SMALL AIRWAY INVOLVEMENT IN MIXED CONNECTIVE-TISSUE DISEASE

We studied pulmonary functions in 17 female patients with mixed connec tive tissue disease (MCTD) to detect early pulmonary involvement in th is disease; in 8 of the 17 patients follow-up studies were also perfor med at 1.2- to 5.9-year intervals. In the first pulmonary function tes ts, decreases in vital capacity (VC) and diffusing capacity (DL(CO)) w ere observed in 6 (35%) and 8 (47%) patients, respectively. The ratio of forced expiratory volume in one second to VC was normal in all the patients, but pulmonary resistance and static compliance were abnormal in 6 (35%) and 10 (59%) patients, respectively. However, frequency de pendence of dynamic compliance was found in all 16 patients tested. Mo reover, 4 (24%) of the 17 patients had normal DL(CO) and DL(CO)-to-alv eolar volume ratio (DL(CO)/VA). Reductions in DL(CO) and DL(CO)/VA wer e significantly correlated with the disease duration. These results su ggest that small airway obstruction is an early and frequent indicatio n of functional pulmonary impairment, and that impairment of alveolar gas exchange is progressive in patients with MCTD.