Model and influence of mitral valve opening during the left ventricular filling

The flow inside a model left ventricle during filling (diastole) is simulated by the numerical solution of the equations of motion under the axisymmetric approximation. The left ventricle is taken with a truncated ellipsoid geometry, and a simple conceptual model is introduced to simulate the presence of the moving mitral valve. A relevant role during the left ventricle diastolic flow, as already discussed by other authors, is played by the travelling vortex wake that is formed from the transmitral jet during the early filling acceleration phase. The presence of a moving valve is found to produce a non-simultaneous spatial development of the entering bulk flow and a slightly more complex vortex wake structure; the results are discussed in comparison with fixed valve ones. They are analysed also in terms of M-mode representation suggesting a physical interpretation of the pattern detected in the clinical measurements that extends the one given previously on the basis of fixed valve models.     

Dynamics of left ventricular wall and mitral valve mechanics--a model study

The relation between global left ventricular pumping characteristics and local cardiac muscle fiber mechanics is represented by a mathematical model of left ventricular mechanics in which the mitral valve papillary muscle system is incorporated. The wall of the left ventricle is simulated by a thick-walled cylinder. Transmural differences in fiber orientation are incorporated by changing the direction of material anisotropy across the wall. The cylinder is free to twist. The upper end of the cylinder is covered by a thin, flexible sheet, representing the base of the left ventricle. The mitral valve is incorporated in this sheet. The tips of the mitral leaflets are connected by chordae tendineae to the papillary muscles which are attached to the bottom of the cylinder. Canine cardiac cycles were simulated for various end-diastolic values of left ventricular volume (25-120 ml, control 60 ml), left atrial pressure (0-2.7 kPa, control 0.22 kPa) and aortic pressure (5-11 kPa, control 11 kPa). In this wide range of preload and afterload mechanical loading of the muscle fibers appeared to be distributed quite evenly (SD: +/- 5% of control value) over all muscular structures of the left ventricle, including the papillary muscles.     

Wave intensity analysis of left ventricular filling

Wave intensity analysis (WIA) is a powerful technique to study pressure and flow velocity waves in the time domain in vascular networks. The method is based on the analysis of energy transported by the wave through computation of the wave intensity dI = dPdU, where dP and dU denote pressure and flow velocity changes per time interval, respectively. In this study we propose an analytical modification to the WIA so that it can be used to study waves in conditions of time varying elastic properties, such as the left ventricle (LV) during diastole. The approach is first analytically elaborated for a one-dimensional elastic tube-model of the left ventricle with a time-dependent pressure-area relationship. Data obtained with a validated quasi-three dimensional axi-symmetrical model of the left ventricle are employed to demonstrate this new approach. Along the base-apex axis close to the base wave intensity curves are obtained, both using the standard method and the newly proposed modified method. The main difference between the standard and modified wave intensity pattern occurs immediately after the opening of the mitral valve. Where the standard WIA shows a backward expansion wave, the modified analysis shows a forward compression wave. The proposed modification needs to be taken into account when studying left ventricular relaxation, as it affects the wave type.     

FSI simulation of asymmetric mitral valve dynamics during diastolic filling

In this article, we present a fluid-structure interaction algorithm accounting for the mutual interaction between two rigid bodies. The algorithm was used to perform a numerical simulation of mitral valve (MV) dynamics during diastolic filling. In numerical simulations of intraventricular flow and MV motion, the asymmetry of the leaflets is often neglected. In this study the MV was rendered as two rigid, asymmetric leaflets. The 2D simulations incorporated the dynamic interaction of blood flow and leaflet motion and an imposed subject-specific, transient left ventricular wall movement obtained from ultrasound recordings. By including the full Jacobian matrix in the algorithm, the speed of the simulation was enhanced by more than 20% compared to using a diagonal Jacobian matrix. Furthermore, our results indicate that important features of the flow field may not be predicted by the use of symmetric leaflets or in the absence of an adequate model for the left atrium.     

