REFERENCE VALUES OF PULMONARY DIFFUSING-CAPACITY DURING EXERCISE BY AREBREATHING TECHNIQUE

Normal reference values of the pulmonary diffusing capacity for carbon monoxide (DL(CO)), diffusing capacity of the membrane (DM(CO)), and p ulmonary capillary blood volume (Vc) were derived by a rebreathing tec hnique in 44 normal, healthy, nonsmoking individuals ranging from 17 t o 68 yr of age. Simultaneous measurements of DL(CO), lung volumes, pul monary blood flow, and septal tissue volume were determined at rest an d during steady-state exercise of 25, 50, and 80% of maximal workload and at two levels of alveolar Oz tension. DM(CO) and Ve were calculate d using the Roughton-Forster relationship. Using stepwise regression a nalysis, DL(CO) and DM(CO) (in mi CO/min/mm Hg) were found to be signi ficantly related to pulmonary blood flow (Qc in L/min), age (in yean), and body surface area (BSA in square meters). Ve (in mi) was found to be significantly related to he and BSA. Normalization of measured dat a with respect to these variables largely eliminated male venus female differences. We conclude that Qc is the most important determinant of the recruitment of diffusing capacity. From rest to near-maximal exer cise, DL(CO), DM(CO), and Ve increase linearly with respect to he with out evidence of reaching a plateau.