Components and mechanisms of thermal hyperpnea

2006 ◽  
Vol 101 (2) ◽  
pp. 655-663 ◽  
Author(s):  
Matthew D. White
Keyword(s):  
Tidal Volume ◽  
Heat Loss ◽  
Respiratory Alkalosis ◽  
Direct Application ◽  
Blood Gas ◽  
Brain Cooling ◽  
Body Temperatures ◽  
Selective Brain Cooling ◽  
Ongoing Research ◽  
Thermal Hyperpnea

The pattern of breathing during a hyperthermia-induced hyperventilation varies across different species. Thermal tachypnea is a first phase panting response adopted during hyperthermia when tidal volume is minimized and the frequency of breathing is maximized. Blood-gas tensions and pH are maintained during this hyperventilation, and the associated heat loss helps the animal regulate its body temperature. A second pattern of breathing adopted in hyperthermia is thermal hyperpnea; this response is the focus of this review. This form of hyperventilation is evident after an increase in core temperature and it is apparent in humans. Increases of tidal volume as well as frequency of breathing are evident during this response that results in a respiratory alkalosis. The cause of thermal hyperpnea is not resolved; evidence of the potential mechanisms underlying this response support that modulators of the response act in either a multiplicative or additive manner with body temperatures. The details of the designs and methodologies of the studies supporting or refuting these two views are discussed. A physiological rationale for thermal hyperpnea is presented in which it is suggested this response serves a heat-loss role and contributes to selective brain cooling in hyperthermic humans. Ongoing research in this area is focused on resolving the mechanisms underlying thermal hyperpnea and its contribution to cranial thermoregulation. The direct application of this research is for the care of febrile and hyperthermic patients.

Selective brain cooling is affected by wearing headgear during exercise

1993 ◽  
Vol 74 (3) ◽  
pp. 1229-1233 ◽  
Author(s):  
W. Rasch ◽  
M. Cabanac
Keyword(s):  
Heat Loss ◽  
Cycle Ergometer ◽  
Tympanic Temperature ◽  
Esophageal Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Exercise Load ◽  
Convective Heat Loss ◽  
The Face ◽  
Skin Temperatures

The purpose of this work is to relate the concept of selective brain cooling (SBC) during exercise to heat loss from the head while either bare or covered. During hyperthermia, SBC is considered to occur if tympanic temperature (Tty) is lower than esophageal temperature (Tes). In experiment I the head heat loss was measured with and without headgear. Each of four subjects took part in three sessions of exercise on a cycle ergometer. The face was cooled to simulate outdoor conditions. The first session (no headgear) served as control for the two following sessions in which a headband and a woolen cap were worn. Evaporative and radiative-convective heat loss were monitored from the head. Wearing a cap significantly reduced the heat loss from the head compared with the control condition. During the headband session the heat loss was not significantly lower than the control values. Tty, Tes, and head skin temperatures (T(sk)) were also recorded. Tty was significantly lower (-0.55 +/- 0.15 degrees C) than Tes at the end of exercise (150-W exercise load) when no headgear was worn. During headgear sessions, Tty was no longer significantly lower than Tes, either during the headband (-0.15 +/- 0.31 degrees C) or during the cap session (-0.30 +/- 0.13 degrees C). In experiment II the influence of wearing headgear on temperature regulation was studied. Hand skin blood flow, hand T(sk), and heat loss from the hand were recorded in addition to the variables monitored in experiment I. Wearing headgear elevated Tty and peripheral vasomotor responses, whereas Tes evolved in the opposite direction.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Absence of selective brain cooling in unrestrained baboons exposed to heat

2007 ◽  
Vol 292 (5) ◽  
pp. R2059-R2067 ◽  
Author(s):  
Shane K. Maloney ◽  
Duncan Mitchell ◽  
Graham Mitchell ◽  
Andrea Fuller
Keyword(s):  
Abdominal Cavity ◽  
Heat Exposure ◽  
Convincing Evidence ◽  
Primate Species ◽  
Brain Cooling ◽  
Body Temperatures ◽  
Selective Brain Cooling ◽  
Hypothalamic Temperature ◽  
Arterial Blood ◽  
Carotid Arterial

To test whether baboons are capable of implementing selective brain cooling, we measured, every 5 min, the temperature in their hypothalamus, carotid arterial bloodstream, and abdominal cavity. The baboons were unrestrained and exposed to 22°C for 7 days and then to a cyclic environment with 15°C at night and 35°C during the day for a further 7 days. During the latter 7 days some of the baboons also were exposed to radiant heat during the day. For three days, during heat exposure, water was withheld. At no time was the hypothalamus cooler than carotid arterial blood, despite brain temperatures above 40°C. With little variation, the hypothalamus was consistently 0.5°C warmer than arterial blood. At high body temperatures, the hypothalamus was sometimes cooler than the abdomen. Abdominal temperature was more variable than arterial blood and tended to exceed arterial blood temperature at higher body temperatures. Hypothalamic temperature cooler than a warm abdomen is not evidence for selective brain cooling. In species that can implement selective brain cooling, the brain is most likely to be cooler than carotid arterial blood when an animal is hyperthermic, during heat exposure, and also dehydrated and undisturbed by human presence. When we exposed baboons to high ambient temperatures while they were water deprived and undisturbed, they never implemented selective brain cooling. We conclude that baboons cannot implement selective brain cooling and can find no convincing evidence that any primate species can do so.

Blood gas changes during panting in a small East African antelope, the dik-dik

1978 ◽  
Vol 44 (4) ◽  
pp. 534-537 ◽  
Author(s):  
M. Maskrey ◽  
P. P. Hoppe ◽  
O. S. Bamford
Keyword(s):  
Heat Stress ◽  
Heat Exposure ◽  
Blood Gases ◽  
Respiratory Alkalosis ◽  
Second Phase ◽  
Blood Gas ◽  
Climatic Chamber ◽  
East African ◽  
Blood Samples ◽  
Arterial Blood

Five adult male dik-dik (Madoqua kirkii) were exposed in a climatic chamber to an air temperature of 45 degrees C. Measurements were made of rectal temperature (Tre) and respiratory frequency (f) and arterial blood samples taken before and during heat exposure were analyzed for pH, PCO2 and PO2. During exposure, Tre and f increased in all animals. In the first 80 min dik-dik displayed thermal tachypnea and minor changes in blood gases. Continued exposure lead to hyperpnea accompanied by a fall in PaCO2 and a rise in pH. PaCO2 at first fell and then increased toward or above control levels. The dik-dik did not display second phase breathing. This observation confirms that second phase breathing is not essential to the development of respiratory alkalosis. The main conclusion of the study is that the dik-dik, unlike another heat-adapted antelope, the wildebeest (Taylor, Robertshaw, and Hoffmann. Am. J. Physiol. 217:907–910, 1969), is unable to resist alkalosis during heat stress.

Selective Brain Cooling in the Horse during Exercise

1994 ◽  
pp. 189-193 ◽  
Author(s):  
F. F. McConaghy ◽  
J. R. S. Hales ◽  
D. R. Hodgson
Keyword(s):  
Brain Cooling ◽  
Selective Brain Cooling

Efficacy of Selective Brain Cooling Using a Nasopharyngeal Method in Piglets

2015 ◽  
Vol 24 (1) ◽  
pp. 140-149 ◽  
Author(s):  
Mohammad Fazel Bakhsheshi ◽  
Errol E. Stewart ◽  
Joo Ho Tai ◽  
Laura Morrison ◽  
Lynn Keenliside ◽  
...  
Keyword(s):  
Brain Cooling ◽  
Selective Brain Cooling
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