Effect of pressure on thermal insulation in humans wearing wet suits

1988 ◽  
Vol 64 (5) ◽  
pp. 1916-1922 ◽  
Author(s):  
Y. H. Park ◽  
J. Iwamoto ◽  
F. Tajima ◽  
K. Miki ◽  
Y. S. Park ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Water Temperature ◽  
Heat Loss ◽  
Thermal Insulation ◽  
Heat Production ◽  
Water Immersion ◽  
The Other ◽  
Body Parts ◽  
Metabolic Heat ◽  
Healthy Males

The present work was undertaken to determine the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 3 h without shivering, of wet-suited subjects during water immersion at different ambient pressures. Nine healthy males wearing neoprene wet suits (5 mm thick) were subjected to immersion to the neck in water at 1, 2, and 2.5 ATA while resting for 3 h. Continuous measurements of esophageal (T(es)) and skin (Tsk) temperatures and heat loss from the skin (Htissue) and wet suits (Hsuit) were recorded. Insulation of the tissue (Itissue), wet suits (Isuit), and overall total (Itotal) were calculated from the temperature gradient and the heat loss. The Tcw increased curvilinearly as the pressure increased, whereas the metabolic heat production during rest and immersion was identical over the range of pressure tested. During the 3rd h of immersion, Tes was identical under all atmospheric pressures; however, Tsk was significantly higher (P less than 0.05) at 2 and 2.5 ATA compared with 1 ATA. A 42 (P less than 0.001) and 50% (P less than 0.001), reduction in Isuit from the 1 ATA value was detected at 2 and 2.5 ATA, respectively. However, overall mean Itissue was maximal and independent of the pressure during immersion at Tcw. The Itotal was also significantly smaller in 2 and 2.5 ATA compared with 1 ATA. The Itissue provided most insulation in the extremities, such as the hand and foot, and the contribution of Isuit in these body parts was relatively small. On the other hand, Itissue of the trunk areas, such as the chest, back, and thigh, was not high compared with the extremities, and Isuit played a major role in the protection of heat drain from these body parts.

Critical water temperature during water immersion at various atmospheric pressures

1988 ◽  
Vol 64 (6) ◽  
pp. 2444-2448 ◽  
Author(s):  
J. Iwamoto ◽  
S. Sagawa ◽  
F. Tajima ◽  
K. Miki ◽  
K. Shiraki
Keyword(s):  
Water Temperature ◽  
High Altitude ◽  
Sea Level ◽  
Heat Loss ◽  
Heat Production ◽  
Atmospheric Pressure ◽  
Water Immersion ◽  
Loss Ratio ◽  
Metabolic Heat ◽  
Healthy Males

The present work was undertaken to determine the effect of atmospheric pressure [ranging from a high altitude of 4,300 m above sea level or 0.6 atmospheres absolute (ATA) to depths of 10 m deep or 2 ATA] on the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 2 h without shivering, of the unprotected subject during water immersion. Nine healthy males wearing only shorts were subjected to immersion to the neck in water at 0.6, 1, and 2 ATA while resting for 2 h. Continuous measurements included esophageal (Tes) and skin (Tsk) temperatures, direct heat loss from the skin (Htissue), and insulation of the tissue (Itissue). The Tcw was significantly higher at 0.6 ATA than 1 and 2 ATA: however, Tcw at 1 ATA was identical to that at 2 ATA. The metabolic heat production remained unchanged among the pressures. During the 2-h immersion in Tcw, Tes was identical among all atmospheric pressures: however, Tsk was significantly higher (P less than 0.05) at 0.6 ATA and was identical between 1 and 2 ATA. The overall mean Itissue was near maximal during immersion in Tcw in each pressure, and no difference was detected among the pressures. However, Itissue at the acral extremities (arm, hand, and foot) decreased significantly at 0.6 ATA, and subsequently heat loss from these parts was increased, which elevated an extremity-to-trunk heat loss ratio to 1.4 at 0.6 ATA from 1.1 at 1 and 2 ATA.

