Respiratory muscle pressures in non-CF bronchiectasis: repeatability and reliability

Respiratory muscle strength is used diagnostically in clinical practice and as an outcome measure in clinical trials in various chronic lung diseases. There is limited data on its repeatability in people with non-CF bronchiectasis. The aim of the present study was to assess the repeatability of maximal inspiratory (P( I)max) and expiratory pressures (P(E)max) in a group of patients with stable, moderate-to-severe non-CF bronchiectasis.

Twenty participants with stable moderate-to-severe non-CF bronchiectasis were recruited. Respiratory muscle strength measurements (three maximal inspiratory and expiratory pressures) were made on 2 separate days. A standard protocol was used, including practice tests, before obtaining three technically acceptable and reproducible readings with a difference of 10% or less between values.

ClinicalTrials.gov: NCT00487149.

The mean (SD) age of the non-CF bronchiectasis group was 63 (9) years. Maximal inspiratory pressures were repeatable with mean (SD) for highest P(I)max, Test 1 and Test 2, 75.90 (20) and 79.40 (19) cmH(2)O, and limits of agreement (mean difference +/- 2SD) -3.50 +/- 20 cmH(2)O, (p = 0.14). Maximal expiratory pressures differed significantly with mean (SD) for highest P(E)max, Test 1 and Test 2, 102.25 (27) and 112.30 (32) cmH(2)O, and limits of agreement (mean difference +/- 2SD) -10.10 +/- 35 cmH(2)O, (p = 0.02). The intraclass correlation coefficient (95% CI) for highest P(I)max and P(E)max was 0.93 (95% CI 0.82 to 0.97) and 0.90 (95% CI 0.76 to 0.96), respectively.

Maximal inspiratory pressure measurements were repeatable during a period of clinical stability in moderate-to-severe non-CF bronchiectasis, suggesting this may be a useful outcome measure in non-CF bronchiectasis. Once a baseline has been established, a second visit is not required. P(E)max was not a repeatable measure and further study is necessary to ascertain how much practice testing is required to obtain an accurate value.