Changes in Pulmonary Function Test Results After 1 Year of Therapy as Predictors of Survival in Patients With Idiopathic Pulmonary Fibrosis

The study group consisted of 58 patients with idiopathic pulmonary fibrosis (IPF) recognized between 1970 and 1991 who were treated for their pulmonary disease, survived for at least 1 year from the time of initiation of treatment, and had forced vital capacity (FVC) measurements at the time of diagnosis and 9 to 15 months later. Forty-four of the patients also had a single-breath diffusing capacity (Dsb) measured initially and after 9 to 15 months of treatment and 33 patients had an arterial blood gas, breathing room air at the time of diagnosis and 9 to 15 months into therapy. Patients' conditions were classified as improved, unchanged, or worse after the year of treatment based on each of the three pulmonary function tests. A ≥ 10% increase in FVC, ≥20% increase in Dsb, and ≥5 mm Hg decrease in alveolar-arterial difference in oxygen partial pressure [P(A-a)O2] defined improved function. A ≥10% decrease in FVC, ≥20% decrease in Dsb, and ≥5 mm Hg increase in P(A-a)O2 defined worse function. Patients with