Peripheral Circulatory and Metabolic Consequences of Thyrotoxicosis: VII. Thermoregulation during Work in Thyrotoxicosis

Abstract

The thermoregulatory response to moderate exercise was studied in 10 patients with thyrotoxicosis. It was found that the mechanical efficiency of work was considerably reduced. The increase in rectal temperature per calorie oxygen consumed during work was no different from that seen in normal subjects. Although excess heat was larger in the thyrotoxic group, the increase in average weighted skin temperature was similar to that in the normal group. The final level of skin temperature was higher, however, in the thyrotoxic group, because the initial level was higher.

Increase in heart rate per calorie of work performed was higher in the thyrotoxic patients. Increase in heart rate per calorie of oxygen consumed was slightly greater, however, in the normal group. That this difference might be due to relatively higher elevatio of skin blood flow in response to a certain oxygen demand in normal subjects was supported by measurement of thermal conductivity of skin. Evaporative heat loss is probably greater in thyrotoxicosis during exercise.

It was concluded that no deficiency of the heat dissipating mechanisms is present in thyrotoxicosis. It was suggested that the cause of the heat intolerance of the thyrotoxic subject during work may be twofold: a higher absolute level of skin temperature, and a lower mechanical efficiency, leading to greater quantities of excess heat.

Key Words:

• Thyrotoxicosis
• oxygen consumption
• blood flow
• exercise test
• body temperature regulation