Reproducibility of measurements of inspiratory work capacity in cystic fibrosis patients

The evaluation of respiratory muscle endurance (RME) is regarded as being clinically relevant to the assessment of respiratory muscle function. The reproducibility of a non-invasive measure of assessing RME was determined by measuring inspiratory work capacity (IWC) (using a computerised system). Measurements were obtained on two occasions in 20 adult cystic fibrosis (CF) patients (22.7 ± 3.4 years, mean ± S.D.) and 20 age (23.4 ± 4.4 years) and gender (10 male, 10 female in each group) matched healthy controls. The coefficients of reliability (CR), intra-class correlation coefficients (ICC) and limits of agreement (bias ± 2 S.D.) were determined. CR values for the CF patients and controls were above 90% and with ICC of 0.99 in both CF patients and controls. The differences in IWC between study days were within ±2 S.D. of the mean difference in all but one CF and one control subject. These data suggest that measures of IWC may be considered reliable when used to assess RM function in both controls and in patients with CF.