Effects of tracheostomy breathing on brain and body temperatures in hyperthermic sheep.

Abstract

SUMMARY1. We measured rectal and hypothalamic temperature in sheep breathing nasally and via a tracheostomy, during hyperthermia resulting from exposure to a hot environment, exercise and fever.2. In normothermic and hyperthermic sheep hypothalamic temperaturc was up to 1-0°C lower than rectal temperature when the sheep breathed nasally. Tracheostomy breathing abolished the rectal-hypothalamic temperature difference.3. In sheep breathing via the tracheostomy and exposed to a dry-bulb temperature of 45-50°C for 2 h, hypothalamic temperature exceeded rectal temperature by about 0 4°C, and was significantly higher than that in sheep breathing nasally in the same environment.4. During exercise on a treadmill and in the post-exercise period, the difference between hypothalamic and rectal temperature was abolished in the sheep while breathing through the tracheostomy, and rectal temperature rose to higher levels compared to those evident in the same activity while breathing nasally.5. After an i.v. injection of 0-4,ug/kg lipopolysaccharide (LPS), the difference between hypothalamic and rectal temperature again was abolished in the sheep when breathing through the tracheostomy, but rectal temperature rose significantly less compared to when breathing nasally.6. Our results indicate that selective brain cooling depends on upper respiratory tract cooling in normo-and hyperthermic states in sheep.

Selective brain cooling in goats: effects of exercise and dehydration.

“…Although this conclusion has been inferred from a number of earlier studies in both resting and exercising panting animals (Baker & Hayward, 1968;Baker, Chapman & Nathanson, 1974;Jessen & Pongratz, 1979;Laburn, Mitchell, Mitchell & Saffy, 1988), this is the first analysis of the relationship over a wide range of body core temperatures and evaporative rates. Kuhnen & Jessen (1991) found a positive relationship between SBC and REHL in resting goats when heat exchangers were used to produce parallel increases in temperature of the blood perfusing the head 689 and the body core, i.e.…”

Regulation of ram scrotal temperature during heat exposure, cold exposure, fever and exercise.

“…The primary input to the control system is brain temperature , leading to a local negative feedback regulatory system. During exercise and fever, the system allows sheep (Laburn, Mitchell, Mitchell & Saffy, 1988) and goats (Baker & Nijland, 1993; to regulate brain temperature independently of Tbody Brain temperature, however, is not the only input; the system is modulated by body core temperature and by non-thermal inputs (Jessen, Laburn, Knight, Kuhnen, Goelst & Mitchell, 1994). We have therefore investigated whether there is local scrotal temperature regulation in rams, and established that there is.…”

Effect of route of breathing on the ventilatory and arousal responses to hypercapnia in awake and sleeping dogs.

“…When the upper airway is bypassed, as in tracheostomy, the effectiveness of these cooling mechanisms may consequently be impaired, resulting in a reduced body-brain temperature gradient (Krabil & Goshal, 1983). Conditions resulting in a rise in body temperature may increase hypothalamic temperature during tracheostomy breathing (Laburn, Mitchell, Mitchell & Safey, 1988). Consequently, a rise in hypothalamic-cortical temperature during upper respiratory bypass may thus increase ventilation (Hales & Bligh, 1969;Maskrey, 1990).…”