Evaporative Heat Loss and Changes in Core Temperature Set‐Point during Different Absolute Workloads

Experiments in conscious goats were done to see whether heat production and respiratory evaporative heat loss show dynamic responses to changing core temperature at constant skin temperature. Core temperature was altered by external heat exchangers acting on blood temperature, while skin temperature was maintained constant by immersing the animals up to the neck in a rapidly circulating water bath. Core temperature was altered at various rates up to 0.9 °C/min. Step deviations of core temperature from control values were always followed by a positive time derivative of effector response, but never by a negative time derivative during sustained displacement of core temperature. Ramp experiments showed that the slopes at which heat production or heat loss rose with core temperature deviating from its control level grew smaller at higher rates of change of core temperature. It is concluded that neither heat production nor respiratory evaporative heat loss respond to the rate of change of core temperature. At constant skin temperature, thermoregulatory effector responses appear to be proportional to the degree to which core temperature deviates from its set level.

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Temperature regulation by hypothalamic proportional control with an adjustable set point

Journal of Applied Physiology ◽

10.1152/jappl.1963.18.6.1146 ◽

1963 ◽

Vol 18 (6) ◽

pp. 1146-1154 ◽

Cited By ~ 228

Author(s):

H. T. Hammel ◽

D. C. Jackson ◽

J. A. J. Stolwijk ◽

J. D. Hardy ◽

S. B. Stromme

Keyword(s):

Heat Loss ◽

Core Temperature ◽

Temperature Regulation ◽

Thermal Response ◽

Hypothalamic Temperature ◽

Set Point ◽

Cold Environments ◽

Hot Environment ◽

Skin Temperatures

The role of the hypothalamic and skin temperatures in controlling the thermal response of a resting animal was studied by measurements of 1) hypothalamic, rectal, ear skin, and trunk skin temperatures on the resting dog and rhesus monkey in hot, neutral, and cold environments; and 2) the thermal and metabolic responses of a dog in neutral and cold environments during and immediately after holding the hypothalamus at approximately 39.0 C by means of six thermodes surrounding the hypothalamus and perfused with water. The results indicate that 1) a resting animal shivers in a cold environment with the same or higher hypothalamic temperature as the same animal in a neutral environment; 2) a resting animal pants in a hot environment with the same or lower hypothalamic temperature as the same animal in a neutral environment; 3) the hypothalamus is nonetheless strongly responsive to an increase or decrease of 1 C; 4) the rate of heat loss increases at the onset of sleep while the hypothalamic temperature is falling; 5) the hypothalamic temperature is 1–2 C lower during sleep even though thermoregulatory responses are the same as when awake; 6) the rate of heat loss decreases upon awakening while the hypothalamic temperature is rising. The discussion of these results includes a suggestion that the set point for temperature regulation is 1) decreased by a rising or elevated skin and extrahypothalamic core temperature, 2) increased by a falling or lowered skin and extrahypothalamic core temperature, 3) decreased upon entering and during sleep and is increased upon awakening. hypothalamic temperature; temperature set point; hypothalamic stimulation; dog temperature regulation; monkey temperature regulation Submitted on October 15, 1962

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

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00642.2010 ◽

2011 ◽

Vol 300 (4) ◽

pp. R958-R968 ◽

Cited By ~ 14

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.

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Control of respiratory evaporative heat loss in exercising goats

Journal of Applied Physiology ◽

10.1152/jappl.1979.46.5.978 ◽

1979 ◽

Vol 46 (5) ◽

pp. 978-983 ◽

Cited By ~ 10

Author(s):

J. B. Mercer ◽

C. Jessen

Keyword(s):

Heat Loss ◽

Core Temperature ◽

Heat Exchangers ◽

The Body ◽

Body Core Temperature ◽

Evaporative Heat Loss ◽

Hypothalamic Temperature ◽

Body Core ◽

Total Body ◽

Rest And Exercise

Investigations were carried out to determine whether a nonthermal input is involved in the control of respiratory evaporative heat loss (REHL) in exercising goats. Two goats were implanted with hypothalamic perfusion thermodes and three goats were implanted with intravascular heat exchangers to clamp hypothalamic temperature and total body core temperature, respectively. At 30 degrees C air temperature REHL was measured while the animals were resting or walking on a treadmill (3 km.h-1, 5 degrees gradient). When the hypothalamic temperature was clamped between 33.0 and 43.0 degrees C the slopes of the responses relating increased REHL to hypothalamic temperature were similar during rest and exercise. However, the threshold hypothalamic temperatures for the increased REHL responses were lower during exercise than at rest, presumably due to higher extrahypothalamic temperatures. When the body core temperature was clamped between 37.0 and 40.4 degrees C the slopes of the responses relating increased REHL to total body core temperature during exercise showed only minor differences compared to those at rest, none of them conclusively indicating nonthermal influences.

