Comparative physiological responses of normotensive and essentially hypertensive men to exercise in the heat

Kenney, W. Larry; Kamon, E.

doi:10.1007/bf00433392

Cited by 39 publications

(39 citation statements)

References 24 publications

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“…cannot be compared to the whole-body observations reported in the present study. Importantly, we show that physiologically-relevant reductions in SkBF, such as those that occur with ageing (Kenney et al , 1997; Minson et al , 1998), and disease (Kenney & Kamon, 1984; Green et al , 2006), are unlikely to affect whole-body heat loss potential.…”

Section: Discussionmentioning

confidence: 79%

Does attenuated skin blood flow lower sweat rate and the critical environmental limit for heat balance during severe heat exposure?

Cramer

Gagnon

Crandall

et al. 2016

Experimental Physiology

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Attenuated skin blood flow (SkBF) is often assumed to impair core temperature (Tc) regulation. Profound pharmacologically-induced reductions in SkBF (~85%) lead to impaired sweating but whether the smaller attenuations in SkBF (~20%) more associated with ageing and certain diseases lead to decrements in sweating and maximum heat loss potential is unknown. Seven healthy males (28±4y) completed a 30-min equilibration period at 41°C and a vapour pressure (Pa) of 2.57 kPa followed by incremental steps in Pa of 0.17 kPa every 6-min to 5.95 kPa. Differences in heat loss potential were assessed by identifying the critical vapour pressure (Pcrit) at which an upward inflection in Tc occurred. Three separate treatments elicited changes in plasma volume to achieve three distinct levels of SkBF: control (CON), diuretic-induced iso-osmotic dehydration to lower SkBF (DEH), and continuous saline infusion to maintain SkBF (SAL). Tc, mean skin temperature (Tsk), heart rate, mean laser-Doppler flux (forearm, thigh; LDFmean), mean local sweat rate (forearm, thigh; LSRmean), and metabolic rate were measured. In DEH, a 14.2±5.7% lower plasma volume resulted in a ~20% lower LDFmean (DEH: 139±23, CON: 176±22, SAL: 186±22 PU; P=0.034). However, LSRmean and whole-body sweat losses were unaffected by treatment throughout (P>0.482). Pcrit for Tc was similar between treatments (CON: 5.05±0.30, DEH: 4.93±0.16, SAL: 5.12±0.10 kPa; P=0.166). Further, no differences were observed in the Tsk−Ta gradient, metabolic rate, or changes in Tc (P>0.197). In conclusion, a ~20% reduction in SkBF alters neither sweat rate nor the upper limit for heat loss from the skin during non-encapsulated passive heat stress.

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Section: Discussionmentioning

confidence: 79%

Does attenuated skin blood flow lower sweat rate and the critical environmental limit for heat balance during severe heat exposure?

Cramer

Gagnon

Crandall

et al. 2016

Experimental Physiology

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show abstract

“…58,59 Meanwhile, Carberry et al 60 found that resting maximal forearm SkBF response to local heating (44°C) was reduced in hypertensive individuals compared with age-and weight-matched normotensive controls. Similarly, during moderate-intensity exercise (40% VO 2max ) in the heat (38°C), Kenney et al 61,62 found attenuated increases in forearm blood flow in hypertensive participants compared with normotensive controls. The authors surmised that structural alterations in the vasculature (thickened media and/or an increase in smooth muscle layers) would diminish vasodilation in response to increased thermal stimuli.…”

Section: Hypertensionmentioning

confidence: 97%

Do Heat Events Pose a Greater Health Risk for Individuals with Type 2 Diabetes?

