Interaction of central and peripheral factors in physiological temperature regulation

1961 ◽  
Vol 200 (3) ◽  
pp. 572-580 ◽  
Author(s):  
M. M. Fusco ◽  
J. D. Hardy ◽  
H. T. Hammel
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Heat Production ◽  
Temperature Regulation ◽  
Physiological Temperature ◽  
Warm Environment ◽  
Quantitative Estimates ◽  
Cool Environment ◽  
Localized Heating ◽  
Environmental Temperatures

To evaluate the relative importance of central and peripheral factors in physiological temperature regulation, calorimetric measurements of thermal and metabolic responses in the unanesthetized dog to localized heating of the supraoptic and preoptic regions were made at various environmental temperatures. At all temperatures, heating the hypothalamus caused an imbalance in the over-all heat exchange, and lowered core temperature by 0.8°–1.0°C. In a neutral environment, this was effected by a 30–40% depression of the resting rate of heat production. In a cool environment, heating inhibited shivering so that heat production, relative to heat loss, was low. In a warm environment, vigorous panting and vasodilatation were elicited, thereby increasing heat loss. On cessation of heating, shivering occurred in response to the lowered core temperature, but differed in intensity depending upon the peripheral thermal drive. Reapplication of heating suppressed shivering in all cases. From these data some quantitative estimates were made of the sensitivity of the hypothalamic thermoregulatory ‘centers’, and of the interaction and relative contributions of central and peripheral control.

Effect of water restriction and environmental temperatures on metabolic rate and physiological parameters in sheep

2000 ◽  
Vol 80 (1) ◽  
pp. 97-104 ◽  
Author(s):  
B. T. Li ◽  
R. J. Christopherson ◽  
S. J. Cosgrove
Keyword(s):  
Metabolic Rate ◽  
Heat Production ◽  
Plasma Osmolality ◽  
Blood Parameters ◽  
Water Restriction ◽  
Creatinine Concentration ◽  
Warm Environment ◽  
Plasma Creatinine Concentration ◽  
Hb Concentration ◽  
Environmental Temperatures

The hypothesis that water restriction reduces metabolic rate and contributes to energy conservation of sheep, and induces changes in blood parameters was tested. Four of eight adult sheep were housed in either a warm (24.8 ± 1.5 °C) or cold (0.4 ± 1.2 °C) environment and fed a diet of alfalfa pellets at 1.2 × maintenance. Each sheep was fasted with or without water according to a crossover design. Average heat production (HP) and rectal temperature (Tr) were higher (P < 0.05) in the cold than in the warm. Fasting decreased HP and Tr (P < 0.05). Water restriction had no additional effect on HP and Tr. Fasting and fasting plus water restriction influenced plasma osmolality and creatinine concentration. Plasma creatinine concentration was lower (P < 0.01) and haemoglobin (Hb) concentration higher in the cold than in the warm environment. Hb concentration was increased with water restriction (P < 0.01) in the warm environment. Plasma cortisol concentration was altered by fasting. Packed cell volume (PCV) in blood, plasma volume and plasma aldosterone were not affected by treatments. The results suggest that water restriction, per se, for 3 d does not suppress metabolic rate in sheep below that resulting from fasting alone. Key words: Heat production, sheep, temperature, water restriction

Heat Production and Heat Loss in the Dog at 8–36°C Environmental Temperature

1958 ◽  
Vol 194 (1) ◽  
pp. 99-108 ◽  
Author(s):  
H. T. Hammel ◽  
C. H. Wyndham ◽  
J. D. Hardy
Keyword(s):  
Heat Loss ◽  
Heat Production ◽  
Vascular System ◽  
Heat Content ◽  
Important Change ◽  
The Body ◽  
Critical Temperatures ◽  
Hot Environment ◽  
Environmental Temperatures ◽  
Made In

