Heat balance and reactivity to endotoxin

1963 ◽  
Vol 204 (4) ◽  
pp. 719-722 ◽  
Author(s):  
F. Robert Fekety
Keyword(s):  
Ambient Temperature ◽  
Heat Balance ◽  
Heat Dissipation ◽  
Body Temperatures ◽  
Endogenous Pyrogen ◽  
Heat Conservation

Shorn rabbits, supine restrained rabbits, and rabbits in the cold had relatively low body temperatures because their caloric losses were greater than normal, and they did not develop fever after endotoxin, adrenaline, or endogenous pyrogen. In such animals, mechanisms of heat conservation seemed maximally operative prior to testing; the absence of fever was related to limits imposed by ambient temperature upon heat conservation by further vasoconstriction in the ear, and shivering responses were not uniformly seen. Ordinarily appropriate late mechanisms of heat dissipation were noted after endotoxin despite the lack of fever. Febrile responses became possible when shorn animals were warmed. After repeated endotoxin injection, greater vasoconstriction over the trunk was feasible, the limitations of ambient temperature upon heat conservation became less decisive, and fever resulted. The unusual circulatory and thermal responses of chilled rabbits should be taken into consideration when performing similar experiments.

Geographic variation in body size of five Australian marsupials supports Bergmann’s thermoregulation hypothesis

2020 ◽  
Vol 101 (4) ◽  
pp. 1010-1020
Author(s):  
Alyson M Stobo-Wilson ◽  
Teigan Cremona ◽  
Brett P Murphy ◽  
Susan M Carthew
Keyword(s):  
Body Size ◽  
Ambient Temperature ◽  
Geographic Variation ◽  
Heat Dissipation ◽  
Geographic Range ◽  
Bergmann’S Rule ◽  
Maximum Temperature ◽  
Bergmann's Rule ◽  
Skull Length ◽  
Heat Conservation

Abstract Despite a large body of research, little agreement has been reached on the ultimate driver(s) of geographic variation in body size (mass and/or length). Here we use skull length measurements (as a surrogate for body mass) from five Australian marsupial species to test the primary hypotheses of geographic variation in body size (relating to ambient temperature, productivity, and seasonality). We used a revised articulation of Bergmann’s rule, wherein evidence for thermoregulation (heat dissipation or heat conservation) is considered supportive of Bergmann’s rule. We modeled the skull lengths of four Petaurid glider species and the common brushtail possum (Trichosurus vulpecula) as a function of indices of ambient temperature, productivity, and seasonality. The skull length of Petaurus ariel, P. notatus, and the squirrel glider (P. norfolcensis), increased with increasing winter minimum temperature, while that of T. vulpecula decreased with increasing summer maximum temperature. The skull length of P. ariel decreased with indices of productivity, falsifying the productivity hypothesis. Only P. ariel met the hypothesis of seasonality, as skull length increased with increasing seasonality. Thermoregulation was the most consistently supported driver of geographic variation in body size, as we found evidence of either heat conservation or heat dissipation in four of the five species examined. We found the geographic range of the individual species and the climate space in which the species occurred was integral to understanding the species’ responses to climate variables. Future studies should use specimens that are representative of a species’ entire geographic range, encompass a variety of climatic regions, and use consistent methodologies and terminology when testing drivers of geographic variation in body size.

scholarly journals The Permissible under Heating Conditions Torque of a Frequency-Controlled Synchronous Motor of Permanent Magnets

2018 ◽  
Vol 61 (6) ◽  
pp. 508-516
Author(s):  
B. I. Firago ◽  
S. V. Aleksandrovsky
Keyword(s):  
Ambient Temperature ◽  
Balance Equation ◽  
Heat Balance ◽  
Heat Dissipation ◽  
Permanent Magnets ◽  
Heat Balance Equation ◽  
Thermal Calculation ◽  
Motor Speed ◽  
Motor Torque ◽  
Electrical Motors

