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)

The effect of face fanning during recovery from exercise hyperthermia

1987 ◽  
Vol 65 (1) ◽  
pp. 87-91 ◽  
Author(s):  
Marc Germain ◽  
Michel Jobin ◽  
Michel Cabanac
Keyword(s):  
Significant Influence ◽  
Recovery Period ◽  
The Other ◽  
Tympanic Temperature ◽  
Esophageal Temperature ◽  
A Value ◽  
The Face ◽  
The Difference

Hyperthermia was induced in nine subjects on two separate occasions by a progressive treadmill run, which resulted in an average esophageal temperature (Tes) of 39.77 ± 0.07 °C after 30–57 min. Fanning the face during exercise to simulate conditions during running (wind at 3.75 m∙s−1) maintained a tympanic temperature (Tty) that was lower than Tes; the difference was 1.5 °C at the end of exercise. In one session, face fanning was interrupted at the end of running, whereas in the other it was maintained for 15 min after exercise stopped. Face fanning had no significant influence on the fall of Tes during recovery, but it markedly influenced the course of Tty during this period. When face fanning was stopped at the end of the run, Tty rose by nearly 0.5 °C, peaked after 4.5 min. and thereafter decreased slowly to a value close to Tes. In contrast, when face fanning was maintained throughout the recovery period, Tty rose only slightly (0.1 °C) and remained significantly lower than Tes at all times. The results suggest that following hyperthermic exercise, face fanning could be helpful in preventing acute cerebral hyperthermia.

No evidence for brain stem cooling during face fanning in humans

1992 ◽  
Vol 72 (2) ◽  
pp. 664-669 ◽  
Author(s):  
C. Jessen ◽  
G. Kuhnen
Keyword(s):  
Relative Humidity ◽  
Brain Stem ◽  
Heat Loss ◽  
Esophageal Temperature ◽  
Air Stream ◽  
Stable Conditions ◽  
The Face ◽  
Stem Temperature ◽  
Condition C ◽  
Condition B

The interpeak latencies (IPLs) of the acoustically evoked brain stem potentials depend on brain stem temperature. This was used to see whether face fanning during hyperthermia lowers brain stem temperature. In 15 subjects, three thermally stable conditions were maintained by a water bath. In each condition the IPLs were determined in 10 separate trials. In condition A esophageal temperature (Tes) was 36.9 +/- 0.3 degrees C and increased to 38.6 +/- 0.2 degrees C in condition B. In conditions A and B the head was enclosed in a ventilated hood (air temperature 38 degrees C, relative humidity 100%) to suppress any direct heat loss from the head. From conditions A to B the IPL at peaks I-V decreased by 0.146 ms/degrees C change in Tes, reflecting a change in brain stem temperature. In condition C the hood was removed and the face was fanned by a cold air-stream (8–15 degrees C, 4–10 m/s) to maximize direct heat loss from the head. Skin temperature at the sweating forehead decreased from 38 to 23 degrees C, whereas Tes in condition C was maintained at the same level as in condition B (38.5 +/- 0.2 degrees C). The IPL at peaks I-V showed no difference between conditions B and C. It is concluded that face fanning in hyperthermic subjects does not dissociate brain stem temperature from Tes.

Bradycardia during face cooling in man may be produced by selective brain cooling

1979 ◽  
Vol 46 (5) ◽  
pp. 905-907 ◽  
Author(s):  
M. Caputa ◽  
M. Cabanac
Keyword(s):  
Venous Return ◽  
Human Subjects ◽  
Cardiac Response ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
The Face ◽  
The Difference ◽  
The Brain ◽  
Face Cooling

In human subjects, bradycardia was produced by immersing the subjects' faces in water at 15 degrees C when they were hyperthermic. When they were hypothermic, the same face cooling produced tachycardia. It is suggested that the difference in cardiac response originates in selective brain cooling during hyperthermia, by venous return from the face to the brain, via ophthalmic veins.

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.

Exercise hyperpnea and hyperthermia in humans

1996 ◽  
Vol 81 (3) ◽  
pp. 1249-1254 ◽  
Author(s):  
M. D. White ◽  
M. Cabanac
Keyword(s):  
Work Capacity ◽  
Cycle Ergometer ◽  
Work Rate ◽  
Brain Cooling ◽  
Supportive Evidence ◽  
Climatic Chamber ◽  
Selective Brain Cooling ◽  
Temperature Thresholds ◽  
Exercise Hyperpnea ◽  
Male Subjects

The problem of the relative hyperpnea occurring at high levels of exercise remains unresolved. This study examined whether the hyperpnea observed in humans during exercise at approximately 70% of maximal work capacity was related to cranial (tympanic) and thoracic (esophageal) temperatures. Six trained male subjects pedaled at approximately 60 revolutions/min on an electrically braked cycle ergometer in a climatic chamber at 25 degrees C and approximately 35% relative humidity in two sessions. The subjects pedaled until exhaustion in two sessions. In one session work rate was increased by 40 W every 2 min and in the other session by 20 W every 2 min. In both exercise sessions, core temperature thresholds for ventilation were evident and subsequently tympanic and esophageal temperatures diverged. This suggested that the hyperpnea in humans observed after approximately 70% of an individual's maximal work rate was determined, in part, by core temperatures and revealed supportive evidence for selective brain cooling in humans.

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.

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