Assessment of whole body and regional evaporative heat loss coefficients in very premature infants using a thermal mannequin: Influence of air velocity

2005 ◽  
Vol 32 (3) ◽  
pp. 752-758 ◽  
Author(s):  
Khalid Belghazi ◽  
Elmountacer Billah Elabbassi ◽  
Pierre Tourneux ◽  
Jean-Pierre Libert
Keyword(s):  
Heat Loss ◽  
Premature Infants ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Air Velocity ◽  
Loss Coefficients ◽  
Very Premature Infants

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

1982 ◽  
Vol 53 (2) ◽  
pp. 316-323 ◽  
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).

Postexercise Activation of Muscle Metaboreceptors Modulates Whole-Body Evaporative Heat Loss

2017 ◽  
Vol 49 (5S) ◽  
pp. 449
Author(s):  
Brian J. Friesen ◽  
Martin P. Poirier ◽  
Dallon T. Lamarche ◽  
Andrew W. D’Souza ◽  
Jung-Hyun Kim ◽  
...  
Keyword(s):  
Heat Loss ◽  
Whole Body ◽  
Evaporative Heat Loss

scholarly journals Postexercise whole-body sweating increases during muscle metaboreceptor activation in young men

2018 ◽  
Vol 43 (4) ◽  
pp. 423-426 ◽  
Author(s):  
Brian J. Friesen ◽  
Martin P. Poirier ◽  
Dallon T. Lamarche ◽  
Andrew W. D’Souza ◽  
Jung-Hyun Kim ◽  
...  
Keyword(s):  
Heat Loss ◽  
Young Men ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Exercise Recovery ◽  
Isometric Handgrip ◽  
Natural Recovery ◽  
Ischemic Period ◽  
And Control ◽  
Late Stages

We assessed the effect of metaboreceptor activation on whole-body evaporative heat loss (WB-EHL) in 12 men (aged 24 ± 4 years) in the early-to-late stages of a 60-min exercise recovery in the heat. Metaboreceptor activation induced by 1-min isometric-handgrip (IHG) exercise followed by 5-min forearm ischemia to trap metabolites increased WB-EHL by 25%–31% and 26%–34% during the ischemic period relative to IHG-only and control (natural recovery only), respectively, throughout recovery. We show that metaboreceptor activation enhances WB-EHL in recovery.

scholarly journals Aging impairs heat loss, but when does it matter?

2015 ◽  
Vol 118 (3) ◽  
pp. 299-309 ◽  
Author(s):  
Jill M. Stapleton ◽  
Martin P. Poirier ◽  
Andreas D. Flouris ◽  
Pierre Boulay ◽  
Ronald J. Sigal ◽  
...  
Keyword(s):  
Aerobic Exercise ◽  
Surface Area ◽  
Heat Loss ◽  
Body Surface Area ◽  
Body Surface ◽  
Aerobic Fitness ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Middle Aged ◽  
Direct Calorimetry

Aging is associated with an attenuated physiological ability to dissipate heat. However, it remains unclear if age-related impairments in heat dissipation only occur above a certain level of heat stress and whether this response is altered by aerobic fitness. Therefore, we examined changes in whole body evaporative heat loss (HE) as determined using whole body direct calorimetry in young ( n = 10; 21 ± 1 yr), untrained middle-aged ( n = 10; 48 ± 5 yr), and older ( n = 10; 65 ± 3 yr) males matched for body surface area. We also studied a group of trained middle-aged males ( n = 10; 49 ± 5 yr) matched for body surface area with all groups and for aerobic fitness with the young group. Participants performed intermittent aerobic exercise (30-min exercise bouts separated by 15-min rest) in the heat (40°C and 15% relative humidity) at progressively greater fixed rates of heat production equal to 300 (Ex1), 400 (Ex2), and 500 (Ex3) W. Results showed that HE was significantly lower in middle-aged untrained (Ex2: 426 ± 34; and Ex3: 497 ± 17 W) and older (Ex2: 424 ± 38; and Ex3: 485 ± 44 W) compared with young (Ex2: 472 ± 42; and Ex3: 558 ± 51 W) and middle-aged trained (474 ± 21; Ex3: 552 ± 23 W) males at the end of Ex2 and Ex3 ( P < 0.05). No differences among groups were observed during recovery. We conclude that impairments in HE in older and middle-aged untrained males occur at exercise-induced heat loads of ≥400 W when performed in a hot environment. These impairments in untrained middle-aged males can be minimized through regular aerobic exercise training.

scholarly journals Whole body heat loss is reduced in older males during short bouts of intermittent exercise

2013 ◽  
Vol 305 (6) ◽  
pp. R619-R629 ◽  
Author(s):  
Joanie Larose ◽  
Heather E. Wright ◽  
Jill Stapleton ◽  
Ronald J. Sigal ◽  
Pierre Boulay ◽  
...  
Keyword(s):  
Heat Loss ◽  
Heat Storage ◽  
Intermittent Exercise ◽  
Heat Content ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Middle Aged ◽  
Young Males ◽  
Body Heat ◽  
Older Males

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.

