Alterations in preload and ejection phase indices of left ventricular performance,

Ejection phase indices such as mean velocity of circumferential fiber shortening (V-cf), 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 ten normal subjects studied in the supine position and after 10 min of 75 degree head-up tilt. Echo VL diameter (D) and carotid pulse recordings were used to calculate LV ejection time, V-cf, 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 LVEDV decreased with tilt (115 plus or minus 8 to 82 plus or minus 7 ml, P smaller than 0.001), as did SV (81 plus or minus 6 to 54 plus or minus 6 ml, P smaller than 0.001), and ejection time (0.31 plus or minus 0.01 to 0.27 plus or minus 0.00 sec, P smaller than 0.001), but there was no significant change in systolic or diastolic BP or HR. V-cf, EF, and MSER were not singificantly altered by tilt (1.09 plus or minsu 0.04 to 1.12 plus or minus 0.05 circ/sec; 0.70 plus or minus 0.02 to 0.65 plus or minus 0.02; and 2.29 plus or minus 0.07 to 2.43 plus or minus 0.08 end-diastolic volumes/sec, respectively). V-cf, MSER, and EF appearrelatively unaffected by acute alterations in preload. That compensatory sympathetic responses blunted potential changes cannot be excluded, although HR was not found to have increased.