse (DVP) signal measured by photoplethysmograph (PPG) technique is a low cost non-invasive method of obtaining vital information related to arterial conditions. In this paper, we present a new two-pulse synthesis (TPS) model for deriving arterial parameters, useful for noninvasive assessment of human vascular health. The model is based on the use of Rayleigh function. Relevance of the proposed model is established by applying it on a sample set of 113 PPG signals, obtained form healthy and treated hypertensive subjects. The TPS model compares well with the conventional methods in determining parameters such as pulse transit time or foot-to-foot delay (D), reflection index (RI), stiffness index (SI) and pulse wave velocity (PWV). A new... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3897104 Mon, 23 Aug 2010 17:59:24 +0100 3897104 http://www.springerlink.com/content/l670659525566515/ Abstract  In this paper, we present design, fabrication and coupled multifield analysis of hollow out-of-plane silicon microneedles with piezoelectrically actuated microfluidic device for transdermal drug delivery (TDD) system for treatment of cardiovascular or hemodynamic disorders such as hypertension. The mask layout design and fabrication process of silicon microneedles and reservoir involving deep reactive ion etching (DRIE) is first presented. This is followed by actual fabrication of silicon hollow microneedles by a series of combined isotropic and anisotropic etching processes using inductively coupled plasma (ICP) etching technology. Then coupled multifield analysis of a MEMS based piezoelectrically actuated device with integrated silicon microneedles is presented.... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3889792 Fri, 20 Aug 2010 17:02:51 +0100 3889792 http://www.springerlink.com/content/v014l31333462p21/ Abstract  Our objective was to design, develop, characterize and validate a prototype device for testing the response of aortic valve tissue to impact forces. With each cardiac cycle, the aortic valve, on closure, is subjected to a substantial impact force and the ability of valvular interstitial cells to withstand such forces without apoptosis has not been examined. Our aim was to correlate impact force with apoptosis, identifying the latter using a terminal transferase dUTP nick end-labelling (Tunel) assay. With our drop tower design, we created reproducible impact forces on heart valve tissue resulting in cellular trauma. The reliability of the impact tester design were verified and results showed that normal tissue can withstand impact forces more than 30× greater than... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3889791 Fri, 20 Aug 2010 17:02:51 +0100 3889791 http://www.springerlink.com/content/14333168328v3126/ In this study, stent stiffness was determined from the force-area reduction curves. Comparing similar stents of various diameters revealed that smaller diameter stent had greater radial force and stiffness than larger diameter stents. Comparing similar stents of various lengths revealed that stents with longer lengths (and greater number of wires) has greater force and stiffness. Overlapping two stents increased the force and stiffness to values greater than the sum of those parameters for the individual stents. These data may have important clinical implications for understanding the effect of oversized and overlapped stents on vessel mechanics. Content Type Journal ArticleDOI 10.1007/s10558-010-9097-9Authors Clifton R. Johnston, Department of Mechanical and Manufacturing Engi... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3878091 Tue, 17 Aug 2010 17:21:18 +0100 3878091 http://www.springerlink.com/content/h425770032316403/ Abstract  Evaluation of the time-varying parameters (Compliance, Resistance, and Inertance) that describe the right and left ventricles has been of interest for some years. Analyses usually involve a particular assertion regarding energy contributions or of the nature of the parameters themselves. It is of interest to engage the issue with a more general approach by restricting prior assumptions only to that raw data measurement may be noisy and that the parameters are non negative. Here a polynomial in time model is utilized to develop each parameter. Coefficients of the polynomials are estimated from the observed data with use of the maximum likelihood method and stochastic calculus. The pump equation was finally evaluated in full from un-processed pressure and flow data ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3873807 Sat, 14 Aug 2010 16:45:38 +0100 3873807 http://www.springerlink.com/content/y927g07j42486534/ Abstract  Venous obstruction is a major complication of transvenous pacemaker placement. Despite the increasing use of pacemakers and implantable cardiac defibrillators, a lack of understanding remains with regard to risk factors for the development of device-associated venous obstruction. We hypothesize that computational fluid dynamics simulations can reveal prothrombogenic locations and define thrombosis risk based on patient-specific anatomies. Using anatomic data derived from computed tomography, computer models of the superior vena cava, subclavian, innominate, and internal jugular veins were constructed for three adult patients with transvenous pacemakers. These models were used to perform patient-specific simulations examining blood flow velocity, wall shear stress,... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3626903 Tue, 01 Jun 2010 06:07:20 +0100 3626903 http://www.springerlink.com/content/mlq56730411470j2/ Abstract  The rate of biosynthesis and turnover of the plasma protein fibrinogen is a marker of metabolic signaling in aging and disease. The rate in the young normal human subject of 0.260 mg/ml/24 h increases to 0.378 in older normal subjects and to 0.466 in age matched coronary thrombosis patients measured by endogenous labeling of fibrinogen with l-glutamic acid-C14. The increased rate of fibrinogen turnover has been traced to generation of fibrin by labeling the polymers with glycine C14 ethyl esters in the presence of activated fibrin stabilizing factor. Circulating fibrin increased 520% above normal in ischemic thrombotic cerebrovascular disease. Long chain saturated free fatty acids (FFA) exercise not only primary control over incorporation of Cl4 labeled a... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3469166 Sat, 10 Apr 2010 07:49:48 +0100 3469166 http://www.springerlink.com/content/25g7648376882615/ The objective of this study is to develop a model of the cardiovascular system capable of simulating the normal operation of the systemic and pulmonary circulation, starts from aorta, and follows by upper and lower extremities vessels, finally ends with pulmonary veins. The model consists of a closed loop lumped elements with 43 compartments representing the cardiovascular system. The model parameters have been extracted from the literature. Using MATLAB software, the mathematical model has been simulated for the cardiovascular system. Each compartment includes a Resistor-Inductor-Capacitor (RLC) segment. The normal cardiovascular operation is characterised by the pressure–volume curves in different parts of the system. Model verification is performed by comparing the simulation re... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3355769 Wed, 10 Mar 2010 15:38:04 +0100 3355769 http://www.springerlink.com/content/9hmg33j5835t8860/ Abstract  Hemodynamic play a very significant role in the pathophysiology of intracranial arteriovenous malformation. The surgical decisions are based on the understanding of the complexities of the flow. Quantification of the abnormal flow is difficult. The mathematical models provide limited information due to the simplicity of the design of these models. Flow of fluid in a tube is very sensitive to small changes in the diameter. We studied the flow characteristics of a fistula by introducing accurately machined acrylic fistulae between the femoral arteries and veins of dogs. The influences of systemic arterial pressure, diameter of the arterial feeders, volume of blood flow, velocity of flow and the diameter of the shunt on the flow of blood across the shunt were studied.... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3355770 Wed, 10 Mar 2010 15:38:03 +0100 3355770 http://www.springerlink.com/content/13651690721v2329/ Abstract  The conventional impedance cardiogram is a record of pulsatile changes in the electrical impedance of the chest with each heartbeat. The signal seems intuitively related to cardiac stroke volume. However doubts persist about the validity of stroke volume measurements based on electrical impedance. This paper presents a new electrical axis for impedance cardiography that is perpendicular to the conventional head-to-foot axis in an anterior-posterior direction. Dual chest and back electrodes are concentric, permitting tetrapolar technique. A relatively simple analytical model is developed, and this model is validated in a three-dimensional finite element model of current flow through the human chest. Three-dimensional simulations show predictable relationships betwe... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3355771 Wed, 10 Mar 2010 15:38:02 +0100 3355771 http://www.springerlink.com/content/b677126353778561/ Abstract  The regulation of valvular endothelial phenotypes by the hemodynamic environments of the human aortic valve is poorly understood. The nodular lesions of calcific aortic stenosis (CAS) develop predominantly beneath the aortic surface of the valve leaflets in the valvular fibrosa layer. However, the mechanisms of this regional localization remain poorly characterized. In this study, we combine numerical simulation with in vitro experimentation to investigate the hypothesis that the previously documented differences between valve endothelial phenotypes are linked to distinct hemodynamic environments characteristic of these individual anatomical locations. A finite-element model of the aortic valve was created, describing the dynamic motion of the valve cusps and bloo... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3223991 Wed, 27 Jan 2010 20:03:37 +0100 3223991 http://www.springerlink.com/content/u1855r2241h05404/ Abstract  Heart failure is a well-known debilitating disease. From clinical point of view, segmentation of left ventricle (LV) is important in a cardiac magnetic resonance (CMR) image. Accurate parameters are desired for better diagnosis. Proper and fast image segmentation of LV is of paramount importance prior to estimation of these parameters. We prefer random walk approach over other existing techniques due to two of its advantages: (1) robustness to noise and, (2) it does not require any special condition to work. Performance of the method solely depends on the selection of initial seed and parameter β. Problems arise while applying this method to different kind of CMR images bearing different ischemia. It is due due to their implicit geometry definitions unlike genera... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3190583 Fri, 15 Jan 2010 18:02:29 +0100 3190583 http://www.springerlink.com/content/8u8v336883r34167/ Absract  The aim of this study is to detect Acute Hypotensive Episodes (AHE) and Mean Arterial Pressure Dropping Regimes (MAPDRs) using ECG signal and Arterial Blood Pressure waveforms. To meet this end, the QRS complexes and end-systolic end-diastolic pulses are first extracted using two innovative Modified Hilbert Transform-Based algorithms namely as ECGMHT and BPMHT. A new smoothing algorithm is next developed based on piecewise polynomial fitting to smooth the fast fluctuations observed in RR-tachogram, systolic blood pressure (SBP) and diastolic blood pressure (DBP) trends. Afterwards, in order to consider the mutual influence of parameters on the evaluation of shock probability, a Sugeno Adaptive Network-based Fuzzy Inference System-ANFIS is trained using Hasdai et al... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3154374 Wed, 06 Jan 2010 18:07:24 +0100 3154374 http://www.springerlink.com/content/10853338p31p7361/ Abstract  The multiscale time irreversibility (MTI) involves the lack of consistency in the properties of a time series if one reverses the reading direction along the time. To analyze the RR time series at rest and during aerobic exercise through the MTI, both in healthy people and cardiac patients. The heartbeat signal was recorded beat to beat for 15 min at rest and 15 min while pedalling on a static bicycle in 10 healthy and active men (age 26.5 ± 3.3 years; height 179.3 ± 6.6 cm; weight 80.4 ± 11.8 kg) and 10 cardiac patients (age 61.1 ± 4.7 years, height 165.3 ± 5.3 cm; weight 86.9 ± 11.1 kg). The MTI was calculated through the asymmetry index (AI), defined as the ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3130700 Tue, 29 Dec 2009 17:59:04 +0100 3130700 http://www.springerlink.com/content/d722m14187lk4751/ Abstract  A new method to predict acute hypotensive episodes (AHE) is proposed in this paper. The AHE is defined as any period of 30 min or more during which at least 90% of mean arterial pressure (MAP) measurements are below 60 mmHg. Since arterial pressure has a direct correlation with heart rate through heart rate (HR) baroreflex and cardiovascular systems, any changes in MAP, directly affect HR and vice versa. Predicting HR using our developed model, the periods in which HR drops to the values less than 40 beat/min are detected. The demonstrated AHE data for twenty patients are picked to validate the proposed algorithm. Results show that the proposed method could truly predict occurrence of the AHE in 17 out of 20 cases analyzed. Results show reliable accuracy... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2896114 Wed, 14 Oct 2009 17:08:39 +0100 2896114 http://www.springerlink.com/content/h4k30982165x5036/ Abstract  The geometry of coronary arteries affects regional atherogenic processes. Accurate images can be assessed using multislice computer tomography (MSCT) to estimate bifurcations angles. We propose a three-dimensional (3D) method to measure true bifurcation angles of coronary arteries and to determine possible correlations between plaque presence and angulations. The left main (LM) coronary artery, left anterior descendent (LAD) and left circumflex artery (LCX) were imaged in 40 atherosclerotic and 35 healthy patients, using 64-rows MSCT. This Y-junction was simplified fitting a 3D cylinder to each vessel to estimate true bifurcation angles and diameters. The method was tested in phantoms and interobserver variability was assessed. Geometrical results were compared be... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2880511 Fri, 09 Oct 2009 06:20:00 +0100 2880511 http://www.springerlink.com/content/72k76r606x032141/ Abstract  To investigate patterns of cardiovascular control, a protocol of head up tilt (HUT) followed by lower body negative pressure (LBNP), which represents a significant cardiovascular control challenge, was employed. Linear regression of beat-to-beat heart rate (HR) and mean blood pressure (MBP) data collected over repeated tests was used to analyze control response during the LBNP phase of the combined HUT + LBNP protocol. Four runs for each of 10 healthy young males reaching presyncope were analyzed. Subjects were classified into 2 groups based on the consistency of MBP regulation in response to central hypovolemia induced by LBNP. The consistent group tended to exhibit consistent HR slope (rate of change of HR over time as calculated by linear regression) ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2877497 Thu, 08 Oct 2009 06:56:42 +0100 2877497 http://www.springerlink.com/content/f9w0w07780221878/ Abstract  Reversible left ventricular failure was produced in conscious dogs by compromise of the coronary circulation. In animals with prior left anterior descending coronary artery occlusion, mean left atrial pressure (LAP) was incorporated into an automatic feedback control system used to inflate a balloon cuff on the circumflex (Cfx) coronary artery. The system could produce stable increases in LAP to 15–20 mm Hg. The dominating system transfer function was the ratio of LAP to balloon volume (BV), which was characterized by a fixed delay (5 s), with LAP/BV = (8e−jωτ )/(0.02 + jω). The system was stabilized by a phase lead network to reduce oscillations of LAP. A total of seven experiments were conducted in three dogs, and testin... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2877496 Thu, 08 Oct 2009 06:56:42 +0100 2877496 http://www.springerlink.com/content/b40582486x474462/ This study examines the effect of a subset of the impedance spectrum, the zeroth and first harmonic impedance moduli (Z 0, Z 1), on RV performance in large animals. An artificial circuit with adjustable resistance and compliance (C) was implanted into the pulmonary circulation of five sheep. Resistance was varied to increase Z 0 in increments of 2 mmHg/(L/min) until Z 0 was 8 mmHg/(L/min) above baseline. At each Z 0, C was adjusted between 0, 0.5 and 2 mL/mmHg or 0, 1, and 5 mL/mmHg. Fourier transforms of the pulmonary artery pressure and flow in each situation were used to calculate the pulmonary impedance. Results show that the percent change in cardiac output (%ΔCO) is linearly related to the change in Z 0 (ΔZ 0). Increases in Z 1 (ΔZ 1) decreased %ΔC... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2848069 Tue, 29 Sep 2009 04:00:39 +0100 2848069 http://www.springerlink.com/content/c58g746280687234/ Abstract  Measuring heart rate variability (HRV) is widely used to assess autonomic nervous system function. It requires accurate measurement of the interval between successive heartbeats. This can be achieved from recording the electrocardiogram (ECG), which is non-invasive and widely available. However, methodological problems inherent in recording and analyzing ECG traces have motivated a search for alternative means of measuring the interval between successive heartbeats. Recording blood oxygenation pulsations (photoplethysmography—PPG) is also convenient, non-invasive and widely available, and has been suggested as an effective alternative to ECG to derive HRV. Moreover, it has been claimed that the pulse waveforms produced by oximetry may be more practicable than R-R... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2767222 Thu, 03 Sep 2009 06:35:03 +0100 2767222 http://www.springerlink.com/content/x6775604423n1057/ The objective of this study is to show that inlet velocity actually depends on the degree of stenosis and thus for severe constriction in coronary artery, a velocity based boundary conditions cannot be realistic. We then prove that regardless of severity of stenosis in coronary arteries, the upstream pressure, systemic pressure, is always constant, thus, should be used as boundary conditions instead. The two sets of boundary conditions are implemented to demonstrate the robustness of each in modeling of stenosed coronary artery in a CFD study. These boundary conditions are applied in a stenosed cylindrical pipe including three categories of symmetrical stenosis (mild, moderate and severe stenosis starting from 15 to 95% diameter reduction) for steady state and pulsatile flow. Results... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2713822 Mon, 17 Aug 2009 18:48:36 +0100 2713822 http://www.springerlink.com/content/56h2452m03064504/ In this study, an analysis of the effects of cuff looseness on mean blood pressure readings was performed. Using a standard adult blood pressure cuff, pressure readings were taken on each arm at a cuff looseness of 0, 2, 4, and 6 cm beyond patient arm circumference. The cuff was then switched to the opposite arm and the procedure repeated. Blood pressure readings taken from the left arm with the cuff at an appropriately snug fit served as the reference. Increasing cuff looseness simulates the possibly incorrect blood pressure cuff placement by health care workers in the clinical setting. Data from 24 subjects support the claims that mean blood pressure increases with respect to increasing cuff looseness. It was shown that measurements taken on left and right arms will result in ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2682996 Fri, 07 Aug 2009 13:21:47 +0100 2682996 http://www.springerlink.com/content/v62g9u1j6w44x63u/ Abstract  Coronary perfusion pressure (CPP) is a major indicator of the effectiveness of cardiopulmonary resuscitation in human and animal research studies, however, methods for calculating CPP differ among research groups. Here we compare the 6 published methods for calculating CPP using the same data set of aortic (Ao) and right atrial (RA) blood pressures. CPP was computed using each of the 6 calculation methods in an anesthetized pig model, instrumented with catheters with Cobe pressure transducers. Aortic and right atrial pressures were recorded continuously during electrically induced ventricular fibrillation and standard AHA CPR. CPP calculated from the same raw data set by the 6 calculation methods ranged from −1 (signifying retrograde blood flow) to 26 mmHg ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2682997 Fri, 07 Aug 2009 13:21:40 +0100 2682997 http://www.springerlink.com/content/5353013316wt1h23/ In conclusion, PTT is a reflection not only of SP but also of cardiac output changes per se and in combination with cardiac output (SP to cardiac output ratio) and should not be used as a pure marker of arterial stiffness under marked exercise cardiovascular and respiratory perturbations. Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-009-9081-4Authors S. N. Kounalakis, University of Athens Department of Sports Medicine & Biology of Exercise, Faculty of Physical Education and Sport Science Athens GreeceN. D. Geladas, University of Athens Department of Sports Medicine & Biology of Exercise, Faculty of Physical Education and Sport Science Athens Greece Journal Cardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Eng... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2679774 Thu, 06 Aug 2009 08:17:20 +0100 2679774 http://www.springerlink.com/content/dwu187k8473280pk/ Abstract  The purpose of the study was to asses the potential use of pulse wave velocity (PWV) and digital volume pulse (DVP) as estimators of systolic (SBP) and diastolic (DPB) blood pressure. Single and multiple correlation studies were conducted, including biometric parameters and risk factors. Brachial-ankle PWV (baPWV) and DVP signals were obtained from a Pulse Trace PWV and Pulse Trace PCA (pulse contour analysis), respectively. The DVP (obtained by photoplethysmography), allowed stiffness (SI) and reflection indexes (RI) to be derived. The first study on 47 healthy volunteers showed that both SBP and DPB correlated significantly both with baPWV and SI. Multiple regression models of the baPWV and the waist-to-hip ratio (WHR) allowed SBP and DBP to be modeled with r&nb... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2679773 Thu, 06 Aug 2009 08:17:20 +0100 2679773 http://www.springerlink.com/content/hw1ll7588q286861/ Abstract  This paper demonstrates quantitatively, using streamlined mathematics, how the transmembrane ionic currents in individual cardiac muscle cells act to produce the body surface potentials of the electrocardiogram (ECG). From fundamental principles of electrostatics, anatomy, and physiology, one can characterize the strength of apparent dipoles along a wavefront of depolarization in a local volume of myocardium. Net transmembrane flow of ionic current in actively depolarizing or repolarizing tissue induces extracellular current flow, which sets up a field of electrical potential that resembles that of a dipole. The local dipole strength depends upon the tissue cross section, the tissue resistivity, the resting membrane potential, the membrane capacitance, the volume ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2487417 Sat, 20 Jun 2009 06:08:25 +0100 2487417 http://www.springerlink.com/content/r364w6u765048147/ Abstract  During untreated ventricular fibrillation (VF), before CPR is applied, different bodily systems deteriorate at different rates. This paper describes the times when the EEG disappears, when respiratory arrest occurs, and when PD-PEA occurs. It also describes the frequency of VF waves over a 7-min period and how the frequency increases with good CPR. Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-009-9076-1Authors L. A. Geddes, Purdue University Weldon School of Biomedical Engineering 206 S. Martin Jischke Drive West Lafayette IN 47907-2032 USAA. Kemeny, Purdue University Basic Medical Sciences West Lafayette IN USAM. Otlewski, Purdue University Basic Medical Sciences West Lafayette IN USAA. E. Lottes, Purdue University Weldon School of Biome... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2487418 Wed, 17 Jun 2009 09:47:47 +0100 2487418 http://www.springerlink.com/content/a6260mn5k8vx1x5k/ Abstract  A frequency domain distributed 55 segment arterial model was constructed from the reflection perspective to predict pressure waveforms in the large systemic arteries. At any node, the predicted pressure waveform was the combination of a forward propagating waveform and a number of repeatedly reflected waveforms from any possible sites. This approach ensured that any single reflected waveform could be traced back to its origin, and thus the causal-effect relation would be precisely known. This model was evaluated in terms of branch reflection coefficient, terminal vascular bed behavior, and wall viscoelasticity. It was found that the model predicted pressure waveforms were most sensitive to the branch reflection coefficient, and this led to the adoption of the zero... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2459392 Thu, 04 Jun 2009 11:23:06 +0100 2459392 http://www.springerlink.com/content/kq6647337166j3xm/ In conclusion, CAR measurements by means of spontaneous oscillations can be obtained stably and the presented parametric approaches can serve for future online application of CAR measurement. Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-009-9072-5Authors Michael Jachan, Freiburg University Center for Data Analysis and Modeling (FDM) Eckerstr. 1/FDM 79104 Freiburg GermanyMatthias Reinhard, University Hospital of Freiburg Department of Neurology Freiburg GermanyLinda Spindeler, Freiburg University Center for Data Analysis and Modeling (FDM) Eckerstr. 1/FDM 79104 Freiburg GermanyAndreas Hetzel, University Hospital of Freiburg Department of Neurology Freiburg GermanyBjörn Schelter, Freiburg University Center for Data Analysis and Modeling (FDM) Eckerstr. 1/FDM 7... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2448864 Thu, 28 May 2009 09:08:04 +0100 2448864 http://www.springerlink.com/content/y45r78pv2742823l/ Abstract  The search for a load-independent index of myocardial contractility has been a focus for nearly 100 years. Nearly all of the parameters developed have yielded insight into cardiac function but their clinical utility has been limited. A new index, dσ*/dt max, has been proposed to be useful in the clinic. This parameter is expressed as the maximum time rate of change of the pressure normalized circumferential wall stress (σ* = σ θ /P, where σ θ is circumferential wall stress and P is pressure) for a thick walled sphere model of the left ventricle (LV). This definition for a contractility index renders dσ*/dt max dependent only on LV wall volume (V m) and maximum time rate of change of the ventricular volume, dV/dt max. The index dσ*/... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2433650 Sun, 24 May 2009 05:58:28 +0100 2433650 http://www.springerlink.com/content/87r328740w76337p/ Abstract  In the present study, we investigated the relationship between blood pressure (BP) and pulse transit time (PTT) and evaluated the accuracy of the PTT-based cuffless BP estimation on 14 normotensive subjects. Least-squares regression was used to estimate BP in the first test and a repeatability test carried out half year later. BP in the repeatability test was also estimated using the regression coefficients in the first test. The results illustrated that in the first and repeatability tests (1) arterial BP increased and PTT decreased acutely after the exercises and (2) systolic BP was highly correlated with PTT. In the repeatability test, the estimation differences from the references were 0.0 ± 5.3 mmHg and 0.0 ± 2.9 mmHg for systolic and diastolic BPs respecti... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2357786 Tue, 21 Apr 2009 11:24:02 +0100 2357786 http://www.springerlink.com/content/r324472u34237083/ Abstract  This examination of brachial artery (BA) differential characteristic impedance, ΔZ c, illustrates that changes in Z c can occur from changes in either BA wall stiffness (Young’s modulus, E) and/or its diameter, D. Furthermore, we assessed how changes in both E and D combine in either an isolated, synergistic, or antagonistic manner to yield the net change in BA Z c. The basis of this analysis is a partial differential equation which approximates ΔZ c as a total differential. The effects on BA ΔZ c of acetylcholine, atenolol, fenoldapine, nitroglycerin, hydrochlorothiazide and other medications are examined using data from previously published studies. Clinical situations which alter BA Z c, such as congestive heart failure, hypertension, and hyperemia, are a... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2332054 Sat, 11 Apr 2009 06:22:56 +0100 2332054 http://www.springerlink.com/content/9m715n688l42050t/ Abstract  Unstable conduction system bifurcations following ischemia and infarction are associated with variations in the electrocardiographic activity spanning the heart beat. In this paper, we investigate a spectral energy measure of morphologic differences (SE-MD) that quantifies aspects of these changes. Our measure uses a dynamic time-warping approach to compute the time-aligned morphology differences between pairs of successive sinus beats in an electrocardiographic signal. While comparing beats, the entire heart beat signal is analyzed in order to capture changes affecting both depolarization and repolarization. We show that variations in electrocardiographic activity associated with death can be distinguished by their spectral characteristics. We developed the SE-MD... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2269782 Fri, 13 Mar 2009 11:51:10 +0100 2269782 http://www.springerlink.com/content/21324m9p3g7p2436/ Abstract  An innovative method was proposed on the basis of vectorcardiography to characterize the location and extent of moderate to large, relatively compact infarcts using ECG evidence. It is assumed that heart vector is proportional to relevant active depolarization area(s). The normal VCG was then used to examine our ideas based on the information of location, amplitude, and direction of heart vector at any instant that is included in it. The model-based comparison of cases under study and relevant normal VCGs gives region and extent of myocardial infarction. Three criteria were finally defined to evaluate the presented method based on Physionet database. EPD, which is the percentage discrepancy between the extent of the infarct as estimated from our proposed method an... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2248694 Thu, 05 Mar 2009 15:03:58 +0100 2248694 http://www.springerlink.com/content/y4365658183r8w5r/ Abstract  We have developed a novel non-invasive device for the measurement of one of the most sensitive indices of myocardial contractility as represented by the rate of increase of intraventricular pressure (left ventricular dP/dt and arterial dP/dt performance index (dP/dtejc). Up till now, these parameters could be obtained only by invasive catheterization methods. The new technique is based on the concept of applying multiple successive occlusive pressures on the brachial artery from peak systole to diastole using a inflatable cuff and plotting the values against time intervals that leads to the reconstruction of the central aortic pressure noninvasively. The following describes the computer simulator developed for providing a mathematical foundation of the new sensor.... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2239108 Wed, 04 Mar 2009 10:50:15 +0100 2239108 http://www.springerlink.com/content/px481444612416n8/ In this study we investigated the effect of alveolar recruitment strategy during cardiopulmonary bypass on postoperative gas exchange and lung function. This prospective randomized study included 32 patients undergoing elective myocardial revascularization with cardiopulmonary bypass. In 16 patients 5 cm H2O of positive end-expiratory pressure was applied after intubation and maintained until extubation (Group I). In the other 16 patients (group II) a positive end expiratory pressure (PEEP) of 5 cm H2O was maintained as well but was increased to 14 cm H2O every 20 min for 2 min during cross clamp. Measurements were taken preoperatively, before skin incision, before and after (3, 24, 48 h) cardiopulmonary bypass and before discharge (6th postoperative day).... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2239109 Wed, 04 Mar 2009 10:50:07 +0100 2239109 http://www.springerlink.com/content/yx164151371jx258/ Abstract  Impedance cardiography (IC) has been used to monitor the pumping function of the heart in terms of stroke volume or cardiac output. We explored the extent to which IC can be used for monitoring transient effects of cardiac alterations on a beat-to-beat basis. A four-spot-electrode configuration was used in the present design. The spatial arrangement of the four electrodes was carefully selected to obtain an optimal result. A constant current source provided a 4 mA, 20 kHz sinusoidal excitation current. Analog signal processing was developed to demodulate and amplify the resultant impedance information, eliminate low frequency motion artifacts and incidental breathing artifacts. Experiments were performed on normal healthy volunteers. Impedance waveforms ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2094451 Thu, 08 Jan 2009 08:54:36 +0100 2094451 http://www.springerlink.com/content/263861l37n5k4371/ Abstract  Connection to a 60-Hz or other voltage source can result in cardiac dysrhythmias, a startle reaction, muscle contractions, and a variety of other physiological responses. Such responses can lead to injury, especially if significant ventricular cardiac dysrhythmias occur, or if a person is working at some height above ground and falls as a result of a musculoskeletal response. Physiological reactions are known to relate to intensity and duration of current exposure. The connection current that flows is a function of the applied voltage at the instant of connection, and the electrical impedance encountered by the voltage source in contact with the skin or other body tissues. In this article we describe a rarely investigated phenomenon, namely a contact, or connectio... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2010599 Tue, 02 Dec 2008 07:28:26 +0100 2010599 http://www.springerlink.com/content/r83678375355552j/ Abstract  A new method is proposed for estimation of nonlinear elastic properties of soft tissues. The proposed approach involves a combination of nonlinear finite element methods with a genetic algorithm for estimating tissue stiffness profile. A multipoint scheme is introduced that satisfies the uniqueness condition, improves the estimation performance, and reduces the sensitivity to image noise. The utility of the proposed techniques is demonstrated using optical coherence tomography (OCT) images. The approach is, however, applicable to other imaging systems and modalities, as well, provided a reliable image registration scheme. The proposed algorithm is applied to realistic (2D) and idealized (3D) arterial plaque models, and proves promising for the estimation of intra-p... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=3093658 Tue, 02 Dec 2008 07:28:25 +0100 3093658 http://www.springerlink.com/content/r83678375355552j/ Abstract  A new method is proposed for estimation of nonlinear elastic properties of soft tissues. The proposed approach involves a combination of nonlinear finite element methods with a genetic algorithm for estimating tissue stiffness profile. A multipoint scheme is introduced that satisfies the uniqueness condition, improves the estimation performance, and reduces the sensitivity to image noise. The utility of the proposed techniques is demonstrated using optical coherence tomography (OCT) images. The approach is, however, applicable to other imaging systems and modalities, as well, provided a reliable image registration scheme. The proposed algorithm is applied to realistic (2D) and idealized (3D) arterial plaque models, and proves promising for the estimation of intra-p... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=2010600 Tue, 02 Dec 2008 07:28:25 +0100 2010600 http://www.springerlink.com/content/0h42556961211512/ The objective is to overcome the limitations of oral therapy such as variable absorption profile and the need for frequent dosing, by fabricating a safe, reliable and cost effective transdermal drug delivery system to dispense various pharmacological agents through the skin for treatment of hemodynamic dysfunction such as hypertension. Moreover, design optimization of a piezoelectrically actuated valveless micropump is presented for the drug delivery system. Because of the complexity in analysis of piezoelectric micropump, which involves structural and fluid field couplings in a complicated geometrical arrangement, finite element (FE) numerical simulation rather than an analytical system has been used. The behavior of the piezoelectric actuator with biocompatible polydimethylsiloxane... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1984353 Sun, 23 Nov 2008 06:55:30 +0100 1984353 http://www.springerlink.com/content/v7m06q069721n844/ Abstract  The esophageal Doppler monitor (EDM) is a clinically useful device for minimally invasive assessment of cardiac output, preload, afterload, and contractility. An empirical model, based upon the logistic function, has been developed. Use of this model illustrates how the EDM could estimate the net effect of aortic and non-aortic contributions to inertia, resistance, and elastance within real time. This is based on an assumed mechanical impedance conceptually resembling that of a series arrangement of a spring, mass, and dashpot. In addition, when used with an invasive radial arterial catheter, the EDM may also estimate aortic pulse wave velocity, as well as aortic characteristic impedance, and characteristic volume. Approximations of left ventricular stroke work an... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1559882 Sat, 28 Jun 2008 08:11:14 +0100 1559882 http://www.springerlink.com/content/w016800286319101/ The objective of this 14-pig study was designed to determine the amount of lung ventilation obtainable by only rhythmic chest compression (100/min, 100 lbs). Tidal volume (TV), dead space (DS), and respiration rate (R) were measured with normal breathing and with rhythmic chest compression during ventricular fibrillation. The ratio of TV/DS was calculated in both cases. For normal breathing the ratio was 2.54 ± 0.68; for chest compression breathing the ratio was 0.80 ± 0.07. Minute alveolar ventilation (TV − DS)R was computed for both cases. With spontaneous breathing, the minute alveolar volume was 5.48 ± 2.1 l/min. With only chest-compression breathing, the alveolar ventilation was −1.49 ± 0.64 l/min. The negat... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1550827 Thu, 26 Jun 2008 06:22:21 +0100 1550827 http://www.springerlink.com/content/uk03n7653414770x/ Abstract  Computer simulation is an important tool to study the interaction between rotary blood pumps (RBPs) and human circulatory system. This interaction is critical for the development of reliable physiological control systems of long-term RBPs. This paper presents a numerical model of the human circulatory system, which innovatively takes the muscle pump into account in dynamic exercise. Simulation results demonstrate that the inclusion of muscle pump will change the response of hemodynamic variables and RBP parameters. These findings also show the necessity to verify the performance of RBPs and their physiological control systems in dynamic exercise with the muscle pump taken into account. By using Matlab Simulink software to simulate real-time circulatory properties,... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1534937 Thu, 19 Jun 2008 08:19:32 +0100 1534937 http://www.springerlink.com/content/452k26037n8g3262/ Abstract  The wavelet transform-based correlation analysis has been used to study skin temperature fluctuations caused by periodic changes in blood flow resulting from oscillations in vasomotor smooth muscle tone. We considered two cases, one in which temperature measurements and blood flow recordings by laser Doppler flowmetry are made simultaneously and another in which two temperature signals are measured concurrently. Twelve healthy subjects participated in our study. The gapped wavelet technique was used to suppress artifacts caused by boundary effects. Simultaneous recordings of skin temperature fluctuations and the signal of the laser Doppler flowmeter provided correlation coefficients essentially exceeding the values obtained for noise signals within three spectral ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1534936 Thu, 19 Jun 2008 08:19:32 +0100 1534936 http://www.springerlink.com/content/p4r26817270k5043/ Abstract  A thorough understanding of ventricular interaction and the effects of septal function on right and left ventricular performance in the human heart requires measurement of interventricular pressure gradients using high fidelity pressure transducers. The advent of newer echocardiographic techniques provides an opportunity to combine high resolution images with bi-ventricular catheterization data in the cardiac catheterization laboratory, and obtain the detailed hemodynamic and echocardiographic information necessary to more fully understand the clinical manifestations of normal and abnormal septal and free wall mechanical function. We have anticipated these developments and modified the description of heart mechanics in our integrated multi-scale model of the human... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1507186 Tue, 10 Jun 2008 06:06:56 +0100 1507186 http://www.springerlink.com/content/wl67n237l4230l63/ Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-007-9053-5Authors Jerry J. Batzel, University of Graz Institute for Mathematics and Scientific Computing Graz AustriaVera Novak, Harvard Medical School Department of Gerontology Boston USAFranz Kappel, University of Graz Institute for Mathematics and Scientific Computing Graz AustriaMette S. Olufsen, North Carolina State University Department of Mathematics Raleigh USAHien T. Tran, North Carolina State University Department of Mathematics Raleigh USA Journal Cardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1155504 Tue, 15 Jan 2008 16:10:30 +0100 1155504 http://www.springerlink.com/content/80688520q1401485/ Abstract  Cardiovascular signals are largely analyzed using traditional time and frequency domain measures. However, such measures fail to account for important properties related to multiscale organization and non-equilibrium dynamics. The complementary role of conventional signal analysis methods and emerging multiscale techniques, is, therefore, an important frontier area of investigation. The key finding of this presentation is that two recently developed multiscale computational tools––multiscale entropy and multiscale time irreversibility––are able to extract information from cardiac interbeat interval time series not contained in traditional methods based on mean, variance or Fourier spectrum (two-point correlation) techniques. These new methods, with careful... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1130594 Thu, 03 Jan 2008 16:30:21 +0100 1130594 http://www.springerlink.com/content/q526335045014864/ In this study, we compare the Nelder–Mead optimization method to two sampling methods: the implicit filtering method and a genetic algorithm. We show that these off-the-shelf optimization methods can work in conjunction with the heart rate model and provide reasonable parameter estimates with little algorithm tuning. In addition, we make use of the thousands of points sampled by the optimizers in the course of the minimization to perform an overall analysis of the model itself. Our findings show that the resulting least-squares problem has multiple local minima and that the non-linear-least squares error can vary over two orders of magnitude due to the complex interaction between the model parameters, even when provided with reasonable bound constraints. Content Type Journal Art... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1130593 Thu, 03 Jan 2008 16:30:21 +0100 1130593 http://www.springerlink.com/content/0q323x52562n4760/ Abstract  Comparing models with data always forces us to deal with uncertainty. This uncertainty may take many different forms and involve multiple scales of resolution in the model and in the experiment. In this paper, we discuss issues surrounding the development of deterministic dynamic models of mean behavior and the associated statistical models of the difference between model and experiment. We touch on a variety of topics, including basic exploratory data analysis, confidence bounds and model reduction hypothesis tests. Tools ranging from nonlinear regression to time series to Bayesian decision theory are presented. Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-007-9052-6Authors Ben G. Fitzpatrick, Loyola Marymount University Department of ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1130592 Thu, 03 Jan 2008 16:30:21 +0100 1130592 http://www.springerlink.com/content/60436h003962452h/ Abstract  Cerebral autoregulation (CA) is an most important mechanism responsible for the relatively constant blood flow supply to brain when cerebral perfusion pressure varies. Its assessment in nonacute cases has been relied on the quantification of the relationship between noninvasive beat-to-beat blood pressure (BP) and blood flow velocity (BFV). To overcome the nonstationary nature of physiological signals such as BP and BFV, a computational method called multimodal pressure-flow (MMPF) analysis was recently developed to study the nonlinear BP–BFV relationship during the Valsalva maneuver (VM). The present study aimed to determine (i) whether this method can estimate autoregulation from spontaneous BP and BFV fluctuations during baseline rest conditions; (ii) whether... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1099838 Sat, 15 Dec 2007 19:38:50 +0100 1099838 http://www.springerlink.com/content/w21g665059640117/ Abstract  The complexity of mathematical models describing the cardiovascular system has grown in recent years to more accurately account for physiological dynamics. To aid in model validation and design, classical deterministic sensitivity analysis is performed on the cardiovascular model first presented by Olufsen, Tran, Ottesen, Ellwein, Lipsitz and Novak (J Appl Physiol 99(4):1523–1537, 2005). This model uses 11 differential state equations with 52 parameters to predict arterial blood flow and blood pressure. The relative sensitivity solutions of the model state equations with respect to each of the parameters is calculated and a sensitivity ranking is created for each parameter. Parameters are separated into two groups: sensitive and insensitive parameters. Small cha... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1099837 Sat, 15 Dec 2007 19:38:49 +0100 1099837 http://www.springerlink.com/content/m38l3873786l4745/ Abstract  Many cardiovascular models involve prediction of changes that occur when a subject is perturbed in some way, to move from one state to another. A successful, predictive model should involve at least two elements: First, the model should include some index of the intensity of the perturbation that elicits the response; effective responses should, in some fashion, be linearly or nonlinearity related to perturbations. Second, the model should factor in subjects’ abilities to meet the challenges posed by the perturbations. This review indicates that these two basic components of a successful model may be difficult to incorporate. In the simple case of passive upright tilt, blood pressure measurements may not accurately indicate the stimulus, because blood pressure r... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1099836 Sat, 15 Dec 2007 19:38:48 +0100 1099836 http://www.springerlink.com/content/f15356061692q15h/ Abstract  This research is aimed to the determination of the changes in the cardiac energetic output for three different modes of cardiac rhythm pacing. The clinical investigation of thirteen patients with the permanent dual-chamber pacemaker implantation was carried out. The patients were taken to echocardiography examination conducted by way of three pacing modes (AAI, VVI and DDD). The myocardial energetic parameters—the stroke work index (SWI) and the myocardial oxygen consumption (MVO2) are not directly measurable, however, their values can be determined using the numerical model of the human cardiovascular system. The 24-segment hemodynamical model (pulsating type) of the human cardiovascular system was used for the numerical simulation of the changes of myocardial ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1097041 Fri, 14 Dec 2007 15:56:00 +0100 1097041 http://www.springerlink.com/content/0435471r4n719566/ Abstract  In this paper we compare several approaches to identifying certain key respiratory control parameters relying on data normally available from non-invasive measurements. We consider a simple model of the respiratory control system and describe issues related to numerical estimates of key parameters involved in respiratory function such as central and peripheral control gains, transport delay, and lung compartment volumes. The combination of model-specific structure and limited data availability influences the parameter estimation process. Methods for studying how to improve the parameter estimation process are examined including classical and generalized sensitivity analysis, and eigenvalue grouping. These methods are applied and compared in the context of clinical... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1081967 Fri, 07 Dec 2007 16:37:14 +0100 1081967 http://www.springerlink.com/content/y80134444q522476/ In this study we describe a model predicting heart rate regulation during postural change from sitting to standing and during head-up tilt in five healthy elderly adults. The model uses blood pressure as an input to predict baroreflex firing-rate, which in turn is used to predict efferent parasympathetic and sympathetic outflows. The model also includes the combined effects of vestibular and central command stimulation of muscle sympathetic nerve activity, which is increased at the onset of postural change. Concentrations of acetylcholine and noradrenaline, predicted as functions of sympathetic and parasympathetic outflow, are then used to estimate the heart rate response. Dynamics of the heart rate and the baroreflex firing rate are modeled using a system of coupled ordinary delay d... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1081966 Fri, 07 Dec 2007 16:37:14 +0100 1081966 http://www.springerlink.com/content/t4285671378h0k17/ Abstract  In this article, we discuss the design and implementation of a receding horizon control (RHC) which will be used to represent the control for the baroreceptor loop in the human cardiovascular system (CVS). This control will be applied to a model of the CVS developed in a previous work by Kappel and Peer. In that earlier work, a linear quadratic control strategy (LQR) was implemented to represent this baroreflex control which was designed to stabilize the system under an ergometric workload. The RHC approach will be examined as an alternate to the LQR implementation. The control parameters in the cost functional of the RHC will be estimated using the same experimental data as was used in the LQR study. The results of the RHQ implementation will be compared with the... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1074485 Wed, 05 Dec 2007 16:34:35 +0100 1074485 http://www.springerlink.com/content/9518t1q6357p9qwm/ Abstract  There is ample evidence to support the notion that chronic exposure to repetitive episodes of interrupted breathing during sleep can lead to systemic hypertension, heart failure, myocardial infarction and stroke. Recent studies have suggested that abnormal autonomic control may be the common factor linking sleep-disordered breathing (SDB) to these cardiovascular diseases. We have developed a closed-loop minimal model that enables the delineation of the major physiological mechanisms responsible for changes in autonomic system function in SDB, and also forms the basis for a noninvasive technique that enables the early detection of cardiovascular control abnormalities. The model is “minimal” in the sense that all its parameters can be estimated through analysis ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1074486 Tue, 04 Dec 2007 20:58:16 +0100 1074486 http://www.springerlink.com/content/x5342w877w945835/ Abstract  Short-term regulation of cerebral blood flow (CBF) is controlled by myogenic, metabolic and neurogenic mechanisms, which maintain flow within narrow limits, despite large changes in arterial blood pressure (ABP). Static cerebral autoregulation (CA) represents the steady-state relationship between CBF and ABP, characterized by a plateau of nearly constant CBF for ABP changes in the interval 60–150 mmHg. The transient response of the CBF–ABP relationship is usually referred to as dynamic CA and can be observed during spontaneous fluctuations in ABP or from sudden changes in ABP induced by thigh cuff deflation, changes in posture and other manoeuvres. Modelling the dynamic ABP–CBFV relationship is an essential step to gain better insight into the physiology... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1062406 Wed, 28 Nov 2007 16:04:25 +0100 1062406 http://www.springerlink.com/content/n176842215601102/ Abstract  Although blood pressure control is often viewed as a paradigmatic example of a “homeostatic” biological control system, blood pressure levels can fluctuate considerably over shorter and longer time scales. In modern signal analysis, coherence between heart rate and blood pressure variability is used to estimate baroreflex gain. However, the shorter the measurement period, the more variability this gain factor reveals. We review evidence that this variability is not due to the technique used for the estimation, but may be an intrinsic property of the circulatory control mechanisms. The baroreflex is reviewed from its evolutionary origin, starting in fishes as a reflex mechanism to protect the gills from excessively high pressures by slowing the heart via the (p... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1062405 Wed, 28 Nov 2007 16:04:25 +0100 1062405 http://www.springerlink.com/content/w101738w87867v4p/ Abstract  A set of multiscale simulations has been created to examine the dynamic behavior of the human aortic valve (AV) at the cell, tissue, and organ length scales. Each model is fully three-dimensional and includes appropriate nonlinear, anisotropic material models. The organ-scale model is a dynamic fluid-structure interaction that predicts the motion of the blood, cusps, and aortic root throughout the full cycle of opening and closing. The tissue-scale model simulates the behavior of the AV cusp tissue including the sub-millimeter features of multiple layers and undulated geometry. The cell-scale model predicts cellular deformations of individual cells within the cusps. Each simulation is verified against experimental data. The three simulations are linked: deformatio... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1039583 Sat, 17 Nov 2007 23:25:55 +0100 1039583 http://www.springerlink.com/content/m7744161236j17q8/ Abstract  Contraction–relaxation coupling is often characterized in terms of its effects on contraction or relaxation parameters, such as the time-constant of isovolumic relaxation (τ). While thermodynamics-based LV function characterization methods exist, landmark relaxation-onset determination studies used surgical methods. One classic, open-chest preparation study found that relaxation-onset occurs during early ejection, i.e. 34% of systolic time, T SYS, defined as the time from end-diastolic pressure to peak negative dP/dt. Because ventricular pumping is a steady state system, the laws of thermodynamics and nonlinear dynamics require that energy generation (during contraction) and energy utilization (during relaxation) must be balanced in a time-averaged (steady-state... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1039582 Sat, 17 Nov 2007 23:25:54 +0100 1039582 http://www.springerlink.com/content/b7613hj186k1kk85/ Abstract  Isolated systolic hypertension (ISH) is prevalent in the elderly and the contributing factors are predominantly vascular in origin. We previously showed that the hemodynamic manifestation of ISH is the result of a concurrently mild increase in peripheral resistance with a large reduction in arterial compliance or greatly increased vascular stiffness. Such elastic mismatching can lead to increased wave reflections. Therefore, we hypothesize that significantly increased pulse wave reflections associated with a drastically reduced arterial compliance beyond normal aging is a principle contributing factor to the production of ISH. To investigate this, we developed a new allometric hemodynamic model that can account for the arterial compliance and peripheral resistance... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1039584 Fri, 16 Nov 2007 16:02:21 +0100 1039584 http://www.springerlink.com/content/y1772m388n15l746/ In this study, the PPG pulse rising edge and corresponding peak position have been investigated non-invasively in human subjects as a function of age. Fifteen healthy subjects were selected and grouped in five age intervals, from 20 to 59 years, based on their comparable systolic-diastolic blood pressure and PPG amplitude. As expected, the peripheral pulse shows a steep rise and early peak in younger subjects. With age, the slope becomes blunted and in older subjects, the rise is very gradual and the pulse peak appears much later. Qualitative results were further verified by a modified 10-element Windkessel model to quantify the lumped parameter changes with ageing. This verification highlighted some specific changes in vascular parameters with aging. The rising edge could be co... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=1019275 Fri, 09 Nov 2007 15:45:03 +0100 1019275 http://www.springerlink.com/content/9576332896123230/ Conclusion Although pacing site has been found to influence the contractile state of the ventricle, this is the first known study to demonstrate no change in τ in an in vivo preparation. This suggests that alteration of electro-mechanical coupling described by MR is not sufficiently robust to provide insight into pacing site and cardiac function in healthy hearts. Content Type Journal ArticleCategory Original PaperDOI 10.1007/s10558-007-9033-9Authors Sarah E. Ahlberg, University of Minnesota Department of Biomedical Engineering Minneapolis MN 55455 USANathan A. Grenz, Medtronic, Inc. Therapy Delivery 7000 Central Ave. NE Minneapolis MN 55432-3576 USADaniel L. Ewert, North Dakota State University Department of Electrical and Computer Engineering Fargo ND 58105 USAPaul A. Iaizzo, Uni... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=887806 Tue, 18 Sep 2007 21:03:25 +0100 887806 http://www.springerlink.com/content/0g814434w7267nx2/ Abstract  We have developed a novel method for estimating subject-specific hemodynamics during hemorrhage. First, a mathematical model representing a closed-loop circulation and baroreceptor feedback system was parameterized to match the baseline physiology of individual experimental subjects by fitting model results to 1 min of pre-injury data. This automated parameterization process matched pre-injury measurements within 1.4  �  1.3% SD. Tuned parameters were then used in similar open-loop models to simulate dynamics post-injury. Cardiac output (CO) estimates were obtained continuously using post-injury measurements of arterial blood pressure (ABP) and heart rate (HR) as inputs to the first open-loop model. Secondarily, total blood volume (TBV) ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=865221 Tue, 11 Sep 2007 08:08:04 +0100 865221 http://www.springerlink.com/content/x37485u6317587ml/ In this study, a mathematical model using only a few empirical parameters and the measured lower limb vascular path length is introduced to estimate ΔPTT when a different posture is adopted. To assess the reliability of the model, 23 healthy children aged 8.4 � 2.3 years were recruited to adopt the sitting and supine position at discrete intervals. PTT measurements were obtained from their toe with respect to an ECG for both postures. The results showed that there was significant correlation between the model and measured ΔPTT (P < 0.05; R� = 0.813). The findings herein suggest that this simple yet practical model can have the accuracy to estimate the ΔPTT value. Moreover, it does not require the use of an ECG or pulse oximeter in its compu... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=786545 Tue, 07 Aug 2007 08:05:49 +0100 786545 http://www.springerlink.com/content/757055514rlr0047/ In this study, we determined the effects of altered upper limb pulse wave velocity (PWV) and local wave reflection parameters on RA pressure waveform augmentation (RA-AIx). Twenty healthy volunteers (10 men) between the ages of 18 and 35 years of age were recruited. Simultaneous pressure waveforms were acquired using arterial tonometers from the right carotid and the radial arteries, prior to and following tourniquet induced hyperemia. The phase velocities from the pressure wave transfer function were used to estimate the pulse wave velocity (PWV∞), the local reflection coefficient (Γ) and an estimate of the terminal impedance of the upper limbs, PWV0+. The RA-AIx was represented as a linear, three-parameter model that included the input (the AIx of the carotid artery pressure ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=780221 Sat, 04 Aug 2007 07:53:22 +0100 780221 http://www.springerlink.com/content/j6qkx32715l0j178/ Abstract  A toolbox for Matlab Simulink (trademark of Mathworks corp. etc.) was developed to simulate various models of flow in the cardiovascular system and study effects of different pathological conditions. The toolbox was based on well-known analog lumped models of blood flow in vessels, the varying elastance heart model, blood flow through vessels, shunts, and valves as well as models of oxygen exchange at lungs and tissue. The toolbox is modular providing the basic building blocks of the cardiovascular system. Parameters for the individual components may be set by the user to adapt the component to the simulated system. Several examples are shown. This modeling system is described and is also available for downloading as an open source for free use. The authors see th... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=670873 Fri, 15 Jun 2007 06:56:36 +0100 670873 http://www.springerlink.com/content/f1h433640l28w607/ We present flow simulations using both structured trees and pure resistance models for the small arteries, and compare the resulting flow and pressure waves under various friction models. Moreover, we show how to couple the one-dimensional equations with the Taylor diffusion limit (Azer, Int J Heat Mass Transfer 2005;48:2735–40; Taylor, Proc R Soc Lond Ser A 1953;219:186–203) of the convection-diffusion equations to drive the concentration of a solute along an artery in time. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=670874 Thu, 14 Jun 2007 07:46:49 +0100 670874 http://www.springerlink.com/content/00826rg86x7q7031/ Abstract  Cardiac performance is quantitatively and continuously assessed from pressure-volume signals by using the conductance catheter technique even in small animals. Conductivity of blood, however, is dependent on hematocrit (Hct). Interdependence between hematocrit and volume measurement by the conductance catheter has been evaluated. In 12 male Wistar rats weighing 400–475 g, anesthetized and artificially ventilated, Hct was gradually lowered by isovolumic hemodilution ranging from 50% to 7%. Heparinized blood samples were drawn at decreasing Hct levels for centrifugation, for automated Hct measurement by a blood gas analyzer, and for conductance catheter volume measurements (CCV) in calibrated cuvettes. Substitution of about 2 ml colloid solution lowered ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=622044 Sat, 19 May 2007 07:49:25 +0100 622044 http://www.springerlink.com/content/x617340093301200/ The objective of this study was to measure the force exerted by 83 trained CPR rescuers and 104 untrained adult laypersons (college students and staff). A bathroom scale was used to measure the force exerted by these subjects with their hands on the bathroom scale in the CPR position. The weight range for both groups was the same. Of the trained rescuers, 60% pressed with more than 125 lbs, whereas only 37% of the laypersons pressed with more than 125 lbs. In view of the American Heart Association (AHA) guidelines (2000) to depress the chest 1.5 to 2 inches, which requires 100–125 lbs, it would appear that most laypersons do not exert enough force for effective CPR. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print IS... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=622045 Fri, 18 May 2007 07:23:55 +0100 622045 http://www.springerlink.com/content/181t7213n5q25809/ Abstract  Stress has been recognized as an important contributing factor to many forms of cardiovascular diseases. Its quantification has been sought for decades, but to no avail. We have developed a wholly noninvasive approach to quantitatively assess mental and physical stress effects on parameters that are associated with global cardiovascular function. Blood pressure, electrocardiogram, respiration and pulse volume are recorded simultaneously in experimental subjects during imposed arithmetic mental stress and Valsalva maneuver. Results show that parameters related to heart rate variability, respiratory rate, T-wave amplitude and pulse transit time are significantly modified during stress. Changes in these parameters involved differing mechanisms, although complex, can ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=622046 Thu, 17 May 2007 07:30:31 +0100 622046 http://www.springerlink.com/content/4843j2654r771514/ Abstract  According to Earnshaw’s Theorem (1839), the passive maglev cannot achieve stable equilibrium and thus an extra coil is needed to make the rotor electrically levitated in a heart pump. The author had developed a permanent maglev centrifugal pump utilizing only passive magnetic bearings, to keep the advantages but to avoid the disadvantages of the electric maglev pumps. The equilibrium stability was achieved by use of so-called “gyro-effect”: a rotating body with certain high speed can maintain its rotation stably. This pump consisted of a rotor (driven magnets and an impeller), and a stator with motor coil and pump housing. Two passive magnetic bearings between rotor and stator were devised to counteract the attractive force between the motor coil iron core and the... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=500212 Fri, 23 Mar 2007 12:15:56 +0100 500212 http://www.springerlink.com/content/u624788w67164536/ Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=481888 Fri, 16 Mar 2007 07:51:06 +0100 481888 http://www.springerlink.com/content/h634760p14314850/ Abstract??Numerical algorithms are presented for the numerical solution of the one-dimensional model of blood flow in the aorta. The pertinent hyperbolic equations are written using Riemann invariants, which are integrated along the characteristics using two efficient algorithms. Because of the hyperbolic nature of the equations shock waves are to be expected, and their occurrence is discussed. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=467229 Wed, 07 Mar 2007 07:45:24 +0100 467229 http://www.springerlink.com/content/n6784m1521608638/ Abstract??We upgraded our human cardiopulmonary (CP) model with additional data that enables it to more accurately simulate normal physiology. We then tested its ability to explain human disease by changing two parameter values that decrease ventricular compliance, and found that it could predict many of the hemodynamic, gas exchange, and autonomic abnormalities found in patients with left ventricular diastolic dysfunction (LVDD). The newly incorporated information includes high-fidelity pressure tracings simultaneously recorded from the RV and LV of a normal human in a cardiac catheterization laboratory, Doppler echocardiographic inlet flow velocity patterns, measures of right and left ventricular impedance, and atrial volumes. The revised cardiovascular section details the hemodynamics o... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=453404 Mon, 05 Mar 2007 22:13:08 +0100 453404 http://www.springerlink.com/content/d34387082jl7481n/ This study focused on the recirculation fraction (RF) and potentiation ratio (PR), obtained from the recovery of the FFR and FIR. These parameters may provide insight on intracellular Ca2+regulation. Left ventricular (LV) pressures and HR were assessed in anesthetized canines (n?=?7). Intrinsic data were collected prior to and following HR increases to 150, 180, and 200?bpm, as well as following delivery of an ES at 280?ms. The RF was calculated as the slope of dP/dtmax(n?+?1)vs. dP/dtmax(n), wheren?=?beat number. The PR was calculated by normalizing dP/dtmaxfrom the first beat following the ES (or the last paced beat) to the steady-state dP/dtmax. The RF due to an ES was not significantly different than that from a HR of 200?bpm. The PR from an ES was not significantly different than from... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=437756 Fri, 23 Feb 2007 07:45:45 +0100 437756 http://www.springerlink.com/content/50371013u7x14843/ Abstract??A new inflation test device was developed to study the mechanical properties of aortic tissue. The device was used to measure failure (rupture) strength and to determine the nonlinear, anisotropic elastic properties of porcine thoracic aorta. The tester was designed to stretch initially flat, circular tissue specimens to rupture under uniform biaxial loading. Water was chosen as the pressurizing fluid. Mechanical stretch and radius of curvature during inflation were measured optically in two orthogonal directions, and the Cauchy stress components were calculated from the deformation and the applied pressure. All porcine samples that ruptured successfully did so via a tear in the circumferential direction. Thus, the failure strength was taken to be the stress in the axial directio... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=305098 Thu, 30 Nov 2006 08:38:17 +0100 305098 http://www.springerlink.com/content/vg3760352423w255/ This article describes the design of such a loop and the simulated response of different physiological states, such as a healthy person in sleep, rest, and mild physical activity, and in different pathological states. The loop consists of: (1) pulsatile left and right cardiac simulators; (2) air/water tanks to model the venous and arterial compliances; (3) tygon tubes to model the venous, arterial, and other system flow resistances; and (4) a tuning clamp to model the variation in system resistance characteristics under different cardiac pressure/flow conditions. The simulated responses were compared to the data found in the literature to validate the loop performance prior to LVAD testing. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=305099 Thu, 30 Nov 2006 08:38:16 +0100 305099 http://www.springerlink.com/content/644837jm14w28479/ Abstract A new theoretical algorithm is presented for high-resolution mitral flow determination based on the indicator dilution principle. The algorithm allows forward as well as backward time-dependent mitral flow estimation with a beat-to-beat resolution. Indices of normal/subnormal left heart functioning, including total stroke volume (TSV), cardiac output (CO), total ejection fraction (TEF), mitral regurgitation volume (MRV) and mitral regurgitation fraction (MRF), are determined. Knowledge of left atrium and ventricle indicator concentration versus time dependencies and the end systolic left atrium and ventricle volumes are sufficient to determine the mitral flow pattern. However, the non-dimensional index of the total ejection fraction can be calculated on the basis of only the indic... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=293975 Wed, 22 Nov 2006 18:34:47 +0100 293975 http://www.springerlink.com/content/210867t24u576v46/ Abstract Huxley’s crossbridge attachment model predicts tension (contractile force) development in isometric (fixed length) cells using constant attachment and detachment rates. Alternative models incorporating time-varying calcium concentrations are complex (coupled linear differential equations) and use time-dependent inputs (calcium, elastance, etc.) to model multiple states. We hypothesize that by incorporating the known significant rise and fall in intracellular calcium, via either an asymmetric damped function or a symmetric Gaussian function, into a time-varying, rather than constant, attachment rate function, the Huxley model prediction for tension (i.e., chamber pressure) in isovolumic (isometric) non-ejecting beats will improve. To test the hypothesis that the time-dependen... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=282376 Fri, 17 Nov 2006 18:38:53 +0100 282376 http://www.springerlink.com/content/t3p0675046581141/ The objective of this research was to add the ability to obtain SaO2 from the same device and to obtain the calibration curve. Another objective was to determine which measurement method (transmittance or reflectance) is preferable. This new oximeter is unlike the conventional pulse oximeter in that it does not require a pulse, making it ideal for measuring oxygen saturation noninvasively in small human subjects with small amplitude pulses or without a pulse. A study was performed in 11 pigs, ranging in weight 20–27 kg. The pig tail was used as the measuring site for %SaO2 measurements. Arterial blood samples were obtained from the femoral artery and oxygen saturation was measured with a blood-gas analyzer. A small blood-pressure cuff was used to render the optical path bloodless. A ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=282375 Fri, 17 Nov 2006 18:32:00 +0100 282375 http://www.springerlink.com/content/k66138m811w35277/ AbstractObjective  To correlate the values in the basic blood pressure groups presented in the JNC 7th with the computed values of the Noninvasive Hemodynamic Analyzer (NHA) and to demonstrate the pathophysiological alterations by three proportional hypertensive models. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=205069 Thu, 21 Sep 2006 09:39:28 +0100 205069 http://www.springerlink.com/content/q7r266r8u52w34h7/ Abstract  Shortening of myocardial fibers occurs following force development in those fibers. The extent, speed and timing of shortening are determined by kinetics and extent of force. However, shortening is also influenced by the elastance/viscosity of the muscle tissue, because that determines the coupling between force and shortening. In the in vivo dog heart, we estimated that coupling by measuring local myocardial force and fiber shortening independently under various conditions. We determined the effect of positive and negative inotropy (by intracoronary injection of dobutamine and acetylcholine, respectively), and of dysfunctional contraction produced by local ischemia/reperfusion and BDM. Under baseline and both positive and negative intropy, most shortening occurred during systo... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=190475 Wed, 13 Sep 2006 22:02:57 +0100 190475 http://www.springerlink.com/content/wn173682mm751238/ Abstract  Tissue elasticity reconstruction is a parameter estimation effort combining imaging, elastography, and computational modeling to build maps of soft tissue mechanical properties. One application is in the characterization of atherosclerotic plaques in diseased arteries, wherein the distribution of elastic properties is required for stress analysis and plaque stability assessment. In this paper, a computational scheme is proposed for elasticity reconstruction in soft tissues, combining finite element modeling (FEM) for mechanical analysis of soft tissues and a genetic algorithm (GA) for parameter estimation. With a model reduction of the discrete elasticity values into lumped material regions, namely the plaque constituents, a robust, adaptive strategy can be used to solve invers... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=190476 Tue, 12 Sep 2006 07:18:48 +0100 190476 http://www.springerlink.com/content/m91j657506x35477/ AbstractBackground  The occurrence rate of atrial fibrillation (AF) after coronary artery bypass grafting, quoted in the literature, is wide ranging from 5% to over 40%. It is speculated that, off-pump coronary artery bypass grafting (OPCAB) and also minimally invasive cardiac surgery reduces the incidence of postoperative AF due to reduced trauma, ischemia, and inflammation. Current data, however, do not clearly answer the question, whether the incidence of postoperative AF is reduced in using minimally invasive techniques, ideally resulting in the combination of both small access and off-pump surgery. The aim of this study was to evaluate the incidence of postoperative AF in patients undergoing totally endoscopic off-pump coronary artery bypass grafting (TECAB). Content TypeJournal Ar... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=190477 Tue, 12 Sep 2006 07:18:45 +0100 190477 http://www.springerlink.com/content/q1863144l6u3385q/ Abstract  Leukocyte adhesion to vascular endothelium is an initial step of many inflammatory diseases. Although the atomic force microscopy (AFM) measurements of leukocyte–endothelial interaction have been recently introduced. with cell adhesion force unbinding curves (CAFUC). We obtained pico-Newton force in the initial interaction between a single living THP-1 cell and HUVEC monolayer using a custom-built laser tweezers (LT) system. The measured quantities included the non-linear force–distance relationship, and the effect of yielding in cell detachment. It is possible to introduce a time scale into the LT cell-detachment experiments for further exploration and more detailed information on the viscoelastic properties of living cells. Content TypeJournal Article JournalCardiov... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=188142 Fri, 08 Sep 2006 07:15:42 +0100 188142 http://www.springerlink.com/content/1m02k05554394062/ In this study, a right ventricular pressure waveform based pulse contour CO algorithm was developed to estimate the amplitude and duration of a hypothetical triangular flow waveform in the pulmonary artery. This algorithm was tested against gold standard blood flow measurements in ten canines during acute perturbations to preload (inferior vena caval occlusion (IVCO), rapid saline infusion), afterload (descending aortic occlusion (DAO), serotonin, angiotensin II, sodium nitroprusside infusion), and cardiac contractility (dobutamine and propranolol infusion). The algorithm correctly predicted the changes in CO (r 2 = 0.82) that varied from − 45 to 31% of the baseline levels. To explain this finding both the pulmonary arterial (PA) and the ascending aortic (AA) input impedances were mo... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=188141 Fri, 08 Sep 2006 07:15:42 +0100 188141 http://www.springerlink.com/content/l807w1g573508837/ Abstract  The transthoracic impedance (T) and its variations may be estimated through the measurement of the electrical impedance between the can and the right ventricular coil of a defibrillation lead. This method may allow the monitoring of fluid overload before a heart failure attack. Aim of this study was to validate in vitro a method to calculate T in case of a standard bipolar pacing lead, by performing 3 measurements: standard unipolar impedance from the tip (Zuni-tip); unipolar impedance from the ring (Zuni-ring); standard bipolar impedance (Zbip). The formula we used is derived from the standard equivalent circuit of a pacing system: T = (Zuni-tip-Zbip+Zuni-ring)/2 Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (S... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180679 Wed, 06 Sep 2006 07:13:26 +0100 180679 http://www.springerlink.com/content/4h01045uj15404r7/ In this report, a model of the closed human cardiovascular loop is developed. This model, using one set of 88 equations, allows variations from normal resting conditions to exercise, as well as to the ultimate condition of a circulation following cardiac arrest. The principal purpose of the model is to evaluate the continuum of physiological conditions to cardiopulmonary resuscitation (CPR) effects within the circulation. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180680 Sat, 08 Jul 2006 06:47:47 +0100 180680 http://www.springerlink.com/content/d12u3m551824t57m/ Conclusion: The results for the estimated elastic coefficients are consistent with the ones obtained from force-displacement diagram. The trend of change in the estimated parameters is also in harmony with the previous studies done using P-V diagram. The only input used in this model is the long axis displacement of the annulus plane, which can also be obtained non-invasively using tissue Doppler or MR imaging. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 Journal VolumeVolume 6 Journal IssueVolume 6, Number 1 / March, 2006 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180682 Sat, 17 Jun 2006 17:08:09 +0100 180682 http://www.springerlink.com/content/50035223l0002530/ We have extended our model of the ovine pulmonary circulation to include a model of a paracorporeal artificial lung (AL) and its attachments to the natural pulmonary circulation in two configurations: in series and in parallel. Our model of the natural lung (NL) circulation is first shown to be in agreement with hemodynamic and input impedance data from the open literature. We then study design efficacy of the AL in terms of its housing and attachments. A sensitivity analysis of the modified pulmonary circulation model reveals that there are three key parameters: inlet graft length (IGL) and the compliances of the inlet compliance chamber (CC) and housing of the artificial lung. Based on literature reports, we assume the right ventricle is well-matched to the impedance of the natural pulmo... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180681 Sat, 17 Jun 2006 17:08:08 +0100 180681 http://www.springerlink.com/content/q863058781310667/ To overcome the complications due to the use of noncompliant large diameter conventional chest drain devices, a flexible small diameter chest drain device was designed and simulated based on computational fluid dynamics (CFD) techniques. It was clearly shown that the pressure drop and velocity increase of the most distal drainage holes, which are located near the suction end, are dominant over other drainage holes. A conventional chest drain device with circular side holes showed higher mass flow rate due to larger cross sectional area. It also showed less dependency on the side hole placement compared to open channel, closed cavity chest drain with rectangular side holes. When all holes are opened the conventional chest drain showed 6% increase in flow rate while the open channel, closed ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180683 Thu, 01 Jun 2006 16:38:52 +0100 180683 http://www.springerlink.com/content/j181k64724526271/ To investigate the possibility of a long-term applicable left ventricular assist device, a 23 mm outer diameter and 31 g weight implantable aortic valvo-pump was developed. It consists of a rotor and a stator; the rotor has a driven magnets assemble and an impeller, the stator has a motor coil with iron core and a outflow guide vane. The device locates the position of aortic valve, delivers the blood directly from left ventricle to aorta. Neither connecting conduits nor “bypass” circuits are necessary. Therefore, the device has promisingly better antithrombogenicity than other heart pumps. In hemodynamic testing, the pump can produce a blood flow of 7 l/min volume with 50 mmHg pressure increase at 15,000 rpm rotating speed, and at zero flow rate the pump can maintain a diastolic p... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180684 Sat, 20 May 2006 08:38:48 +0100 180684 http://www.springerlink.com/content/p36x78j617k18268/ Biomechanical studies were designed to determine the dynamic progression of the uterine cervix of pregnant rats at various stages of gestation and to determine its functions in retaining the fetus while at the same time undergoing characteristic softening to allow for dilatation at parturition. Whole cervices from Sprague-Dawley rats at 10, 15, and 21 days gestation and at 3 days postpartum were subjected to detailed biomechanical studies. Tension–length change, tension–diameter, pressure–area, stress–diameter, and stress–strain curves were calculated using analytical methods adopted from vascular mechanics. The circular diameter of the tissue was greatly increased as pregnancy advanced. Cervix volume increased, while tissue wall stress and cervix pressure were both maintained in... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180685 Thu, 22 Dec 2005 07:44:06 +0100 180685 http://www.springerlink.com/content/f08q75314151h327/ Conclusions: The VCR system appears to be not able to provide enough coronary blood flow to maintain regional and global myocardial function. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 Journal VolumeVolume 5 Journal IssueVolume 5, Number 4 / December, 2005 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180688 Thu, 22 Dec 2005 07:44:04 +0100 180688 http://www.springerlink.com/content/72k3j5hj57760473/ Conclusion: The NHA clinical decision system can differentiate among the reported clinical conditions of the “Seattle Heart Watch” report. We were able to comparatively evaluate physiological and pathophysiological principles, such as, coronary flow reserve, endocardial autoregulation, and remodeling. Further medical trials will reveal the practical clinical importance and applicability of our NHA system. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 Journal VolumeVolume 5 Journal IssueVolume 5, Number 4 / December, 2005 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180687 Thu, 22 Dec 2005 07:44:03 +0100 180687 http://www.springerlink.com/content/y806v4263kt45450/ Our laboratory is studying the influence of the volume fractions and the organization of various macromolecules and cells in vascular tissue on the physical properties of vessel wall. The current investigation reports various mechanical properties of aorta, vena cava, carotid artery and iliac artery of the swine including: low-strain and high-strain moduli, transition from low-strain to high-strain behavior, the ultimate tensile stress, and the ultimate strain. Tissues were tested using a uniaxial incremental stress–strain technique, which allowed us to capture viscous, elastic, and total data simultaneously. Vessels were strained throughout their entire strain range until failure was achieved. Low-strain modulus showed sporadic differences between blood vessels and some dependence on st... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180686 Thu, 22 Dec 2005 07:44:02 +0100 180686 http://www.springerlink.com/content/b5p16053r20tu052/ This study presents a rigorous geometrical analysis of vessel bifurcations to understand problems associated with tubular stents in order to help optimize stent placements. A 2-D bifurcating geometrical model of the side branch vessel (SB) angulations to the main vessel (MV) was analyzed and examined: (a) side branch exposed stent length (SBExpSt), (b) the side branch horizontal distance of the stent overhang (SBStOvH) into the MV, (c) side branch longitudinal axis of the ostial opening (SBLongOp), (d) the “saddle gap” at the ostium of branch to the wall of the MV. Formulas for SBExpStent, SBStOvH, SBLongOp, and saddle gap were derived. Results showed a curvilinear relation between the SBExpStent, the SBStOvH, and the SBLongOp to the SB angulations (θ). The relationship between saddle... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180693 Fri, 30 Sep 2005 08:39:26 +0100 180693 http://www.springerlink.com/content/f5705q8262u8455u/ The dynamics of the coronary system is complicated by its dependence on the mechanical properties of the coronary vessels, the anatomical distribution of the vasculature, the biochemical and neurohormonal regulation, and the effect of myocardial contraction. Several types of coronary system models were proposed, focusing on different aspects of coronary system behavior and supported by different animal experiment methodologies. The lumped models were based on well-controlled coronary pressure–flow measurement and simplified assumptions. They are probably most useful for interpreting hemodynamic data measured in modern catheterizaton labs. Anatomical models, with the advancement in morphometric research, coronary angiography, and video densitometry, provided branching pattern, geometric d... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180692 Fri, 30 Sep 2005 08:39:26 +0100 180692 http://www.springerlink.com/content/72qv2q8t38006723/ In this study, we obtained respiratory signal derived from the ECG in 17 normal adult controls without a history of heart disease and quantified the time of occurrence of peaks and amplitudes or the QRS complex and performed cross-spectral analysis between R-R (interbeat) interval and the QRS-amplitude time series sampled at 4 Hz. Our findings show that the supine QRS amplitude HF power (0.15–0.5 Hz) correlates significantly with the R-R HF power (r (0.62; n (17; p ((0.004). However, this was negatively correlated in standing posture (r (−0.5; n (17; p (0.04). While there was a significant decrease of R-R HF power upon standing (p(0.01), there was a significant increase in QRS amplitude HF power (p (0.004). These findings indicate that the variability of QRS amplitude behaves different... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180691 Fri, 30 Sep 2005 08:39:26 +0100 180691 http://www.springerlink.com/content/3748t5648308lh78/ This report describes the left ventricle and its immediate environment as the core of a larger mathematical model. The model works normally under physiological conditions, and is specifically designed to allow understanding of flow, pressure, and volume phenomena under CPR as an extreme pathophysiological scenario. Using impedance-defined flow, the importance of valves for both the contracting as well as the asystolic ventricle is quantified. It demonstrates the role of venous pressure, sloshing of blood and flow around the cardiovascular circuit. The flow of 8 mL/s, in a pathological situation is demonstrated to be due not to cardiac compression, but to venous pressure. The principal conclusions are that the model functions in the physiological situation and that in an asystolic left vent... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180690 Fri, 30 Sep 2005 08:39:26 +0100 180690 http://www.springerlink.com/content/k3486972w7182861/ Several lumped models have been proposed to characterize the elastic behavior of the epicardial coronary artery, which are based on well-controlled animal experiments. It is still unclear as to which model is most suitable for analyzing the physiological pressure-flow data for the normal catheterization labs. In this research, different perfusion pressure patterns measured from a mongrel dog were used to drive four mathematical models to investigate the influence of the pressure dependence and viscoelastic effect on epicardial capacitive flow. Results show that the nonlinear behavior of the epicardial capacitance can be approximated with a linear model, and the viscoelastic effect only slightly reduces the amplitude of the protosystolic peak. Further analysis in frequency and time domain r... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180689 Fri, 30 Sep 2005 08:39:26 +0100 180689 http://www.springerlink.com/content/w04580632j265l71/ We have developed an integrative model of the ovine cardiovascular system that simulates the effects of posture and ventricular function to help design the circulatory and pulmonary assist devices often tested in conscious sheep that stand and recline during chronic experiments. Our present focus is the simulation itself and not the evaluation of specific assist devices. Adjusted parameters of the model provide good fits to in vivo experimental data and can describe the hemodynamic changes that follow balloon occlusion of the inferior vena cava and standing. Since circulatory assist devices are often tested in animal preparations of left heart failure, we extended the model to study the effects that standing and inferior vena cava occlusion would have in sheep with primarily systolic left ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180698 Tue, 02 Aug 2005 08:47:26 +0100 180698 http://www.springerlink.com/content/p3335636w1457136/ Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 Journal VolumeVolume 5 Journal IssueVolume 5, Number 2 / June, 2005 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180697 Tue, 02 Aug 2005 08:47:26 +0100 180697 http://www.springerlink.com/content/w051xq13017q2233/ The objective of this paper was to compute cardiac output (CO) noninvasively and other hemodynamic parameters by a new computer-aided decision system: a Noninvasive Hemodynamic Analyzer (NHA), and use the obtained data to demonstrate hemodynamic instability of two hypertensive patients. The NHA is composed of several instruments, including an electronic blood pressure instrument (with pulse curve detection), oxymeter (SpO2), hemoglobinometer and a core-body thermometer. Their data inputs are the dynamic characteristics of the patient’s condition. The static characteristics including, date of birth, sex, height, weight and test date are entered manually or via computer. These inputs are analyzed by a high performance multi-function data acquisition computer. In a recently published retros... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180696 Tue, 02 Aug 2005 08:47:26 +0100 180696 http://www.springerlink.com/content/v77211u068468483/ The EEG disappearance time was measured from the onset of electrically induced ventricular fibrillation (VF) in a study involving nine anesthetized swine, ranging in weight from 20 to 30 kg. The frequency of the VF waves was also measured to beyond the EEG disappearance time. At the onset of VF, the EEG frequency was 5–6 s−1; by 90 s, the EEG was isoelectric in all trials. The frequency of the VF waves at the onset of VF ranged from 6 to 15 s−1; the mean frequency was 10.1± 2.1 s−1. At 90 s it was 5.9± 1.0 s−1 and at 180 s it was 4.0± 0 s−1. Although the frequency of the VF waves decreased with the passage of time, the most marked decrease occurred within the first minute. It is concluded, in view of human and animal experience, that the EEG disappearance time is not a good ... Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180695 Tue, 02 Aug 2005 08:47:26 +0100 180695 http://www.springerlink.com/content/g202610384769772/ During cardiopulmonary resuscitation (CPR), the amplitude of chest motion during mouth-to-mouth breathing is a biofeedback signal to evaluate the adequacy of lung inflation. However, there is no sign to identify the effectiveness of each chest compression. This paper describes a device that produces an audible tone, the pitch of which is proportional to the amplitude of the pulse produced by each chest compression. Content TypeJournal Article JournalCardiovascular EngineeringOnline ISSN 1573-6806Print ISSN 1567-8822 Journal VolumeVolume 5 Journal IssueVolume 5, Number 2 / June, 2005 (Source: Cardiovascular Engineering) Cardiovascular Engineering journals http://www.medworm.com/rss/comments.php?id=180694 Tue, 02 Aug 2005 08:47:26 +0100 180694