Numerical modeling of ventricular filling

Doppler mitral inflow variables time course after treadmill stress echo with and without ischemic response

This study evaluated Doppler mitral inflow variables changes from rest to post-exercise among 104 subjects with and without echocardiographic evidence of ischemic response (IR) to exercise (63.9 ± 11 years, 54% male, 32% with IR) who underwent a clinically indicated treadmill stress echo (TSE) test. The time from exercise cessation to imaging (TIME) was recorded. The changes (after TSE minus baseline values) in the peak E-wave velocity (∆E) [34.2 vs. 24.2, p = 0.024] and E-wave deceleration rate (∆DR) [348.0 vs. 225.7, p = 0.010] were bigger in ischemic than in nonischemic subjects, while the changes in the peak A-wave velocity (∆A) did not differ [7.9 vs. 15.0, p = 0.082]. The correlations between Doppler variables and IR, TIME, and TIME × IR interaction were analyzed. We observed a significant interaction between TIME and IR regarding ∆E and ∆DR. The differences in the regression line slopes of time courses for ∆E and ∆DR based on IR were significant: ∆E (- 0.09 vs. - 8.17, p = 0.037) and ∆DR (11.23 vs. - 82.60, p = 0.022). Main findings: (1) Time courses after exercise of ∆E and ∆DR in subjects with and without IR were different. (2) ∆E and ∆DR did not differ between subjects with and without IR at exercise cessation (TIME = 0). (3) The simple main effect of ischemia on ∆E and ∆DR was significant at TIME of ≥ 3 min. Divergent time courses of ∆E and ∆DR after exercise might be promising for detecting diastolic dysfunction caused by ischemia. After the cessation of exercise, ΔE and ΔDR in nonischemic but not in ischemic subjects quickly tend to zero. The differences in ΔE and ΔDR between the two groups only became significant for TIME of ≥ 3 min. At the time of exercise cessation, the values of ΔE and ΔDR (taken from the regression lines) were not significantly different between the patients with and without IR. This divergent response is promising for detecting diastolic dysfunction caused by ischemia.

Noninvasive Estimation of Pressure Changes Using 2-D Vector Velocity Ultrasound: An Experimental Study With In Vivo Examples

A noninvasive method for estimating intravascular pressure changes using 2-D vector velocity is presented. The method was first validated on computational fluid dynamic (CFD) data and with catheter measurements on phantoms. Hereafter, the method was tested in vivo at the carotid bifurcation and at the aortic valve of two healthy volunteers. Ultrasound measurements were performed using the experimental scanner SARUS, in combination with an 8 MHz linear array transducer for experimental scans and a carotid scan, whereas a 3.5-MHz phased array probe was employed for a scan of an aortic valve. Measured 2-D fields of angle-independent vector velocities were obtained using synthetic aperture imaging. Pressure drops from simulated steady flow through six vessel geometries spanning different degrees of diameter narrowing, running from 20%-70%, showed relative biases from 0.35% to 12.06%, depending on the degree of constriction. Phantom measurements were performed on a vessel with the same geometry as the 70% constricted CFD model. The derived pressure drops were compared to pressure drops measured by a clinically used 4F catheter and to a finite-element model. The proposed method showed peak systolic pressure drops of -3 kPa ± 57 Pa, while the catheter and the simulation model showed -5.4 kPa ± 52 Pa and -2.9 kPa, respectively. An in vivo acquisition of 10 s was made at the carotid bifurcation. This produced eight cardiac cycles from where pressure gradients of -227 ± 15 Pa were found. Finally, the aortic valve measurement showed a peak pressure drop of -2.1 kPa over one cardiac cycle. In conclusion, pressure gradients from convective flow changes are detectable using 2-D vector velocity ultrasound.

