Respiratory responses of the anesthetized rabbit to vagotomy and thoracic dorsal rhizotomy

Abstract

Spirograms have been recorded in anesthetized rabbits breathing room air or a hypercapnic mixture, intact and after vagotomy and/or thoracic dorsal rhizotomy. The results suggest that respiratory activity is strongly controlled by the vagi, which promote inhibition of inspiratory discharge (tidal volume and inspiratory duration) and facilitation of expiratory activity (expiratory duration). On the other hand, the chest wall afferents demonstrate a facilitatory influence on the tidal volume and an inhibitory influence on the breathing rate. When both reflex pathways are interrupted, the result of the two opposing effects is such that the tidal volume and the breathing rate are similar to control during air breathing. During hypercapnia, inspiratory duration decreases whereas expiratory duration increases. These reciprocal changes, which presumably are characteristic of the respiratory center with no feedback from the lungs or chest wall, are such that the breathing rate does not change significantly.