Non-Uniform, Age-Related Decrements in Regional Sweating and Skin Blood Flow.
ABSTRACT Aging is associated with attenuated thermoregulatory function which varies regionally over the body. Decrements in vasodilation and sweating are well documented with age yet limited data are available concerning the regional relation between these responses. We aimed to examine age-related alterations in the relation between regional sweating (RSR) and skin blood flow (SkBF) to thermal and pharmacological stimuli. Four microdialysis fibers were inserted in the ventral forearm, abdomen, thigh, and lower back of eight healthy aged subjects (64±7 years) and nine young (23±3 years) during 1) acetylcholine dose response (ACh 1x10(-7) - 0.1 M, mean skin temperature 34°C) and 2) passive whole body heating to Δ1°C rise in oral temperature (Tor). RSR and SkBF were measured over each microdialysis membrane using ventilated capsules and laser-Doppler flowmetry. Maximal SkBF was measured at the end of both protocols (50mM SNP). Regional sweating thresholds and RSR were attenuated in aged versus young at all sites (p<0.0001) during whole body heating. Vasodilation thresholds were similar between groups (p>0.05). Attenuated SkBF were observed at the arm and back in the aged, representing 56% and 82% of those in the young at these sites, respectively (0.5 ΔTor). During ACh perfusion SkBF (p=0.137) and RSR were similar between groups (p= 0.326). Together these findings suggest regional age-related decrements in heat-activated sweat gland function but not cholinergic sensitivity. Functional consequences of such thermoregulatory impairment include the compromised ability of older individuals to defend core temperature during heat exposure, and a subsequently greater susceptibility to heat-related illness and injury.