Metabolic and thermal responses of three dogs were made in a rapid responding calorimeter at temperatures ranging from 8°C to 36°C. These dogs were acclimatized to a kennel temperature of 27°C and had critical temperatures between 23°C and 25°C. The only physiological responses to low environmental temperatures were a moderate decrease in total heat content and an increase in heat production. The tissue conductance and the cooling constant of the fur did not effectively decrease below the levels obtaining throughout the neutral zone. In a hot environment heat loss from the respiratory tract was greatly increased. Although there was a great increase in the tissue conductance in the hot environment, conductance of heat through the tissue became decreasingly important as the air temperature approached body temperature so that panting became increasingly important for maintaining thermal balance. It is concluded that the vasomotor response of the peripheral vascular system is primarily a mechanism for dissipating excess heat produced during exercise; it is practically unimportant as a heat conserving mechanism. Effective changes in the total insulation of the fur can only be achieved by changing the surface area of the body, particularly those areas which are thinly furred, and not by any important change in the fur thickness through pilomotor activity.

No dynamic effector responses to fast changes of core temperature at constant skin temperature

1987 ◽  
Vol 65 (6) ◽  
pp. 1339-1346 ◽  
Author(s):  
Ulrike Roos ◽  
Claus Jessen
Keyword(s):  
Skin Temperature ◽  
Heat Loss ◽  
Core Temperature ◽  
Heat Production ◽  
Control Level ◽  
Time Derivative ◽  
Rate Of Change ◽  
Dynamic Responses ◽  
Evaporative Heat Loss ◽  
Blood Temperature

Experiments in conscious goats were done to see whether heat production and respiratory evaporative heat loss show dynamic responses to changing core temperature at constant skin temperature. Core temperature was altered by external heat exchangers acting on blood temperature, while skin temperature was maintained constant by immersing the animals up to the neck in a rapidly circulating water bath. Core temperature was altered at various rates up to 0.9 °C/min. Step deviations of core temperature from control values were always followed by a positive time derivative of effector response, but never by a negative time derivative during sustained displacement of core temperature. Ramp experiments showed that the slopes at which heat production or heat loss rose with core temperature deviating from its control level grew smaller at higher rates of change of core temperature. It is concluded that neither heat production nor respiratory evaporative heat loss respond to the rate of change of core temperature. At constant skin temperature, thermoregulatory effector responses appear to be proportional to the degree to which core temperature deviates from its set level.

scholarly journals Blunted sweating does not alter the rise in core temperature in people with multiple sclerosis exercising in the heat

2020 ◽  
Author(s):  
Georgia K Chaseling ◽  
Davide Filingeri ◽  
Dustin R. Allen ◽  
Michael Barnett ◽  
Steve Vucic ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Heat Loss ◽  
Core Temperature ◽  
Heat Production ◽  
Sweat Rate ◽  
Onset Time ◽  
Local Sweat Rate ◽  
Temperature Heat ◽  
C 30 ◽  
Exercise Induced

Purpose: To determine whether thermoregulatory capacity is altered by MS during exercise in the heat. Methods: Sixteen MS (EDSS: 2.9±0.9; 47±8 y; 77.6±14.0 kg) and 14 healthy (CON) control participants (43±11 y; 78.6±17.0 kg) cycled at a heat production of 4 W.kg-1 for 60 minutes at 30˚C, 30%RH (WARM). A subset of 8 MS (EDSS: 2.6±0.5; 44±8 y; 82.3±18.2 kg) and 8 CON (44±12 y; 81.2±21.1 kg) also exercised at 35°C, 30%RH (HOT). Rectal (Tre), mean skin (Tsk) temperature, and local sweat rate on the upper-back (LSRback) and forearm (LSRarm), were measured. Results: All CON, yet only 9 of 16, and 7 of 8 MS participants completed 60 min of exercise in WARM and HOT trials, respectively. All MS participants unable to complete exercise stopped with ∆Tre between 0.2-0.5˚C. The time to reach a ∆Tre of 0.2˚C was similar (MS:28±15 min, CON: 32±18 min; P=0.51). For MS participants completing 60-min of exercise in WARM, ∆Tre (P=0.13), ∆Tsk (P=0.45), LSRback (P=0.69) and LSRarm (P=0.54) were similar to CON, but ΔTb (MS:0.16±0.13˚C, CON:0.07±0.06˚C; P=0.02) and onset time (MS:16±10 min, CON:8±5 min; P=0.02) for sweating were greater. Similarly, in HOT, ∆Tre (P=0.52), ∆Tsk (P=0.06), LSRback (P=0.59) and LSRarm (P=0.08) were similar, but ΔTb (MS: 0.19±0.16˚C, CON: 0.06±0.04˚C; P=0.04) and onset time (MS:13±7 min, CON:6±3 min; P=0.02) for sweating were greater with MS. Conclusion: Even at 35˚C, a delayed sweating onset didn't alter heat loss to sufficiently affect exercise-induced rises in core temperature. Heat intolerance with MS does not seem attributable to thermoregulatory impairments.

