[Change of pulmonary diffusing capacity, membrane diffusing capacity and pulmonary capillary blood volume in patients...

Studying the changes of pulmonary diffusing capacity (DL), alveolar capillary membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc) in patients with COPD and connective tissue disease (CTD) at rest and post-exercise; evaluating the diagnostic values of DL, Dm and Vc in early stage of pulmonary involvement of CTD.

Spirometry was performed in the sit position. Several measurements of diffusing capacity of the lung for carbon monoxide (DLCO) were measured by single-breath method at increasing alveolar oxygen tension. The estimations of Dm and Vc were done by the method of Roughton and Forster.

(1) In COPD group, the values of DL were lower than that of the control group at rest. The decreases were due to the reduction of Dm, but Vc were normal. In CTD group, all the value of DL, Dm and Vc were lower than that of its control group at rest. (2) COPD patients had the higher DL, Dm and Vc after the end of exercise than that of at rest. But the changes of DL Dm and Vc in COPD patients were lower compared with the control group. In contrast to the control group, DL, Dm and Vc did not increase or even decreased after the end of exercise in CTD group. (3) There was no significant differences of DL, Dm and Vc between the 7 CTD patients with normal pulmonary volume and DLCO and the control subjects at rest. But after the end of exercise, DL, Dm and Vc of CTD patients kept unchanging or even decreasing. The difference between CTD patients and its control group was found significant.

The measurements of post-exercise Dm and Vc are sensitive tests for pulmonary involvement in of CTD patients. The results are abmormal much earlier in subject with minimal dyspnea and roentgenologic change. They are useful tests for early stage CTD.