AJP - Heart and Circulatory Physiology, Vol 242, Issue 6 942-H948, Copyright © 1982 by American Physiological Society
Mechanism of higher oxygen consumption rate: pressure-loaded vs. volume-loaded heart
H. Suga, R. Hisano, S. Hirata, T. Hayashi and I. Ninomiya
The greater cardiac oxygen consumption (VO2) under pressure than under
volume load has been accounted for by the greater ventricular wall force
under pressure load. We cannot fully agree with this because the wall force
has not always been uniquely correlated with VO2. We attempted to account
for the greater VO2 under pressure load by the ventricular systolic
pressure-volume area (PVA), which we previously showed uniquely correlated
with VO2. In isolated supported canine hearts, we produced servo-controlled
ejecting contractions the stroke work (SW) of which was doubled from
control by doubling ejection pressure (P) with comparable stroke volume
(SV) and by doubling Sv with comparable P. Despite comparable increments in
SW from 370 to 680 mmHg.ml under two different loads, VO2 and PVA increased
significantly more under pressure load (from 0.033 ml O2/beat and 800
mmHg.ml to 0.0560 and 1,800, respectively) than under volume load
(increasing to 0.038 and 1,200, respectively; P less than 0.01). These
results suggested to us a new mechanism underlying the greater VO2 under
pressure load.
