Sweating and cardiovascular responses of aged men to heat exposure.

In this study, 6 older and 10 younger Japanese men were exposed, while sitting, to 40 degrees C and 40% relative humidity for up to 130 min. All participants were heat unacclimatized. Physiological measurements included sweat responses, esophageal and skin temperatures, nonevaporative heat exchange, heart rate, cardiac output, blood pressure, forearm blood flow, and metabolic heat production. There was no significant difference in sweat rate or in onset of sweating between the older and younger men; however, esophageal temperature at the onset of sweating was greater in the older men. Changes in skin temperature, nonevaporative heat exchange, metabolic heat production, heart rate, and cardiac output were the same during heat exposure in both age groups. However, forearm blood flow before and after exposure to heat was significantly lower in the elderly group. These data suggest that the greater health risk posed to resting, yet healthy, aged men by hot environments is not a consequence of inadequate sweating but could be associated with retardation of the vasodilation reflex, which can prevent effective transfer of the body heat to its shell, thus resulting in greater heat storage.