Blunted Effects of Elevated Serum Osmolality on Whole‐body Heat Loss and Rectal Temperature in Middle‐aged‐to‐older Men Exercising in Dry Heat

Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short-duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (H E) and changes in body heat content (ΔHb) between young (20–30 yr), middle-aged (40–45 yr), and older males (60–70 yr) of similar body mass and surface area, during successive exercise (4 × 15 min) and recovery periods (4 × 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). H E was lower in older males vs. young males during each exercise (Ex1: 283 ± 10 vs. 332 ± 11 kJ, Ex2: 334 ± 10 vs. 379 ± 5 kJ, Ex3: 347 ± 11 vs. 392 ± 5 kJ, and Ex4: 347 ± 10 vs. 387 ± 5 kJ, all P < 0.02), whereas H E in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 ± 13, Ex2: 355 ± 13, Ex3: 371 ± 13, and Ex4: 365 ± 8 kJ). H E was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ΔHb in older (267 ± 33 kJ; P = 0.016) and middle-aged adults (245 ± 16 kJ; P = 0.073) relative to younger counterparts (164 ± 20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-aged males had a progressively greater rate of heat storage compared with young males over 2 h of intermittent exercise.

Download Full-text

Whole‐body heat exchange in black‐African and Caucasian men during exercise eliciting matched heat‐loss requirements in dry heat

Experimental Physiology ◽

10.1113/ep088091 ◽

2019 ◽

Vol 105 (1) ◽

pp. 7-12 ◽

Cited By ~ 1

Author(s):

Caroline M. Muia ◽

Sean R. Notley ◽

Samah Saci ◽

Andrew W. D'Souza ◽

Glen P. Kenny

Keyword(s):

Heat Exchange ◽

Heat Loss ◽

Whole Body ◽

Black African ◽

Dry Heat ◽

Caucasian Men ◽

Body Heat

Download Full-text

Do older adults experience greater thermal strain during heat waves?

Applied Physiology Nutrition and Metabolism ◽

10.1139/apnm-2013-0317 ◽

2014 ◽

Vol 39 (3) ◽

pp. 292-298 ◽

Cited By ~ 30

Author(s):

Jill M. Stapleton ◽

Joanie Larose ◽

Christina Simpson ◽

Andreas D. Flouris ◽

Ronald J. Sigal ◽

...

Keyword(s):

Older Adults ◽

Heat Loss ◽

Heat Waves ◽

Thermal Strain ◽

Heat Content ◽

Whole Body ◽

Evaporative Heat Loss ◽

Older Individuals ◽

Dry Heat ◽

Body Heat

Heat waves are the cause of many preventable deaths around the world, especially among older adults and in countries with more temperate climates. In the present study, we examined the effects of age on whole-body heat loss and heat storage during passive exposure to environmental conditions representative of the upper temperature extremes experienced in Canada. Direct and indirect calorimetry measured whole-body evaporative heat loss and dry heat exchange, as well as the change in body heat content. Twelve younger (21 ± 3 years) and 12 older (65 ± 5 years) adults with similar body weight (younger: 72.0 ± 4.4 kg; older: 80.1 ± 4.2 kg) and body surface area (younger: 1.8 ± 0.1 m2; older: 2.0 ± 0.1 m2) rested for 2 h in a hot–dry [36.5 °C, 20% relative humidity (RH)] or hot–humid (36.5 °C, 60% RH) environment. In both conditions, evaporative heat loss was not significantly different between groups (dry: p = 0.758; humid: p = 0.814). However, the rate of dry heat gain was significantly greater (by approx. 10 W) for older adults relative to younger adults during the hot–dry (p = 0.032) and hot–humid exposure (p = 0.019). Consequently, the cumulative change in body heat content after 2 h of rest was significantly greater in older adults in the hot–dry (older: 212 ± 25 kJ; younger: 131 ± 27 kJ, p = 0.018) as well as the hot–humid condition (older: 426 ± 37 kJ; younger: 317 ± 45 kJ, p = 0.037). These findings demonstrate that older individuals store more heat during short exposures to dry and humid heat, suggesting that they may experience increased levels of thermal strain in such conditions than people of younger age.

Download Full-text

The independent effect of sex on whole‐body heat loss during exercise in the heat

The FASEB Journal ◽

10.1096/fasebj.25.1_supplement.1053.12 ◽

2011 ◽

Vol 25 (S1) ◽

Author(s):

Daniel Gagnon ◽

Glen P Kenny

Keyword(s):

Heat Loss ◽

Whole Body ◽

Independent Effect ◽

Body Heat

Download Full-text

Impaired whole-body heat loss in type 1 diabetes during exercise in the heat: a cause for concern?