Diastolic right ventricular filling vortex in normal and volume overload states

Functional imaging computational fluid dynamics simulations of right ventricular (RV) inflow fields were obtained by comprehensive software using individual animal-specific dynamic imaging data input from three-dimensional (3-D) real-time echocardiography (RT3D) on a CRAY T-90 supercomputer. Chronically instrumented, lightly sedated awake dogs (n = 7) with normal wall motion (NWM) at control and normal or diastolic paradoxical septal motion (PSM) during RV volume overload were investigated. Up to the E-wave peak, instantaneous inflow streamlines extended from the tricuspid orifice to the RV endocardial surface in an expanding fanlike pattern. During the descending limb of the E-wave, large-scale (macroscopic or global) vortical motions ensued within the filling RV chamber. Both at control and during RV volume overload (with or without PSM), blood streams rolled up from regions near the walls toward the base. The extent and strength of the ring vortex surrounding the main stream were reduced with chamber dilatation. A hypothesis is proposed for a facilitatory role of the diastolic vortex for ventricular filling. The filling vortex supports filling by shunting inflow kinetic energy, which would otherwise contribute to an inflow-impeding convective pressure rise between inflow orifice and the large endocardial surface of the expanding chamber, into the rotational kinetic energy of the vortical motion that is destined to be dissipated as heat. The basic information presented should improve application and interpretation of noninvasive (Doppler color flow mapping, velocity-encoded cine magnetic resonance imaging, etc.) diastolic diagnostic studies and lead to improved understanding and recognition of subtle, flow-associated abnormalities in ventricular dilatation and remodeling.     

Determinants of left ventricular shape change during filling

Left ventricular shape and shape change are easy to measure and their analysis has been proposed as a noninvasive method to determine myocardial anisotropy. In preparation for applying this approach to studies of rats with experimentally induced cardiac hypertrophy, the goals of this study were to describe normal shape changes during diastolic filling in the rat and to utilize a finite-element model to estimate the relative importance of three factors that determine left ventricular shape change during filling: global chamber compliance, fiber to crossfiber stiffness ratio, and fiber architecture. The results suggest that left ventricular shape change is least sensitive to fiber to cross fiber stiffness ratio, and that this will likely limit the practical utility of using shape changes to diagnose changes in myocardial anisotropy.     

Time-resolved DPIV analysis of vortex dynamics in a left ventricular model through bileaflet mechanical and porcine heart valve prostheses

The performance of the heart after a mitral valve replacement operation greatly depends on the flow character downstream of the valve. The design and implanting orientation of valves may considerably affect the flow development. A study of the hemodynamics of two orientations, anatomical and anti-anatomical, of the St. Jude Medical (SJM) bileaflet valve are presented and compared with those of the SJM Biocor porcine valve, which served also to represent the natural valve. We document the velocity field in a flexible, transparent (LV) using time-resolved digital particle image velocimetry (TRDPIV). Vortex formation and vortex interaction are two important physical phenomena that dominate the filling and emptying of the ventricle. For the three configurations, the following effects were examined: mitral valve inlet jet asymmetry, survival of vortical structures upstream of the aortic valve, vortex-induced velocities and redirection of theflow in abidance of the Biot-Savart law, domain segmentation, resonant times of vortical structures, and regions of stagnantflow. The presence of three distinct flow patterns, for the three configurations, was identified by the location of vortical structures and level of coherence corresponding to a significant variation in the turbulence level distribution inside the LV. The adverse effect of these observations could potentially compromise the efficiency of the LV and result in flow patterns that deviate from those in the natural heart.     

Influence of dilated cardiomyopathy and a left ventricular assist device on vortex dynamics in the left ventricle

Together with new developments in mechanical cardiac support, the analysis of vortex dynamics in the left ventricle has become an increasingly important topic in literature. The aim of this study was to develop a method to investigate the influence of a left ventricular assist device (LVAD) on vortex dynamics in a failing ventricle. An axisymmetric fluid dynamics model of the left ventricle was developed and coupled to a lumped parameter model of the complete circulation. Simulations were performed for healthy conditions and dilated cardiomyopathy (DCM). Vortex structures in these simulations were analysed by means of automated detection. Results show that the strength of the leading vortex ring is lower in a DCM ventricle than in a healthy ventricle. The LVAD further influences the maximum strength of the vortex and also causes the vortex to disappear earlier in time with increasing LVAD flows. Understanding these phenomena by means of the method proposed in this study will contribute to enhanced diagnostics and monitoring during cardiac support.     

