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

Abstract

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