Diabetologia ◽

10.1007/s00125-019-4858-5 ◽

2019 ◽

Vol 62 (6) ◽

pp. 1087-1089 ◽

Cited By ~ 4

Author(s):

Sean R. Notley ◽

Martin P. Poirier ◽

Jane E. Yardley ◽

Ronald J. Sigal ◽

Glen P. Kenny

Keyword(s):

Type 1 Diabetes ◽

Heat Loss ◽

Whole Body ◽

Body Heat

Download Full-text

Intermittent sequential pneumatic compression does not enhance whole-body heat loss in elderly adults during extreme heat exposure

Applied Physiology Nutrition and Metabolism ◽

10.1139/apnm-2019-0364 ◽

2019 ◽

Vol 44 (12) ◽

pp. 1383-1386

Author(s):

Andrew W. D’Souza ◽

Sean R. Notley ◽

Robert D. Meade ◽

Glen P. Kenny

Keyword(s):

Mean Arterial Pressure ◽

Arterial Pressure ◽

Heat Loss ◽

Lower Limb ◽

Vascular Function ◽

Heat Exposure ◽

Extreme Heat ◽

Whole Body ◽

Elderly Adults ◽

Body Heat

Lower-limb intermittent sequential pneumatic compression (ISPC) improves circulation and vascular function in elderly adults. We evaluated the hypothesis that ISPC would also augment whole-body heat loss (WBHL) in elderly adults (aged 69 ± 4 years) resting in extreme heat (40 °C). While ISPC increased mean arterial pressure (91 ± 9 mm Hg) relative to no-ISPC (83 ± 5 mm Hg; P = 0.013) at the end of the exposure, no influence on WBHL was observed (81 ± 7 and 86 ± 11 W for ISPC and no-ISPC, respectively, P = 0.310). Novelty When assessed in elderly adults during an extreme heat exposure, intermittent sequential pneumatic compression augmented mean arterial pressure but did not enhance whole-body heat loss.

Download Full-text

Light masking of circadian rhythms of heat production, heat loss, and body temperature in squirrel monkeys

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1999.276.2.r298 ◽

1999 ◽

Vol 276 (2) ◽

pp. R298-R307 ◽

Cited By ~ 1

Author(s):

Edward L. Robinson ◽

Charles A. Fuller

Keyword(s):

Body Temperature ◽

Heat Loss ◽

Heat Production ◽

Whole Body ◽

Direct Calorimetry ◽

Set Point ◽

Subjective Night ◽

Timing System ◽

Circadian Timing System ◽

Body Heat

Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism ( n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.

Download Full-text

Effect of heating rate on evaporative heat loss in the microwave-exposed mouse

Journal of Applied Physiology ◽

10.1152/jappl.1982.53.2.316 ◽

1982 ◽

Vol 53 (2) ◽

pp. 316-323 ◽

Cited By ~ 13

Author(s):

C. J. Gordon

Keyword(s):

Body Temperature ◽

Heat Loss ◽

Heat Dissipation ◽

Dew Point ◽

Whole Body ◽

Evaporative Heat Loss ◽

Heat Absorption ◽

Deep Body Temperature ◽

The Difference ◽

Body Heat

Male CBA/J mice were administered heat loads of 0–28 J X g-1 at specific absorption rates (SARs) of either 47 or 93 W X kg-1 by exposure to 2,450-MHz microwave radiation at an ambient temperature of 30 degrees C while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. At an SAR of 47 W X kg-1 a threshold heat load of 10.5 J X g-1 had to be exceeded before EHL increased. An approximate doubling of SAR to 93 W X kg-1 reduced the threshold to 5.2 J X g-1. Above threshold the slopes of the regression lines were 1.15 and 0.929 for the low- and high-SAR groups, respectively. Thus the difference in threshold and not slope attributes to the significant increase in EHL when mice are exposed at a high SAR (P less than 0.02). In separate experiments a SAR of 47 W X kg-1 raised the deep body temperature of anesthetized mice at a rate of 0.026 degrees C X s-1, whereas 93 W X kg-1 raised temperature at 0.049 degrees C X s-1. Hence the sensitivity of the EHL mode of heat dissipation is directly proportional to the rate of heat absorption and to the rate of rise in body temperature. These data contradict the notion that mammals have control over whole-body heat exchange only (i.e., thermoregulation) but instead indicate that the EHL system is highly responsive to the rate of heat absorption (i.e., temperature regulation).

Download Full-text