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Air velocity influences thermoregulation and endurance exercise capacity in the heat

Applied Physiology Nutrition and Metabolism ◽

10.1139/apnm-2017-0448 ◽

2018 ◽

Vol 43 (2) ◽

pp. 131-138 ◽

Cited By ~ 11

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.

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Hyperhydration: thermoregulatory effects during compensable exercise-heat stress

Journal of Applied Physiology ◽

10.1152/jappl.1997.83.3.860 ◽

1997 ◽

Vol 83 (3) ◽

pp. 860-866 ◽

Cited By ~ 59

Author(s):

William A. Latzka ◽

Michael N. Sawka ◽

Scott J. Montain ◽

Gary S. Skrinar ◽

Roger A. Fielding ◽

...

Keyword(s):

Heat Stress ◽

Heat Loss ◽

Lean Body Mass ◽

Body Mass ◽

Core Temperature ◽

Whole Body ◽

Threshold Temperature ◽

Evaporative Heat Loss ◽

Sweating Rate ◽

Total Body

Latzka, William A., Michael N. Sawka, Scott J. Montain, Gary S. Skrinar, Roger A. Fielding, Ralph P. Matott, and Kent B. Pandolf.Hyperhydration: thermoregulatory effects during compensable exercise-heat stress. J. Appl. Physiol. 83(3): 860–866, 1997.—This study examined the effects of hyperhydration on thermoregulatory responses during compensable exercise-heat stress. The general approach was to determine whether 1-h preexercise hyperhydration [29.1 ml/kg lean body mass; with or without glycerol (1.2 g/kg lean body mass)] would improve sweating responses and reduce core temperature during exercise. During these experiments, the evaporative heat loss required (Ereq = 293 W/m2) to maintain steady-state core temperature was less than the maximal capacity (Emax = 462 W/m2) of the climate for evaporative heat loss (Ereq/Emax= 63%). Eight heat-acclimated men completed five trials: euhydration, glycerol hyperhydration, and water hyperhydration both with and without rehydration (replace sweat loss during exercise). During exercise in the heat (35°C, 45% relative humidity), there was no difference between hyperhydration methods for increasing total body water (∼1.5 liters). Compared with euhydration, hyperhydration did not alter core temperature, skin temperature, whole body sweating rate, local sweating rate, sweating threshold temperature, sweating sensitivity, or heart rate responses. Similarly, no difference was found between water and glycerol hyperhydration for these physiological responses. These data demonstrate that hyperhydration provides no thermoregulatory advantage over the maintenance of euhydration during compensable exercise-heat stress.

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Changes in serotonin contents in brain affect metabolic heat production of rabbits in cold

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1978.235.1.r41 ◽

1978 ◽

Vol 235 (1) ◽

pp. R41-R47

Author(s):

M. T. Lin ◽

I. H. Pang ◽

S. I. Chern ◽

W. Y. Chia

Keyword(s):

Blood Flow ◽

Amino Acid ◽

Heat Loss ◽

Acid Decarboxylase ◽

Evaporative Heat Loss ◽

Decarboxylase Inhibitor ◽

Ambient Temperatures ◽

Amino Acid Decarboxylase ◽

Metabolic Heat ◽

Normal Limits

Elevating serotonin (5-HT) contents in brain with 5-hydroxytryptophan (5-HTP) reduced rectal temperature (Tre) in rabbits after peripheral decarboxylase inhibition with the aromatic-L-amino-acid decarboxylase inhibitor R04-4602 at two ambient temperatures (Ta), 2 and 22 degrees C. The hypothermia was brought about by both an increase in respiratory evaporative heat loss (Eres) and a decrease in metabolic rate (MR) in the cold. At a Ta of 22 degrees C, the hypothermia was achieved solely due to an increase in heat loss. Depleting brain contents of 5-HT with intraventricular, 5,7-dihydroxytryptamine (5,7-DHT) produced an increased Eres and ear blood flow even at Ta of 2 degrees C. Also, MR increased at all but the Ta of 32 degrees C. However, depleting the central and peripheral contents of 5-HT with p-chlorophenylalanine (pCPA) produced lower MR accompanied by lower Eres in the cold compared to the untreated control. Both groups of pCPA-treated and 5,7-DHT-treated animals maintained their Tre within normal limits. The data suggest that changes in 5-HT content in brain affects the MR of rabbits in the cold. Elevating brain content of 5-HT tends to depress the MR response to cold, while depleting brain content of 5-HT tends to enhance the MR response to cold.