Some characteristics of core temperature signals in the conscious goat

1984 ◽  
Vol 247 (3) ◽  
pp. R456-R464 ◽  
Author(s):  
C. Jessen ◽  
G. Feistkorn
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Temperature Difference ◽  
Heat Production ◽  
Heat Exchangers ◽  
Response Curve ◽  
Temperature Response ◽  
Warm Receptors ◽  
Core Sensors Of Temperature ◽  
Head Temperature

In three conscious goats, head and trunk temperatures were altered independently of each other by means of extracorporeal carotid heat exchangers and intravascular heat exchangers in the trunk veins. In 35 experiments heat production and heat loss were measured while head temperature was varied between 35.4 and 42.2 degrees C and trunk temperature between 34.5 and 42.4 degrees C. The largest temperature difference between head and trunk amounted to 6.6 degrees C. Head and trunk generated approximately equal fractions of the total core temperature input to the controller. The distribution of combinations of head and trunk temperatures resulting in constant levels of heat production and heat loss was consistent with the hypothesis that the total core temperature input to the controller equaled the sum of two identical inputs, both rising exponentially with temperature. The hypothesis implies that the input generated by core sensors of temperature in head and trunk is a continuum and conforms with the temperature-response curve of warm receptors.

Hypoglycaemia, Hypothermia and Shivering in Man

1981 ◽  
Vol 61 (4) ◽  
pp. 463-469 ◽  
Author(s):  
E. A. M. Gale ◽  
T. Bennett ◽  
J. Hilary Green ◽  
I. A. MacDonald
Keyword(s):  
Skin Temperature ◽  
Core Temperature ◽  
Heat Production ◽  
Plasma Glucose ◽  
Room Temperature ◽  
Insulin Infusion ◽  
Central Body ◽  
Cool Environment ◽  
Peripheral Vasodilatation ◽  
Male Subjects

1. The present experiments were designed to elucidate the reasons for the fall in central body temperature during hypoglycaemia. 2. The first experiment was carried out at a room temperature of 25 °C on 11 male subjects. Hypoglycaemia was induced by infusion of insulin. Heat production (calculated from respiratory gas exchange) rose from a baseline of 5.10 ± 0.13 kJ/min (mean ± sem) to a peak of 6.25 ± 0.21 kJ/min (P < 0.001), but core temperature fell concurrently by 0.51 ± 0.08°C and skin temperature fell by 1.1 ± 0.2°C. The net heat loss was due to peripheral vasodilatation and sweating. 3. To determine the effect of insulin-induced hypoglycaemia on thermoregulation in a cool environment, the experiment was repeated at a room temperature of 18–19°C on five of the subjects who had air blown over them until shivering was sustained. During this time heat production rose to 10.13 ± 1.67 kJ/min, but core temperature remained constant. Shivering stopped as plasma glucose fell below 2.5 mmol/l during insulin infusion and the subjects said they no longer felt cold. 4. During hypoglycaemia in the cold peripheral vasodilatation and sweating occurred, skin temperature fell by up to 0.8°C and core temperature fell below 35°C, so subjects had to be rewarmed. 5. Recovery of plasma glucose after hypoglycaemia in the cold was impaired at low body temperatures, but shivering was restored within seconds when glucose was given intravenously.

