CHANGES IN REGIONAL PULMONARY BLOOD NOW DURING LOBAR BRONCHIAL OCCLUSION IN MAN

1. Acute hypoxic pulmonary vasoconstriction is important in the restor ation of ventilation-perfusion balance in the presence of regional alv eolar hypoventilation. However, the magnitude and time course of this response in man has not been adequately characterized in regions small er than an entire lung. We have studied the effectiveness of hypoxic v asoconstriction in diverting blood from hypoxic lobes in normal supine subjects, and have documented the redistribution of pulmonary blood f low under these conditions. 2. Lobar hypoxia was induced for 80-300 s by placing occluding balloon-tipped catheters in lobar bronchi during fibreoptic bronchoscopy in 10 normal subjects. Respiratory gas partial pressures within occluded lobes were measured with a mass spectromete r. The percentage reduction in blood flow to the hypoxic lobes was ass essed after injection of Tc-99m-labelled albumin by gamma-scintigraphy , and compared with a control scan performed 1 week later. A computer program was used to analyse changes in regional pulmonary perfusion. 3 . During lobar bronchial occlusion respiratory gas partial pressures r apidly approached reported values for mixed venous partial pressures. After a mean time of occlusion of 3.5 min lobar blood flow was reduced by 47 +/- 5%. During occlusions pulmonary blood flow was not evenly r edistributed, but was preferentially redistributed to more cranial lun g regions. 4. We conclude that acute hypoxic pulmonary vasoconstrictio n in occluded lobes is more effective at rapidly diverting pulmonary b lood flow away from hypoxic lung regions than has previously been repo rted in man during unilateral hypoxia of an entire lung. Non-uniform r edistribution of pulmonary blood flow in the supine subject is likely to be due to compression of the lung bases by the diaphragm in the sup ine position.