Thermal responses in humans exposed to cold hyperbaric helium-oxygen

1980 ◽  
Vol 49 (6) ◽  
pp. 1099-1106 ◽  
Author(s):  
C. A. Piantadosi ◽  
E. D. Thalmann
Keyword(s):  
Heat Loss ◽  
Heat Production ◽  
Cold Water ◽  
Minute Ventilation ◽  
Water Immersion ◽  
Heat Losses ◽  
Metabolic Heat Production ◽  
Metabolic Heat ◽  
Respiratory Heat Loss ◽  
Wide Range

The relationship of metabolic heat production to skin and core temperatures, cutaneous heat flow, and respiratory heat loss was measured in 10 male subjects cooled in hyperbaric helium at 20.7 ATA and 15 or 20 degrees C for 60-120 min. Under these conditions, metabolic heat production tended to compensate for the sum of convective and radiant heat losses from the skin but did not increase sufficiently to compensate for additional respiratory heat losses. There was a positive correlation between respiratory heat loss and fall in rectal temperature. Individual variability in ventilatory response to cold hyperbaric helium exposure as shown by a wide range of minute ventilation-to-oxygen consumption ratios (VE/VO2) was similar to that reported during cold water immersion. Subjects with high VE/VO2 had low mean physiological shell insulation values and lost more heat through the skin as well as through the respiratory tract than subjects with low VE/VO2.

Hair density, wind speed, and heat loss in mammals

1965 ◽  
Vol 20 (4) ◽  
pp. 796-801 ◽  
Author(s):  
R. T. Tregear
Keyword(s):  
Wind Speed ◽  
Temperature Gradient ◽  
Heat Loss ◽  
Thermal Insulation ◽  
Hair Density ◽  
Wind Speeds

The heat loss from excised pelts of rabbits, horses, and pigs has been measured at various wind speeds. The temperature gradient through the fur was also measured. The thermal insulation of fur is highly dependent on the hair density (i.e., number of hairs/ cm2), and on the wind passing over its surface. If there are less than 1,000 hairs/cm2, an 8-mph wind penetrates deep into the fur, but at higher hair densities an 18-mph wind penetrates only a little way into the fur. fur insulation; obstruction of wind by hair Submitted on September 10, 1964

Mechanisms of thermal stability during flight in the honeybee apis mellifera

1999 ◽  
Vol 202 (11) ◽  
pp. 1523-1533 ◽  
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.

scholarly journals Sex-related differences in local and whole-body heat loss responses: Physical or physiological?

2014 ◽  
Vol 39 (7) ◽  
pp. 843-843
Author(s):  
Daniel Gagnon
Keyword(s):  
Sex Differences ◽  
Heat Loss ◽  
Heat Production ◽  
Experimental Studies ◽  
Metabolic Heat Production ◽  
Whole Body ◽  
Fixed Rate ◽  
The Third ◽  
Metabolic Heat ◽  
Body Heat

The current thesis examined whether sex differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrated that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W·°C−1, p = 0.05) during exercise performed at a fixed rate of metabolic heat production. The second study showed that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W·m−2 (496 ± 139 vs. 483 ± 185 W·m−2·°C−1, p = 0.91) and 300 W·m−2 (283 ± 70 vs. 211 ± 66 W·m−2·°C−1, p = 0.17), only becoming greater in males at a requirement for heat loss of 350 W·m−2 (197 ± 61 vs. 82 ± 27 W·m−2·°C−1, p = 0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg·min−1·cm−2, p = 0.02) and methacholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg·min−1·cm−2, p = 0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.

Academic genealogy and direct calorimetry: a personal account

2011 ◽  
Vol 35 (2) ◽  
pp. 120-127 ◽  
Author(s):  
Donald C. Jackson
Keyword(s):  
Heat Production ◽  
Animal Studies ◽  
The Other ◽  
Metabolic Heat Production ◽  
Personal Account ◽  
Direct Calorimetry ◽  
Metabolic Heat ◽  
Academic Genealogy ◽  
The Way

Each of us as a scientist has an academic legacy that consists of our mentors and their mentors continuing back for many generations. Here, I describe two genealogies of my own: one through my PhD advisor, H. T. (Ted) Hammel, and the other through my postdoctoral mentor, Knut Schmidt-Nielsen. Each of these pathways includes distingished scientists who were all major figures in their day. The striking aspect, however, is that of the 14 individuals discussed, including myself, 10 individuals used the technique of direct calorimetry to study metabolic heat production in humans or other animals. Indeed, the patriarchs of my PhD genealogy, Antoine Lavoisier and Pierre Simon Laplace, were the inventors of this technique and the first to use it in animal studies. Brief summaries of the major accomplishments of each my scientific ancestors are given followed by a discussion of the variety of calorimeters and the scientific studies in which they were used. Finally, readers are encouraged to explore their own academic legacies as a way of honoring those who prepared the way for us.

