To clarify conflicting reports concerning the effects of ischemia on left ventricular chamber stiffness, we compared the effects of hypoxia at constant coronary perfusion with those of global ischemia on left ventricular diastolic chamber stiffness using isolated, perfused rabbit hearts in which the left ventricle was contracting isovolumically. Since chamber volume was held constant, increases in left ventricular end diastolic pressure (LVEDP) reflected increases in chamber stiffness. At a control coronary flow rate (30 ml/min), 2 min of hypoxia and pacing tachycardia (4.0 Hz) produced major increases in postpacing LVEDP (10±1 to 24±3 mm Hg, P < 0.01) and the relaxation time constant, T, (40±4 to 224±37 ms, P < 0.001), while percent lactate extraction ratio became negative (+ 18±2 to −48±15%, P < 0.001). Coronary perfusion pressure decreased (72±5 to 52±3 mm Hg, P < 0.01), and since coronary flow was held constant, the fall in coronary perfusion pressure reflected coronary dilation and a decrease in coronary vascular resistance. Following an average of 71±6s reoxygenation and initial heart rate (2.0 Hz), LVEDP and relaxation time constant T returned to control. Hypoxia alone (without pacing tachycardia) produced similar although less marked changes (LVEDP, 10±1 to 20±3 mm Hg; and T, 32±3 to 119±22 ms; P < 0.01 for both) and there was a strong correlation between LVEDP and T (r = 0.82, P < 0.001).
Takashi Serizawa, W. Mark Vogel, Carl S. Apstein, William Grossman
