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 (Q̇c) 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 Q̇c in the remaining lung. We measured the relationship between DL and Q̇c 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 Q̇c and contains 58% of the DL, DL of the right lung increased with Q̇c in accordance with the following relationships before and after left pneumonectomy: right lung DL (before pneumonectomy) = 6.44 + 2.40 (Q̇c) (r = 0.963) and right lung DL (after pneumonectomy) = 7.51 + 1.75(Q̇c) (r = 0.958). Only ~7% of the increase in DL from rest to peak exercise could be attributed to the increase in VS during exercise before pneumonectomy and ~ 15% after pneumonectomy. After pneumonectomy, DL at any given Q̇c 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.
ASJC Scopus subject areas
- Physiology (medical)