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Evaporative Heat Loss Mechanisms of the Newborn Calf, Bos Taurus

British Veterinary Journal ◽

10.1016/s0007-1935(17)39556-8 ◽

1968 ◽

Vol 124 (2) ◽

pp. 83-88 ◽

Cited By ~ 8

Author(s):

J.R.S. Hales ◽

J.D. Findlay ◽

D. Robertshaw

Keyword(s):

Heat Loss ◽

Bos Taurus ◽

Evaporative Heat Loss ◽

Loss Mechanisms

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Effects of environmental temperature and humidity on evaporative heat loss through firefighter suit materials made with semi-permeable and microporous moisture barriers

Textile Research Journal ◽

10.1177/00405175211026537 ◽

2021 ◽

pp. 004051752110265

Author(s):

Huipu Gao ◽

Anthoney Shawn Deaton ◽

Xiaomeng Fang ◽

Kyle Watson ◽

Emiel A DenHartog ◽

...

Keyword(s):

Heat Loss ◽

Environmental Temperature ◽

Moisture Absorption ◽

Evaporative Heat Loss ◽

Total Heat Loss ◽

Evaporative Resistance ◽

Environmental Testing ◽

Permeable Barrier ◽

Moisture Condensation ◽

Moisture Barriers

The goal of this research was to understand how firefighter protective suits perform in different operational environments. This study used a sweating guarded hotplate to examine the effect of environmental temperature (20–45°C) and relative humidity (25–85% RH) on evaporative heat loss through firefighter turnout materials. Four firefighter turnout composites containing three different bi-component (semi-permeable) and one microporous moisture barriers were selected. The results showed that the evaporative resistance of microporous moisture barrier systems was independent of environmental testing conditions. However, absorbed moisture strongly affected evaporative heat loss through semi-permeable moisture barriers coated with a layer of nonporous hydrophilic polymer. Moisture absorption in mild environment (20–25°C) tests, or when testing at high humidity (>85% RH), significantly increased water vapor transmission in semi-permeable turnout systems. It was also found that environmental conditions used in the total heat loss (THL) test (25°C and 65% RH) produced moisture condensation in bi-component barrier systems, making them appear more breathable than could be expected when worn in hotter environments. Regression models successfully qualified the relationships between moisture uptake levels in semi-permeable barrier systems and evaporative resistance and THL. These findings reveal the limitations in relying on THL, the heat strain index currently called for by the NFPA 1971 Standard for Structural Firefighter personal protective equipment, and supports the need to measure turnout evaporative resistance at 35°C (Ret), in addition to THL at 25°C.

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Respiratory water and heat loss of the black duck during flight at different ambient temperatures

Canadian Journal of Zoology ◽

10.1139/z71-112 ◽

1971 ◽

Vol 49 (5) ◽

pp. 767-774 ◽

Cited By ~ 29

Author(s):

M. Berger ◽

J. S. Hart ◽

O. Z. Roy

Keyword(s):

Heat Loss ◽

Water Loss ◽

Pulmonary Ventilation ◽

Evaporative Heat Loss ◽

Total Heat Loss ◽

Ambient Temperatures ◽

Black Duck ◽

Respiratory Heat Loss ◽

Metabolic Water ◽

Expired Air

Pulmonary ventilation and temperature of expired air and of the respiratory passages has been measured by telemetry during flight in the black duck (Anas rubripes) and the respiratory water and heat loss has been calculated.During flight, temperature of expired air was higher than at rest and decreased with decreasing ambient temperatures. Accordingly, respiratory water loss as well as evaporative heat loss decreased at low ambient temperatures, whereas heat loss by warming of the inspired air increased. The data indicated respiratory water loss exceeded metabolic water production except at very low ambient temperatures. In the range between −16 °C to +19 °C, the total respiratory heat loss was fairly constant and amounted to 19% of the heat production. Evidence for the independence of total heat loss and production from changes in ambient temperature during flight is discussed.

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