Performance of hypothermic isolated rat heart at various levels of blood acid-base status

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Abstract
The effects of respiratory-induced pH variation on mechanical function and myocardial oxygenation of isolated, blood-perfused working rat hearts were studied in hypothermia (26.degree. C) and compared with control values (37.degree. C). In these experiments, the change of plasma pH during hypothermia was parallel to the change in pH of neutral water. At 37.degree. C, pH was varied from 7.15-7.62; heart rate increased with pH, both cardiac output and external work remaining unaltered. An increase in pH induced a decrease in coronary flow and an increase in the O2 arteriovenous difference. In hypothermia, hemodynamic performance and myocardial O2 consumption decreased proportionately, with no change in cardiac efficiency. At 26.degree. C, the cardiac capacity to react to acid-base variations (pH from 7.34-7.86) was preserved, i.e., heart rate increased with pH. As at 37.degree. C, regulation of both coronary flow and myocardial oxygenation was maintained. Myocardial function of a working isolated rat heart undergoing hypothermia was preserved. Moderate variations in extracellular acid-base status during hypothermia did not impair either myocardial function or the O2 supply-to-demand ratio.