Regional lung function in spontaneous pneumothorax.

Using xenon-133, we measured regional lung volumes in three seated young men with 25 to 40 per cent pneumothorax. There was no gravitational gradient of regional lung expansion in the lung affected by the pneumothorax. There was no gravitational gradient of regional lung expansion in the lung affected by the pneumothorax, whereas an apex-to-base gradient of regional volume was apparent on the contralateral, normal side. When over-all lung volume increased from residual volume to 20 per cent of vital capacity, there was little volume change in the lungs with pneumothoraces. These lungs received relatively small fractions of boluses inhaled at residual volume and bolus distributuion was even from apex to base on the sides with the pneumothoraces. Regional washout half-times were not prolonged in lungs with pneumothoraces and did not differ from apex to base, whereas in unaffected lungs, half-times at the apex exceeded those at the base. The results indicated that regional volume and half-time gradients were absent when gravitational gradients of pleural surface pressure were abolished by pneumothorax. Lungs with pneumothorax demonstrated uniform airway closure at low lung volumes, and it is suggested that this is the chief cause of ventilation maldistribution in spontaneous pneumothorax.