Alterations in preload and ejection phase indices of left ventricular performance

Abstract

Ejection phase indices such as mean velocity of circumferential fiber shortening (V), ejection fraction (EF), and mean normalized systolic ejection rate (MSER) are thought to reflect the level of left ventricular (LV) inotropic state. Although known to be influenced by changes in afterload, their response to altered preload is less certain. This question was examined in 10 normal subjects studied in the supine position and after 10 min of 75° head up tilt. Echo LV diameter (D) and carotid pulse recordings were used to calculate LV ejection time, V, MSER, LV end diastolic and stroke volumes (EDV and SV, by D3 formula), and ejection fraction. Systemic blood pressure (BP) was measured by cuff, and heart rate (HR) counted from the ECG. Calculated LV EDV decreased with tilt (115±8 to 82±7 ml, P<0.001), as did SV (81±6 to 54±6 ml, P<0.001), and ejection time (0.31±0.01 to 0.27±0.00 sec, P<0.001), but there was no significant change in systolic or diastolic BP or HR. V, EF, and MSER were not significantly altered by tilt (1.09±0.04 to 1.12±0.05 circ/sec; 0.70±0.02 to 0.65±0.02; and 2.29±0.07 to 2.43±0.08 end diastolic volumes/sec, respectively). V, MSER, and EF appear relatively unaffected by acute alterations in preload. That compensatory sympathetic responses blunted potential changes cannot be excluded, although HR was not found to have increased.