Blood flow and other thermoregulatory changes with acclimatization to heat

Fox, R. H.; Goldsmith, Ralph S.; Kidd, D. J.; Lewis, H. E.

doi:10.1113/jphysiol.1963.sp007122

Cited by 96 publications

(48 citation statements)

References 13 publications

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“…An expanded plasma volume is better able to withstand fluid loss via sweating. Thus, when working at a given intensity, stroke volume is larger and cardiac frequency lower following heat adaptation 16,48) , permitting superior regulation of blood pressure, an elevation in skin blood flow, and a lowering of the vasodilatory threshold 22) . These physiological adaptations facilitate a more rapid transfer of heat from the body core to the periphery for dissipation.…”

Section: Heat Adaptationmentioning

confidence: 99%

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Challenges to Temperature Regulation When Working in Hot Environments

Taylor

2006

Ind Health

108

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The focus of this review is upon acute exposure to hot environments and the accompanying physiological changes. The target audience includes physiologists, physicians and occupational health and safety practitioners. Using the principles of thermodynamics, the avenues for human heat exchange are explored, leading to an evaluation of some methods used to assess thermally-stressful environments. In particular, there is a critique of the wet-bulb globe temperature (WBGT) index, and an overview of an alternative means by which such assessments may be undertaken (the heat stress index). These principles and methods are combined to illustrate how one may evaluate the risk of heat illness. Three general areas of research are briefly reviewed: the physiological impact of wearing thermal protective clothing, heat adaptation (acclimation) and whole-body pre-cooling. These topics are considered as potential pre-exposure techniques that may be used to reduce the threat of hyperthermia, or to enhance work performance in the heat.

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Section: Heat Adaptationmentioning

confidence: 99%

“…· Self-regulated exercise methods: The person dictates the work rate during heat exposure. · Controlled-hyperthermia (isothermal) methods: The work rate is adjusted to maintain a constant thermal strain, so the work rate is progressively elevated as acclimation progresses 22) .…”

Section: Heat Adaptationmentioning

confidence: 99%

Challenges to Temperature Regulation When Working in Hot Environments

Taylor

2006

Ind Health

108

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“…Buono et al (3) were perhaps the first to suggest that the reduced sweating threshold accompanying heat acclimation may be associated with a lower resting body temperature. This presumption was extrapolated from Fox et al (8) and Shvartz et al (37), although neither group described the relationship. Likewise, data from Stephenson et al (39) indicate parallel reductions of resting body and sweat threshold temperatures over the circadian cycle.…”

mentioning

confidence: 99%

“…These thresholds display considerable plasticity and are readily influenced by thermal stimuli outside the thermoneutral zone, with a reduced sweating threshold typically accompanying heat acclimation (6,8,24,37). A reduction in resting body temperature is often observed as acclimation progresses.…”

mentioning

confidence: 99%

“…The latter can elicit a reduced core temperature (T c ) threshold for sweating onset (6,8,24,37), a greater sensitivity to changes in T c (13,32,40), an elevated steady-state expulsion rate (24-26, 37), eccrine gland hypertrophy (33), and an apparent redistribution of sweating toward the limbs (15, 31, 37), representing our potentially most potent adaptive responses to chronic heat stress. In this paper, we focus on sudomotor threshold and local sweat rate (ṁ sw ) changes accompanying humid heat acclimation.…”

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Humid heat acclimation does not elicit a preferential sweat redistribution toward the limbs

Patterson

Stocks

Taylor

2004

American Journal of Physiology-Regulatory, Integrative and Comp

109

124

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We tested the hypothesis that local sweat rates would not display a systematic postadaptation redistribution toward the limbs after humid heat acclimation. Eleven nonadapted males were acclimated over 3 wk (16 exposures), cycling 90 min/day, 6 days/wk (40°C, 60% relative humidity), using the controlled-hyperthermia acclimation technique, in which work rate was modified to achieve and maintain a target core temperature (38.5°C). Local sudomotor adaptation (forehead, chest, scapula, forearm, thigh) and onset thresholds were studied during constant work intensity heat stress tests (39.8°C, 59.2% relative humidity) conducted on days 1, 8, and 22 of acclimation. The mean body temperature (T b) at which sweating commenced (threshold) was reduced on days 8 and 22 (P Ͻ 0.05), and these displacements paralleled the resting thermoneutral T b shift, such that the T b change to elicit sweating remained constant from days 1 to 22. Whole body sweat rate increased significantly from 0.87 Ϯ 0.06 l/h on day 1 to 1.09 Ϯ 0.08 and 1.16 Ϯ 0.11 l/h on days 8 and 22, respectively. However, not all skin regions exhibited equivalent relative sweat rate elevations from day 1 to day 22. The relative increase in forearm sweat rate (117 Ϯ 31%) exceeded that at the forehead (47 Ϯ 18%; P Ͻ 0.05) and thigh (42 Ϯ 16%; P Ͻ 0.05), while the chest sweat rate elevation (106 Ϯ 29%) also exceeded the thigh (P Ͻ 0.05). Two unique postacclimation observations arose from this project. First, reduced sweat thresholds appeared to be primarily related to a lower resting T b, and more dependent on T b change. Second, our data did not support the hypothesis of a generalized and preferential trunk-to-limb sweat redistribution after heat acclimation.body core temperature; sweating; sweat threshold THE PRINCIPAL AVENUE for heat dissipation in hot environments is via evaporative cooling, with sudomotor enhancement accompanying endurance training and heat adaptation. The latter can elicit a reduced core temperature (T c ) threshold for sweating onset (6,8,24,37), a greater sensitivity to changes in T c (13,32,40), an elevated steady-state expulsion rate (24-26, 37), eccrine gland hypertrophy (33), and an apparent redistribution of sweating toward the limbs (15, 31, 37), representing our potentially most potent adaptive responses to chronic heat stress. In this paper, we focus on sudomotor threshold and local sweat rate (ṁ sw ) changes accompanying humid heat acclimation.Höfler (15) and Shvartz et al. (37) first reported heat acclimation induced a peripheral redistribution of sweating, such that postacclimation limb ṁ sw appeared to be elevated more than at central body sites. This apparent peripheral shift in secretion could facilitate greater heat dissipation, if lower preacclimation limb ṁ sw (5, 12, 19) was also associated with less than optimal local evaporation rates. Because limbs have a relatively large surface area:mass ratio, an elevation in sweating and evaporation could enhance thermal homeostasis. However, while data from Höfler (15) First, these obs...

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Peripheral Circulation

Laughlin

Davis

Secher

et al. 2012

Comprehensive Physiology

211

234

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Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

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Blood flow and other thermoregulatory changes with acclimatization to heat

Cited by 96 publications

References 13 publications

Challenges to Temperature Regulation When Working in Hot Environments

Challenges to Temperature Regulation When Working in Hot Environments

Humid heat acclimation does not elicit a preferential sweat redistribution toward the limbs

Peripheral Circulation

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