Fluid-structure interaction of an aortic heart valve prosthesis driven by an animated anatomic left ventricle

We develop a novel large-scale kinematic model for animating the left ventricle (LV) wall and use this model to drive the fluid-structure interaction (FSI) between the ensuing blood flow and a mechanical heart valve prosthesis implanted in the aortic position of an anatomic LV/aorta configuration. The kinematic model is of lumped type and employs a cell-based, FitzHugh-Nagumo framework to simulate the motion of the LV wall in response to an excitation wavefront propagating along the heart wall. The emerging large-scale LV wall motion exhibits complex contractile mechanisms that include contraction (twist) and expansion (untwist). The kinematic model is shown to yield global LV motion parameters that are well within the physiologic range throughout the cardiac cycle. The FSI between the leaflets of the mechanical heart valve and the blood flow driven by the dynamic LV wall motion and mitral inflow is simulated using the curvilinear immersed boundary (CURVIB) method [1, 2] implemented in conjunction with a domain decomposition approach. The computed results show that the simulated flow patterns are in good qualitative agreement with in vivo observations. The simulations also reveal complex kinematics of the valve leaflets, thus, underscoring the need for patient-specific simulations of heart valve prosthesis and other cardiac devices.

Left intraventricular diastolic and systolic pressure gradients

To describe left ventricular (LV) function comprehensively, it is crucial to characterize precisely transmitral, intraventricular and transaortic pressure–flow relations. The site of measurement is important; as the measurement location is moved from the mitral valve toward the apex and the outflow tract, important regional pressure differences are recorded inside the LV. These intraventricular pressure gradients (IVPGs) play an important role in ventricular filling in the normal heart and may be abolished by systolic or diastolic dysfunction. Despite their apparent importance in ventricular filling and diastolic function, IVPGs have never been utilized in clinical cardiology, due to the complexity of their acquisition. The application of Doppler echocardiography allows the reconstruction of diastolic IVPGs completely non-invasively, thus avoiding the risk and expense of a cardiac catheterization. Regional pressure gradients are also present during ventricular emptying but their correlation with systolic function is not so clear. The current minireview highlights theories and experimental data on invasive and non-invasive assessment of diastolic and systolic IVPGs and their role in LV filling and emptying. We also review the pathophysiological modulation of regional gradients, their importance in understanding and evaluating the complex phenomena underlying ventricular filling, as well as their potential clinical application.

Nonconvective forces: a critical and often ignored component in the echocardiographic assessment of transvalvular pressure gradients

Echocardiography is routinely used to assess ventricular and valvular function, particularly in patients with known or suspected cardiac disease and who have evidence of hemodynamic compromise. A cornerstone to the use of echocardiographic imaging is not only the qualitative assessment, but also the quantitative Doppler-derived velocity characteristics of intracardiac blood flow. While simplified equations, such as the modified Bernoulli equation, are used to estimate intracardiac pressure gradients based upon Doppler velocity data, these modified equations are based upon assumptions of the varying contributions of the different forces that contribute to blood flow. Unfortunately, the assumptions can result in significant miscalculations in determining a gradient if not completely understood or they are misapplied. We briefly summarize the principles of fluid dynamics that are used clinically with some of the inherent limitations of routine broad application of the simplified Bernoulli equation.

Coupling multi-physics models to cardiac mechanics

We outline and review the mathematical framework for representing mechanical deformation and contraction of the cardiac ventricles, and how this behaviour integrates with other processes crucial for understanding and modelling heart function. Building on general conservation principles of space, mass and momentum, we introduce an arbitrary Eulerian-Lagrangian framework governing the behaviour of both fluid and solid components. Exploiting the natural alignment of cardiac mechanical properties with the tissue microstructure, finite deformation measures and myocardial constitutive relations are referred to embedded structural axes. Coupling approaches for solving this large deformation mechanics framework with three dimensional fluid flow, coronary hemodynamics and electrical activation are described. We also discuss the potential of cardiac mechanics modelling for clinical applications.

