Activity, blood temperature and brain temperature of free-ranging springbok

1997 ◽  
Vol 167 (5) ◽  
pp. 335-343 ◽  
Author(s):  
Duncan Mitchell ◽  
Shane K. Maloney ◽  
Helen P. Laburn ◽  
Michael H. Knight ◽  
Gernot Kuhnen ◽  
...  
Keyword(s):  
Brain Temperature ◽  
Blood Temperature ◽  
Free Ranging

Thermoregulation in ratites: a review

2008 ◽  
Vol 48 (10) ◽  
pp. 1293 ◽  
Author(s):  
Shane K. Maloney
Keyword(s):  
Tidal Volume ◽  
Water Loss ◽  
Production Systems ◽  
Brain Temperature ◽  
Respiratory Alkalosis ◽  
Evaporative Water ◽  
Hypothalamic Temperature ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Free Ranging

Laboratory and free-ranging studies on the emu, ostrich and kiwi show ratites to be competent homeotherms. While body temperature and basal metabolic rate are lower in ratites than other birds, all of the thermoregulatory adaptations present in other birds are well established in ratites. The thermoneutral zone has been established for the emu and kiwi, and extends to 10°C. Below that zone, homeothermy is achieved via the efficient use of insulation and elevated metabolic heat production. In the heat, emus and ostriches increase respiratory evaporative water loss and use some cutaneous water loss. Respiratory alkalosis is avoided by reducing tidal volume. In severe heat, tidal volume increases, but the emu becomes hypoxic and hypocapnic, probably by altering blood flow to the parabronchi, resulting in ventilation/perfusion inhomogeneities. Ostriches are capable of uncoupling brain temperature from arterial blood temperature, a phenomenon termed selective brain cooling. This mechanism may modulate evaporative effector responses by manipulating hypothalamic temperature, as in mammals. The implications of thermal physiology for ratite production systems include elevated metabolic costs for homeothermy at low ambient temperature. However, the emu and ostrich are well adapted to high environmental temperatures.

Blood and brain temperatures of free-ranging black wildebeest in their natural environment

1994 ◽  
Vol 267 (6) ◽  
pp. R1528-R1536 ◽  
Author(s):  
C. Jessen ◽  
H. P. Laburn ◽  
M. H. Knight ◽  
G. Kuhnen ◽  
K. Goelst ◽  
...  
Keyword(s):  
Brain Temperature ◽  
Natural Habitat ◽  
Radiant Heat ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Data Loggers ◽  
Free Ranging ◽  
Arterial Blood Temperature

Using miniature data loggers, we measured the temperatures of carotid blood and brain in four wildebeest (Connochaetes gnou) every 2 min for 3 wk and every 5 min, in two of the animals, for a further 6 wk. The animals ranged freely in their natural habitat, in which there was no shelter. They were subject to intense radiant heat (maximum approximately 1,000 W/m2) during the day. Arterial blood temperature showed a circadian rhythm with low amplitude (< 1 degree C) and peaked in early evening. Brain temperature was usually within 0.2 degrees C of arterial blood temperature. Above a threshold between 38.8 and 39.2 degrees C, brain temperature tended to plateau so that the animals exhibited selective brain cooling. However, selective brain cooling sometimes was absent even when blood temperature was high and present when it was low. During helicopter chases, selective brain cooling was absent, even though brain temperature was near 42 degrees C. We believe that selective brain cooling is controlled by brain temperature but is modulated by sympathetic nervous system status. In particular, selective brain cooling may be abolished by high sympathetic activity even at high brain temperatures.

Rectal temperature measurement results in artifactual evidence of selective brain cooling

2001 ◽  
Vol 281 (1) ◽  
pp. R108-R114 ◽  
Author(s):  
Shane K. Maloney ◽  
Andrea Fuller ◽  
Graham Mitchell ◽  
Duncan Mitchell
Keyword(s):  
Rectal Temperature ◽  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood ◽  
The Status ◽  
Conscious Sheep ◽  
Surrogate Measures ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5°C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40°C exposure and not at all during the 5°C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

2007 ◽  
Vol 293 (1) ◽  
pp. R438-R446 ◽  
Author(s):  
Andrea Fuller ◽  
Leith C. R. Meyer ◽  
Duncan Mitchell ◽  
Shane K. Maloney
Keyword(s):  
Drinking Water ◽  
Brain Temperature ◽  
Heat Exposure ◽  
Plasma Osmolality ◽  
Threshold Temperature ◽  
Evaporative Heat Loss ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 ± 3 kg, means ± SD). The animals, housed in a climatic chamber at 23°C, were exposed for nine days to a cyclic protocol with daytime heat (40°C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 ± 4% of body mass, and plasma osmolality had increased from 290 ± 8 to 323 ± 9 mmol/kg ( P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 ± 0.18°C) than in euhydration (−0.05 ± 0.14°C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27°C) and dehydration (39.14°C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 ± 0.31) than in euhydrated animals (0.87 ± 0.11, P = 0.003). Return of drinking water at 39°C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.