Effects of phentolamine on thermoregulatory functions of rats to different ambient temperatures

1979 ◽  
Vol 57 (12) ◽  
pp. 1401-1406 ◽  
Author(s):  
M. T. Lin ◽  
Andi Chandra ◽  
T. C. Fung
Keyword(s):  
Heat Loss ◽  
Rectal Temperature ◽  
Heat Production ◽  
Room Temperature ◽  
Metabolic Heat Production ◽  
Central Component ◽  
Evaporative Heat Loss ◽  
Central Administration ◽  
Ambient Temperatures ◽  
Metabolic Heat

The effects of both systemic and central administration of phentolamine on the thermoregulatory functions of conscious rats to various ambient temperatures were assessed. Injection of phentolamine intraperitoneally or into a lateral cerebral ventricle both produced a dose-dependent fall in rectal temperature at room temperature and below it. At a cold environmental temperature (8 °C) the hypothermia in response to phentolamine was due to a decrease in metabolic heat production, but at room temperature (22 °C) the hypothermia was due to cutaneous vasodilatation (as indicated by an increase in foot and tail skin temperatures) and decreased metabolic heat production. There were no changes in respiratory evaporative heat loss. However, in the hot environment (30 °C), phentolamine administration produced no changes in rectal temperature or other thermoregulatory responses. A central component of action is indicated by the fact that a much smaller intraventricular dose of phentolamine was required to exert the same effect as intraperitoneal injection. The data indicate that phentolamine decreases heat production and (or) increases heat loss which leads to hypothermia, probably via central nervous system actions.

Effect of 5-hydroxytryptamine and acetylcholine on the energy budget of chickens

1980 ◽  
Vol 239 (1) ◽  
pp. R57-R61
Author(s):  
P. E. Hillman ◽  
N. R. Scott ◽  
A. van Tienhoven
Keyword(s):  
Physical Activity ◽  
Heart Rate ◽  
Body Temperature ◽  
Heat Loss ◽  
Energy Budget ◽  
Heat Production ◽  
Evaporative Heat Loss ◽  
Neural Pathways ◽  
Metabolic Heat ◽  
Intraventricular Injections

Intraventricular injections of 5-hydroxytryptamine-HCl (258 nmol) or acetylcholine-HCl (550 nmol) in the chicken caused body temperature to rise at 35 degrees C ambient, a result of decreased evaporative heat loss due to bradypnea. At 10 and 20 degrees C ambient, neither drug affected body temperature. Although these drugs decreased physical activity or shivering or both at 10 and 20 degrees C, metabolic heat production was not depressed enough to alter body temperature significantly. Heart rate decreased simultaneously with decreased activity at 20 degrees C. This study is the first to inject 5-hydroxytryptamine as a salt of HCl, instead of creatinine sulfate, as is commonly used. It is suggested that some of the differences reported herein, compared to other studies, are due to the type of salt used. It is postulated that either 5-hydroxytryptamine or acetylcholine, rather than norepinephrine, may be an important neurotransmitter in the neural pathways for thermoregulation in chickens, even though their action on thermoregulation is minor compared with norepinephrine.

scholarly journals Unique fur and skin structure in harbour seals ( Phoca vitulina )—thermal insulation, drag reduction, or both?

2015 ◽  
Vol 12 (104) ◽  
pp. 20141206 ◽  
Author(s):  
Nicola Erdsack ◽  
Guido Dehnhardt ◽  
Martin Witt ◽  
Andreas Wree ◽  
Ursula Siebert ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Heat Loss ◽  
Thermal Insulation ◽  
The Body ◽  
Body Parts ◽  
Skin Structure ◽  
Harbour Seals ◽  
Reduce Heat Loss ◽  
Mammalian Skin ◽  
New Type

Vertebrate surface structures, including mammalian skin and hair structures, have undergone various modifications during evolution in accordance with functional specializations. Harbour seals rely on their vibrissal system for orientation and foraging. To maintain tactile sensitivity even at low temperatures, the vibrissal follicles are heated up intensely, which could cause severe heat loss to the environment. We analysed skin samples of different body parts of harbour seals, and expected to see higher hair densities at the vibrissal pads as a way to reduce heat loss. In addition to significantly higher hair densities around the vibrissae than on the rest of the body, we show a unique fur structure of hair bundles consisting of broad guard hairs along with hairs of a new type, smaller than guard hairs but broader than underhairs, which we defined as ‘intermediate hairs’. This fur composition has not been reported for any mammal so far and may serve for thermal insulation as well as drag reduction. Furthermore, we describe a scale-like skin structure that also presumably plays a role in drag reduction.

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