Diffusing capacity of the lung and nifedipine in systemic sclerosis. Lung involvement in systemic sclerosis may be due in part to a functional abnormality of the pulmonary vasculature. To investigate the possible role of a pulmonary vasospastic process in this disorder, 21 non-smoking patients who had no evidence of cardiac disease or pulmonary hypertension were evaluated with pulmonary function tests prior to administration of nifedipine, 30 minutes after a single oral dose of nifedipine (20 mg), and after 4 weeks of treatment with nifedipine (10 mg 3 times daily). Treatment with nifedipine did not significantly change any of the pulmonary function values, except for the carbon monoxide diffusing capacity (DLCO). The linear trend between the individual DLCO values at baseline and their changes immediately following the initial 20-mg dose of nifedipine (r = -0.603, P = 0.02) and after 4 weeks of treatment (r = -0.636, P = 0.01) showed that the lower the DLCO value at baseline, the greater the improvement caused by nifedipine. These findings support the hypothesis of a potentially reversible pulmonary vasospasm in systemic sclerosis and suggest that nifedipine may be useful in the treatment of lung disease in these patients; however, further studies are needed. 