Model of local temperature changes in brain upon functional activation

2004 ◽  
Vol 97 (6) ◽  
pp. 2051-2055 ◽  
Author(s):  
Christopher M. Collins ◽  
Michael B. Smith ◽  
Robert Turner
Keyword(s):  
Brain Temperature ◽  
Human Subjects ◽  
Potential Temperature ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Human Head ◽  
Bioheat Equation ◽  
Three Dimensional Model ◽  
Temperature Changes ◽  
Blood Temperature

Experimental results for changes in brain temperature during functional activation show large variations. It is, therefore, desirable to develop a careful numerical model for such changes. Here, a three-dimensional model of temperature in the human head using the bioheat equation, which includes effects of metabolism, perfusion, and thermal conduction, is employed to examine potential temperature changes due to functional activation in brain. It is found that, depending on location in brain and corresponding baseline temperature relative to blood temperature, temperature may increase or decrease on activation and concomitant increases in perfusion and rate of metabolism. Changes in perfusion are generally seen to have a greater effect on temperature than are changes in metabolism, and hence active brain is predicted to approach blood temperature from its initial temperature. All calculated changes in temperature for reasonable physiological parameters have magnitudes <0.12°C and are well within the range reported in recent experimental studies involving human subjects.

scholarly journals Brain Cooling: An Economy Mode of Temperature Regulation in Artiodactyls

Physiology ◽  
1998 ◽  
Vol 13 (6) ◽  
pp. 281-286 ◽  
Author(s):  
Claus Jessen
Keyword(s):  
Heat Stress ◽  
Body Temperature ◽  
Heat Loss ◽  
Temperature Regulation ◽  
Thermal Damage ◽  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Free Ranging ◽  
The Brain

Artiodactyls employ selective brain cooling (SBC) regularly during experimental hyperthermia. In free-ranging antelopes, however, SBC often was present when body temperature was low but absent when brain temperature was near 42°C. The primary effect of SBC is to adjust the activity of the heat loss mechanisms to the magnitude of the heat stress rather than to the protection of the brain from thermal damage.

Variation in body temperature in free-ranging western grey kangaroos Macropus fuliginosus.

2004 ◽  
Vol 26 (2) ◽  
pp. 135 ◽  
Author(s):  
SK Maloney ◽  
A Fuller ◽  
PR Kamerman ◽  
G Mitchell ◽  
D Mitchell
Keyword(s):  
Body Temperature ◽  
Early Morning ◽  
Measured Temperature ◽  
Ambient Conditions ◽  
Blood Temperature ◽  
Early Evening ◽  
Average Maximum ◽  
Globe Temperature ◽  
Free Ranging ◽  
Black Globe Temperature

Using implanted temperature loggers we measured temperature in the carotid artery in five (4 male, 1 female) western grey kangaroos (Macropus fuliginosus) every 5 min for between 39 and 74 days. Dry bulb temperature during the study ranged from an average minimum of (mean � SD) 11 � 3�C to maximum of 24 � 5�C. Black globe temperature measured in the southern shade of a grass tree, the habitat chosen by kangaroos during the day, ranged from an average minimum of 10 � 4�C to an average maximum of 30 � 6�C. There were nine days where maximum shade globe temperature exceeded 40�C. Carotid blood temperature averaged 36.5 � 0.1�C (n = 5), ranging from an average minimum of 35.5 � 0.3�C to a maximum of 37.3 � 0.1�C The resultant average daily range was 1.8 � 0.3�C. Body temperature was highest during the night and dropped rapidly early in the morning, reaching a nadir at 1000 hours, after ambient temperature and solar radiation had begun increasing. Body temperature then rose gradually during the day to reach a peak in the early evening. The nychthemeral variation in carotid blood temperature was largely independent of ambient conditions. There was a weak but significant association between early morning radiation levels and the minimum body temperature reached, suggesting that peripheral warming influences the morning decrease in core temperature.