Subject-specific computational simulation of left ventricular flow based on magnetic resonance imaging

A detailed investigation of left ventricle (LV) flow patterns could improve our understanding of the function of the heart and provide further insight into the mechanisms of heart failure. This study presents patient-specific modelling with magnetic resonance imaging (MRI) to investigate LV blood flow patterns in normal subjects. In the study, the prescribed LV wall movements based on the MRI measurements drove the blood flow in and out of the LV in computational fluid dynamics simulation. For the six subjects studied, the simulated LV flow swirls towards the aortic valve and is ejected into the ascending aorta with a vertical flow pattern that follows the left-hand rule. In diastole, the inflow adopts a reasonably straight route (with no significant secondary flow) towards the apex in the rapid filling phase with slight variations in the jet direction between different cases. When the jet reaches about two thirds of the distance from the inflow plane to the apex, the blood flow starts to change direction and swirls towards the apex. In the more slowly filling phase, a centrally located jet is evident with vortices located on both sides of the jet on an anterior—posterior plane that passes through the mitral and aortic valves. In the inferior—superior plane, a main vortex appears for most of the cases in which an anticlockwise vortex appears for three cases and a clockwise vortex occurs for one case. The simulated flow patterns agree well qualitatively with MRI-measured flow fields.

Intraventricular Pressure Gradients in Left Ventricular Aneurysms Determined by Color M-Mode Doppler Method: An Animal Study

BACKGROUND

Left ventricular aneurysm (LVA) may affect diastolic intraventricular blood flow. Color M-mode (CMM) Doppler flow propagation patterns are abnormal in the presence of apical aneurysms. The aim of this study was to validate the accuracy of CMM echocardiography for assessing the existence and size of LVA and to determine the intraventricular pressure gradient in LVA.

METHODS

CMM of the transmitral inflow in early diastole was obtained from the apical 4-chamber view in 19 sheep. The presence of the break point where the velocity decreased abruptly in the mitral inflow (point D) was determined and the distance between the apex and point D was measured. The intraventricular pressure difference between the base and the apex was measured by a catheter while it was calculated using CMM with the Euler equation.

RESULTS

The presence of the break point D showed 84% sensitivity and 100% specificity for determining the existence of an LVA. Distance between the apex and point D correlated well with scar size. Catheter- and CMM-derived intraventricular pressure difference correlated and agreed well (y = 1.0 x -0.2, r = 0.94).

CONCLUSIONS

The point of abrupt decrease in propagation velocity of the CMM recording indicated the presence and size of LVA. Intraventricular pressure gradients were determined noninvasively by CMM echocardiography with reasonable accuracy.

Relationship among diastolic intraventricular pressure gradients, relaxation, and preload: impact of age and fitness

Diastolic intraventricular pressure gradients (IVPGs) are a measure of the ability of the ventricle to facilitate its filling using diastolic suction. We assessed 15 healthy young but sedentary subjects, aged <50 yr (young subjects; age, 35 ± 9 yr); 13 healthy but sedentary seniors, aged >65 yr with known reductions in ventricular compliance (elderly sedentary subjects; age, 70 ± 4 yr); and 12 master athletes, aged >65 yr, previously shown to have preserved ventricular compliance (elderly fit subjects; age, 68 ± 3 yr). Pulmonary capillary wedge pressure (PCWP) and echocardiography measurements were performed at baseline, during load manipulation by lower body negative pressure at −15 and −30 mmHg, and after saline infusion of 10 and 20 ml/kg (elderly) or 15 and 30 ml/kg (young). IVPGs were obtained from color M-mode Doppler echocardiograms. Baseline IVPGs were lower (1.2 ± 0.4 vs. 2.4 ± 0.7 mmHg, P < 0.0001), and the time constant of pressure decay (τ0) was longer (60 ± 10 vs. 46 ± 6 ms, P < 0.0001) in elderly sedentary than in young subjects, with no difference in PCWP. Although PCWP changes during load manipulations were similar ( P = 0.70), IVPG changes were less prominent in elderly sedentary than in young subjects ( P = 0.02). Changes in stroke volume and IVPGs during loading manipulations correlated ( r = 0.96, P = 0.0002). PCWP and τ0 were strong multivariate correlates of IVPGs ( P < 0.001, for both). IVPG response to loading interventions in elderly sedentary and elderly fit subjects was similar ( P = 0.33), despite known large differences in ventricular compliance. The ability to regulate IVPGs during changes in preload is impaired with aging. Preserving ventricular compliance during aging by lifelong exercise training does not prevent this impairment.

