Cardiovascular function during experimental hyperthermia with specific reference to circulatory failure

Abstract

The cardiovascular system is regarded as the "first line of defence" to an elevation in body temperature, and cardiovascular adaptations as the major event during acclimatisation to heat. Although cardiovascular strain is a consistent finding during heat exposure of unacclimatised individuals, circulatory failure is not regarded as a primary factor in the pathogenesis of tissue damage in heatstroke. Certain findings do, however, support a contrary view. In this respect it would appear that exercise-induced heatstroke manifests profound circulatory instability which may constitute the cause/result of the initiation of heatstroke. In contrast, heatstroke of environmental origin per se, exhibits little cardiovascular involvement. The mechanism of circulatory failure during heat exposure is explained by conflicting theories. Electrocardiographic and serum enzyme analyses consistently reflect some form of myocardial damage but the magnitude of damage is not regarded as sufficient to cause circulatory failure. In addition, cardiac tissue, inherently susceptible to heat damage in vitro , appears to be heat resistant in vivo, although serious biochemical derangements have been denonstrated.