AJP - Heart and Circulatory Physiology, Vol 256, Issue 1 222-H232, Copyright © 1989 by American Physiological Society
Influence of nonuniformity on rate of left ventricular pressure fall in the dog
W. Y. Lew and C. M. Rasmussen
Department of Medicine, Veterans Administration Medical Center, San Diego, Calfornia.
We examined the influence of nonuniformity in regional ventricular function
on the rate of left ventricular pressure fall in 10 anesthetized dogs.
Ultrasonic segment gauges were implanted in the midwall of the anterior,
lateral, and posterior left ventricle. In seven dogs, nonuniformity was
produced by infusing isoproterenol (0.4 microgram/ml) into the mid-left
anterior descending coronary artery at low flow (0.5 +/- 0.7 ml/min) and
high flow (1.5 +/- 1.2 ml/min) rates, for total doses of 0.1 +/- 0.1 and
0.3 +/- 0.2 micrograms, respectively. This produced a dose-dependent
increase in anterior segment shortening so that shortening was completed
earlier and marked segment lengthening occurred during isovolumic
relaxation. Lateral and posterior segments were not directly stimulated.
The heart rate, left ventricular end-diastolic pressure, and peak systolic
pressure remained constant. However, tau, the time constant of left
ventricular pressure fall, increased from 32 +/- 8 to 37 +/- 10 ms with the
low dose, and from 35 +/- 6 to 49 +/- 12 ms with the high dose of
isoproterenol. Similar results occurred in two dogs when isoproterenol was
infused into the proximal, mid, or distal left anterior descending and in
three dogs with infusions in the left circumflex coronary artery. We
conclude that nonuniformity of regional left ventricular function is an
important and independent factor regulating the rate of pressure fall in
the intact ejecting left ventricle.