Relationship of diastolic intraventricular pressure gradients and aerobic capacity in patients with diastolic heart failure

We sought to elucidate the relationship between diastolic intraventricular pressure gradients (IVPG) and exercise tolerance in patients with heart failure using color M-mode Doppler. Diastolic dysfunction has been implicated as a cause of low aerobic potential in patients with heart failure. We previously validated a novel method to evaluate diastolic function that involves noninvasive measurement of IVPG using color M-mode Doppler data. Thirty-one patients with heart failure and 15 normal subjects were recruited. Echocardiograms were performed before and after metabolic treadmill stress testing. Color M-mode Doppler was used to determine the diastolic propagation velocity ( Vp) and IVPG off-line. Resting diastolic function indexes including myocardial relaxation velocity, Vp, and E/ Vp correlated well with V̇o2 max ( r = 0.8, 0.5, and −0.5, respectively, P < 0.001 for all). There was a statistically significant increase in Vp and IVPG in both groups after exercise, but the change in IVPG was higher in normal subjects compared with patients with heart failure (2.6 ± 0.8 vs. 1.1 ± 0.8 mmHg, P < 0.05). Increase in IVPG correlated with peak V̇o2 max ( r = 0.8, P < 0.001) and was the strongest predictor of exercise capacity. Myocardial relaxation is an important determinant of exercise aerobic capacity. In heart failure patients, impaired myocardial relaxation is associated with reduced diastolic suction force during exercise.

Multiphysics simulation of left ventricular filling dynamics using fluid-structure interaction finite element method

To relate the subcellular molecular events to organ level physiology in heart, we have developed a three-dimensional finite-element-based simulation program incorporating the cellular mechanisms of excitation-contraction coupling and its propagation, and simulated the fluid-structure interaction involved in the contraction and relaxation of the human left ventricle. The FitzHugh-Nagumo model and four-state model representing the cross-bridge kinetics were adopted for cellular model. Both ventricular wall and blood in the cavity were modeled by finite element mesh. An arbitrary Lagrangian Eulerian finite element method with automatic mesh updating has been formulated for large domain changes, and a strong coupling strategy has been taken. Using electrical analog of pulmonary circulation and left atrium as a preload and the windkessel model as an afterload, dynamics of ventricular filling as well as ejection was simulated. We successfully reproduced the biphasic filling flow consisting of early rapid filling and atrial contraction similar to that reported in clinical observation. Furthermore, fluid-structure analysis enabled us to analyze the wave propagation velocity of filling flow. This simulator can be a powerful tool for establishing a link between molecular abnormality and the clinical disorder at the macroscopic level.

Noninvasive measurement of time-varying three-dimensional relative pressure fields within the human heart

Understanding cardiac blood flow patterns is important in the assessment of cardiovascular function. Three-dimensional flow and relative pressure fields within the human left ventricle are demonstrated by combining velocity measurements with computational fluid mechanics methods. The velocity field throughout the left atrium and ventricle of a normal human heart is measured using time-resolved three-dimensional phase-contrast MRI. Subsequently, the time-resolved three-dimensional relative pressure is calculated from this velocity field using the pressure Poisson equation. Noninvasive simultaneous assessment of cardiac pressure and flow phenomena is an important new tool for studying cardiac fluid dynamics.

