RECOVERY OF NEONATAL LAMBS FROM HYPOTHERMIA WITH THERMAL ASSISTANCE

1988 ◽  
Vol 68 (1) ◽  
pp. 183-190 ◽  
Author(s):  
J. B. ROBINSON ◽  
B. A. YOUNG
Keyword(s):  
Core Temperature ◽  
Heat Production ◽  
Substantial Reduction ◽  
Heat Content ◽  
Metabolic Heat Production ◽  
Warm Water ◽  
Body Core Temperature ◽  
Cotton Cloth ◽  
Metabolic Heat ◽  
Neonatal Lambs

Metabolic heat production and body core temperature were measured in 12 newborn lambs (4.7 ± 0.2 kg) prior to and during the induction of acute hypothermia (Tc = 30 °C), as well as during recovery to euthermia. Hypothermia was induced by immersion in 14–28 °C water. Rewarming was achieved by one of three procedures: (A) immersion of the lambs in warm water (38 °C); (B) exposure of the lambs in an air environment to a 250-watt infrared heat lamp; or (C) wrapping the lambs in a cotton cloth. Prehypothermia resting heat production was 4.3 ± 0.2 W kg−1. During the induction of hypothermia, summit metabolic heat production was 20.9 ± 0.5 W kg−1; however, as core temperature decreased from 35 to 31 °C, maximum metabolic rate declined by 1.33 W kg−1 per °C decline in core temperature. Recovery of the lambs to an euthermic state was achieved in 28, 38 and 50 ± 1.8 min in the warm water, infrared lamp and cotton cloth rewarming treatments with metabolic costs during recovery of 21.2, 33.2 and 40.6 ± 0.8 kJ kg−1, respectively. Recovery of hypothermic lambs in 38 °C water resulted in a thermal contribution to body heat content from the water and a substantial reduction in recovery time and in metabolic effort by the lambs. Key words: Hypothermia, rewarming, metabolic heat, supplemental heat, neonates, lambs

Hypoxia similarly impairs metabolic responses to cutaneous and core cold stimuli in conscious rats

1994 ◽  
Vol 77 (2) ◽  
pp. 726-730 ◽  
Author(s):  
G. G. Giesbrecht ◽  
J. E. Fewell ◽  
D. Megirian ◽  
R. Brant ◽  
J. E. Remmers
Keyword(s):  
Ambient Temperature ◽  
Core Temperature ◽  
Heat Production ◽  
Metabolic Response ◽  
Metabolic Heat Production ◽  
Conscious Rats ◽  
Metabolic Heat ◽  
Thermoregulatory Responses ◽  
Body Core ◽  
Core Cooling

Cold exposure elicits several thermoregulatory responses, including an increased metabolic heat production from shivering and nonshivering thermogenesis. The increased metabolism can be in response to body core and/or body cutaneous cooling. Hypoxic hypoxia has been shown to attenuate the metabolic response to cutaneous cooling. We measured metabolic heat production in adult conscious rats during independent cutaneous and core cooling, during normoxia and hypoxia, to 1) test the hypothesis that hypoxia suppresses the metabolic response to independent core cooling and 2) determine whether hypoxia acts preferentially on the response to cutaneous or core cooling. The animals were studied in a temperature-controlled metabolic chamber, and body core temperature was controlled by an abdominal heat exchange coil. Ambient temperature was varied (10, 19, and 28 degrees C) while core temperature was clamped at 37 degrees C or core temperature was varied (33, 35, and 37 degrees C) at a stable ambient temperature of 28 degrees C. Our data indicate that although the sensitivity of the metabolic response to core cooling is about five to six times that to cutaneous cooling. Hypoxia similarly attenuates thermoregulatory responses to both stimuli.

SHORT-TERM THERMAL AND METABOLIC RESPONSES OF SHEEP TO RUMINAL COOLING: EFFECTS OF LEVEL OF COOLING AND PHYSIOLOGICAL STATE

1990 ◽  
Vol 70 (3) ◽  
pp. 833-843 ◽  
Author(s):  
A. M. NICOL ◽  
B. A. YOUNG
Keyword(s):  
Heat Loss ◽  
Heat Production ◽  
Physiological State ◽  
Heat Content ◽  
Metabolic Heat Production ◽  
Mean Body Temperature ◽  
Metabolic Heat ◽  
Reduced Body ◽  
Cooling Effects ◽  
Body Heat

