Regulation of respiration by bronchopulmonary receptors in conscious dogs.

In awake dogs, the Hering-Breuer inflation reflex (HBIR) was present but weaker than during anaesthesia. Auditory or visual distraction, increased body temperature, and exercise decreased or abolished HBIR. Bilateral complete vagal blockade resulted in slow deep breathing, but arterial PCO2, and apnoeic threshold PCO2, were unafected. Vagal blockade decreased the response of frequency of respiration during hypoxemia and hypercapnia, but did not affect the response to increasing body temperature or to exercise. Progressive cooling of the exteriorized vagal loops from 16 to 9 degrees Celsius resulted in progressive abolition of HBIR, but the respiratory response to inhaled histamine was unaffected. There was a decrease in the expiratory phase of respiration and in tidal volume; the dogs hyperventilated at rest and had an increased respiratory response to inhaled CO2. Further cooling of the vagal loops sufficient to abolish the respiratory response to inhaled histamine resulted in the slow, deep breathing pattern and impaired respiratory frequency response to inhaled CO2 typical of the completely vagotomized animal.