Estimation of diastolic intraventricular pressure gradients by Doppler M-mode echocardiography

Previous studies have shown that small intraventricular pressure gradients (IVPG) are important for efficient filling of the left ventricle (LV) and as a sensitive marker for ischemia. Unfortunately, there has previously been no way of measuring these noninvasively, severely limiting their research and clinical utility. Color Doppler M-mode (CMM) echocardiography provides a spatiotemporal velocity distribution along the inflow tract throughout diastole, which we hypothesized would allow direct estimation of IVPG by using the Euler equation. Digital CMM images, obtained simultaneously with intracardiac pressure waveforms in six dogs, were processed by numerical differentiation for the Euler equation, then integrated to estimate IVPG and the total (left atrial to left ventricular apex) pressure drop. CMM-derived estimates agreed well with invasive measurements (IVPG: y = 0.87 x + 0.22, r = 0.96, P < 0.001, standard error of the estimate = 0.35 mmHg). Quantitative processing of CMM data allows accurate estimation of IVPG and tracking of changes induced by β-adrenergic stimulation. This novel approach provides unique information on LV filling dynamics in an entirely noninvasive way that has previously not been available for assessment of diastolic filling and function.

Diastolic dysfunction as a cause of exercise intolerance

Tachycardia accompanying exercise shortens the duration of diastole, reducing the time available for the left ventricular (LV) filling. Thus, the LV must fill more rapidly for the stroke volume to increase (or even be maintained) during exercise. Normally, this is accomplished without requiring an excessive increase in left atrial (LA) pressure by an acceleration of LV relaxation and a fall in LV early diastolic pressure during exercise. This response is lost following the development of heart failure due to systolic dysfunction, both in experimental animals and in patients. In fact, in such situations, LV relaxation slows and LV early diastolic pressure increases due to exercise. Thus, any diastolic dysfunction present at rest in CHF during systolic dysfunction is exacerbated during exercise. Similarly, patients with primary diastolic dysfunction heart failure with preserved systolic function may not be able to augment LV filling rates without an abnormal increase in LA pressure. Thus, diastolic dysfunction may contribute to exercise intolerance, both in systolic dysfunction and primary diastolic dysfunction. Acute studies suggest that treatment with angiotensin II receptor blockers or verapamil may improve exercise tolerance in some patients with primary diastolic dysfunction.

Noninvasive estimation of transmitral pressure drop across the normal mitral valve in humans: importance of convective and inertial forces during left ventricular filling

OBJECTIVES

We hypothesized that color M-mode (CMM) images could be used to solve the Euler equation, yielding regional pressure gradients along the scanline, which could then be integrated to yield the unsteady Bernoulli equation and estimate noninvasively both the convective and inertial components of the transmitral pressure difference.

BACKGROUND

Pulsed and continuous wave Doppler velocity measurements are routinely used clinically to assess severity of stenotic and regurgitant valves. However, only the convective component of the pressure gradient is measured, thereby neglecting the contribution of inertial forces, which may be significant, particularly for nonstenotic valves. Color M-mode provides a spatiotemporal representation of flow across the mitral valve.

METHODS

In eight patients undergoing coronary artery bypass grafting, high-fidelity left atrial and ventricular pressure measurements were obtained synchronously with transmitral CMM digital recordings. The instantaneous diastolic transmitral pressure difference was computed from the M-mode spatiotemporal velocity distribution using the unsteady flow form of the Bernoulli equation and was compared to the catheter measurements.

RESULTS

From 56 beats in 16 hemodynamic stages, inclusion of the inertial term ([deltapI]max = 1.78+/-1.30 mm Hg) in the noninvasive pressure difference calculation significantly increased the temporal correlation with catheter-based measurement (r = 0.35+/-0.24 vs. 0.81+/-0.15, p< 0.0001). It also allowed an accurate approximation of the peak pressure difference ([deltapc+I]max = 0.95 [delta(p)cathh]max + 0.24, r = 0.96, p<0.001, error = 0.08+/-0.54 mm Hg).

