Minimal important difference in field walking tests in non-cystic fibrosis bronchiectasis following exercise training

Abstract

Background: The 6-min walk distance (6MWD) and incremental shuttle walk distance (ISWD) are clinically meaningful measures of exercise capacity in people with non-cystic fibrosis (CF) bronchiectasis, but the change in walking distance which constitutes clinical benefit is undefined. This study aimed to determine the minimal important difference for the 6MWD and ISWD in non-CF bronchiectasis.

Methods: Thirty-seven participants with mean FEV1 70% predicted completed both field walking tests before and after an 8-week exercise program. The minimal important difference was calculated using a distribution-based and anchor-based method, with the global rating of change scale used.

Results: The mean change in 6MWD in participants who reported themselves to be unchanged was 10 m, compared to 36 m (small change) and 45 m (substantial change) (p = 0.01). For the ISWD, the mean change in participants who reported themselves to be unchanged was 33 m, compared to 54 m (small change) and 73 m (substantial change) (p = 0.04). The anchor-based method defined the minimal important difference for 6MWD as 24.5 m (AUC 0.76, 95% CI 0.61-0.91) and for ISWD as 35 m (AUC 0.88, 95% CI 0.73-0.99), based on participant's global rating of change. The distribution-based method indicated a value of 22.3 m for the 6MWD and 37 m for the ISWD. There was excellent agreement between the two methods for the 6MWD (kappa = 0.91) and the ISWD (kappa = 0.92).

Conclusions: Small changes in 6MWD and ISWD may represent clinically important benefits in people with non-CF bronchiectasis. These data are likely to assist in the interpretation of change in exercise capacity following intervention.

Keywords: Bronchiectasis; Exercise capacity; Minimal important difference.