Validation of the Incremental Shuttle Walk Test as a Clinical End Point in Bronchiectasis

Abstract

Background: A validated clinical end point is needed to assess response to therapies in bronchiectasis.

Objectives: The goal of this study was to assess the reliability, validity, and responsiveness of the incremental shuttle walk test (ISWT) as a clinical end point in bronchiectasis.

Methods: In clinically stable patients (n = 30), the ISWT was performed twice, 6 months apart. Correlation between the St. George's Respiratory Questionnaire (SGRQ) and the ISWT (n = 94) was performed. The 1-year gentamicin study was reanalyzed to assess the area under the curve (percent change of ISWT with a ≥ 4 unit improvement in total SGRQ). ISWT was performed prior to and following 14 days of antibiotics for an exacerbation (94 oral courses and 30 IV courses, n = 124) and reanalysis of the 1-year gentamicin study (n = 57).

Results: The ISWT did not significantly change over 6 months while clinically stable. The ISWT correlated inversely with the SGRQ (rs = -0.60; P < .0001), Bronchiectasis Severity Index score (rs = -0.44; P < .0001), and sedentary time (rs = -0.48; P = .0007) but correlated with physical activity (rs = 0.42; P = .004). The area under the curve for percent change in ISWT with ≥ 4 unit improvement in SGRQ was 0.79 (95% CI, 0.66-0.91; P = .001). A threshold of 5% improvement in the ISWT had a 92% sensitivity but 50% specificity, and from the responsiveness studies would capture 73% of all patients.

Conclusions: This study confirmed the ISWT to be reliable, valid, and responsive to change in patients with bronchiectasis. The authors propose that a minimum clinically important difference of 5% improvement in the ISWT would be a useful objective end point to assess therapies in bronchiectasis.

Keywords: bronchiectasis; clinical endpoint; incremental shuttle walk test; validation.