CONCLUSIONS

Inertial forces are significant components of the maximal pressure drop across the normal mitral valve. These can be accurately estimated noninvasively using CMM recordings of transmitral flow, which should improve the understanding of diastolic filling and function of the heart.

Cardiovascular responses to facial cooling are age and fitness dependent

PURPOSE

Aging of the cardiovascular system may be altered by differences in physical fitness. We investigated the cardiovascular responses to brief periods of facial cooling (5 degrees C) in 20 healthy men differing in age and aerobic fitness (VO2max).

METHODS

Facial cooling was administered at rest in the supine position during 60-s quiet breathing to 6 fit young (FY; VO2max = 75.8 +/- 18 mL x kg(-1) x min(-1); 29 +/- 7 yr), 6 sedentary young (SY; VO2max = 36.0 +/- 2.2 mL x kg(-1) x min(-1); 27 +/- 3 yr), 6 fit old (FO; VO2max = 56.1 +/- 4.0 mL x kg(-1) x min(-1); 54 +/- 5 yr), and 6 sedentary old (SO; VO2max = 29.6 +/- 5.0 mL x kg(-1) x min(-1); 62 +/- 2 yr) volunteers. The following were measured before and after facial cooling: heart rate (HR), mean arterial blood pressure (MAP), pressure-rate product (PRP), and M-mode echocardiographically determined left ventricular internal dimensions, peak circumferential shortening (peak V(CF)), and ejection fraction (EF).

RESULTS

Facial cooling produced a statistically significant bradycardia in all groups except for the SO whereas MAP was increased in the young groups but unchanged in the older groups. Pressure-rate product was significantly reduced in the FY, unchanged in the SY and FO, and significantly increased in the SO group. None of the groups showed a change in left ventricular dimensions, whereas only the SO group showed an increase in peak V(CF) (P < 0.05).

CONCLUSIONS

These data suggest that endurance training and fitness level do not significantly alter cardiovascular responses to facial cooling in young men or physically fit older men. However, in older subjects, a sedentary lifestyle appears to be associated with an absent facial cooling reflex bradycardia, an increased PRP, and contractility (peak V(CF)).

Digital storage and analysis of color Doppler echocardiograms

Color Doppler flow mapping has played an important role in clinical echocardiography. Most of the clinical work, however, has been primarily qualitative. Although qualitative information is very valuable, there is considerable quantitative information stored within the velocity map that has not been extensively exploited so far. Recently, many researchers have shown interest in using the encoded velocities to address the clinical problems such as quantification of valvular regurgitation, calculation of cardiac output, and characterization of ventricular filling. In this article, we review some basic physics and engineering aspects of color Doppler echocardiography, as well as drawbacks of trying to retrieve velocities from video tape data. Digital storage, which plays a critical role in performing quantitative analysis, is discussed in some detail with special attention to velocity encoding in DICOM 3.0 (medical image storage standard) and the use of digital compression. Lossy compression can considerably reduce file size with minimal loss of information (mostly redundant); this is critical for digital storage because of the enormous amount of data generated (a 10 minute study could require 18 Gigabytes of storage capacity). Lossy JPEG compression and its impact on quantitative analysis has been studied, showing that images compressed at 27:1 using the JPEG algorithm compares favorably with directly digitized video images, the current goldstandard. Some potential applications of these velocities in analyzing the proximal convergence zones, mitral inflow, and some areas of future development are also discussed in the article.

