Thermal, Metabolic, and Cardiovascular Responses to Various Degrees of Cold Stress

1975 ◽  
Vol 53 (2) ◽  
pp. 293-298 ◽  
Author(s):  
Peter B. Raven ◽  
James E. Wilkerson ◽  
Steven M. Horvath ◽  
Nils W. Bolduan
Keyword(s):  
Cardiac Output ◽  
Steady State ◽  
Ambient Temperature ◽  
Heat Production ◽  
Thermal Gradient ◽  
Cardiovascular Responses ◽  
Whole Body ◽  
Third Order ◽  
Ambient Temperatures ◽  
Body Heat

The metabolic, thermal, and cardiovascular responses of two male Caucasians to a 2 h exposure to ambient temperatures ranging between 28 °C and 5 °C were studied and related to the respective ambient temperatures. The metabolic heat production increased linearly with decreasing ambient temperature, where heat production (kcal∙m−2∙h−1) = −2.79 Ta °C + 103.4, r = −0.97, P < 0.001. During all exposures below 28 °C, the rate of decrease in mean skin temperature [Formula: see text] was found to be an exponential function dependent upon the ambient temperature (Ta) and the time of exposure. Reestablishment of [Formula: see text] steady state occurred at 90–120 min of exposure, and the time needed to attain steady state was linearly related to decreasing Ta. The net result was that a constant ratio of 1.5 of the external thermal gradient to the internal thermal gradient was obtained, and at all experimental temperatures, the whole body heat transfer coefficient remained constant. Cardiac output was inversely related to decreasing Ta, where cardiac output [Formula: see text], r = −0.92, P < 0.01. However, the primary reason for the increased [Formula: see text], the stroke output, was also described as a third-order polynomial, although the increasing stroke volume throughout the Ta range (28–5 °C) was linearly related to decreasing ambients. The nonlinear response of this parameter which occurred at 20 °C ≥ Ta ≥ 10 °C suggested that the organism's cardiac output response was an integration of the depressed heart rate response and the increasing stroke output at these temperatures.

Light masking of circadian rhythms of heat production, heat loss, and body temperature in squirrel monkeys

1999 ◽  
Vol 276 (2) ◽  
pp. R298-R307 ◽  
Author(s):  
Edward L. Robinson ◽  
Charles A. Fuller
Keyword(s):  
Body Temperature ◽  
Heat Loss ◽  
Heat Production ◽  
Whole Body ◽  
Direct Calorimetry ◽  
Set Point ◽  
Subjective Night ◽  
Timing System ◽  
Circadian Timing System ◽  
Body Heat

Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism ( n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.

Whole body and hindlimb cardiovascular responses of the anesthetized dog during CO hypoxia

1984 ◽  
Vol 62 (7) ◽  
pp. 769-774 ◽  
Author(s):  
C. E. King ◽  
S. M. Cain ◽  
C. K. Chapler
Keyword(s):  
Carbon Monoxide ◽  
Blood Flow ◽  
Cardiac Output ◽  
Sympathetic Innervation ◽  
Cardiovascular Responses ◽  
The Body ◽  
Whole Body ◽  
Total Resistance ◽  
Intact Group ◽  
Anesthetized Dogs

To compare with earlier studies of anemic hypoxia obtained by hemodilution, O2 carring capacity was decreased by carbon monoxide (CO) hypoxia. Arterial O2 content was reduced either 50% (moderate CO) or 65% (severe CO). In two groups of anesthetized dogs (moderate and severe CO) hindlimb innervation remained intact while in a third group (moderate CO) the hindlimb was denervated. Measurements were obtained prior to and at 30 and 60 min of CO hypoxia. Cardiac output was elevated at 30 min of CO hypoxia in all groups (p < 0.01) and in the severe CO group at 60 min (p < 0.01). Hindlimb blood flow remained unchanged during CO hypoxia in the intact groups. In the denervated group, hindlimb blood flow was greater (p < 0.05) than that in the intact groups throughout the experiment. A decrease in mean arterial pressure (p < 0.01) in all groups was associated with a fall in total resistance (p < 0.01). Hindlimb resistance remained unchanged during moderate CO hypoxia in the intact group but increased (p < 0.05) in the denervated group. In the severe CO group hindlimb resistance was decreased (p < 0.05) at 60 min. The results indicate that the increase in cardiac output during CO hypoxia was directed to nonmuscle areas of the body and that intact sympathetic innervation was required to achieve this redistribution.

