Vagal control of the breathing pattern and respiratory mechanics in the adult and newborn rabbit.

In an attempt to define the role of SARs on the breathing pattern and respiratory mechanics, we have studied adult rabbits anaesthetised, supine and tracheostomised during air breathing (A), after SO2 breathing (200 ppm for a period long enough to abolish the apnea following lung inflation, 10-30 min) (S), and after bilateral vagotomy (V). Tidal volume and inspiratory time increased, while breathing frequency decreased from A to V. The effects of S depended upon the type of anaesthesia used, with a definite increase in volume and a drop in frequency in the urethane anaesthetized animals and a trend toward opposite changes with barbiturate anaesthesia. Total and lung compliance increased and total pulmonary resistance decreased from A to S; no further changes were observed with V. The combined changes in breathing pattern and mechanics decreased the respiratory work per minute from A to V, suggesting that the primary concern of the vagal afferent information is to regulate the breathing pattern. Finally, in newborn rabbits it was not possible to block the apnea following lung inflation even with SO2 concentration up to 330 ppm for 30 min. From A to V the changes in breathing pattern and compliance were similar to those observed in the adult.