Experimental and numerically modeled effects of altered loading conditions on pulmonary venous flow and left atrial pressure in patients with mitral regurgitation

Pulmonary venous flow measured by pulsed-wave Doppler transesophageal echocardiography reflects the effects of mitral regurgitation on left atrial pressure contour. To assess the relationship between pulmonary venous flow and left atrial pressure in patients with mitral regurgitation under altered loading conditions, we studied 25 patients with 3+ or 4+ mitral regurgitation and a control group by measuring pulmonary venous flow with transesophageal echocardiography and left atrial pressures after administering saline solution (n = 6), nitroglycerin (n = 6), phenylephrine (n = 6), or nitroprusside (n = 7). After administration, the left atrial pressure v wave increased in the group given phenylephrine, concomitant with an increased diastolic flow. In contrast, the left atrial pressure v wave decreased in the group given nitroglycerin, concomitant with a decreased diastolic flow. Changes in diastolic flow were closely related to changes in the left atrial pressure v wave under all loading conditions (r = 0.91; p < 0.0001). Numeric modeling of left atrial pressure and pulmonary venous diastolic flow corroborated the experimental findings. We conclude that changes in pulmonary venous diastolic flow are closely related to changes in the left atrial pressure v wave in mitral regurgitation, under altered loading conditions.

Dynamics of systolic pulmonary venous flow in mitral regurgitation: mathematical modeling of the pulmonary venous system and atrium

The noninvasive assessment of mitral regurgitation has been an elusive clinical goal. Recent studies have highlighted the value of pulmonary venous (PV) flow reversal in indicating the presence of severe regurgitation. The purpose of this study was to explore the basic determinants of PV inflow in the presence and absence of regurgitation. In particular, the hypothesis that systolic PV flow depends on the interaction of regurgitant volume with atrial and PV properties (compliance, initial volume, total area of the pulmonary veins at the atrial junction, and the inertia of PV inflow) was tested and further, that the combination of these variables, rather than regurgitant volume alone, determines PV inflow. A mathematical model of the atrium and pulmonary veins was developed. Atrial and PV pressure were modeled as the product of chamber elastance and volume, where atrial elastance varied in time to simulate atrial relaxation and descent of the mitral anulus. A simplification of the modified unsteady Bernoulli equation was used to compute the PV velocities that resulted from the developed pressure gradient. The modeling was performed over a range of initial atrial elastances (0.77 to 0.2 mm Hg/cc), initial atrial volumes (20 to 75 cc), total PV areas (3.12 to 5.12 cm2), and PV inflow inertances (8 to 18 gm/cm2), with and without the addition of two regurgitant jets (regurgitant volume of 20 and 60 cc). The model realistically simulated the systolic PV waveform in magnitude and morphology. As the volume of regurgitation increased, PV peak flow velocity decreased, and eventually late systolic flow reversal occurred. However, the peak flow velocity, the time to peak flow, and the presence and magnitude of flow reversal were influenced by atrial compliance, volume, total atrial inlet area, and PV inflow inertia. This study found that PV flow blunting and reversal increased as atrial compliance, volume, and PV inertia decreased and as atrial inlet area increased. Atrial and PV properties (compliance, volume, total PV atrial inlet area, and PV inflow inertia), acting in combination, mediate the physiologic impact of the regurgitant lesion in terms of the resulting rise in atrial pressure as reflected by the pattern of systolic PV influx. For example, PV flow reversal is more likely in acute compared with chronic regurgitation because the atrium is less compliant and has a smaller initial volume. Therefore, the clinical assessment of mitral regurgitation using changes in systolic PV flow must be viewed in the context of atrial and PV properties.

Cardiac mechanics: basic and clinical contemporary research

This survey of cardiac hemodynamics updates evolving concepts of myocardial and ventricular systolic and diastolic loading and function. The pumping action of the heart and its interactions with arterial and venous systems in health and disease provide an extremely rich and challenging field of research, viewed from a fluid dynamic perspective. Many of the more important problems in this field, even if the fluid dynamics in them are considered in isolation, are found to raise questions which have not been asked in the history of fluid dynamics research. Biomedical engineering will increasingly contribute to their solution.