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

Abstract

Background: 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. Objectives: We aimed to investigate the clinical significance of serial 6MWT in patients with IPF, especially in Asian patients. Design: This is a single-center retrospective cohort study. Methods: 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. Results: 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 (SpO 2 ) 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 SpO 2 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). Conclusions: Baseline lower minimum SpO 2 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.