The Reliability of Maximal Inspiratory Pressure Measurement and Its Correlation With Submaximal Exercise Test in Persons With Chronic Obstructive Pulmonary Disease

Purpose: Maximal inspiratory pressure (MIP) is a simple measure that reflects inspiratory muscle strength, which is often impaired in individuals with chronic obstructive pulmonary disease (COPD). This study aimed to assess the test–retest reliability, minimal detectable change (MDC) of MIP in persons with COPD, as well as to revisit its relationship with the 1-minute sit-to-stand test (1STST). Methods: Individuals with stable COPD were recruited. The study protocol included 2 visits. During the first visit, participants performed the MIP measurement and the 1STST with a 30-minute interval. The second visit was repeated within 10 days to assess between-day test–retest reliability. Results were reported as mean and SD. Results: The MIP measurement demonstrated excellent test–retest reliability (intraclass correlation coefficients [ICC] = 0.94, 95% CI: 0.89, 0.97, P = .001). Bland–Altman plots revealed a mean bias in the MIP measurement of 3.3 cmH 2 O, with limits of agreement ranging from −17.7 to 24.3 cmH 2 O. The MDC for MIP was estimated to be 7.3 cmH2O, respectively. A weak positive correlation (r = 0.29, P = .03) was observed between MIP and 1STST performance. Conclusions: This study demonstrated excellent between-day test–retest reliability of MIP measurement in persons with mild to moderate COPD. In addition, a weak positive correlation was found between 1STST and MIP in this population.