Temperature regulation by hypothalamic proportional control with an adjustable set point

1963 ◽  
Vol 18 (6) ◽  
pp. 1146-1154 ◽  
Author(s):  
H. T. Hammel ◽  
D. C. Jackson ◽  
J. A. J. Stolwijk ◽  
J. D. Hardy ◽  
S. B. Stromme
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Temperature Regulation ◽  
Thermal Response ◽  
Hypothalamic Temperature ◽  
Set Point ◽  
Cold Environments ◽  
Hot Environment ◽  
Skin Temperatures

The role of the hypothalamic and skin temperatures in controlling the thermal response of a resting animal was studied by measurements of 1) hypothalamic, rectal, ear skin, and trunk skin temperatures on the resting dog and rhesus monkey in hot, neutral, and cold environments; and 2) the thermal and metabolic responses of a dog in neutral and cold environments during and immediately after holding the hypothalamus at approximately 39.0 C by means of six thermodes surrounding the hypothalamus and perfused with water. The results indicate that 1) a resting animal shivers in a cold environment with the same or higher hypothalamic temperature as the same animal in a neutral environment; 2) a resting animal pants in a hot environment with the same or lower hypothalamic temperature as the same animal in a neutral environment; 3) the hypothalamus is nonetheless strongly responsive to an increase or decrease of 1 C; 4) the rate of heat loss increases at the onset of sleep while the hypothalamic temperature is falling; 5) the hypothalamic temperature is 1–2 C lower during sleep even though thermoregulatory responses are the same as when awake; 6) the rate of heat loss decreases upon awakening while the hypothalamic temperature is rising. The discussion of these results includes a suggestion that the set point for temperature regulation is 1) decreased by a rising or elevated skin and extrahypothalamic core temperature, 2) increased by a falling or lowered skin and extrahypothalamic core temperature, 3) decreased upon entering and during sleep and is increased upon awakening. hypothalamic temperature; temperature set point; hypothalamic stimulation; dog temperature regulation; monkey temperature regulation Submitted on October 15, 1962

The effect of environmental conditions on food utilisation by sheep

1959 ◽  
Vol 1 (1) ◽  
pp. 1-12 ◽  
Author(s):  
D. G. Armstrong ◽  
K. L. Blaxter ◽  
N. McC. Graham ◽  
F. W. Wainman
Keyword(s):  
Critical Temperature ◽  
Heat Loss ◽  
Heat Production ◽  
Environmental Conditions ◽  
Environmental Temperature ◽  
Heat Losses ◽  
The Body ◽  
Food Utilisation ◽  
Metabolisable Energy ◽  
Environmental Temperatures

1. A series of calorimetric experiments was conducted with sheep which had fleeces ranging in thickness from 0·1 cm. to 12 cm. at environmental temperatures between 8 and 32° C. Heat production, heat loss by radiation, by convection and conduction, by vaporisation of water and due to warming food and water to body temperature were measured together with losses of energy in faeces, in urine and as methane.2. The effects of a rise in environmental temperature on digestion of the food and on the loss of energy in urine or as methane resulted in a slight rise in the metabolisable energy of the ration by 6 Cal./° C.3. Environmental temperature had a marked effect on heat production, particularly when the fleece was short. The critical temperature (i.e. the environmental temperature at which heat production was minimal) of the closely-clipped sheep varied from 24° C. at a high level of feeding to 38°C. at a sub-maintenance level of feeding. These critical temperatures are similar to that of naked, resting man but much higher than that of the pig when fed similarly.4. As the fleece grew the critical temperature fell. Thus, on a maintenance level of feeding, a sheep with a fleece of 0·1 cm. had a critical temperature of 32° C.; when the fleece had grown to 2·5 cm. the critical temperature was 13° C. while with a 12 cm. fleece the critical temperature was 0° C.5. Below the critical temperature heat losses increase more rapidly in sheep with light fleeces. Thus a heavy fleece not only depresses the critical temperature but also reduces the rate of increase of heat loss with falling temperature under sub-critical conditions.6. At environmental temperatures well below the critical, the heat losses of the sheep per unit surface were identical. Under such conditions, when the whole of the metabolisable energy of the food is used to keep the animal warm, the criterion of ration adequacy is a high content of meta-bolisable energy in small bulk.7. At environmental temperatures above 32° C. the heat production on a constant ration increased, the rise being greatest with the highest level of feeding. Consequently the net energy value of the food declined at these high environmental temperatures.8. The calorimetric experiments were supplemented by two comparative feeding trials in which the effects of normal outdoor environmental conditions on the body weight of groups of Cheviot and Blackface sheep were measured. Control groups were kept indoors in heated pens.9. During the mild winter of 1956-7 the out-wintered Blackface wethers i n full fleece did not loose any more weight than those fed the same rations indoors.10. During the more severe winter of 1957-8, Cheviot, in-lamb ewes kept on a maintenance diet gained 2·3 lb.; those kept outside on the same ration lost 3·3 lb. With Blackface, in·lamb ewes the difference between the two groups was 0·3 lb. in favour of the indoor group.11. The food utilisation of sheep is affected considerably by environmental conditions. With little fleece the critical temperature is high and even when in full fleece an effect of cold can be demonstrated under practical conditions.

