Nonuniform, age-related decrements in regional sweating and skin blood flow

Abstract

Smith CJ, Alexander LM, Kenney WL. Nonuniform, age-related decrements in regional sweating and skin blood flow. Am J Physiol Regul Integr Comp Physiol 305: R877-R885, 2013. First published August 7, 2013 doi:10.1152/ajpregu.00290.2013.-Aging is associated with attenuated thermoregulatory function that 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 Ϯ 7 yr) and nine young (23 Ϯ 3 yr) during 1) ACh dose response (1 ϫ 10 Ϫ7 to 0.1 M, mean skin temperature 34°C) and 2) passive whole body heating to ⌬1°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 (50 mM SNP). Regional sweating thresholds and RSR were attenuated in aged vs. young at all sites (P Ͻ 0.0001) during whole body heating. Vasodilation thresholds were similar between groups (P Ͼ 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 ⌬Tor). During ACh perfusion, SkBF (P ϭ 0.137) and RSR were similar between groups (P ϭ 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.sweating; aging; laser-Doppler flowmetry; skin blood flow; sweating HUMAN AGING IS ASSOCIATED with altered thermoregulatory function during both passive and exercise-induced hyperthermia, including attenuated reflex cutaneous vasodilation (26) and eccrine sweating responses (3,18,24). A functional loss of active cholinergic vasodilation cotransmitter function and dysfunction of second-messenger pathways (i.e., nitric oxide bioavailability) (8,11,12,31) contribute to attenuated cutaneous vasodilatory responses to elevations in core temperature (T core ), hindering convective heat loss. An age-related decline in thermoregulatory sweating further compromises heat loss and increases thermal strain in warm ambient conditions and during exercise. Reduced evaporative heat loss from the skin surface results from a decline in thermoregulatory sweating, due to a decreased thermal sensitivity (32) and atrophy of the sweat glands (17, 19), producing a lower sweat output per gland (23,24,39).Regional variation in sweating and skin blood flow (SkBF) responses to passive heating are well documented (29); howev...

Sex differences in age-related changes on peripheral warm and cold innocuous thermal sensitivity

“…Age-dependent neural degeneration observed in thermoreceptors can reduce both physiological and perceptual thermal sensitivity. Impaired cutaneous vascular function and delays in the sweating and shivering thresholds have been reported in age comparison studies [2,3,4,5,6]. Likewise, reduced thermal sensations in older adults have been reported, alongside a number of other tactile responses (touch, pressure and noxious thermal sensitivity) [7,8,9,10,11].…”

“…Thermophysiological papers, whether they be autonomic thermoregulation studies or behavioural/perceptual studies are often done on one location and sometimes generalised for the entire body. However, there has been in increase more recently in the awareness of this issue and more papers are being published to address it (Gerrett et al 2014;Smith et al 2013; Smith & Havenith 2012 etc). Therefore we wish for the location data to be included in the analysis and a theme of this paper.…”

Heat Waves, Aging, and Human Cardiovascular Health

“…Along with a drop in cutaneous perfusion, aging is associated with a decreased sweat rate (60) and decreased sweat output per gland (2). Regional sweating patterns also change with aging, with the largest reductions in sweating occurring in the abdomen and less significant reductions occurring in the lower back, thigh, and arm (60).…”

“…Regional sweating patterns also change with aging, with the largest reductions in sweating occurring in the abdomen and less significant reductions occurring in the lower back, thigh, and arm (60). An attenuated evaporative heat loss results in greater heat storage in older men and women (41, 42) which can exacerbate the cardiovascular strain described above.…”

Cerebral Vascular Control and Metabolism in Heat Stress

“…Furthermore, heat loss capacity is diminished with age as a result of a (297), decreased sweat rate (428), mediated in part by a decreased sweat output per gland (20). In short, heat tolerance in older populations is compromised due to the reduced efficiency of their heat loss mechanisms; in turn, cardiovascular strain is elevated.…”