Evaluation of vapor permeation through garments during exercise

1985 ◽  
Vol 58 (3) ◽  
pp. 928-935 ◽  
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.

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).

Influence of beta-adrenergic blockade on the control of sweating in humans

1986 ◽  
Vol 61 (5) ◽  
pp. 1701-1705 ◽  
Author(s):  
G. W. Mack ◽  
L. M. Shannon ◽  
E. R. Nadel
Keyword(s):  
Skin Temperature ◽  
Sweat Rate ◽  
Energy Balance Equation ◽  
Cycle Ergometer ◽  
Beta Blockade ◽  
Evaporative Heat Loss ◽  
Adrenergic Blockade ◽  
Beta Adrenergic ◽  
Local Skin ◽  
Ergometer Exercise

To evaluate the role of beta-adrenergic receptors in the control of human sweating, we studied six subjects during 40 min of cycle-ergometer exercise (60% maximal O2 consumption) at 22 degrees C 2 h after oral administration of placebo or nonselective beta-blockade (BB, 80 mg propranolol). Internal temperature (esophageal temperature, Tes), mean skin temperature (Tsk), local chest temperature (Tch), and local chest sweat rate (msw) were continuously recorded. The control of sweating was best described by the slope of the linear relationship between msw and Tes and the threshold Tes for the onset of sweating. The slope of the msw-Tes relationship decreased 27% (P less than 0.01), from 1.80 to 1.30 mg X cm-2 X min-1 X degree C-1 during BB. The Tes threshold for sweating (36.8 degrees C) was not altered as the result of BB. These data suggest that BB modified the control of sweating via some peripheral interaction. Since Tsk was significantly (P less than 0.05) reduced during BB exercise, from a control value of 32.8 to 32.2 degrees C, we evaluated the influence of the reduction in local skin temperature (Tsk) in the altered control of sweating. Reductions in Tch accounted for only 45% of the decrease in the slope of the msw-Tes relationship during BB. Since evaporative heat loss requirement during exercise with BB, as estimated from the energy balance equation, was also reduced 18%, compared with control exercise, we concluded that during BB the reduction in sweating at any Tes is the consequence of both a decrease in local Tsk and a direct effect on sweat gland.

Heat exchange during upper- and lower-body exercise

1984 ◽  
Vol 57 (4) ◽  
pp. 1050-1054 ◽  
Author(s):  
M. N. Sawka ◽  
R. R. Gonzalez ◽  
L. L. Drolet ◽  
K. B. Pandolf
Keyword(s):  
Heat Exchange ◽  
Heat Loss ◽  
Dew Point ◽  
Upper Body ◽  
Evaporative Heat Loss ◽  
Lower Body ◽  
Transfer Coefficients ◽  
Cycle Exercise ◽  
Upper Body Exercise ◽  
Dry Heat

This study examined evaporative and dry heat exchange during upper- and lower-body exercise. Four male subjects performed arm-crank or cycle exercise at the same O2 uptake level (approximately 1.6 l/min) in an environment facilitating dry heat exchange [radiative and convective (R + C)] [ambient temperature (Ta) = 18 degrees C, dew-point temperature (Tdp) = 14 degrees C] and an environment facilitating evaporative heat loss (Esk) (Ta = 35 degrees C, Tdp = 14 degrees C). (R + C) was determined from the torso with a net radiometer and from the limbs with heat flow discs, whereas Esk was determined from the torso and limbs by ventilated dew-point sensors. In both environments neither esophageal temperature nor mean skin temperature were different between exercise types (P greater than 0.05). Torso (R + C) was significantly (P less than 0.05) greater during arm-crank than during cycle exercise in both environments. Torso Esk, as well as arm (R + C), and arm Esk were not different (P greater than 0.05) between exercise types in each environment. Leg (R + C) was greater (P less than 0.05) during cycle than during arm-crank exercise in the 18 degrees C environment, whereas leg Esk was greater (P less than 0.05) during cycle than during arm-crank exercise in the 35 degrees C environment. These data indicate that to compensate for greater torso sensible heat loss during upper body exercise lower body exercise elicits additional (R + C) or Esk from the legs. The avenue for this compensatory sensible and insensible heat loss depends upon the differential heat transfer coefficients which influence tissue conductivity and mass transfer.

Is there evidence for nonthermal modulation of whole body heat loss during intermittent exercise?

2010 ◽  
Vol 299 (1) ◽  
pp. R119-R128 ◽  
Author(s):  
Glen P. Kenny ◽  
Daniel Gagnon
Keyword(s):  
Heat Loss ◽  
Intermittent Exercise ◽  
Progressive Increase ◽  
Cycle Ergometer ◽  
Lower Limbs ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Active Recovery ◽  
Mean Body Temperature ◽  
Passive Recovery

This study compared the effect of active, passive, and inactive recoveries on whole body evaporative and dry heat loss responses during intermittent exercise at an air temperature of 30°C and a relative humidity of 20%. Nine males performed three 15-min bouts of upright seated cycling at a fixed external workload of 150 W. The exercise bouts were separated by three 15-min recoveries during which participants 1) performed loadless pedaling (active recovery), 2) had their lower limbs passively compressed with inflatable sleeves (passive recovery), or 3) remained upright seated on the cycle ergometer (inactive recovery). Combined direct and indirect calorimetry was employed to measure rates of whole body evaporative heat loss (EHL) and metabolic heat production (M-W). Mean body temperature (Tb) was calculated from esophageal and mean skin temperatures, and mean arterial pressure (MAP) was measured continuously. Active and passive recoveries both reversed the reduction in MAP associated with inactive recovery ( P ≤ 0.05). This response was paralleled by greater levels of EHL during active (207 ± 53 W) and passive recoveries (203 ± 55 W) compared with the inactive condition (168 ± 53 W, P ≤ 0.05). However, the greater rate of EHL during active recovery was paralleled by a greater M-W (194 ± 16 W) compared with inactive recovery (149 ± 27 W, P ≤ 0.001). In contrast, M-W during passive recovery (139 ± 20 W) was not significantly different from the inactive condition ( P = 0.468). Furthermore, there were no differences in Tb between inactive and passive conditions during the recovery periods ( P = 0.820). As such, passive recovery resulted in greater levels of EHL for a given change in Tb compared with inactive recovery ( P ≤ 0.05). These results strongly suggest that the progressive increase in core temperature during successive exercise/rest cycles is primarily the result of a baroreflex-mediated attenuation of postexercise whole body evaporative heat loss.

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

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.

Evaporative Heat Loss Mechanisms of the Newborn Calf, Bos Taurus

1968 ◽  
Vol 124 (2) ◽  
pp. 83-88 ◽  
Author(s):  
J.R.S. Hales ◽  
J.D. Findlay ◽  
D. Robertshaw
Keyword(s):  
Heat Loss ◽  
Bos Taurus ◽  
Evaporative Heat Loss ◽  
Loss Mechanisms

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

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.

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

1971 ◽  
Vol 49 (5) ◽  
pp. 767-774 ◽  
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.

Energy balance in ovariectomized rats with and without estrogen replacement

1980 ◽  
Vol 238 (5) ◽  
pp. R400-R405 ◽  
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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