The effect of lung deflation on breathing in man.

1. The effect of lung deflation was studied during treatment of patients for spontaneous pneumothorax: (a) in four patients acute lung deflation was produced by opening the chest drain to the atmosphere and the immediate effect on breathing was observed and (b) breath-holding time and the ventilatory response to CO 2 were determined on admission to hospital and after recovery in a further four patients. 2. Allowing one lung to deflate suddenly produced an immediate increase in respiratory rate and electrical activity in inspiratory muscles. 3. Maximum breath-holding times were always decreased by pneumothorax. 4. In the presence of pneumothorax, the ventilatory response to rebreathing CO 2 was increased at the break point, the respiratory rate was increased and the P co 2 at the breakpoint decreased in three out of four patients. 5. These results are consistent with the hypothesis that lung deflation has a reflex excitatory effect on breathing (Hering—Breuer deflation reflex). If this hypothesis is correct, it would appear that the threshold for the reflex is higher than for other mammalian species.