Direct cooling of the human brain by heat loss from the upper respiratory tract

Abstract

This study is the first report on human intracranial temperature in conscious patients during and after an upper respiratory bypass. Temperatures were measured in four subjects subdurally between the frontal lobes and cribriform plate (T(cr)) and on the vault of the skull (T(sd)). Further measurements were taken in the esophagus (T(es)) and on the tympanic membrane. Reinstitution of airflow in the upper respiratory tract under conditions of mild hyperthermia gave a rapid drop in T(cr) of 0.4-0.8 degrees C. In three patients the intracranial temperature at the basal aspect of the frontal lobes fell below T(es). Thus local selective cooling of the brain surface below that of the trunk temperature was shown to occur. Intensive breathing by the patients after extubation for a 3-min period produced a cooling at the site of T(cr) measurement at a rate of up to 0.1 degrees C/min, and this response could be evoked on demand. The results support the view that cooling of the upper airway can directly influence human brain temperature.

Selective Brain Cooling in Mammals and Birds.

“…The thickness of the bony cribriforme plate between the nose and the floor of the anterior cranial fossa is only a fraction of a millimeter so that the basal layers of the adjacent frontal lobes of the brain could be cooled by conduction. This was confirmed by a recent study in patients recovering from neurosurgery [37]. Upon transition from breathing through an endotracheal tube to nasal breathing, the temperature in the subdural space between the cribriforme plate and the frontal lobe fell by 0.4°C, and the temperature at the convexity of the brain changed in parallel with esophageal temperature.…”

Middle cerebral artery blood velocity is reduced with hyperthermia during prolonged exercise in humans

“…It may be that hyperventilation is a type of thermoregulatory panting (White & Cabanac, 1996) and it seems that a substantial fraction of the total cephalic heat loss can be liberated via this mechanism across a range of environmental conditions (Hanson, 1974;Rasch et al 1991). Furthermore, heat loss from the upper respiratory tract may have a significant cooling effect on the brain (Mariak et al 1999). Another explanation for the hyperventilation could be an increased feed-forward activation of the respiratory system as the effort to maintain the required a-motor output increases (Asmussen et al 1965).…”

Reproducibility of relationships between human ventilation, its components and oesophageal temperature during incremental exercise

“…In each plot, dotted lines are the line of identity and the solid line is the best-fit line. Intraclass correlation coefficients are given in each plot in parentheses small increases in ventilation in the upper airways gives marked decreases in intracranial temperature measured on the cribriform plate of the ethmoid bone (Mariak et al 1999). The nature of cranial heat balance, however, still appears to not be completely resolved since Nybo et al (2002) report greater jugular venous than aortic temperatures in humans at rest or during exercise.…”

“…This measurement site of core temperature has brought these results into question (Cotes 1955;Cunningham and O'Riordan 1957;Martin et al 1979;Saxton 1981;Strange-Petersen and Vejby-Christensen 1973;Whipp and Wassermann 1970). This is since rectal temperature has a low reproducibility and responds slowly to central body temperature transients, including temperatures measured in the human central blood (Hayward et al 1984;Mariak et al 1999) or in the human cranium (Mariak et al 1999). Oesophageal temperature employed presently has been shown to be a good index of central blood temperature (Hayward et al 1984) and a reasonable index of cranial temperatures (Mariak et al 1994).…”