Effects of age and acclimation on responses to passive heat exposure.
To examine the effect of chronological age on thermoregulation during passive heat exposure, six older (O, 61 +/- 1 yr) and six young (Y, 26 +/- 2 yr) men sat at rest during a 30-min baseline period (dry-bulb temperature = 28 degrees C), a 60-min thermal transient (28-46 degrees C by 2 degrees C steps every 5 min), and 30 min at 46 degrees C dry-bulb temperature. Subjects were matched for maximal O2 consumption, anthropometry, and body composition. Testing was repeated after a 9-day active heat acclimation protocol. There were no age differences in rectal (Tre), mean skin (Tsk), or mean body temperature (Tb = 0.8Tre + 0.2Tsk) before or after acclimation, but heart rate was lower (P < 0.01) in the O group in both acclimation states. Heat acclimation resulted in a significantly lower baseline Tre and Tb in both groups, which remained lower throughout the passive heat stress (P < 0.05). To examine the effects of age and acclimation on thermoregulatory effector function, forearm blood flow (by venous occlusion plethysmography) and chest sweating rate (SRch, by dew-point hygrometry) were plotted against Tb. The slope of the forearm blood flow-Tb relationship was significantly (P < 0.05) lower in the O group before and after acclimation. A lower maximal SRch (P < 0.05) was achieved by the O group, but neither the slope of SRch-Tb relationship nor the Tb threshold for sweating was affected by age. Predictably, acclimation resulted in a lower Tb threshold for the onset of sweating and skin vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)
Armstrong
C G
CG
Laboratory for Human Performance Research, Pennsylvania State University, University Park 16802-6900.
Kenney
W L
WL
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001132:Arm / Q000098:blood supply; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D015444:Exercise / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D012039:Regional Blood Flow / Q000502:physiology; D013546:Sweating / Q000502:physiology; D014664:Vasodilation / Q000502:physiology