Angularis oculi vein blood flow modulates the magnitude but not the control of selective brain cooling in sheep

2011 ◽  
Vol 300 (6) ◽  
pp. R1409-R1417 ◽  
Author(s):  
Andrea Fuller ◽  
Robyn S. Hetem ◽  
Leith C. R. Meyer ◽  
Shane K. Maloney
Keyword(s):  
Water Deprivation ◽  
Brain Temperature ◽  
Heat Exposure ◽  
Venous Drainage ◽  
Threshold Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Before And After

To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we measured brain and carotid blood temperatures in six adult female Dorper sheep. Halfway through the study, a section of the AOV, just caudal to its junction with the dorsal nasal vein, was extirpated on both sides. Before and after AOV surgery, the sheep were housed outdoors at 21–22°C and were exposed in a climatic chamber to daytime heat (40°C) and water deprivation for 5 days. In sheep outdoors, SBC was significantly lower after the AOV had been cut, with its 24-h mean reduced from 0.25 to 0.01°C ( t5 = 3.06, P = 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day ( t5 = 3.68, P = 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 ± 0.28°C) and after (38.85 ± 0.39°C) AOV surgery ( t5 =0.00, P = 1.00), but above the threshold, SBC magnitude was about twofold less after surgery. SBC after AOV surgery also was less during heat exposure and water deprivation. However, SBC increased progressively by the same magnitude (0.4°C) over the period of water deprivation, and return of drinking water led to rapid cessation of SBC in sheep before and after AOV surgery. We conclude that the AOV is not the only conduit for venous drainage contributing to SBC in sheep and that, contrary to widely held opinion, control of SBC does not involve changes in the vasomotor state of the AOV.

scholarly journals Guttural pouches, brain temperature and exercise in horses

2006 ◽  
Vol 2 (3) ◽  
pp. 475-477 ◽  
Author(s):  
Graham Mitchell ◽  
Andrea Fuller ◽  
Shane K Maloney ◽  
Nicola Rump ◽  
Duncan Mitchell
Keyword(s):  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Free Living ◽  
Heat Injury ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Exchange Function ◽  
The Brain ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as the lowering of brain temperature below arterial blood temperature. Artiodactyls employ a carotid rete, an anatomical heat exchanger, to cool arterial blood shortly before it enters the brain. The survival advantage of this anatomy traditionally is believed to be a protection of brain tissue from heat injury, especially during exercise. Perissodactyls such as horses do not possess a carotid rete, and it has been proposed that their guttural pouches serve the heat-exchange function of the carotid rete by cooling the blood that traverses them, thus protecting the brain from heat injury. We have tested this proposal by measuring brain and carotid artery temperature simultaneously in free-living horses. We found that despite evidence of cranial cooling, brain temperature increased by about 2.5 °C during exercise, and consistently exceeded carotid temperature by 0.2–0.5 °C. We conclude that cerebral blood flow removes heat from the brain by convection, but since SBC does not occur in horses, the guttural pouches are not surrogate carotid retes.

Jugular bulb temperature: comparison with brain surface and core temperatures in neurosurgical patients during mild hypothermia

1996 ◽  
Vol 85 (1) ◽  
pp. 98-103 ◽  
Author(s):  
C. Michael Crowder ◽  
René Tempelhoff ◽  
M. Angèle Theard ◽  
Mary Ann Cheng ◽  
Alexandre Todorov ◽  
...  
Keyword(s):  
Pulmonary Artery ◽  
Tympanic Membrane ◽  
Mild Hypothermia ◽  
Brain Temperature ◽  
Jugular Bulb ◽  
Content Type ◽  
Blood Temperature ◽  
Brain Surface ◽  
Bladder Temperature ◽  
Neurosurgical Patients

✓ Blood temperature at the jugular bulb was monitored in 10 patients undergoing neurovascular procedures that used induced mild hypothermia, and its correlation with surface brain, core, and peripheral temperatures was determined. The study was motivated by the difficulty encountered in directly measuring global brain temperature and the poor correlations between various core and peripheral sites temperatures and brain temperature, particularly during deep hypothermia. Although not statistically significant, previous studies have suggested a trend toward higher brain temperatures. Temperatures from the jugular bulb (collected using a No. 5 French Swan—Ganz catheter) as well as from subdural, pulmonary artery, esophagus, tympanic membrane, and bladder sites were analyzed during three surgical conditions: prior to incision, with the dura open, and after closure of the dura. No complications related to placement of the jugular bulb catheter, induced hypothermia, or temperature monitoring were seen. The authors found that jugular bulb temperature was similar to pulmonary artery and esophageal temperatures; although prior to incision it tended to be higher than that found at the pulmonary artery, most commonly by 0.2°C. Surface brain temperature was cooler than all other temperatures (p < 0.05), except that of the tympanic membrane, and was particularly sensitive to environmental variations. Finally, as has been shown by others, bladder temperature lagged substantially behind core temperatures particularly during rapid cooling and rewarming of the patient. In summary, monitoring of jugular bulb temperature is a feasible technique, and temperatures measured in the jugular bulb are similar to core temperatures.

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