Clinical implications of six-minute walk test in patients with idiopathic pulmonary fibrosis: a retrospective cohort study.

Abstract

A six-minute walk test (6MWT) is a reproducible, easily performed test, and is widely used to determine functional exercise capacity in patients with idiopathic pulmonary fibrosis (IPF). However, there is currently a paucity of data on the clinical significance of baseline and serial 6-minute walk tests in patients with IPF, especially in Asian patients. We aimed to investigate the clinical significance of serial 6MWT in patients with IPF, especially in Asian patients. This is a single-center retrospective cohort study. Clinical data of patients diagnosed with IPF at a tertiary center in Korea were retrospectively analyzed. IPF diagnosis was defined according to the clinical guidelines of the American Thoracic Society (ATS)/European Respiratory Society (ERS)/Japanese Respiratory Society/Latin American Thoracic Association. There were 216 patients diagnosed with IPF from December 2012 to January 2022, of whom 198 had a baseline of 6MWT data. The mean age of the cohort was 66.9 ± 8.6, and 89% were male. The non-survivors showed significantly lower six-minute walk distance (6MWD), minimum saturation of peripheral oxygen (SpO2) during 6MWT, forced vital capacity, and diffusing capacity of the lung for carbon monoxide than survivors at baseline. A multivariate Cox analysis demonstrated that lower minimum SpO2 was independently associated with increased mortality rates (Hazard ratio (HR): 1.081, 95% confidence interval (CI): 1.024-1.142, p = 0.005). Higher mortality rates were also associated with echocardiographic-determined pulmonary hypertension (HR: 2.466, 95% CI: 1.149-5.296, p = 0.021) at diagnosis. Among 144 patients with 6MWT results at 12 months, patients with a decline of 50 m or more in the 6MWD showed poorer overall survival than others (median survival: 45.0 months vs 58.0 months, p < 0.001). Baseline lower minimum SpO2 during 6MWT was an independent prognostic factor in patients with IPF, and a decline in 6MWD in serial follow-up was also associated with a poorer prognosis. These findings suggest that both baseline 6MWT and follow-up data are important in the prognostication of patients with IPF.