AJP - Heart and Circulatory Physiology, Vol 247, Issue 5 861-H868, Copyright © 1984 by American Physiological Society
O2 reserve of left ventricle of isolated, saline-perfused rabbit heart
N. F. Paradise, J. M. Surmitis and C. L. Mackall
The heart from the pentobarbital-anesthetized rabbit was isolated, and a
fluid-filled balloon was placed in the left ventricular chamber for
assessment of isovolumic pressure development. The bicarbonate-buffered,
physiological perfusate was aerated initially with 95% O2-5% CO2, and then
progressive decreases in arterial O2 content (CaO2) were produced in a
stepwise fashion by substituting N2 for O2 in the aerating gas mixture. If,
for a specified set of experimental conditions, no change in ventricular
function occurred after the initial decrease in CaO2, it was concluded that
the heart was oxygenated adequately prior to the first CaO2 decrement.
Accordingly, with perfusate flow constant at 35 ml/min, adequate
oxygenation was achieved during aeration of perfusate with 95% O2 when
ventricular contraction rate was 30 beats/min and temperature (T) 22
degrees C. The preparation may have been just marginally O2 sufficient when
rate was 60 beats/min (T, 25 or 30 degrees C), but probably was hypoxic
when contraction rate was 120 beats/min (T, 30 or 37 degrees C). Perfusion
with pressure kept constant at 80 mmHg did not appear to alleviate this
hypoxia when metabolism was elevated (rate, 120 beats/min; T, 37 degrees
C). Thus, unless the contraction rate is very low, the addition of an
O2-carrying vehicle to the perfusate appears to be necessary if O2 delivery
to the isolated rabbit heart preparation is to be supramaximal.
