ABSTRACT
Increased blood flow to superficial body tissues to transport heat, water, electrolytes, metabolites, and humoral agents is necessary to increase heat loss during hyperthermia. The marked increase in peripheral blood flow during hyperthermia requires compensatory actions to avoid a fall in arterial blood pressure which may occur during prolonged heat stress as a consequence of the breakdown of cardiovascular homeostasis. Knowledge of the consequences of hyperthermia for brain blood flow is highly desirable with respect to the cancer patient. The essential regulation of this pressure within “normal” limits depends upon cardiac output and the flow resistance of peripheral vascular beds. Conscious sheep were at rest in a thermoneutral environment then exposed to a hot, humid environment to produce progressive hyperthermia. Heat exposure was terminated when the animal became extremely distressed and was verging on ataxia, i.e., after 1.5 to 2 hr when rectal temperature had changed from approximately 39.8 to 42.3°C.
