Colour M-mode velocity propagation: a glance at intra-ventricular pressure gradients and early diastolic ventricular performance.

The physiology of early-diastolic filling comprises ventricular performance and fluid dynamical principles. Elastic recoil and myocardial relaxation rate determine left ventricular early diastolic performance. The integrity of left ventricular synchrony and geometry is essential to maintain the effect of their timely action on early diastolic left ventricular filling. These factors not only are prime determinants of left ventricular pressure decay during isovolumic relaxation and immediately after mitral valve opening; they also instigate the generation of a sufficient intra-ventricular pressure gradient, which enhances efficient early diastolic left ventricular filling. Accurate assessment of diastolic (dys)function by non-invasive techniques has important therapeutic and prognostic implications but remains a challenge to the cardiologist. The evaluation of left ventricular relaxation by the standard Doppler echocardiographic parameters is hindered by their preload dependency. The colour M-mode velocity propagation of early diastolic inflow (Vp) correlates with intra-ventricular pressure gradients and is a largely preload independent index of ventricular diastolic performance. In this article, the physiologic background, utility and limitations of this promising new tool for the study of early diastolic filling are reviewed.

Predicting ATS Open Pivot heart valve performance with computational fluid dynamics.

BACKGROUND AND AIM OF THE STUDY: In-vitro studies on the ATS heart valve have indicated that valve opening is less in an expanding conduit than in a straight conduit. METHODS: Bileaflet valve behavior was studied using a new computational fluid-structure interaction model. A three-dimensional model of the ATS valve was studied in two geometries, simulating the valve in a geometry with sudden expansion downstream of the valve, and in a straight conduit. Mitral and aortic flow patterns were simulated. RESULTS: The ATS valve in the expanding geometry showed opening to a maximum angle of 77.5 degrees; this was confirmed in previous clinical and in-vitro studies. The mean and maximum transvalvular Doppler pressure gradients were 1.1 and 4.3 mmHg, respectively. The maximum shear stress calculated on the leaflet was 25 Pa. Maximum opening of the valve was achieved in the straight conduit; with mean and maximum pressure gradients of 2.1 and 4.6 mmHg, respectively. The maximum shear stress calculated on the leaflet was 35 Pa. CONCLUSION: The results of this numerical study confirmed that valve hemodynamics and leaflet motion were dependent on the geometrical conditions of the valve: the presence of a diverging flow influenced the maximum opening angle of the valve leaflets. This model could be used to predict pressure gradients, effective orifice area, performance index and shear stress loading of mechanical heart valves, and in future will serve as a major research tool to characterize the hemodynamics of existing and new mechanical heart valves.

Hydrodynamics of color M-mode Doppler flow wave propagation velocity V(p): a computer study.

This study was designed to show the hydrodynamic mechanism of left ventricular (LV) flow wave propagation and to relate this propagated velocity to 2-dimensional (2D) color and color M-mode Doppler echocardiograms. A computer model is developed describing 3-dimensional axisymmetrical LV filling flow. The unsteady Navier-Stokes flow equations are solved in an LV truncated ellipsoid geometry with moving LV walls, including relaxation and compliance of the wall. The computed results confirm both intraventricular flow and pressure patterns during filling. Vortices are formed during the acceleration phases of the early and atrial filling waves. During the deceleration phases, the vortices are amplified and convected into the ventricle. The vortices are recognized on the derived 2D color echocardiograms as in vivo. The propagation of this vortex determines the propagation of the maximum velocity observed in the color M-mode Doppler echocardiogram. For pseudonormal filling of the left ventricle, the LV flow wave propagation velocity decreases.