Distance-saturation product of the 6-minute walk test predicts mortality of patients with non-cystic fibrosis bronchiectasis

Background: Previous surveillance methods to monitor the prognoses of patients with bronchiectasis are too complex for use in daily practice. The 6-minute walk test (6MWT) is a simple exercise test to predict the prognosis of chronic obstructive airway disease and numerous chronic lung diseases, including idiopathic pulmonary fibrosis. No studies have investigated exercise-induced oxygen desaturation (EID) and distancesaturation product (DSP) of 6MWT to predict the prognoses of patients with bronchiectasis. Methods: This was a prospective study to identify correlations between variables of 6MWT and mortality in patients with bronchiectasis over a 6-year period. The study cohort included 69 patients with stable noncystic fibrosis (non-CF) bronchiectasis who were regularly evaluated for functional status via 6-minute walk distance (6MWD), spirometry, BODE index, EID, and DSP. Results: Of the 69 patients, 9 (13%) died and 60 (87%) survived during the 6-year follow-up period. The percentage of EID was higher [7 of 9 patients (78%) vs. 22 of 60 patients (27%), P=0.003] in the non-survivors group. The 6MWD (466.1 +/- 78.0; 359.4 +/- 113.6 m, P=0.001) was higher in the survivors group. DSP was significantly lower in the non-survivors group [433.0 (340.0-482.0) vs. 249.0 (230.0-315.0) m%, P<0.001]. Multivariate analysis showed that DSP (OR = 0.983; 95% CI: 0.974-0.993, P=0.001) was the best parameter of 6MWT to predict mortality. Patients with a lower DSP of < 280 m% were at a 66.5-fold greater risk (OR = 66.5; 95% CI: 9.4-469.2) of 6-year mortality compared with those with DSP >280 m% (P<0.001). Conclusions: DSP is a simple parameter to predict 6-year mortality in patients with non-CF bronchiectasis.