Interval microclimate cooling with the Dry Air Comfort (DAC) method: An effective strategy to sustain evaporative heat loss

We assessed the longitudinal distribution of intra-airway heat and water exchanges and their effects on airway wall temperature by directly measuring respiratory fluctuations in airstream temperature and humidity, as well as airway wall temperature, at multiple sites along the airways of endotracheally intubated dogs. By comparing these axial thermal and water profiles, we have demonstrated that increasing minute ventilation of cold or warm dry air leads to 1) further penetration of unconditioned air into the lung, 2) a shift of the principal site of total respiratory heat loss from the trachea to the bronchi, and 3) alteration of the relative contributions of conductive and evaporative heat losses to local total (conductive plus evaporative) heat loss. These changes were not accurately reflected in global measurements of respiratory heat and water exchange made at the free end of the endotracheal tube. Raising the temperature of inspired dry air from frigid to near body temperature principally altered the mechanism of airway cooling but did not influence airway mucosal temperature substantially. When local heat loss was increased from both trachea and bronchi (by increasing minute ventilation), only the tracheal mucosal temperature fell appreciably (up to 4.0 degrees C), even though the rise in heat loss from the bronchi about doubled that in the trachea. Thus it appears that the bronchi are better able to resist changes in airway wall temperature than is the trachea. These data indicate that the sites, magnitudes, and mechanisms of respiratory heat loss vary appreciably with breathing pattern and inspired gas temperature and that these changes cannot be predicted from measurements made at the mouth. In addition, they demonstrate that local heat (and presumably, water) sources that replenish mucosal heat and water lost to the airstream are important in determining the degree of local airway cooling (and presumably, drying).

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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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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.

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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.

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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).

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Thermal sweating in different body regions of sheep

The Journal of Agricultural Science ◽

10.1017/s0021859600063073 ◽

1979 ◽

Vol 92 (2) ◽

pp. 511-512 ◽

Cited By ~ 1

Author(s):

A. K. Rai ◽

B. S. Mehta ◽

M. Singh

Keyword(s):

Thermal Stress ◽

Ambient Temperature ◽

Heat Loss ◽

Evaporative Cooling ◽

Sweat Glands ◽

Evaporative Heat Loss ◽

Body Regions ◽

Time Period ◽

Sweat Production ◽

Thermal Sweating

Although sheep combat thermal stress mainly by panting, a sizeable amount (40%) of total evaporative heat loss, is from sources other than panting (Hales & Brown, 1974). The frequency of sporadic discharge of sweat glands increases with increase in ambient temperature and is accompanied by a decline in respiration rate (Bligh, 1961). The wool coat can reduce evaporative cooling but sweating may have cooling value in sheep breeds with open fleeces (Rai, Singh & More, 1978). In sheep, the number and size of the sweat glands (Waites & Voglmayr, 1962) and the quantum of sweat production in a particular time period (Ghoshal et al. 1977) varies in different body regions. In view of the possible significance of surface evaporative cooling, thermal sweating in different body regions of sheep was investigated.

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Evaluation of vapor permeation through garments during exercise

Journal of Applied Physiology ◽

10.1152/jappl.1985.58.3.928 ◽

1985 ◽

Vol 58 (3) ◽

pp. 928-935 ◽

Cited By ~ 15

Author(s):

R. R. Gonzalez ◽

K. Cena

Keyword(s):

Heat Loss ◽

Cycle Ergometer ◽

Dew Point ◽

Evaporative Heat Loss ◽

Local Skin ◽

Vapor Permeation ◽

Skin Wettedness ◽

Latent Heat Loss ◽

Saturation Vapor ◽

Practical Dimension

Five males [age 28 +/- 8 yr; maximum O2 uptake (VO2max) 50 +/- 6 ml O2 . kg-1 . min-1; body wt 70 +/- 3 kg; DuBois surface area 1.85 +/- 0.02 m2] exercised on a cycle ergometer, placed on a Potter scale, at 31% VO2max for up to 2 h at an ambient temperature (Ta) of 25 degrees C and a dew-point temperature of 15 degrees C. Air movement was varied from still air to 0.4 and 2 m/s. Each subject, in separate runs, wore a track suit (TS ensemble) of 60% polyester-40% cotton (effective clo = 0.5); a Gortex parka (GOR ensemble), covering a sweat shirt and bottom of TS (effective clo = 1.4); or the TS ensemble covered by polyethylene overgarment (POG ensemble). Esophageal, skin temperature (Tsk) at eight sites, and heart rate were continuously recorded. Dew-point sensors recorded temperatures under the garments at ambient and chest (windward site) and midscapular sites. Local skin wettedness (loc w) and ratio of evaporative heat loss (Esk) to maximum evaporative capacity were determined. An observed average effective permeation (Pe, W . m-2 . Torr-1) was calculated as Esk/loc w (Ps,sk - Pw), where w is the average of chest and back loc w and (Ps,sk - Pw) is the gradient of skin saturation vapor pressure at Tsk and Ta. Additionally, the local effective evaporative coefficient was determined for chest and back sites by Esk/(Ps,dpl - Pw). The GOR ensemble produced an almost as high a Pe as the TS ensemble (82–86% of Pe with TS in still air and 0.4- and 2-m/s conditions). Direct dew-point recording offers an easy practical dimension to the study of efficacy of latent heat loss and skin wettedness properties through garments.

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