In a series of studies to simulate the ingestion of cold food, the rumen of adult sheep was cooled by 0–400 kJ over 1 h. Ruminal cooling reduced body heat content, increased rate of metabolic heat production and reduced apparent rate of heat loss to the environment. On average, each 100 kJ of cooling reduced heat content by 46 kJ, increased heat production by 20 kJ and reduced heat loss by 70 kJ. Precooling thermal status of the sheep affected the magnitude of the responses to cooling. A 0.1 °C higher precooling mean body temperature decreased the response in metabolic heat production by 6 kJ and increased the reduction in body heat content by 4.6 kJ. The heat production associated with eating reduced the heat loss response to ruminal cooling but did not affect the change in heat content. Well-insulated sheep were less affected by ruminal cooling. Key words: Sheep, rumen, cooling, heat production, temperature

Heat Balance and Distribution during the Core-Temperature Plateau in Anesthetized Humans

1995 ◽  
Vol 83 (3) ◽  
pp. 491-499. ◽  
Author(s):  
Andrea Kurz ◽  
Daniel I. Sessler ◽  
Richard Christensen ◽  
Martha Dechert
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Heat Production ◽  
Heat Balance ◽  
Thermal Flux ◽  
The Body ◽  
Metabolic Heat Production ◽  
The Core ◽  
Metabolic Heat ◽  
Temperature Plateau

Background Once triggered, intraoperative thermoregulatory vasoconstriction is remarkably effective in preventing further hypothermia. Protection results from both vasoconstriction-induced decrease in cutaneous heat loss and altered distribution of body heat. However, the independent contributions of each mechanism have not been quantified. Accordingly, we evaluated overall heat balance and distribution of heat within the body during the core-temperature plateau. Methods Nine minimally clothed male volunteers were anesthetized with propofol and isoflurane and maintained in an approximately 22 degrees C environment. They were monitored for approximately 2 h before vasoconstriction and for 3 h subsequently. Overall heat balance was determined from the difference between cutaneous heat loss (thermal flux transducers) and metabolic heat production (oxygen consumption). Arm and leg tissue heat contents were determined from 19 intramuscular temperatures, ten skin temperatures, and "deep" foot temperature. Heat constrained by vasoconstriction to the trunk and head was calculated by subtracting the expected change in that region (overall heat balance multiplied by the fractional weight of the trunk and head) from the actual change (change in distal esophageal temperature multiplied by the specific heat of human tissue and the weight of the trunk and head); the result represents the amount by which core heat exceeded that which would be expected based on overall heat balance, assuming that the change was evenly distributed throughout the body. Results Vasoconstriction and passive tissue cooling decreased heat loss but not to the level of heat production. Consequently, heat loss exceeded metabolic heat production throughout the study. Core temperature decreased approximately 1.3 C during the 2-h prevasoconstriction period; however, core temperature remained virtually constant during the subsequent 3 h. In the 3 h after vasoconstriction, arm and leg heat content decreased 57 +/- 9 kcal, and vasoconstriction constrained 22 +/- 8 kcal to the trunk and head. Conclusions These results confirm the efficacy of thermo-regulatory vasoconstriction in preventing additional core hypothermia. Decreased cutaneous heat loss and constraint of metabolic heat to the core thermal compartment contributed to the plateau.

scholarly journals Human thermoregulatory responses during serial cold-water immersions

1998 ◽  
Vol 85 (1) ◽  
pp. 204-209 ◽  
Author(s):  
John W. Castellani ◽  
Andrew J. Young ◽  
Michael N. Sawka ◽  
Kent B. Pandolf
Keyword(s):  
Body Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Alternative Explanation ◽  
Cold Water ◽  
Metabolic Heat Production ◽  
Normal Body Temperature ◽  
Repeat Trial ◽  
Metabolic Heat ◽  
Made In

This study examined whether serial cold-water immersions over a 10-h period would lead to fatigue of shivering and vasoconstriction. Eight men were immersed (2 h) in 20°C water three times (0700, 1100, and 1500) in 1 day (Repeat). This trial was compared with single immersions (Control) conducted at the same times of day. Before Repeat exposures at 1100 and 1500, rewarming was employed to standardize initial rectal temperature. The following observations were made in the Repeat relative to the Control trial: 1) rectal temperature was lower and heat debt was higher ( P < 0.05) at 1100; 2) metabolic heat production was lower ( P < 0.05) at 1100 and 1500; 3) subjects perceived the Repeat trial as warmer at 1100. These data suggest that repeated cold exposures may impair the ability to maintain normal body temperature because of a blunting of metabolic heat production, perhaps reflecting a fatigue mechanism. An alternative explanation is that shivering habituation develops rapidly during serially repeated cold exposures.

