Evaporative Heat Loss Mechanisms of the Newborn Calf, Bos Taurus

The effects of the catecholamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) on the thermoregulatory responses of conscious rabbits to different ambient temperatures (Ta) (2, 22, and 32 °C) were assessed. Intravenous administration of L-DOPA alone, intravenous administration of L-DOPA plus R04-4602 (a peripheral decarboxylase inhibitor), and intraventricular administration of L-DOPA or norepinephrine all produced a hypothermia at Ta 2 °C. The hypothermia was due to a decrease in metabolic heat production (M). On the other hand, L-DOPA or norepinephrine produced both behavioral excitation and hyperthermia at both Ta 22 and 32 °C. At Ta 22 °C, the hyperthermia was due to decreased ear skin blood flow (EBF) and slightly increased M (due to behavioral excitation) whereas at Ta 32 °C the hyperthermia was due to decreased EBF, decreased respiratory evaporative heat loss, and slightly increased M (due to behavioral excitation). Further, the temperature effects induced by L-DOPA were antagonized by pretreatment with 6-hydroxydopamine (a relative depletor of catecholaminergic nerve fibers) but not with haloperidol (a relative blocker of dopaminergic receptors). The data indicate that activation of central adrenergic receptors via the endogenous release of norepinephrine with L-DOPA inhibits both heat production and heat loss mechanisms in the rabbit.

Download Full-text

Physiological Responses and Lactation to Cutaneous Evaporative Heat Loss in Bos indicus, Bos taurus, and Their Crossbreds

Asian-Australasian Journal of Animal Sciences ◽

10.5713/ajas.14.0526 ◽

2015 ◽

Vol 28 (11) ◽

pp. 1558-1564 ◽

Cited By ~ 5

Author(s):

Wang Jian ◽

Yang Ke ◽

Lu Cheng

Keyword(s):

Heat Loss ◽

Bos Taurus ◽

Physiological Responses ◽

Bos Indicus ◽

Evaporative Heat Loss

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

Energy balance in ovariectomized rats with and without estrogen replacement

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1980.238.5.r400 ◽

1980 ◽

Vol 238 (5) ◽

pp. R400-R405 ◽

Cited By ~ 13

Author(s):

M. L. Laudenslager ◽

C. W. Wilkinson ◽

H. J. Carlisle ◽

H. T. Hammel

Keyword(s):

Energy Balance ◽

Heat Loss ◽

Body Mass ◽

Heat Production ◽

Hormone Treatment ◽

Ovariectomized Rats ◽

Dark Phase ◽

Evaporative Heat Loss ◽

Estrogen Replacement ◽

Dry Heat

The effect of estrogen replacement on several parameters of energy balance was investigated in ovariectomized rats tested during the dark phase of their diurnal cycle. Estrogen replacement, either as 17 beta-estradiol or beta-estradiol-3-benzoate via subcutaneous Silastic capsules, was associated with elevated rates of heat production and dry heat loss relative to untreated ovariectomized controls. Estrogen treatment reduced body mass and retarded fur growth. The effects of estrogen replacement on heat production and dry heat loss could not be attributed to these differences in body mass and fur growth or locomotor activity. Estrogen replacement had no effect on rate of evaporative heat loss. If estrogen replacement was delayed 75 days following ovariectomy, the increase in heat production and dry heat loss was not observed. There was no effect of the hormone treatment on rectal temperature. It was concluded that either heat production was elevated, with dry heat loss increased to compensate for the additional thermal load, or dry heat loss was accelerated with heat production elevated in compensation.

Download Full-text

Mechanisms of thermal stability during flight in the honeybee apis mellifera

Journal of Experimental Biology ◽

10.1242/jeb.202.11.1523 ◽

1999 ◽

Vol 202 (11) ◽

pp. 1523-1533 ◽

Cited By ~ 11

Author(s):

S.P. Roberts ◽

J.F. Harrison

Keyword(s):

Thermal Stability ◽

Heat Loss ◽

Heat Production ◽

Radiative Heat ◽

Carbon Dioxide Production ◽

Metabolic Heat Production ◽

Evaporative Heat Loss ◽

Radiative Heat Loss ◽

Convective Heat Loss ◽

Metabolic Heat

Thermoregulation of the thorax allows honeybees (Apis mellifera) to maintain the flight muscle temperatures necessary to meet the power requirements for flight and to remain active outside the hive across a wide range of air temperatures (Ta). To determine the heat-exchange pathways through which flying honeybees achieve thermal stability, we measured body temperatures and rates of carbon dioxide production and water vapor loss between Ta values of 21 and 45 degrees C for honeybees flying in a respirometry chamber. Body temperatures were not significantly affected by continuous flight duration in the respirometer, indicating that flying bees were at thermal equilibrium. Thorax temperatures (Tth) during flight were relatively stable, with a slope of Tth on Ta of 0.39. Metabolic heat production, calculated from rates of carbon dioxide production, decreased linearly by 43 % as Ta rose from 21 to 45 degrees C. Evaporative heat loss increased nonlinearly by over sevenfold, with evaporation rising rapidly at Ta values above 33 degrees C. At Ta values above 43 degrees C, head temperature dropped below Ta by approximately 1–2 degrees C, indicating that substantial evaporation from the head was occurring at very high Ta values. The water flux of flying honeybees was positive at Ta values below 31 degrees C, but increasingly negative at higher Ta values. At all Ta values, flying honeybees experienced a net radiative heat loss. Since the honeybees were in thermal equilibrium, convective heat loss was calculated as the amount of heat necessary to balance metabolic heat gain against evaporative and radiative heat loss. Convective heat loss decreased strongly as Ta rose because of the decrease in the elevation of body temperature above Ta rather than the variation in the convection coefficient. In conclusion, variation in metabolic heat production is the dominant mechanism of maintaining thermal stability during flight between Ta values of 21 and 33 degrees C, but variations in metabolic heat production and evaporative heat loss are equally important to the prevention of overheating during flight at Ta values between 33 and 45 degrees C.

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