AJP - Heart and Circulatory Physiology, Vol 235, Issue 6 720-H727, Copyright © 1978 by American Physiological Society
Effects of acute global ischemia on diastolic relaxation in canine hearts
I. Palacios, J. B. Newell and W. J. Powell Jr
It is not known whether ventricular relaxation can be altered by ischemia
independent of associated hemodynamic changes. The effect of acute
myocardial ischemia on diastolic relaxation was studied under controlled
hemodynamic conditions in 16 anesthetized dogs on right-heart bypass. In
nine dogs, left ventricular end-diastolic pressure was maintained constant
throughout the experiments. Ischemia produced a significant prolongation of
the isovolumetric relaxation period (IVRP) from 29 +/- 3 (SE) to 88 +/- 7
ms (P less than 0.01). Ischemia, per se, the associated decrease in
contractility, or the fall in peak left ventricular pressure (LVP) may have
contributed to the increase in IVRP. The latter was not the only mechanism
involved, because in seven dogs studied with constant peak LVP, IVRP again
was prolonged from 64 +/- 8 to 95 +/- 8 ms (P less than 0.01). Moreover, in
five nonischemic hearts in which peak LVP was maintained constant,
contractility was decreased by sodium pentobarbital to the same extent as
with ischemia; IVRP did not change. Thus, the additional prolongation of
the IVRP in the ischemia experiments is secondary to a direct effect of
ischemia on the relaxation process of the myocardium.