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.

scholarly journals Whole body and muscle energy metabolism in preruminant calves: effects of nutrient synchrony and physical activity

2007 ◽  
Vol 97 (4) ◽  
pp. 667-675 ◽  
Author(s):  
Joost J. G. C. van den Borne ◽  
Jean-François Hocquette ◽  
Martin W. A. Verstegen ◽  
Walter J. J. Gerrits
Keyword(s):  
Physical Activity ◽  
Heat Production ◽  
Enzyme Activities ◽  
Citrate Synthase ◽  
Human Subjects ◽  
Fat Content ◽  
Oxidative Enzyme ◽  
Whole Body ◽  
Muscle Energy ◽  
Body Heat

The effects of asynchronous availability of amino acids and glucose on muscle composition and enzyme activities in skeletal muscle were studied in preruminant calves. It was hypothesized that decreased oxidative enzyme activities in muscle would explain a decreased whole body heat production with decreasing nutrient synchrony. Preruminant calves were assigned to one of six degrees of nutrient synchrony, step-wise separating the intake of protein and lactose over the two daily meals. Calves at the most synchronous treatment received two identical meals daily. At the most asynchronous treatment, 85 % of the daily protein and 20 % of the daily lactose supply were fed in one meal and the remainder in the other meal. Daily intakes of all dietary ingredients were identical for all treatments. Oxidative enzyme activities and fat content increased with decreasing nutrient synchrony inM. Rectus Abdominis(RA), but not inM. Semitendinosus. Cytochrome-c-oxidase activity was positively correlated with fat content in RA (r0·49;P < 0·01). Oxidative enzyme activities in both muscles were not correlated with average daily heat production, but citrate synthase activity in RA was positively correlated (P < 0·01) with the circadian amplitude (r0·53) and maximum (r0·61) of heat production associated with physical activity. In conclusion, this study indicates that muscle energy stores are regulated by nutrient synchrony. The lack of correlation between muscle oxidative enzyme activities and average daily heat production was in contrast with findings in human subjects. Therefore, oxidative enzyme activity in muscle should not be used as an indicator for whole body heat production in growing calves.

Energy utilization in the laying hen in relation to ambient temperature

1973 ◽  
Vol 81 (1) ◽  
pp. 173-177 ◽  
Author(s):  
R. H. Davis ◽  
O. E. M. Hassan ◽  
A. H. Sykes
Keyword(s):  
Ambient Temperature ◽  
Energy Intake ◽  
Heat Production ◽  
Egg Production ◽  
Energy Utilization ◽  
Ambient Temperatures ◽  
Thermoneutral Zone ◽  
Energy Retention ◽  
The Difference ◽  
Energy Balances

SummaryEnergy balances have been determined, using the comparative slaughter procedure, over 3-week periods on groups of laying hens kept at ambient temperatures of 7·2, 15·6, 23·9, 29·4 and 35 °C.Energy intake declined as the environment became warmer (kcal ME/kg¾/day = 203· 1·13°C); heat production, as measured by the difference between energy intake and energy retention, also declined with increasing ambient temperature (kcal/kg¾/day = 151 – 1·11°C). There was a linear relationship between heat production and ambient temperature with no thermoneutral zone or critical temperature.The energy available for egg production remained almost constant at 50 kcal/kg¾/day equivalent to a rate of egg production of 82% at each ambient temperature.

scholarly journals Modelflow underestimates cardiac output in heat-stressed individuals