Physical fitness and thermoregulatory reactions in a cold environment in men

1988 ◽  
Vol 65 (5) ◽  
pp. 1984-1989 ◽  
Author(s):  
J. H. Bittel ◽  
C. Nonotte-Varly ◽  
G. H. Livecchi-Gonnot ◽  
G. L. Savourey ◽  
A. M. Hanniquet
Keyword(s):  
Physical Fitness ◽  
Cold Stress ◽  
Heat Production ◽  
Ambient Air ◽  
Metabolic Heat Production ◽  
Adult Males ◽  
Fitness Level ◽  
Metabolic Heat ◽  
Air Temperatures ◽  
Thermoregulatory Reactions

The relationship between the physical fitness level (maximal O2 consumption, VO2max) and thermoregulatory reactions was studied in 17 adult males submitted to an acute cold exposure. Standard cold tests were performed in nude subjects, lying for 2 h in a climatic chamber at three ambient air temperatures (10, 5, and 1 degrees C). The level of physical fitness conditioned the intensity of thermoregulatory reactions to cold. For all subjects, there was a direct relationship between physical fitness and 1) metabolic heat production, 2) level of mean skin temperature (Tsk), 3) level of skin conductance, and 4) level of Tsk at the onset of shivering. The predominance of thermogenic or insulative reactions depended on the intensity of the cold stress: insulative reactions were preferential at 10 degrees C, or even at 5 degrees C, whereas colder ambient temperature (1 degree C) triggered metabolic heat production abilities, which were closely related to the subject's physical fitness level. Fit subjects have more efficient thermoregulatory abilities against cold stress than unfit subjects, certainly because of an improved sensitivity of the thermoregulatory system.

Acclimatization of calves to a hot dry environment

1959 ◽  
Vol 52 (3) ◽  
pp. 296-304 ◽  
Author(s):  
W. Bianca
Keyword(s):  
Heart Rate ◽  
Respiratory Rate ◽  
Rectal Temperature ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Metabolic Heat ◽  
Physiological Reactions

1. Three calves were individually exposed in a climatic room to an environment of 45° C. dry-bulb and 28° C. wet-bulb temperature for 21 successive days up to 5 hr. each day.2. In the 21-day period, mostly during the first half of it, the following changes in the physiological reactions of the animals were observed: progressive reductions in rectal temperature, in heart rate and in respiratory rate with a change of breathing from a laboured to a less laboured type.3. It was suggested that a decrease in metabolic heat production might play a part in the observed acclimatization.

Effects of solar radiation and wind speed on metabolic heat production by two mammals with contrasting coat colours.

1995 ◽  
Vol 198 (7) ◽  
pp. 1499-1507 ◽  
Author(s):  
G E Walsberg ◽  
B O Wolf
Keyword(s):  
Wind Speed ◽  
Solar Radiation ◽  
Heat Production ◽  
Metabolic Heat Production ◽  
Heat Gain ◽  
Solar Heat ◽  
Wind Speeds ◽  
Convective Heat Loss ◽  
Metabolic Heat ◽  
Solar Heat Gain

We report the first empirical data describing the interactive effects of simultaneous changes in irradiance and convection on energy expenditure by live mammals. Whole-animal rates of solar heat gain and convective heat loss were measured for representatives of two ground squirrel species, Spermophilus lateralis and Spermophilus saturatus, that contrast in coloration. Radiative heat gain was quantified as the decrease in metabolic heat production caused by the animal's exposure to simulated solar radiation. Changes in convective heat loss were quantified as the variation in metabolic heat production caused by changes in wind speed. For both species, exposure to 780 W m-2 of simulated solar radiation significantly reduced metabolic heat production at all wind speeds measured. Reductions were greatest at lower wind speeds, reaching 42% in S. lateralis and 29% in S. saturatus. Solar heat gain, expressed per unit body surface area, did not differ significantly between the two species. This heat gain equalled 14-21% of the radiant energy intercepted by S. lateralis and 18-22% of that intercepted by S. saturatus. Body resistance, an index of animal insulation, declined by only 10% in S. saturatus and 13% in S. lateralis as wind speed increased from 0.5 to 4.0 ms-1. These data demonstrate that solar heat gain can be essentially constant, despite marked differences in animal coloration, and that variable exposure to wind and sunlight can have important consequences for both thermoregulatory stress experienced by animals and their patterns of energy allocation.

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.

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