Regional pulmonary function during experimental unilateral pneumothorax in the awake state.

This study examines changes in regional pulmonary function during unilateral pneumothorax, immediately after, and 2 hours following re-expansion in awake dogs. Respiratory rate, tidal volume, physiologic dead space, arterial blood gases, and pulmonary shunt fraction were determined at each stage. Cardiac output (thermodilution), vascular pressures, and regional ventilation and perfusion (133Xe scans) were also measured. Chest roentgenogram confirmed the presence of UP. Respiratory rate increased 124 percent (p less than 0.01) during UP while alveolar ventilation remained unchanged. Pulmonary shunt fraction rose 93 percent (p less than 0.01) during UP, causing PaO2 to fall from 86 to 51 mm. Hg (p less than 0.01). PaCO2, pH, and cardiac output were not altered by UP. UP caused a relative underventilation of the collapsed lung (V/Q = 0.73 (p less than 0.01)) and an overventilation of the contralateral lung (V/Q = 1.74) (p less than 0.01). Immediately after re-expansion of the collapsed lung, all the above changes reverted to the control values. All variables remained unchanged 2 hours following complete re-expansion.