Acclimization in a hot, humid environment: cardiovascular adjustments

Wyndham, C. H.; Rogers, G. G.; Senay, L. C.; Mitchell, Duncan

doi:10.1152/jappl.1976.40.5.779

Cited by 101 publications

(63 citation statements)

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“…During the prolonged treadmill work requiring 30 It/ o VOzmax in the warm humid and hot dry environ-ments, as compared to similar performance in the thermoneutral environment, our subjects exhibited the typical signs of unacclimated persons when initially exposed to work in a hot environment (2,5,15,34), ie, elevated heart rate and rectal temperature and reduced physical performance, as evidenced by the 41 070 rate of premature test interruptions. Only three subjects were able to achieve a circulatory and thermal steady state in both of the hot environments.…”

Section: Discussionmentioning

confidence: 76%

“…When people work for the first tim e in a hot enviro nment, their work performance is often reduced, their heart rate and internal body temperatures may increase greatly, and they are prone to heat disorders such as heat syncope and heat exhaustion (2,15,34). Depending on the severity of the environment and work load, man can adjust to a certain extent to heat stress by increased sweating and skin blood flow and thus atta in a physiological stead y state.…”

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confidence: 99%

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Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

Smolander¹,

Ilmarinen²,

Korhonen³

et al. 1987

Scand J Work Environ Health

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(1987) 37 -46. Eight ph ysicalIy tra ined and eight untrained , una cclimated men walked on a treadmill at 30 010 of their maximum oxygen consumption up to 3.5 h in a the rmoneutral [20°C / 40 010 relative humid ity {RH) J, a warm hum id (30°C /8 0 % RH), and a hot dry (40°C I2 0 010 RH ) environment while wearing indu str ial work clothing. Their oxygen consumption, rectal and skin temperat ures, sweat ing, card iac output, hea rt rate, stroke volume, and peripheral blood pressure were measured du ring the tests . Thirteen of the 32 heat stress tests were prematurely stopped du e to high rectal temperature, high heart rate, subjective fa tigue, or heat syncope . The physiological str ain, as indicated by the rectal tempe ratur e and heart rate, was not significantl y different between th e warm humid and hot dr y environmen ts (wet bulb globe temperature -28°C). Th e rectal temp eratur e and heart rat e responses of the physicalIy train ed and untrained subjects did not diff er in any of the environments . In th e heat, the heart ra te was significa ntly higher than in the thermoneut ral environm ent , but becau se of the markedly redu ced stroke volume the average ca rdiac output was not differen t between the three environ ments. The impaired work perform an ce in the hea t seemed mainly to be related to the circulat ory instability accompanying the increased cuta neous circulation .Key terms: bod y temp erature, central circulation, heat stress indices, hot dry environment, peripheral circulati on , physical fitn ess, prol onged exercise, sweating, warm humid environment, work perform an ce.

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Section: Discussionmentioning

confidence: 76%

mentioning

confidence: 99%

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

Smolander¹,

Ilmarinen²,

Korhonen³

et al. 1987

Scand J Work Environ Health

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“…This suggests that, in terms of cardiovascular adjustment, the subjects were not fully acclimated although they were from tropical areas. According to Wyndham et al (1976) their results indicated that the causes of the changes in HR during acclimatization are complex. HR is significantly correlated with both SV and T re suggesting that both an increase in SV and a fall in T re are independently associated with the decrease in HR.…”

Section: Discussionmentioning

confidence: 99%

“…It is not clear, however, whether this transient hemodilution during exercise-heat exposure following acclimatization is large enough to compensate for the displacement of blood volume into the cutaneous veins and thus provide an explanation for the reduced HR component. The proposition that a reduced HR and increased SV is the result of expansion in plasma volume during the early stages of exercise-HA has been challenged by Wyndham et al (1976). They observed that SV increases as plasma volume increased during the first six days of a ten-day acclimatization study.…”

Section: Discussionmentioning

confidence: 99%

Effects of Short-term Exercise in the Heat on Thermoregulation, Blood Parameters, Sweat Secretion and Sweat Composition of Tropic-dwelling Subjects