The variable speed electrical drives for industrial mechanisms with a constant static torque usually operate in a large range of speeds and loads. Along with this, for any speed of a given range the electrical drive motor is to provide a continuous permissible torque without overheating. Mostly the electrical motors have self-ventilation; the ventilator being located on the motor shaft. In such motors heat dissipation depends on a motor speed. The permissible continuous motor torque is determined out of a heat balance equation where power losses being converted into heat must be transferred in the ambient space and the motor temperature must not be over a permitted level for a given class of winding insulation under the certain ambient temperature. A heat balance equation is usually obtained on a basis of a one-mass motor heat model, i. e. the model that was used in this research. But even the one-mass heat model gives a non-linear heat balance equation. In order to get convenient analytical expressions out of the motor heat balance equation, it is necessary to take some justified assumptions; the latter was also implemented in this research. As a result, formulas have been obtained by which the long-term permissible motor torque can be calculated as a function of the relative speed of the rotor at a given ambient temperature. For the examples presented in the articles we chose (20 and 40 °С as a standard temperature for the thermal calculation of electrical machines). Dependences of a relative permissible continuous motor torque m on a relative frequency value (or relative rotor speed) are presented for three synchronous motors with permanent magnets and rated power of 3; 25 and 250 kW.

scholarly journals Influence of Ambient Temperature on Radiative and Convective Heat Dissipation Ratio in Polymer Heat Sinks

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2286
Author(s):  
Jan Kominek ◽  
Martin Zachar ◽  
Michal Guzej ◽  
Erik Bartuli ◽  
Petr Kotrbacek
Keyword(s):  
Heat Transfer ◽  
Ambient Temperature ◽  
Convective Heat ◽  
Heat Dissipation ◽  
High Surface ◽  
Heat Sinks ◽  
Fourth Power ◽  
Molding Process ◽  
Ambient Temperatures ◽  
University Of Technology

Miniaturization of electronic devices leads to new heat dissipation challenges and traditional cooling methods need to be replaced by new better ones. Polymer heat sinks may, thanks to their unique properties, replace standardly used heat sink materials in certain applications, especially in applications with high ambient temperature. Polymers natively dispose of high surface emissivity in comparison with glossy metals. This high emissivity allows a larger amount of heat to be dissipated to the ambient with the fourth power of its absolute surface temperature. This paper shows the change in radiative and convective heat transfer from polymer heat sinks used in different ambient temperatures. Furthermore, the observed polymer heat sinks have differently oriented graphite filler caused by their molding process differences, therefore their thermal conductivity anisotropies and overall cooling efficiencies also differ. Furthermore, it is also shown that a high radiative heat transfer leads to minimizing these cooling efficiency differences between these polymer heat sinks of the same geometry. The measurements were conducted at HEATLAB, Brno University of Technology.

Body temperature regulation and oxygen consumption in young chicks fed thyroid hormone

1991 ◽  
Vol 69 (7) ◽  
pp. 1842-1847 ◽  
Author(s):  
Gregory K. Snyder ◽  
Joseph R. Coelho ◽  
Dalan R. Jensen
Keyword(s):  
Oxygen Consumption ◽  
Thyroid Hormone ◽  
Body Temperature ◽  
Ambient Temperature ◽  
Cold Exposure ◽  
Elevated Serum ◽  
Body Temperatures ◽  
Serum Thyroid Hormone ◽  
Regulate Body Temperature ◽  
Young Chicks

In chicks the ability to regulate body temperature to adult levels develops during the first 2 weeks of life. We examined whether the ability of young chicks to regulate body temperature is increased by elevated levels of the thyroid hormone 3,3′5-triiodothyronine. By 13 days following hatch, body temperatures of chicks were not significantly different from those expected for adult birds. Furthermore, at an ambient temperature of 10 °C, 13-day-old control chicks were able to maintain body temperature, and elevated serum thyroid hormone levels did not increase rates of oxygen consumption or body temperature above control values. Six-day-old chicks had body temperatures that were significantly lower than those of the 13-day-old chicks and were not able to regulate body temperature when exposed to an ambient temperature of 10 °C. On the other hand, 6-day-old chicks with elevated serum thyroid hormone had significantly higher rates of oxygen consumption than 6-day-old control chicks, and were able to maintain constant body temperatures during cold exposure. The increased oxygen consumption rates and improved ability to regulate body temperature during cold exposure were correlated with increased citrate synthase activity in skeletal muscle. Our results support the argument that thyroid hormones play an important role in the development of thermoregulatory ability in neonate birds by stimulating enzyme activities associated with aerobic metabolism.

