785-4 Relative Importance of Convective and Inertial Forces During Left Ventricular Filling

Abstract

Doppler measurements of trans mitral velocity profiles are commonly used to assess left ventricular diastolic function. However these velocity measurements provide only information on the convective forces involved in left ventricular filling. The Inertial forces are completely neglected. In this study we evaluated the relative contributions of convective and inertial forces during early left ventricular filling. Left atrial and ventricular pressures were measured using Millar catheters while simultaneous transmitral color Doppler M-mode velocities were obtained during a series of four open chested canine experiments. The convective contribution ΔP c = pv 2 /2 was calculated from the maximum transvalvular velocities. Assuming that viscous forces can be neglected, the inertial contribution (ΔP i ) to the early diastolic filling gradient, was calculated as the difference between the invasively measured gradient (ΔP) and ΔPc. The instantaneous ratio of inertial (I) to convective (C) contributions I/C = ΔP i /ΔP c , was computed. The maximum ratio during early filling, I/C max , and the ratio at the time of the peak filling gradient, I/C ΔPmax , were calculated. The figure illustrates a typical catheter gradient (ΔP) and the convective contribution (ΔP c ) with the instantaneous I/C ratio during diastolic filling. During early filling, inertial forces initially dominate the convective contributions to the transvalvular gradient. The I/C max = 5.51 ± 2.26; and I/CΔP max = 3.87 ± 1.56. Inertial forces dominate convective forces during early diastolic filling and can not be negleted in the calculation of transvalvular gradients across normal mitral valves. Assessment of inertial forces is important in the interpretation of noninvasive Doppler parameters to assess diastolic left ventricular function function.