Control of brain temperature in dogs: effects of tracheostomy

Abstract

Using chronically implanted thermocouples, the authors measured the temperature of the hypothalamus, the cerebral arterial blood, and the carotid arterial blood in two dogs before and after tracheostomies were performed. In warm environments (30–45 °C), the dogs maintained normal brain and deep body temperatures as long as they breathed through the upper respiratory passages. When they respired directly through the tracheostomy, an immediate rise in the temperature of the cerebral arterial blood and the hypothalamus occurred. The rise in brain temperature during tracheostomy breathing increased with increasing ambient temperatures. Brain temperature always rose more than carotid arterial temperature during tracheostomy breathing in warm environments, suggesting that carotid arterial blood is cooled on its way to the brain in dogs which are breathing through intact respiratory passages. Since hypothalamic temperature is an important factor in control of respiration in panting animals, the use of tracheostomized animals in studies of respiratory function may introduce a significant variable into the experiments.