The adaptation of energy utilization in the laying hen to warm and cool ambient temperatures

1972 ◽  
Vol 79 (2) ◽  
pp. 363-369 ◽  
Author(s):  
R. H. Davis ◽  
O. E. M. Hassan ◽  
A. H. Sykes
Keyword(s):  
Body Weight ◽  
Energy Intake ◽  
Heat Production ◽  
Egg Production ◽  
Energy Utilization ◽  
Ambient Temperatures ◽  
Warm Environment ◽  
Cool Environment ◽  
High Level ◽  
Energy Balances

SUMMARYTwo experiments have been performed to study the acclimatization of laying hens to cool or warm environmental temperature, using the comparative slaughter procedure to measure energy utilization. In the first experiment the energy balances over a 3-week period at either 10 or 35 °C were compared; in the second experiment a comparison was made of the energy balances over six consecutive weekly periods at similar cool and warm temperatures.The first experiment confirmed that production could be maintained (88%) in the warm environment even though food intake was markedly reduced (95 and 63 g/day at 10 and 35 °C respectively). In both environments a loss of body weight indicated, that energy intake was insufficient to meet demands for at least part of the period.During the first week of the second experiment there was a small loss of body weight in the cool environment and food consumption was slightly depressed. The results for energy intake, egg production and heat production suggest that acclimatization was complete after 1 week. In the warm environment egg production fell initially (62%) but returned to a high level (86%) during the second week. However, energy intake, body weight and heat production did not reach steady levels until the fourth week. Comparing the first 3 weeks with the subsequent 3 weeks the daily ME consumption was 137 and 161 kcal/kg¾ and the daily heat production was 126 and 116 kcal/kg¾. Similar, although less marked differences were observed in the cool environment. These results therefore emphasize the need to allow adequate time for acclimatization to the environment in studies of energy metabolism.

Temperature regulation in the new-born lamb. III. Effect of environmental temperature on metabolic rate body temperatures, and respiratory quotient

1961 ◽  
Vol 12 (6) ◽  
pp. 1152 ◽  
Author(s):  
G Alexander
Keyword(s):  
Body Temperature ◽  
Heat Loss ◽  
Heat Production ◽  
Temperature Regulation ◽  
Low Temperatures ◽  
Environmental Temperature ◽  
Body Temperatures ◽  
Normal Body Temperature ◽  
Ambient Temperatures ◽  
New Born

Studies were made on temperature regulation of lambs in a closed circuit indirect calorimeter. Dry new-born lambs were able to maintain normal body temperature in ambient temperatures as low as -5°C. This was accomplished by increasing heat production to 2–3 times "basal" levels, apparently by increased oxidation of fats, and by reducing heat loss through the extremities by vasoconstriction. The lower limit of the zone of thermal neutrality was about 29°C. In unsuckled lambs within 24 hr of birth, the heat produced in response to cold appeared to be independent of pre-natal nutrition and age. It was considerably lower in lambs with hairy coats than in lambs with fine coats. Milk intake increased heat production, and this increase was abolished after 12 hr of fasting in lambs up to 3 days old, but the increase persisted in older lambs. The increase was accompanied by, and was apparently due to, elevated heat loss from the extremities, which persisted even at low temperatures. The maximal thermal insulation of the tissues, calculated from these results, was about 1 Clo; that of the fleece plus air was only 1 to 2 Clo.

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