Induced hyperthermia in sedated humans and the concept of critical thermal maximum

Bynum, Gaither D.; Pandolf, Kent B.; Schuette, William H.; Goldman, Rachel; Lees, David Eric; Whang‐Peng, Jacqueline; Atkinson, Eve; Bull, Joan M C

doi:10.1152/ajpregu.1978.235.5.r228

Cited by 88 publications

(68 citation statements)

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“…Pandolf and Goldman 34) and Mairiaux and Malchaire 35) suggested that the T cr of 39 to 40°C might be taken as the tolerance limits for men at work in hot environment, in view of the critical thermal maximum (i.e., the least high T cr that is lethal to a human being) 36) . The present volunteers surpassed 39°C T cr in most exposures beyond 34.4°C WBGT (Fig.…”

Section: Discussionmentioning

confidence: 99%

Thermal Limits of Men in Moderate to Heavy Work in Tropical Farming

Nag

Ashtekar

2007

Ind Health

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The farmers in tropical climate are exposed to high heat during the summer months. The study examined the physiological strains of farmers (N=26) to six combined exposures of work and high heat, with moderate and heavy work (26 to 50%, and 51 to 75% VO 2max ) and three ambient conditions, i.e., 34.4 to 42.2°C WBGT (inside) in an environmental chamber. While the cardiorespiratory responses and T cr were predominantly influenced by the work severity (p<0.001), the environmental warmth greatly influenced the sweating response (p<0.001). The importance was placed on the segmental T sk as the first rank indicator of the bodily heat strain. Both the environmental warmth and work severity had independent discernable effects on the dynamic equilibrium of the central and peripheral mechanism to regulate the body temperature. The segmental and compartmental (core, muscle, fat and skin) heat balance analysis indicated the span of convergence of the segmental core and muscle temperatures to the divergence of skin and fat temperatures (CORE-SHELL) as a quantitative estimate of the segmental gradient for heat transfer. The summation of heat exchange across the compartments and segments yielded the transient change in T cr (0.06 to 0.12°C/min), with significant difference between the moderate and heavy work. The T cr of 39°C was taken as the limit of tolerance for the farmers, and by defining the criteria limit of T cr of ~2.5°C gradient from the basal T cr and the rate of change in T cr , the tolerance times were estimated. Corollary to the development of ISO 7933 standard (PHS index), the predictions of tolerance times from the transient change in T cr or the exponential relationship with the WBGT (tolerance time, min = 1,841 e -0.103 WBGT ) were useful to suggest the protective limit for men at work in extremely hot environment. The simplicity of prediction lies in using WBGT as a criterion. The exponential equation estimated the tolerance time of 55 min at 34°C WBGT, and up to 38°C WBGT, the decrease in tolerance time was 4 to 5 min per degree increase in environmental warmth. Beyond 38°C WBGT, the estimated tolerance time decreased by 2 to 3 min per degree increase in WBGT. Further optimization and validation of the knowledge for men and women farmers in different age groups will have application in managing heat illnesses and disorders in tropical farming.

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Section: Discussionmentioning

confidence: 99%

Thermal Limits of Men in Moderate to Heavy Work in Tropical Farming

Nag

Ashtekar

2007

Ind Health

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“…Human skin temperature is strongly regulated at 35°C or below under normal conditions, because the skin must be cooler than body core in order for metabolic heat to be conducted to the skin (17). Sustained skin temperatures above 35°C imply elevated core body temperatures (hyperthermia), which reach lethal values (42-43°C) for skin temperatures of 37-38°C even for acclimated and fit individuals (18,19,20,21). We would thus expect sufficiently long periods of T W > 35°C to be intolerable.…”

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confidence: 99%

An adaptability limit to climate change due to heat stress

Sherwood

Huber

2010

Proc. Natl. Acad. Sci. U.S.A.

883

647

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Despite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wetbulb temperature T W , is surprisingly similar across diverse climates today. T W never exceeds 31°C. Any exceedence of 35°C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7°C, calling the habitability of some regions into question. With 11-12°C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12°C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.climate impacts | global warming | mammalian physiology | paleoclimate

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“…When endotoxemia can be prevented or tolerated and heat exposure is prolonged, the other pathway of heat stroke can be triggered by the direct thermal effect of heat on tissue cells, causing tissue damage. Heat-induced tissue damage is likely to occur at T c Ͼ 42°C, where proteins begin to denature (8,11). These two pathways of heat stroke are likely to exist in a continuum, with some degree of overlap in their activation (35).…”

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confidence: 99%

Pre-existing inflammatory state compromises heat tolerance in rats exposed to heat stress

Lim¹,

Wilson²,

Brown³

et al. 2007

American Journal of Physiology-Regulatory, Integrative and Comp

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This study investigated the roles of endotoxemia and heat-induced tissue damage in the pathology of heat stroke. In groups of eight, male Wistar rats were treated with heat exposure only (HE), or heat exposure with turpentine (TϩHE), dexamethasone (DϩHE), and turpentine and dexamethasone combined (TDϩHE). The rats remained sedated for 2 h after receiving the respective treatments, followed by heat exposure until the core temperature (T c) was 42°C for 15 min; control rats received turpentine (T), dexamethasone (D), and turpentine and dexamethasone (TD) without heat stress. Blood samples were collected before treatment (baseline I), after 2 h of passive rest (baseline II), at T c 40°C (T40), and 15 min after achieving T c 42°C (T42). No rats died in the nonheat-stressed groups. Survival rate was lowest in the TDϩHE rats (37.5%), followed by the HE (62.5%), TϩHE (75%), and DϩHE (100%) rats (P Ͻ 0.05). The duration of survival at T42°C was shortest in the TDϩHE rats (9.9 Ϯ 6.2 min) (P Ͻ 0.01), followed by the TϩHE (11.3 Ϯ 6.1 min) and the HE (12.2 Ϯ 4 min) (P Ͻ 0.05) rats. The increase in plasma IL-6 concentrations was highest in the TϩHE (352%) and HE (178%) rats (P Ͻ 0.05). DϩHE treatment suppressed the increases in plasma aspartate transaminase, alanine aminotransferase, and IL-6 and LPS concentrations during severe heat stress. Heat stroke can be triggered by endotoxemia or heat-induced tissue damage, and preexisting inflammation compromises heat tolerance, whereas blocking endotoxemia increases heat tolerance.

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Induced hyperthermia in sedated humans and the concept of critical thermal maximum

Cited by 88 publications

References 0 publications

Thermal Limits of Men in Moderate to Heavy Work in Tropical Farming

Thermal Limits of Men in Moderate to Heavy Work in Tropical Farming

An adaptability limit to climate change due to heat stress

Pre-existing inflammatory state compromises heat tolerance in rats exposed to heat stress

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