Saat

Sirisinghe

Singh

et al. 2005

J. Physiol. Anthropol.

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This study investigates the effects of a shortterm aerobic training program in a hot environment on thermoregulation, blood parameters, sweat secretion and composition in tropic-dwellers who have been exposed to passive heat. Sixteen healthy Malaysian-Malay male volunteers underwent heat acclimation (HA) by exercising on a bicycle ergometer at 60% ofVO 2 max for 60 min each day in a hot environment (Ta: 31.1Ϯ0.1°C, rh: 70.0Ϯ4.4%) for 14 days. All parameters mentioned above were recorded on Day 1 and at the end of HA (Day 16). On these two days, subjects rested for 10 min, then cycled at 60% of V O 2 max for 60 min and rested again for 20 min (recovery) in an improvised heat chamber. Rectal temperature (T re ), mean skin temperature (T sk ) heart rate (HR), ratings of perceived exertion (RPE), thermal sensation (TS), local sweat rate and percent dehydration were recorded during the test. Sweat concentration was analysed for sodium [Na ϩ ] sweat and potassium. Blood samples were analysed for biochemical changes, electrolytes and hematologic indices. Urine samples were collected before and after each test and analysed for electrolytes.After the period of acclimation the percent dehydration during exercise significantly increased from 1.77Ϯ0.09% (Day 1) to 2.14Ϯ0.07% (Day 16). Resting levels of hemoglobin, hematocrit and red blood cells decreased significantly while [Na ϩ ] sweat increased significantly. For T re and T sk there were no differences at rest. T re , HR, RPE, TS, plasma lactate concentration, hemoglobin and hematocrit at the 40th min of exercise were significantly lower after the period of acclimation but mean corpuscular hemoglobin and serum osmolality were significantly higher while no difference was seen in [Na ϩ ] sweat and T sk . It can be concluded that tropicdwelling subjects, although exposed to prolonged passive heat exposure, were not fully heat acclimatized. To achieve further HA, they should gradually expose themselves to exercise-heat stress in a hot environment.

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“…It is well-known that exercise heat acclimation induces a significant reduction in HR, and core and skin temperatures during exercise, as well as a significant increase in SR (Gisolfi and Cohen 1979;Eichna et al 1950;Mitchell et al 1976;Wyndham et al 1976). As we did not observe a significant increase in whole-body SR throughout exercise heat acclimation, or an increase in local SR during passive heating, it is likely that the magnitude of the adaptation induced by heat acclimation was mild in the present study.…”

Section: Discussionmentioning

confidence: 99%

Determination of the maximum rate of eccrine sweat glands’ ion reabsorption using the galvanic skin conductance to local sweat rate relationship

et al. 2015

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Purpose The purpose of the present study was to develop and describe a simple method to evaluate the rate of ion reabsorption of eccrine sweat glands in human using the measurement of galvanic skin conductance (GSC) and local sweating rate (SR). This purpose was investigated by comparing the SR threshold for increasing GSC with following two criteria of sweat ion reabsorption in earlier studies such as 1) the SR threshold for increasing sweat ion was at approximately 0.2 to 0.5 mg/cm 2 /min and 2) exercise-heat acclimation improved the sweat ion reabsorption ability and would increase the criteria 1.Methods Seven healthy non-heat-acclimated male subjects received passive heat treatment both before and after 7 days of cycling in hot conditions (50% maximum oxygen uptake, 60 min/day, ambient temperature 32°C, and 50% relative humidity).Results Subjects became partially heat-acclimated, as evidenced by the decreased end-exercise heart rate (p<0.01), rate of perceived exhaustion (p<0.01), and oesophageal temperature (p=0.07), without alterations in whole-body sweat loss, from the first to the last day of training. As hypothesised, we confirmed that the SR threshold for increasing GSC was near the predicted SR during passive heating before exercise heat acclimation, and increased significantly after training (0.19 ± 0.09 to 0.32 ± 0.10 mg/cm 2 /min, p<0.05).Conclusions The reproducibility of sweat ion reabsorption by the eccrine glands in the present study suggests that the relationship between GSC and SR can serve as a new index for assessing the maximum rate of sweat ion reabsorption of eccrine sweat glands in humans.

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Acclimization in a hot, humid environment: cardiovascular adjustments

Cited by 101 publications

References 0 publications

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

Effects of Short-term Exercise in the Heat on Thermoregulation, Blood Parameters, Sweat Secretion and Sweat Composition of Tropic-dwelling Subjects

Determination of the maximum rate of eccrine sweat glands’ ion reabsorption using the galvanic skin conductance to local sweat rate relationship

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