Influence of dilated cardiomyopathy and a left ventricular assist device on vortex dynamics in the left ventricle

Together with new developments in mechanical cardiac support, the analysis of vortex dynamics in the left ventricle has become an increasingly important topic in literature. The aim of this study was to develop a method to investigate the influence of a left ventricular assist device (LVAD) on vortex dynamics in a failing ventricle. An axisymmetric fluid dynamics model of the left ventricle was developed and coupled to a lumped parameter model of the complete circulation. Simulations were performed for healthy conditions and dilated cardiomyopathy (DCM). Vortex structures in these simulations were analysed by means of automated detection. Results show that the strength of the leading vortex ring is lower in a DCM ventricle than in a healthy ventricle. The LVAD further influences the maximum strength of the vortex and also causes the vortex to disappear earlier in time with increasing LVAD flows. Understanding these phenomena by means of the method proposed in this study will contribute to enhanced diagnostics and monitoring during cardiac support.     

Influence of the pericardium on right and left ventricular filling in the dog

We compared the influence of the pericardium on left and right ventricular (LV, RV) filling by measuring LV and RV pressures and segment lengths (SL, LV free wall, and RV inflow and outflow tracts) in six open-chest, pentobarbital sodium-anesthetized dogs before and after pericardiectomy. End-diastolic pressure (EDP) was varied by partial caval occlusion and dextran infusion. At each site the ln EDP-SL relation was fitted by linear regression and characterized by its slope and 1-Torr EDP intercept. The slope and 1-Torr intercept of the LV ln EDP-SL relation changed variably after pericardiectomy, but in each dog a change occurred that shifted this relation downward. In contrast, the RV inflow tract slope invariably decreased significantly after pericardiectomy, whereas its intercept was unchanged in all but one dog. The RV outflow tract results were similar to the inflow tract but less consistent. By the use of the raw EDP-SL data points, we calculated that the absolute contribution of the pericardium to EDP (i.e., the effective pericardial surface pressure) was similar at the three sites. However, as EDP values increased the proportional contribution of the pericardium to right ventricular end-diastolic pressure (RVEDP) increased, whereas that to left ventricular end-diastolic pressure (LVEDP) remained relatively constant. As a result, at the higher EDP values tested, the pericardium was responsible for a larger proportion of RVEDP than LVEDP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fluid dynamics of the left ventricular filling in dilated cardiomyopathy

Modifications in diastolic function occur in a broad range of cardiovascular diseases and there is an increasing evidence that abnormalities in left ventricular function may contribute significantly to the symptomatology. The flow inside the left ventricle during the diastole is here investigated by numerical solution of the Navier-Stokes equations under the axisymmetric assumption. The equation are written in a body-fitted, moving prolate spheroid, system of coordinates and solved using a fractional step method. The system is forced by a given volume time-law derived from clinical data, and varying the two-degrees-of-freedom ventricle geometry on the basis of a simple model. The solution under healthy conditions is analysed in terms of vorticity dynamics, showing that the flow field is characterised by the presence of a vortex wake; it is attached to the mitral valve during the accelerating phase of the E-wave, and it detaches and translate towards the ventricle apex afterwards. The flow evolution is discussed, results are also reported as an M-mode representation of colour-coded Doppler velocity maps. In the presence of ventricle dilatation the mitral jet extends farther inside the ventricle, propagation velocity decreases, and the fluid stagnates longer at the apex.     

