Test/Retest Reliability of Maximum Mouth Pressure Measurements With the MicroRPM in Healthy Volunteers

BACKGROUND: Respiratory muscle strength is an important part of lung function. Assessment of the respiratory muscles' ability to generate force is important for recognizing respiratory muscle weakness in both sick and healthy people. OBJECTIVE: To assess the test/retest reliability of the MicroRPM portable manometer's measurements of maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) in the sitting and standing positions; the number of expiratory maneuvers needed with the MicroRPM for reliability in MIP and MEP measurement; and the MicroRPM's test/retest reliability in other respiratory function indices, such as the maximum rate of pressure development (MRPD), the time constant of relaxation (tau), and the maximum relaxation rate (MRR). METHODS: We recruited 15 healthy volunteers (mean age 21.6 ± 1.1 years). We assessed respiratory muscle strength on 3 separate occasions, each a week apart. We calculated reliability with the intraclass correlation coefficient (ICC), the standard error of measurement (SEM) and the smallest detectable difference (SDD). RESULTS: MicroRPM reliably measured MIP and MEP in both the sitting position (ICC 0.86-0.90, SEM 9-10, SDD 18-22) and standing position (ICC 0.78-0.83, SEM 12-14, SDD 23-26). After a 5-breath practice, 2 expiratory/inspiratory maneuvers on each testing occasion gave adequate MIP and MEP reliability (ICC > 0.90). MRR reliability was moderate to excellent (ICC 0.58-0.87), MRPD reliability was moderate (ICC 0.59-0.64), and tau reliability was insufficient (ICC 0.27-0.67). CONCLUSIONS: The MicroRPM reliably measures MIP and MEP, but its MRPD, MRR, and tau measurements should be considered with caution.