Yardley

Stapleton

Sigal

et al. 2013

Diabetes Technology & Therapeutics

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Chronic medical conditions such as type 2 diabetes may alter the body's normal response to heat. Evidence suggests that the local heat loss response of skin blood flow (SkBF) is affected by diabetes-related impairments in both endothelium-dependent and non-endothelium-dependent mechanisms, resulting in lower elevations in SkBF in response to a heat or pharmacological stimulus. Thermoregulatory sweating may also be diminished by type 2 diabetes, impairing the body's ability to transfer heat from its core to the environment. Diabetes-associated co-morbidities and the medications (particularly those affecting fluid balance) required to treat these conditions may exacerbate the risk of heat-related illness by decreasing SkBF and sweating further. Unfortunately, the majority of studies measure local heat loss responses in the hands and feet and lack measures of core temperature. Therefore, the impact of these impairments on whole-body heat loss remains unknown. This review addresses heat-related vulnerability in individuals with type 2 diabetes by examining the literature related to heat loss responses in this population. Type 2 diabetes, its associated co-morbidities, and the medications required in their treatment may cause dehydration, lower SkBF, and reduced sweating, which could consequently impair thermoregulation. This effect is most evident in individuals with poor blood glucose control. Although type 2 diabetes can be associated with impairments in SkBF and sweating, more physically active individuals requiring fewer medications and having good blood glucose control may be able to tolerate heat as well as those of similar age and body composition.

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“…During exerciseinduced heat stress, people with hypertension experience an elevated blood pressure response and possibly greater thermal strain than people with normotension. 44 In earlier studies, Kenney and collaborators 44,45 found that the increases in forearm blood flow during exercise-induced hyperthermia, which are primarily confined to the skin, 46 were markedly reduced in people with hypertension relative to people with normotension. This effect could result in a reduction in heat transfer from the body core to the skin, which would increase the potential for heat illness.…”

Section: Hypertensionmentioning

confidence: 99%

Heat stress in older individuals and patients with common chronic diseases

Kenny

Yardley²,

Brown³

et al. 2009

Canadian Medical Association Journal

456

313

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Key points• People with age over 60 years, obesity, cardiovascular disease, pulmonary disease or long-standing diabetes are at increased risk of heat-related illness during heat waves because of physiological impairments in the regulation of body core temperature in hot conditions.• A homebound lifestyle, lack of contact with other people and decreased mobility can also contribute to an increased risk of heat-related illness.• Working home air conditioners, fans, access to transportation and access to cool environments during prolonged heat events have a protective effect against heat-related illness and deaths.• Physicians should be aware of these risk factors and protective factors against heat illness, and should counsel at-risk patients accordingly.CMAJ 2009. DOI:10.1503/cmaj.081050Previously published at www.cmaj.caReview rise in body core temperature may lead to heat illness and eventually death. Exposure to the combination of external heat stress and metabolically generated heat can lead to heat-related disorders. The prevalence of heat stress symptoms increases in direct proportion to the elevation of body core temperature. The major heat-related disorders -heat cramps, heat exhaustion and heatstroke -involve various degrees of thermoregulatory failure, which occurs when a person is exposed to excessive heat or elevations in body core temperature over a prolonged period. Risk factors for heat stress AgeObservational studies have shown that people aged 60 years and older are among the worst affected by extreme heat, 3−5 with those living in institutions, confined to bed or living alone having the highest rates of illness, injury and death. 5,8,15−17 In their ecological time-series study, Fouillet and associates 2 showed that during the 2003 heat wave in Europe, mortality ratios (ratios of observed deaths to expected deaths) in France increased continuously with age, from 1.3 for people 35-74 years of age to more than 1.7 for those over the age of 75 (Figure 1). Although the greater prevalence of comorbidities and medication use in this population may be responsible for some of the heat-related deaths, laboratory-based physiological studies have indicated that the ability to sense heat 20 and to manifest appropriate behavioural (especially fluid intake) 21−26 and physiological (e.g., blood distribution, sweating) responses 27−33 during exposure to heat may be compromised in otherwise healthy older individuals.The ability to physiologically maintain body core temperature during heat stress becomes compromised with age. 27 This decrease in thermoregulatory ability can be attributed to a combination of factors, including changes in sweating, [28][29][30]34 blood flow to the skin 30,31,34,35 and cardiovascular function. 32The problem can be exacerbated by the decreases in overall physical fitness and increases in body adiposity that may accompany aging. 36 Experts have suggested that, in combination, these age-related changes in thermoregulatory and cardiovascular function can decrease the body's abilit...

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Comparative physiological responses of normotensive and essentially hypertensive men to exercise in the heat

Cited by 39 publications

References 24 publications

Does attenuated skin blood flow lower sweat rate and the critical environmental limit for heat balance during severe heat exposure?

Does attenuated skin blood flow lower sweat rate and the critical environmental limit for heat balance during severe heat exposure?

Do Heat Events Pose a Greater Health Risk for Individuals with Type 2 Diabetes?

Heat stress in older individuals and patients with common chronic diseases

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