RECRUITMENT OF LUNG DIFFUSING-CAPACITY WITH EXERCISE BEFORE AND AFTER PNEUMONECTOMY IN DOGS

Although the left lung constitutes 42% of the total by weight and volume in dogs, carbon monoxide diffusing capacity (DL) after left pneumonectomy in adults falls < 30% at rest, indicating a significant increase of DL in the remaining lung. DL normally increases during exercise, presumably by recruitment of alveolar capillaries and surface area as lung volume (Vs) and pulmonary blood flow (Qc) increase. We asked whether the increase of DL in the remaining lung after pneumonectomy in adult dogs could be explained by this kind of passive recruitment by the increased volume and Qc in the remaining lung. We measured the relationship between DL and Qc with a rebreathing technique at increasing treadmill loads in adult foxhounds, before and 6 mo after left pneumonectomy, and the relationship between DL and Vs by the same technique under anesthesia as Vs was expanded. DL was reduced by 29.1% at rest and 26.5% with heavy exercise after left pneumonectomy, indicating either recruitment or new growth in the right lung. With the assumption that the right lung normally receives 58% of the Qc and contains 58% of the DL, DL of the right lung increased with Qc in accordance with the following relationships before and after left pneumonectomy: right lung DL(before pneumonectomy) = 6.44 + 2.40(Qc) (r = 0.963) and right lung DL(after pneumonectomy) = 7.51 + 1.75(Qc) (r = 0.958). Only approximately 7% of the increase in DL from rest to peak exercise could be attributed to the increase in Vs during exercise being pneumonectomy and approximately 15% after pneumonectomy. After pneumonectomy, DL at any given Qc at rest and during exercise was the same or lower in the right lung compared with that before; hence all the compensatory increase of DL in the right lung could be explained by recruitment of existing reserves. New growth need not be postulated. An upper limit of DL was never reached at increasing work loads either before or after pneumonectomy.