Exercise-rest cycles do not alter local and whole body heat loss responses

2011 ◽  
Vol 300 (4) ◽  
pp. R958-R968 ◽  
Author(s):  
Daniel Gagnon ◽  
Glen P. Kenny
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Intermittent Exercise ◽  
Sweat Rate ◽  
Heat Content ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Esophageal Temperature ◽  
Direct Calorimetry ◽  
Body Heat

Previous studies have suggested that greater core temperatures during intermittent exercise (Ex) are due to attenuated sweating [upper back sweat rate (SR)] and skin blood flow (SkBF) responses. We evaluated the hypothesis that heat loss is not altered during exercise-rest cycles (ER). Ten male participants randomly performed four 120-min trials: 1) 60-min Ex and 60-min recovery (60ER); 2) 3 × 20-min Ex separated by 20-min recoveries (20ER); 3) 6 × 10-min Ex separated by 10-min recoveries (10ER), or 4) 12 × 5-min Ex separated by 5-min recoveries (5ER). Exercise was performed at a workload of 130 W at 35°C. Whole body heat exchange was determined by direct calorimetry. Core temperature, SR (by ventilated capsule), and SkBF (by laser-doppler) were measured continuously. Evaporative heat loss (EHL) progressively increased with each ER, such that it was significantly greater ( P ≤ 0.05) at the end of the last compared with the first Ex for 5ER (299 ± 39 vs. 440 ± 41 W), 10ER (425 ± 51 vs. 519 ± 45 W), and 20ER (515 ± 63 vs. 575 ± 74 W). The slope of the EHL response against esophageal temperature significantly increased from the first to the last Ex within the 10ER (376 ± 56 vs. 445 ± 89 W/°C, P ≤ 0.05) and 20ER (535 ± 85 vs. 588 ± 28 W/°C, P ≤ 0.05) conditions, but not during 5ER (296 ± 96 W/°C vs. 278 ± 95 W/°C, P = 0.237). In contrast, the slope of the SkBF response against esophageal temperature did not significantly change from the first to the last Ex (5ER: 51 ± 23 vs. 54 ± 19%/°C, P = 0.848; 10ER: 53 ± 8 vs. 56 ± 21%/°C, P = 0.786; 20ER: 44 ± 20 vs. 50 ± 27%/°C, P = 0.432). Overall, no differences in body heat content and core temperature were observed. These results suggest that altered local and whole body heat loss responses do not explain the previously observed greater core temperatures during intermittent exercise.

Air velocity influences thermoregulation and endurance exercise capacity in the heat

2018 ◽  
Vol 43 (2) ◽  
pp. 131-138 ◽  
Author(s):  
Hidenori Otani ◽  
Mitsuharu Kaya ◽  
Akira Tamaki ◽  
Phillip Watson ◽  
Ronald J. Maughan
Keyword(s):  
Skin Temperature ◽  
Heat Loss ◽  
Exercise Capacity ◽  
Core Temperature ◽  
Endurance Exercise ◽  
Temperature Rise ◽  
Time To Exhaustion ◽  
Evaporative Heat Loss ◽  
Air Velocity ◽  
Hot Environment

This study examined the effects of variations in air velocity on time to exhaustion and thermoregulatory and perceptual responses to exercise in a hot environment. Eight male volunteers completed stationary cycle exercise trials at 70% peak oxygen uptake until exhaustion in an environmental chamber maintained at 30 °C and 50% relative humidity. Four air velocity conditions, 30, 20, 10, and 0 km/h, were tested, and the headwind was directed at the frontal aspect of the subject by 2 industrial fans, with blade diameters of 1 m and 0.5 m, set in series and positioned 3 m from the subject’s chest. Mean ± SD time to exhaustion was 90 ± 17, 73 ± 16, 58 ± 13, and 41 ± 10 min in 30-, 20-, 10-, and 0-km/h trials, respectively, and was different between all trials (P < 0.05). There were progressive elevations in the rate of core temperature rise, mean skin temperature, and perceived thermal sensation as airflow decreases (P < 0.05). Core temperature, heart rate, cutaneous vascular conductance, and perceived exertion were higher and evaporative heat loss was lower without airflow than at any given airflow (P < 0.05). Dry heat loss and plasma volume were similar between trials (P > 0.05). The present study demonstrated a progressive reduction in time to exhaustion as air velocity decreases. This response is associated with a faster rate of core temperature rise and a higher skin temperature and perceived thermal stress with decreasing airflow. Moreover, airflow greater than 10 km/h (2.8 m/s) might contribute to enhancing endurance exercise capacity and reducing thermoregulatory, cardiovascular, and perceptual strain during exercise in a hot environment.

scholarly journals Fitness-related differences in the rate of whole-body evaporative heat loss in exercising men are heat-load dependent

2017 ◽  
Vol 103 (1) ◽  
pp. 101-110 ◽  
Author(s):  
Dallon T. Lamarche ◽  
Sean R. Notley ◽  
Jeffrey C. Louie ◽  
Martin P. Poirier ◽  
Glen P. Kenny
Keyword(s):  
Heat Loss ◽  
Heat Load ◽  
Whole Body ◽  
Evaporative Heat Loss

Do older adults experience greater thermal strain during heat waves?

2014 ◽  
Vol 39 (3) ◽  
pp. 292-298 ◽  
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.

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