Depressed myocardial function in the goat at high altitude

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Abstract
To determine if depressed myocardial function contributes to the reported decrease in cardiac performance at high altitude, 6 chronically instrumented, unsedated goats were studied before, during and after 2 wk exposure to hypobaric (PaO2 [partial arterial O2 tension] 44 mmHg). Undistorted ventricular pressure wave form was obtained from a minature transducer implanted in the left ventricular cavity. The relationship between (dP/dt [change in pressure with time])/28P and P was extrapolated to obtain Vmax as an index of myocardial function. With .beta. sympathetic blockade (practolol) and pacing to reproduce heart rates, Vmax was uniformly and significantly depressed (P < 0.01) during chronic hypoxia, and returned to control values following descent to low altitude. Likewise, stroke volume following saline infusion was decreased at high altitude and returned to control values following descent. Acute relief of hypoxia at high altitude by administration of 100% O2 by mask did not reverse the depressed Vmax. Chronic hypobaric hypoxia may produce a depression of myocardial function which is reversible by chronic but not acute relief of hypoxia.

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