THE BREUER-HERING REFLEX IN HUMANS - EFFECTS OF PULMONARY DENERVATIONAND HYPOCAPNIA

Passive lung inflation in humans causes reflex expiratory prolongation that is abolished by vagal blockade. We have studied two aspects of t his classic Breuer-Hering reflex in humans: the effect of pulmonary de nervation from bilateral lung transplantation, and the effect of alveo lar hypocapnia. Lung inflations were performed in six normal subjects and four lung transplant patients during triazolam-induced sleep using a negative pressure body box. Lung inflation with isocapnic gas in no rmal subjects resulted in expiratory prolongation lasting up to 60 s a nd occurring at a volume threshold of 40 to 60% of inspiratory capacit y (1.1 to 1.7 L). Expiratory prolongation increased in a graded fashio n as volume of lung inflation increased. Inhibition of inspiration at any given inflation volume was prolonged by inflations with air as com pared with inflations with isocapnic gas. In lung transplant patients lung inflations of up to 2 L caused no prolongation of expiration. We conclude that bilateral lung transplantation abolished expression of t he reflex in humans, and that in normal intact humans the duration of expiratory prolongation with lung inflation is prolonged by alveolar h ypocapnia.