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Effects of hypothermia and pyrexia on left ventricular function in the intact animal

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      Abstract

      Left ventricular contractile function was studied during hypothermia and pyrexia in the intact anesthetized dog. Changes of body temperature were rapidly induced with a heat exchanger which conducted blood from a femoral artery to a femoral vein. Measurements were made of left ventricular contractile capacity (P12.5 index), pressure-rise velocity (dP/dtmax.), blood temperature and cardiac output by methods previously described. Pharmacologic autonomic and adrenergic blockade were utilized to evaluate the role of the sympathetic nervous system in these experiments, and vagal stimulation was used to evaluate changes of heart rate.
      It was found that hypothermia diminished left ventricular contractile capacity in the intact animal, probably because reduction of cardiac sympathetic tone superseded the direct stimulant effect of hypothermia which was evident in some experiments during autonomic blockade. Pyrexia, on the other hand, directly augmented left ventricular contractile capacity, even during adrenergic or autonomic blockade. It was also observed that a dose of ouabain (0.03 mg./kg.) which augmented left ventricular contractile capacity at normal body temperature was ineffective during hypothermia.
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