2011 ◽  
Vol 300 (2) ◽  
pp. R486-R491 ◽  
Author(s):  
Manabu Shibasaki ◽  
Thad E. Wilson ◽  
Morten Bundgaard-Nielsen ◽  
Thomas Seifert ◽  
Niels H. Secher ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Heat Stress ◽  
Arterial Pressure ◽  
Lower Body Negative Pressure ◽  
Whole Body ◽  
Arterial Cannulation ◽  
Artery Cannulation ◽  
Whole Body Heat Stress ◽  
Acute Changes ◽  
Body Heat

An estimation of cardiac output can be obtained from arterial pressure waveforms using the Modelflow method. However, whether the assumptions associated with Modelflow calculations are accurate during whole body heating is unknown. This project tested the hypothesis that cardiac output obtained via Modelflow accurately tracks thermodilution-derived cardiac outputs during whole body heat stress. Acute changes of cardiac output were accomplished via lower-body negative pressure (LBNP) during normothermic and heat-stressed conditions. In nine healthy normotensive subjects, arterial pressure was measured via brachial artery cannulation and the volume-clamp method of the Finometer. Cardiac output was estimated from both pressure waveforms using the Modeflow method. In normothermic conditions, cardiac outputs estimated via Modelflow (arterial cannulation: 6.1 ± 1.0 l/min; Finometer 6.3 ± 1.3 l/min) were similar with cardiac outputs measured by thermodilution (6.4 ± 0.8 l/min). The subsequent reduction in cardiac output during LBNP was also similar among these methods. Whole body heat stress elevated internal temperature from 36.6 ± 0.3 to 37.8 ± 0.4°C and increased cardiac output from 6.4 ± 0.8 to 10.9 ± 2.0 l/min when evaluated with thermodilution ( P < 0.001). However, the increase in cardiac output estimated from the Modelflow method for both arterial cannulation (2.3 ± 1.1 l/min) and Finometer (1.5 ± 1.2 l/min) was attenuated compared with thermodilution (4.5 ± 1.4 l/min, both P < 0.01). Finally, the reduction in cardiac output during LBNP while heat stressed was significantly attenuated for both Modelflow methods (cannulation: −1.8 ± 1.2 l/min, Finometer: −1.5 ± 0.9 l/min) compared with thermodilution (−3.8 ± 1.19 l/min). These results demonstrate that the Modelflow method, regardless of Finometer or direct arterial waveforms, underestimates cardiac output during heat stress and during subsequent reductions in cardiac output via LBNP.

Responses of young calves to low ambient temperatures at two levels of feeding

1992 ◽  
Vol 55 (3) ◽  
pp. 397-405 ◽  
Author(s):  
J. W. Schrama ◽  
A. Arieli ◽  
M. J. W. Heetkamp ◽  
M. W. A. Verstegen
Keyword(s):  
Energy Metabolism ◽  
Ambient Temperature ◽  
Rectal Temperature ◽  
Heat Production ◽  
Experimental Period ◽  
Metabolizable Energy ◽  
Ambient Temperatures ◽  
Feeding Level ◽  
Holstein Friesian ◽  
Maintenance Requirements

AbstractSeven groups of five or six Holstein-Friesian male calves were transported to an experimental farm at 2 to 3 days of age. At 6 days of age, heat production (HP) and metabolizable energy (ME) intake were measured for an 8-day period. During this period, calves were exposed to various ambient temperatures: 6, 9, 12 and 15°C. Ambient temperature was constant within days, but changed between days. Calves were fed below (four groups) or near (three groups) the maintenance requirements (290 or 460 kJ ME per kg M0·75 per day).From 6 to 14 days of age the lower critical temperature (Tc) was 12·5°C and HP increased by 8·4 kJ/kg M0·75 per day per °Cfall in ambient temperature below Tc. Both Tc and increase in HP below Tc were not affected by feeding level. Rectal temperature was lower at low ambient temperatures. The decrease in rectal temperature with ambient temperature was greatest at the low feeding level.During the experimental period, calves were not in a steady-state regarding energy metabolism. Heat production decreased with time. This decrease was affected by feeding level and ambient temperature. After arrival, the influence of both ambient temperature and feeding level on the energy metabolism of young calves increased with time.