Ambient Temperature as a Strong Zeitgeber of Circadian Rhythms in Response to Temperature Sensitivity and Poor Heat Dissipation Abilities in Subterranean African Mole-Rats

2021 ◽  
pp. 074873042110342
Author(s):  
Daniel W. Hart ◽  
Barry van Jaarsveld ◽  
Kiara G. Lasch ◽  
Kerryn L. Grenfell ◽  
Maria K. Oosthuizen ◽  
...  
Keyword(s):  
Circadian Rhythms ◽  
Ambient Temperature ◽  
Heat Dissipation ◽  
Direct Consequence ◽  
Ecological Constraints ◽  
Photic Entrainment ◽  
Mole Rat ◽  
Intimate Link ◽  
Response To Temperature ◽  
First Time

Mammals have evolved circadian rhythms in internal biological processes and behaviors, such as locomotor activity (LA), to synchronize to the environmental conditions they experience. Photic entrainment of LA has been well established; however, non-photic entrainment, such as ambient temperature ( Ta), has received much less attention. To address this dearth of knowledge, we exposed two subterranean endothermic-homeothermic African mole-rat species, the solitary Cape mole-rat ( Georychus capensis [GC]) and social Mahali mole-rat ( Cryptomys hottentotus mahali [CHM]), to varying Ta cycles in the absence of light. We showed that the LA rhythms of these two species entrain to Ta cycles and that the majority of LA occurred during the coolest 12-h period. LA confined to the coolest Ta periods may be the direct consequence of the poor heat dissipation abilities of African mole-rats brought about by physiological and ecological constraints. Recently, it has been hypothesized that Ta is only a strong zeitgeber for circadian rhythms in species whose thermoregulatory abilities are sensitive to changes in Ta (i.e., heterotherms and ectotherms), which previously has excluded endothermic-homeothermic mammals. However, this study demonstrates that Ta is a strong zeitgeber or entrainer for circadian rhythms of LA in subterranean endothermic-homeothermic mammals as a consequence of their sensitivity to changes in Ta brought about by their poor heat dissipation abilities. This study reinforces the intimate link between circadian rhythms and thermoregulation and conclusively, for the first time, provides evidence that Ta is a strong zeitgeber for endothermic-homeothermic mammals.

Heat balance, haematology and serum chemistry of layers under varying stocking density reared in locally fabricated metal-type cage system

2020 ◽  
Vol 40 (2) ◽  
pp. 92-103
Author(s):  
K. O. Bello ◽  
A. E. Adiatu ◽  
M. O. Osunlakin ◽  
O. O. Oni
Keyword(s):  
Relative Humidity ◽  
Ambient Temperature ◽  
Rectal Temperature ◽  
Heat Balance ◽  
Total Protein ◽  
Stocking Density ◽  
Fabricated Metal ◽  
Cage System ◽  
Chemical Measurements ◽  
Metal Type

One hundred and thirty five 18weeks old Bovans Nera Black strain pullets were used in a 10week study to determine their heat balance and blood profile under varying stocking density in locally fabricated metal-type cage system. The cages were stocked 2, 3 and 4birds/cell. Daily ambient temperature and relative humidity of the cage and rectal temperature of the birds were taken and heat balance calculated. Record of Packed cell volume (PCV), Haemoglobin concentration (Hb), Red blood cell (RBC), White blood count (WBC) and differential of the birds were taken at beginning and end of the study for the haematological indices while blood glucose, total protein, Albumin and blood urea were taken for the bio-chemical measurements. Ambient temperature, relative humidity, and heat balance showed no significant (P>0.05) difference with cage stocking density. Cage stocking density had significant (P<0.05) effect on rectal temperature of layers. Bird stocked 3/cell recorded the least (41.14oC) rectal temperature while those stocked 4/cell recorded the highest (41.27oC). All the haematological parameters of the birds were not significantly (P>0.05) influenced by stocking density of the cage type. Bio-chemical measurements were not significantly (P>0.05) different among layers under varying stocking density of the cage except total protein (P<0.05). Layers stocked 4/cell recorded highest (5.22g/dl) total protein while those stocked 3/cell had the least value (4.37g/dl). However, the values were within the normal range recommended for healthy chicken. The study concluded that locally fabricated metal-type battery cage could be used to rear layers and stocking density of 3birds/cell is ideal without compromising the welfare of the birds.

Heat balance precedes stabilization of body temperatures during cold water immersion

2003 ◽  
Vol 95 (1) ◽  
pp. 89-96 ◽  
Author(s):  
Peter Tikuisis
Keyword(s):  
Heat Balance ◽  
Cold Water ◽  
Water Immersion ◽  
Heat Content ◽  
Cold Water Immersion ◽  
The Body ◽  
Body Temperatures ◽  
Mean Body Temperature ◽  
The Core ◽  
Region Temperature

