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

Lung diffusing capacity for carbon monoxide (DL(co)) and its component s, membrane diffusing capacity (Dm(co)) and capillary blood volume (Vc ), as well as pulmonary blood flow (Qc), were measured at rest at seve ral lung volumes and during treadmill exercise by a rebreathing techni que in four adult dogs after right pneumonectomy (R-PNX) and in six ma tched 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 D m(co) but not in Vc. After R-PNX, total DL(co) was lower by 30% at pea k 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 outp ut equivalent to 34 l/min through both lungs of the Sham dog. There wa s no evidence of an upper limit of DL(co) being reached. The augmentat ion 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 contr ol dogs without reaching an upper limit, suggesting a much larger alve olar-capillary reserve for gas exchange by diffusion than previously r ecognized At higher levels of blood flow through the remaining lung, D L(co) was greater in adult dogs after R-PNX than after left pneumonect omy (Carlin et al. J. Appl. Physiol. 70: 135-142, 1991), suggesting th at additional sources of compensation, e.g., lung growth, exist after removal of >50% of lung.