Gait-speed and oxygen flow during six-minute walk test predicts mortality in patients with advanced lung disease

The six-minute walk test (6MWT) is a useful tool to predict outcomes in patients with advanced lung diseases. Greater distance walked has been shown to have independent prognostic value. We reviewed the medical records of 164 patients with advanced lung disease who underwent lung transplant evaluation. Results of the 6MWT (distance walked, oxygen required to maintain oxygen saturation >90%, and gait speed) were recorded and analyzed with respect to mortality. 6MWT mean oxygen (O-2) flow via nasal cannula was 3.5 +/- 3.7 l/min. The distance walked in meters (m) and percent predicted distance were inversely associated with mortality, hazard ratio (HR): 0.995 per meter (95% CI 0.992-0.998) for walk distance in meters and 0.970 per % predicted distance (95% CI 0.950-0.990). Patients who walked <200 meters [HR: 2.1 ( 95% CI 1.1-4.0)] or <45% of predicted, HR: 2.7 (95% CI 1.2-5.7) had higher mortality. O-2 flow during the test had a direct association with mortality (HR: 1.1 per L/min (95% CI 1.0-1.2). In multivariate analysis, O-2 flow >3.5 L/min remained predictive of mortality, HR: 1.1 per l/min (95% CI 1.0-1.2). Gait speed was higher in patients who survived through follow-up compared to patients who died (mean 0.83 +/- 0.35 m/s vs 0.69 +/- 0.33 m/s, p=0.03). Gait speed >0.8 m/s was a predictor of survival, HR 3.4 (1.1, 10.6). In summary, distance walked and O-2 flow during the 6MWT were predictors of mortality in patients with advanced lung disease. Patients who required more than 3.5 l/m of O-2 to maintain oxygen saturation >90% had a higher mortality. Faster gait speed during the 6MWT was also associated with better survival.