Differences in respiratory patterns after acute and chronic pulmonary denervation

Abstract

The role of pulmonary vagal information in the control of respiratory patterns was assessed in awake and anaesthetised rats in which pulmonary denervation was effected by bilateral cervical vagotomy or by right cervical vagotomy combined with left pneumonectomy or left intrathoracic vagotomy. Acute denervation led to increases of tidal volume (V t), inspiratory duration (T i) and expiratory duration (T e) in both awake and halothane anaesthetised animals; in awake rats the increase of T e rapidly subsided. Chronic pulmonary denervation produced markedly smaller increases of V t and T i and no change of T e from control values. In hypercapnia, awake animals with combined pneumonectomy and vagotomy consistently increased respiratory frequency by reductions in T i and T e; awake animals with combined intrathoracic and cervical vagotomy showed no increase in f because decreases in T e; in anaesthetised rats with acute bilateral cervical vagotomy there was a consistent fall in respiratory frequency due to an expiratory pause. The results demonstrate that (1) the role of vagal activity in the production of respiratory patterns is unlikely to be accounted for solely in terms of influences arising from pulmonary stretch receptors; (2) vagal influences of T e are transitory; (3) under halothane anaesthesia hypercapnia induces an expiratory pause; and (4) the combination of pneumonectomy with contralateral vagotomy makes possible studies in awake rats although pulmonary denervation is less complete than with bilateral intrathoracic vagotomy.