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Predicting Acute Hypotensive Episodes Based on HR Baroreflex Model EstimationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 validat...
Source: Cardiovascular Engineering - October 14, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Coronary Arteries Simplified with 3D Cylinders to Assess True Bifurcation Angles in Atherosclerotic PatientsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 vess...
Source: Cardiovascular Engineering - October 9, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Patterns of Cardiovascular Control During Repeated Tests of Orthostatic LoadingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - October 8, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

A Servo-controlled Canine Model of Stable Severe Ischemic Left Ventricular FailureEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - October 8, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

The Relationship Between Pulmonary System Impedance and Right Ventricular Function in Normal SheepEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 pulmonar...
Source: Cardiovascular Engineering - September 29, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Limitations of Oximetry to Measure Heart Rate Variability MeasuresEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - September 3, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Boundary Conditions in Simulation of Stenosed Coronary ArteriesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 includ...
Source: Cardiovascular Engineering - August 17, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Loose Cuff HypertensionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 sup...
Source: Cardiovascular Engineering - August 7, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Methods for Calculating Coronary Perfusion Pressure During CPREmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 fibril...
Source: Cardiovascular Engineering - August 7, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

The Role of Pulse Transit Time as an Index of Arterial Stiffness During ExerciseEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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, Fa...
Source: Cardiovascular Engineering - August 6, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Pulse Wave Velocity and Digital Volume Pulse as Indirect Estimators of Blood Pressure: Pilot Study on Healthy VolunteersEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 D...
Source: Cardiovascular Engineering - August 6, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Quantitative Prediction of Body Surface Potentials from Myocardial Action Potentials Using a Summed Dipole ModelEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ...
Source: Cardiovascular Engineering - June 20, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

CPR Degradation DiagramEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 Bas...
Source: Cardiovascular Engineering - June 17, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

A Novel Wave Reflection Model of the Human Arterial SystemEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 visc...
Source: Cardiovascular Engineering - June 4, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Parametric Versus Nonparametric Transfer Function Estimation of Cerebral Autoregulation from Spontaneous Blood-Pressure OscillationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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, ...
Source: Cardiovascular Engineering - May 28, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Assessment of dσ*/dtmax, a Load Independent Index of Contractility, in the CanineEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ...
Source: Cardiovascular Engineering - May 24, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

An Evaluation of the Cuffless Blood Pressure Estimation Based on Pulse Transit Time Technique: a Half Year Study on Normotensive SubjectsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 correla...
Source: Cardiovascular Engineering - April 21, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Brachial Artery Differential Characteristic Impedance: Contributions from Changes in Young’s Modulus and DiameterEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - April 11, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Spectral Energy of ECG Morphologic Differences to Predict DeathEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 repol...
Source: Cardiovascular Engineering - March 13, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Characterization of the Location and Extent of Myocardial Infarction Using Heart Vector AnalysisEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 evalua...
Source: Cardiovascular Engineering - March 5, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

A New Noninvasive Device for Measuring Central Ejection dP/dt Mathematical Foundation of Cardiac dP/dt Measurement Using a Model for a Collapsible ArteryEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 reconstr...
Source: Cardiovascular Engineering - March 4, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Alveolar Recruitment Strategy During Cardiopulmonary Bypass Does Not Improve Postoperative Gas Exchange and Lung FunctionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 clam...
Source: Cardiovascular Engineering - March 4, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Noninvasive Monitoring of Transient Cardiac Changes with Impedance CardiographyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - January 8, 2009 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Electrophysiology of Connection Current SpikesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 encoun...
Source: Cardiovascular Engineering - December 2, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Estimation of Nonlinear Mechanical Properties of Vascular Tissues via ElastographyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ima...
Source: Cardiovascular Engineering - December 2, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Three Dimensional Transient Multifield Analysis of a Piezoelectric Micropump for Drug Delivery System for Treatment of Hemodynamic DysfunctionsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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, fi...
Source: Cardiovascular Engineering - November 23, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Development and Application of a Logistic-Based Systolic Model for Hemodynamic Measurements Using the Esophageal Doppler MonitorEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ED...
Source: Cardiovascular Engineering - June 28, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

How Much Lung Ventilation is Obtained with Only Chest-compression CPR?Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ...
Source: Cardiovascular Engineering - June 26, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Effects of Muscle Pump on Rotary Blood Pumps in Dynamic Exercise: A Computer Simulation StudyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ph...
Source: Cardiovascular Engineering - June 19, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Wavelet-based Correlations of Skin Temperature and Blood Flow OscillationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 fluctua...
Source: Cardiovascular Engineering - June 19, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

A Mechanical Model of the Human Heart Relating Septal Function to Myocardial Work and EnergyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 an...
Source: Cardiovascular Engineering - June 10, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Introduction to the Special Issues: Short-term Cardiovascular–Respiratory Control MechanismsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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)
Source: Cardiovascular Engineering - January 15, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Multiscale Analysis of Heart Rate Dynamics: Entropy and Time Irreversibility MeasuresEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 i...
Source: Cardiovascular Engineering - January 3, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Modeling Heart Rate Regulation—Part II: Parameter Identification and AnalysisEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ov...
Source: Cardiovascular Engineering - January 3, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Statistical Considerations and Techniques for Understanding Physiological Data, Modeling, and TreatmentsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ...
Source: Cardiovascular Engineering - January 3, 2008 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Nonlinear Assessment of Cerebral Autoregulation from Spontaneous Blood Pressure and Cerebral Blood Flow FluctuationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 pre...
Source: Cardiovascular Engineering - December 15, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Sensitivity Analysis and Model Assessment: Mathematical Models for Arterial Blood Flow and Blood PressureEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 par...
Source: Cardiovascular Engineering - December 15, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Arterial Baroreflexes and Cardiovascular ModelingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - December 15, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Determination of myocardial energetic output for cardiac rhythm pacingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 cardiovas...
Source: Cardiovascular Engineering - December 14, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

A Respiratory System Model: Parameter Estimation and Sensitivity AnalysisEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 p...
Source: Cardiovascular Engineering - December 7, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Modeling Heart Rate Regulation—Part I: Sit-to-stand Versus Head-up TiltEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 outf...
Source: Cardiovascular Engineering - December 7, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Receding Horizon Controller for the Baroreceptor Loop in a Model for the Cardiovascular SystemEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 cos...
Source: Cardiovascular Engineering - December 5, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Modeling of Autonomic Control in Sleep-Disordered BreathingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - December 4, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Cerebral Autoregulation: From Models to Clinical ApplicationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 thig...
Source: Cardiovascular Engineering - November 28, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Variability in Cardiovascular Control: The Baroreflex ReconsideredEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - November 28, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Transient, Three-dimensional, Multiscale Simulations of the Human Aortic ValveEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 ...
Source: Cardiovascular Engineering - November 17, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Pressure Phase-plane Based Determination of the Onset of Left Ventricular RelaxationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 thermodynamic...
Source: Cardiovascular Engineering - November 17, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Allometric Hemodynamic Analysis of Isolated Systolic Hypertension and AgingEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 fact...
Source: Cardiovascular Engineering - November 16, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Analysis of the Effect of Ageing on Rising Edge Characteristics of the Photoplethysmogram using a Modified Windkessel ModelEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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...
Source: Cardiovascular Engineering - November 9, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals

Effect of Pacing Site on Systolic Mechanical Restitution Curves in the In Vivo Canine ModelEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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 A...
Source: Cardiovascular Engineering - September 18, 2007 Category: Cardiology Tags: Cardiovascular Engineering Source Type: journals