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.
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ABSTRACT: This brief review is based on a President's Lecture presented at the Annual Meeting of the American College of Sports Medicine in 2013. The purpose of this review is to assess the effects of climate change and consequent increases in environmental heat stress on the aging cardiovascular system. The earth's average global temperature is slowly but consistently increasing, and along with mean temperature changes come increases in heat wave frequency and severity. Extreme passive thermal stress resulting from prolonged elevations in ambient temperature, as well as prolonged physical activity in hot environments, creates a high demand on the left ventricle to pump blood to the skin to dissipate heat. Even healthy aging is accompanied by altered cardiovascular function, which limits the extent to which older individuals can maintain stroke volume, increase cardiac output, and increase skin blood flow when exposed to environmental extremes. In the elderly, the increased cardiovascular demand during heat waves is often fatal due to increased strain on an already compromised left ventricle. Not surprisingly, excess deaths during heat waves 1) occur predominantly in older individuals and 2) are overwhelmingly cardiovascular in origin. Increasing frequency and severity of heat waves coupled with a rapidly growing at-risk population dramatically increases the extent of future untoward health outcomes.Medicine and science in sports and exercise 03/2014; 46(10). DOI:10.1249/MSS.0000000000000325 · 4.46 Impact Factor
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ABSTRACT: Nitric oxide (NO) is a signalling molecule which contributes to the control of many physiological pathways including the heat loss response of skin vasodilation. Recently, NO has been implicated in the control of sweating during exercise in young adults. We tested the hypothesis that aging reduces NO-dependent sweating during exercise in the heat. Ten young (23 ± 3 years) and older (64 ± 5 years) males, matched for body surface area, performed 3 successive 15-min bouts of exercise (Ex) at the same rate of metabolic heat production (300 W m−2) in the heat (35°C, 20% relative humidity). Each exercise was interspersed with a 15-min recovery period. Local sweat rate (ventilated capsule) was measured on two forearm skin sites which were continuously perfused via intradermal microdialysis with: 1) 0.9% saline as control (CON) or 2) 10 mm NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor. Local sweat rate at the end of Ex1 was lower at the CON condition in the older versus young males (0.69 ± 0.19 vs. 0.90 ± 0.17 mg min−1 cm−2, P = 0.018). In the young males, local sweat rate was reduced at the L-NAME treated condition compared to the CON condition at the end of Ex1 (0.67 ± 0.14 vs. 0.90 ± 0.17 mg min−1 cm−2, P = 0.004), Ex2 (0.78 ± 0.20 vs. 1.03 ± 0.20 mg min−1 cm−2, P = 0.013) and Ex3 (0.78 ± 0.20 vs. 1.03 ± 0.21 mg min−1 cm−2, P = 0.014). In the older males, there was no main effect of treatment condition on local sweat rate (P = 0.537) such that local sweat rate at the L-NAME treated and CON conditions were similar (Ex1: 0.65 ± 0.20 vs. 0.69 ± 0.19 mg min−1 cm−2; Ex2: 0.80 ± 0.27 vs. 0.91 ± 0.29 mg min−1 cm−2; and, Ex3: 0.84 ± 0.31 vs. 0.94 ± 0.38 mg min−1 cm−2). We conclude that aging attenuates the influence of NO in the control of local forearm sweating observed in young adults during short 15 min bouts of exercise in the heat. This mechanism may in part, explain the age-related impairments in sweating.This article is protected by copyright. All rights reservedExperimental physiology 04/2014; 99(6). DOI:10.1113/expphysiol.2013.077644 · 2.87 Impact Factor
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ABSTRACT: This study examined the progression of impairments in heat dissipation as a function of age and environmental conditions. Sixty males (n=12/group; 20-30, 40-44, 45-49, 50-54 and 55-70 years) performed four intermittent exercise/recovery cycles for a duration of 2-h in dry (35ºC/20%RH) and humid (35ºC/60%RH) conditions. Evaporative heat loss (HE) and metabolic heat production were measured by direct and indirect calorimetry respectively. Body heat storage was measured as the temporal summation of heat production and heat loss during the sessions. HE was reduced during exercise in the humid versus dry condition in age groups 20-30 (-17%), 40-44 (-18%), 45-49 (-21%), 50-54 (-25%) and 55-70 (-20%) years. HE fell short of being significantly different between groups in the dry condition, but was greater in age group 20-30 years (279±10W) compared to age groups 45-49 (248±8W), 50-54 (242±6W) and 55-70 (240±7W) years in the humid condition. As a result of a reduced rate of heat dissipation predominantly during exercise, age groups 40-70 years stored between 37-45% and 11-28% more heat than age group 20-30 years in the dry and humid conditions respectively. These age-related differences in heat dissipation and heat storage were not paralleled by significant differences in local sweating and skin blood flow, or by differences in core temperature between groups. From a whole-body perspective, combined heat and humidity impeded heat dissipation to a similar extent across age groups, but more importantly, intermittent exercise in dry and humid heat stress conditions created a greater thermoregulatory challenge for middle-aged and older adults.Journal of Applied Physiology 05/2014; 117(1). DOI:10.1152/japplphysiol.00123.2014 · 3.43 Impact Factor