Prognostic value of the 6-min walk test derived attributes in patients with idiopathic pulmonary fibrosis

Abstract

Introduction: Idiopathic pulmonary fibrosis (IPF) is a fatal progressive fibrosing lung disease. A decreased 6-min walk distance (6MWD) and exercise-induced oxygen desaturation measured during the 6-min walk test (6MWT), are known predictors of mortality in patients with IPF. However, the use of antifibrotic drugs showed a survival benefit in IPF. Therefore, this study aimed to evaluate to what extend 6MWT-derived attributes are associated with two-year survival when antifibrotic drugs were introduced as part of standard IPF-care.

Methods: This real-world data-study included patients with IPF with a 6MWT between 2015 and 2020, and used composite outcome: mortality or lung transplantation within 2 years of follow-up. Data were collected systematically, including demographics, pulmonary function tests, comorbidities, medications and 6MWT-derived attributes. The prediction attributes of 6MWT were studied with a Cox Proportional-Hazards model and Kaplan-Meier survival curves. The best discriminating attribute to predict mortality was added to the prediction model Gender-Age-Physiology (GAP).

Results: In 216 patients, 2-year transplant-free survival cut-off points were identified for the 6MWD (≥413 m), 6MWD %predicted (≥83 %), SpO₂-nadir (≥86 %) and distance-saturation-product (≥374 m%), with the best discriminative value for SpO₂-nadir (area under the curve: 0.761). 2-Year survival percentage of patients with SpO₂-nadir below or above threshold (86 %) was 37.1 % and 80.0 %, respectively. Exercise-induced oxygen desaturation added to the GAP model showed an improvement in its predictive power.

Conclusion: Patients with IPF who have an exercise-induced oxygen desaturation have worse prognosis. Addition of SpO₂-nadir to the GAP model seems promising for use in clinical care of IPF patients.

Keywords: 6-min walk test (6MWT); Functional exercise capacity; GAP (Gender-Age-Physiology) model; Idiopathic pulmonary fibrosis (IPF); Physiotherapy; Prognostic.