CARDIOPULMONARY ADAPTATIONS TO PNEUMONECTOMY IN DOGS .4. MEMBRANE DIFFUSING-CAPACITY AND CAPILLARY BLOOD-VOLUME

Lung diffusing capacity for carbon monoxide (DL(co)) and its components, membrane diffusing capacity (Dm(co)) and capillary blood volume (Vc), as well as pulmonary blood flow (Qc), were measured at rest at several lung volumes and during treadmill exercise by a rebreathing technique in four adult dogs after right pneumonectomy (R-PNX) and in six matched control dogs (Sham) 6-12 mo after surgery. In both groups, lung inflation at rest was associated with a small increase in DL(co) and Dm(co) but not in Vc. After R-PNX, total DL(co) was lower by 30% at peak exercise compared with control values. When compared with DL(co) in a normal left lung, DL(co) in the remaining lung continued to increase along the normal relationship with respect to Qc up to a cardiac output equivalent to 34 l/min through both lungs of the Sham dog. There was no evidence of an upper limit of DL(co) being reached. The augmentation of DL(co) from rest to exercise was associated with corresponding increases in Dm(co) and Vc; after R-PNX, both Dm(co) and Vc continued to increase with respect to Qc along similar relationships as in control dogs without reaching an upper limit, suggesting a much larger alveolar-capillary reserve for gas exchange by diffusion than previously recognized At higher levels of blood flow through the remaining lung, DL(co) was greater in adult dogs after R-PNX than after left pneumonectomy (Carlin et al. J. Appl. Physiol. 70: 135-142, 1991), suggesting that additional sources of compensation, e.g., lung growth, exist after removal of >50% of lung.