Effects of changes in left ventricular loading and pleural pressure on mitral flow

The cause of the fall in left ventricular (LV) stroke volume (SV) during a fall in pleural pressure (Pp1) has been in dispute for over a century. We have defined the changes in the temporal relationship between LV inflow (Qm) and outflow (Qa) in a canine preparation to test the mutually exclusive hypotheses that the fall in LVSV is caused only by changes during diastole (e.g., ventricular interdependence) or only by changes during systole (e.g., afterload). The ability of the experimental preparation to measure the results of acute changes in right heart volume or output and acute changes in LV afterload was validated in open-chest studies with and without pericardial constraint. In closed-chest studies, with a fall in Pp1 during a Mueller maneuver Qm reached both its inspiratory minimum and expiratory maximum before Qa in 80% of the Mueller maneuvers, invalidating both hypotheses, which each required that one flow lead the other in 100% of the Mueller maneuvers. Review of individual records suggested that if the rapid changes in Pp1 occurred during systole, Qa could vary in a manner independent of the preceding Qm. These studies suggest that both diastolic and systolic events may contribute to the fall in SV, while causing opposite changes in LV volumes.     

Global longitudinal strain to predict left ventricular dysfunction in asymptomatic patients with severe mitral valve regurgitation: literature review

Netherlands Heart Journal - The optimal treatment strategy for asymptomatic patients with severe mitral valve regurgitation (MR) and preserved left ventricular (LV) function is challenging. This...     

The role of displacement of the mitral annulus in left atrial filling and emptying in the intact dog

The variations in ventricular-atrial mitral annular position during the cardiac cycle and the simultaneous changes in left atrial silhouette area (obtained by angiography after injections of contrast material into the main pulmonary artery) were investigated in six experiments on intact dogs with chronically implanted intracardiac markers. Frame-by-frame measurements of the angiograms (120 frames/s) were used to determine, under various hemodynamic conditions, the duration, magnitude, and average rate of the mitral annular motion and of the simultaneous changes in left atrial area during atrial filling (ventricular systole) and atrial emptying (early in ventricular diastole). The mitral annulus was seen to move towards the ventricular apex during systole and towards the atrium early in diastole with the duration, average rate, and magnitude of displacement (although varying widely) showing good statistical correlations (P less than 0.0005-0.005) with the changes in projected left atrial area. These findings suggest that the duration, rate, and magnitude of atrial filling and emptying may be, in the intact heart, determined by the movements of the atrioventricular junction.     

Developmental changes in left and right ventricular diastolic filling patterns in mice

Developmental changes in left and right ventricular diastolic filling patterns were determined noninvasively in isoflurane-anesthetized outbred ICR mice. Blood velocities in the mitral and tricuspid orifices were recorded in 16 embryos at days 14.5 (E14.5) and 17.5 of gestation (E17.5) using an ultrasound biomicroscope and also serially in three groups of postnatal mice aged 1-7 days (n = 23), 1-4 wk (n = 18), and 4-12 wk (n = 27) using 20-MHz pulsed Doppler. Postnatal body weight increased rapidly to 8 wk. Heart rate increased rapidly from approximately 180 beats/min at E14.5 to approximately 380 beats/min at 1 wk after birth and then more gradually to plateau at approximately 450 beats/min after 4 wk. Ventricular filling was quantified using the ratio of peak velocity of early ventricular filling due to active relaxation (E wave) to that of the late ventricular filling caused by atrial contraction (A wave) (peak E/A ratio) and the ratio of the peak E velocity to total time-velocity integral of E and A waves (peak E/total TVI ratio). Both ventricles had similar diastolic filling patterns in embryos (peak E/A ratio of 0.28 +/- 0.02 for mitral flow and 0.27 +/- 0.02 for tricuspid flow at E14.5). After birth, mitral peak E/A increased to >1 between the third and fifth day, continued to increase to 2.25 +/- 0.25 at approximately 3 wk, and then remained stable. The tricuspid peak E/A ratio increased much less but stabilized at the same age (increased to 0.79 +/- 0.03 at 3 wk). The peak E/total TVI ratio showed similar left-right differences and changes with development. Age-related changes were largely due to increases in peak E velocity. The results suggest that diastolic function matures approximately 3 wk postnatally, presumably in association with maturation of ventricular recoil and relaxation mechanisms.