Contribution of shivering in leg muscles to heat production in Japanese quail

1986 ◽  
Vol 64 (4) ◽  
pp. 889-892 ◽  
Author(s):  
E. Don Stevens ◽  
J. Ferguson ◽  
V. G. Thomas ◽  
E. Hohtola
Keyword(s):  
Ambient Temperature ◽  
Japanese Quail ◽  
Heat Production ◽  
Open Circuit ◽  
Linear Rate ◽  
Ambient Temperatures ◽  
Coturnix Coturnix ◽  
Metabolic Heat ◽  
Leg Muscles ◽  
Flight Muscles

We estimated heat production in Japanese quail (Coturnix coturnix japonica) by measuring oxygen uptake using open-circuit respirometry as ambient temperature was decreased gradually from 26 to 3.5 °C. At the same time, the intensity of shivering was estimated in both the leg muscles and the flight muscles by measuring electromyograms. Metabolic heat production increased in a linear fashion as ambient temperature decreased. Shivering intensity increased at the same linear rate in the leg muscles as in the flight muscles as ambient temperature decreased. The leg muscles produce a substantial fraction (about 1/4) of the total shivering heat production at low ambient temperatures. Shivering occurred in bursts; the onset of a burst in the leg muscles was precisely synchronized with the onset of a burst in the flight muscles.

A mechanism by which helium increases metabolism in small mammals

1960 ◽  
Vol 199 (2) ◽  
pp. 243-245 ◽  
Author(s):  
H. A. Leon ◽  
S. F. Cook
Keyword(s):  
Thermal Conductivity ◽  
Oxygen Consumption ◽  
Ambient Temperature ◽  
Skin Temperature ◽  
Heat Loss ◽  
Small Mammals ◽  
Thermal Gradient ◽  
Oxygen Mixture ◽  
Ambient Temperatures ◽  
Long Evans

The oxygen consumption of male Long-Evans rats was determined at three different ambient temperatures in air and in an equivalent helium-oxygen mixture. It was found that when the ambient temperature is near the skin temperature of the rat, the effect of helium is insignificant. If the ambient temperature is lowered, helium induces an increased metabolism over air at the same temperature. Since helium has a thermal conductivity about six times greater than nitrogen, it is concluded that the accelerated metabolism is in response to the greater heat loss in the presence of helium and the magnitude of this response is proportional to the thermal gradient between the animal and the environment.

Temperature regulation and cold acclimation in the golden hamster

1965 ◽  
Vol 20 (3) ◽  
pp. 405-410 ◽  
Author(s):  
Hermann Pohl
Keyword(s):  
Oxygen Consumption ◽  
Body Temperature ◽  
Ambient Temperature ◽  
Cold Acclimation ◽  
Heat Production ◽  
Golden Hamster ◽  
Thermal Conductance ◽  
Muscular Activity ◽  
The Body ◽  
Ambient Temperatures

Characteristics of cold acclimation in the golden hamster, Mesocricetus auratus, were 1) higher metabolic rate at -30 C, 2) less shivering when related to ambient temperature or oxygen consumption, and 3) higher differences in body temperature between cardiac area and thoracic subcutaneous tissues at all ambient temperatures tested, indicating changes in tissue insulation. Cold-acclimated hamsters also showed a rise in temperature of the cardiac area when ambient temperature was below 15 C. Changes in heat distribution in cold-acclimated hamsters suggest higher blood flow and heat production in the thoracic part of the body in the cold. The thermal conductance through the thoracic and lumbar muscle areas, however, did not change notably with lowering ambient temperature. Marked differences in thermoregulatory response to cold after cold acclimation were found between two species, the golden hamster and the thirteen-lined ground squirrel, showing greater ability to regulate body temperature in the cold in hamsters. hibernator; oxygen consumption— heat production; body temperature — heat conductance; muscular activity — shivering; thermoregulation Submitted on July 6, 1964

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