Contribution of long axis motion of left ventricular outflow to calculation of left ventricular stroke volume
Stroke volume can be calculated by using noninvasive Doppler techniques. The products of pulsed Doppler stroke distance of left ventricular outflow and left ventricular outflow area can often be used to calculate stroke volume. However, left ventricular outflow also moves longitudinally toward the apex of the ventricle during systole, so that zero velocity flow cannot be detected by the usual pulsed Doppler studies. We evaluated the contribution of these zero velocity flow to the noninvasive estimation of left ventricular stroke volume in 20 patients with left ventricular disease and in 20 age matched healthy controls. Left ventricular stroke distance was calculated by summing the Doppler stroke distance and the outflow long axis motion. The percentage of zero velocity flow for total stroke volume was calculated in each group. Cardiac output was also measured by thermo-dilution technique. The percentage of zero velocity flow for total noninvasive stroke volume in patients with left ventricular disease was 2.5±1.1 ml (4.0±1.5%), significantly lower than in normal subjects, 3.6±1.0 ml (5.5±1.5%) (p<0.05). These long axis motions are significantly reduced, especially in left ventricular disease. Amplitudes of the left ventricular outflow long axis motion were correlated with Doppler stroke distance in all (r=0.54, p<0.01). In patients with myocardial infarction, stroke volume by thermo-dilution methods and calculated stroke volume showed good correlation both only by Doppler stroke distance (y=1.044x+0.547, r=0.968) and by Doppler and long axis motion (y=0.989x+0.521, r=0.974). Compared with stroke volume measured by thermodilution method, stroke volume calculated only by Doppler stroke distance was underestimated. We thus demonstrated the influence of zero velocity flow on left ventricular outflow both in patients with left ventricular disease and in normal subjects.