Maintenance of aortic pressure and total peripheral resistance during exercise in heat

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Abstract
At 25.6 and 43.3[degree]C, proximal aortic blood pressure was recorded with a specially designed manometric system before and after cardiac output determinations in 6 normal, unacclimatized young men during four grades of treadmill exercise requiring from 43 to 87% of maximal O2 intake. Unlike peripheral arterial blood pressure, peoximal aortic pressure remained almost constant, indicating close regulation at baroreceptor sites during exercise. Constancy of pulse pressure exceeded that of systolic, diastolic, or mean pressure. At 43.3[degree]C, blood pressure was always slightly lower than 25.6[degree]C. Total peripheral resistance (TPR) fell as workload increased; it diminished more at low workloads at 43.3[degree]C but equaled values at 25.6[degree]C at the 2 higher workloads. Exercise to exhaustion in the heat was not associated with peripheral circulatory collapse and hypotension. Summation of vaso-dilatation in skin and working muscles was previously shown to initiate even greater regional redistribution of blood flow. This effectively maintained central blood pressure and TPR.

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