Certain previous studies suggest, as hypothesized herein, that heat balance (i.e., when heat loss is matched by heat production) is attained before stabilization of body temperatures during cold exposure. This phenomenon is explained through a theoretical analysis of heat distribution in the body applied to an experiment involving cold water immersion. Six healthy and fit men (mean ± SD of age = 37.5 ± 6.5 yr, height = 1.79 ± 0.07 m, mass = 81.8 ± 9.5 kg, body fat = 17.3 ± 4.2%, maximal O2 uptake = 46.9 ± 5.5 l/min) were immersed in water ranging from 16.4 to 24.1°C for up to 10 h. Core temperature (Tco) underwent an insignificant transient rise during the first hour of immersion, then declined steadily for several hours, although no subject's Tco reached 35°C. Despite the continued decrease in Tco, shivering had reached a steady state of ∼2 × resting metabolism. Heat debt peaked at 932 ± 334 kJ after 2 h of immersion, indicating the attainment of heat balance, but unexpectedly proceeded to decline at ∼48 kJ/h, indicating a recovery of mean body temperature. These observations were rationalized by introducing a third compartment of the body, comprising fat, connective tissue, muscle, and bone, between the core (viscera and vessels) and skin. Temperature change in this “mid region” can account for the incongruity between the body's heat debt and the changes in only the core and skin temperatures. The mid region temperature decreased by 3.7 ± 1.1°C at maximal heat debt and increased slowly thereafter. The reversal in heat debt might help explain why shivering drive failed to respond to a continued decrease in Tco, as shivering drive might be modulated by changes in body heat content.

scholarly journals Body Temperatures in Some Australian Mammals II.Peramelidae

1962 ◽  
Vol 15 (2) ◽  
pp. 386 ◽  
Author(s):  
PR Morrison
Keyword(s):  
Body Temperature ◽  
Ambient Temperature ◽  
Active Phase ◽  
Temperature Measurements ◽  
Temperature Cycle ◽  
Body Temperatures ◽  
Ambient Temperatures ◽  
Diurnal Temperature

Body temperature measurements on the short-nosed bandicoot (Thylacis obeaulus) have shown a nocturnal cycle with a range of 1� 2�C and a short active phase at 2200-0400 hr. The bilby or rabbit bandicoot (Macrotis lagoti8) had a sharply defined temperature cycle, with a range of almost 3�C after several months of captivity, during which the day-time resting temperature was progressively lowered from 36� 4 to 34� 2�C. Forced activity raised the diurnal temperature substantially but not to the nocturnal level. Forced activity did not raise the nocturnal level which was similar in the two species (37' O�C). Both species could regulate effectively at an ambient temperature of 5�C, but only Thylaci8 showed regulation at ambient temperatures of between 30 and 40�C.

Parasympathetic influence on heart rate in euthermic and hibernating ground squirrels.

1995 ◽  
Vol 198 (4) ◽  
pp. 931-937 ◽  
Author(s):  
M B Harris ◽  
W K Milsom
Keyword(s):  
Heart Rate ◽  
Ambient Temperature ◽  
Parasympathetic Nervous System ◽  
Ground Squirrels ◽  
Relative Role ◽  
Body Temperatures ◽  
Inotropic Effects ◽  
Ambient Temperatures ◽  
Isolated Hearts ◽  
C 32

The relative role of the parasympathetic nervous system during deep hibernation is enigmatic. Conflicting hypotheses exist, and both sides draw support from investigations of vagal influence on the heart. Recent studies have shown cardiac chronotropic and inotropic effects of parasympathetic stimulation and inhibition in isolated hearts and anesthetized animals at hibernating body temperatures. No studies, however, have demonstrated such occurrences in undisturbed deeply hibernating animals. The present study documents respiratory-related alterations in heart rate during euthermia and hibernation at ambient temperatures of 15, 10 and 5 degrees C mediated by parasympathetic influence. During quiet wakefulness, euthermic squirrels breathed continuously and exhibited a 29% acceleration in heart rate during inspiration. During deep undisturbed hibernation, at 15, 10 and 5 degrees C ambient temperature, animals exhibited an episodic breathing pattern and body temperatures were slightly above ambient temperature. At each temperature, heart rate during the respiratory episode was greater than that during the apnea. The magnitude of this ventilatory tachycardia decreased with ambient temperature, being 108% at 15 degrees C, 32% at 10 degrees C and 11.5% at 5 degrees C. Animals exposed to 3% CO2 at 5 degrees C, which significantly increased ventilation, still exhibited an 11.7% increase in heart rate during breathing. Thus, the magnitude of the ventilation tachycardia was independent of the level of ventilation, at least over the range studied. Inhibition of vagus nerve conduction at 5 degrees C was achieved using localized nerve block. This led to an increase in apneic heart rate and abolished the ventilatory tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

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