Baseline Functional Reserve and Serial Six-Minute Walk Assessment Identify Dynamic Risk Trajectories in Fibrotic Interstitial Lung Disease.

BACKGROUND: Risk stratification in fibrotic interstitial lung disease (F-ILD) traditionally relied on baseline physiological parameters. However, these static assessments may not adequately capture the dynamic nature of disease progression. Whether serial functional assessments provide prognostic information beyond baseline functional reserve remains uncertain. METHODS: We analyzed a prospectively established cohort of patients with fibrotic ILD who underwent routine functional assessments, including the one-minute sit-to-stand test (1MSTS) and the six-minute walk test (6MWT). Baseline predictors of mortality were evaluated using conventional Cox proportional hazards models, whereas longitudinal changes in functional performance were assessed using time-dependent Cox regression models. Overall survival was further examined according to baseline functional reserve and subsequent trajectories of functional change. RESULTS: Among 323 patients with fibrotic ILD, both baseline 1MSTS performance and six-minute walk distance (6MWD) were significantly associated with mortality. In time-dependent analyses, longitudinal decline in 6MWD remained an independent predictor of mortality, whereas longitudinal changes in 1MSTS did not provide additional prognostic value beyond baseline performance. Patients with impaired baseline walking capacity (<490 m) who subsequently experienced further decline had the highest mortality, whereas those with preserved baseline capacity and stable functional trajectories exhibited very low long-term mortality. CONCLUSION: Baseline functional capacity and serial six-minute walk assessments provide complementary information for longitudinal risk stratification in fibrotic ILD. Serial monitoring of walking capacity may facilitate identification of clinically meaningful disease trajectories in routine clinical practice.