Lung function in patients with collagen vascular diseases: a study of non-smokers with normal chest roentgenograms.

Lung function was assessed in 52 patients with collagen vascular diseases (CVD) who had neither a smoking history nor an abnormality in their chest x-ray films. Values of the maximum mid-expiratory flow and the maximum expiratory flow after 50% or 75% of the forced vital capacity had been exhaled were decreased and the ratio of closing capacity to total lung capacity was increased in 36-100% (varied among categories of CVD) of patients with CVD, and the carbon monoxide diffusing capacity was decreased in 27-56% of the patients. These findings indicate that small airway diseases and a decrease in diffusing capacity are not rare in CVD patients, even if they had neither a smoking history nor abnormal findings in their chest x-ray films. Regular and routine tests on lung functions are thought to be effective to detect early pulmonary involvement in patients with CVD.