The reliability of a new measure of inspiratory muscle function in patients with COPD

Abstract

Rationale: Maximal inspiratory pressure (MIP) is an accepted effort-dependent measure of global inspiratory muscle strength. Prolonged MIP (PMIP) area is a new measure of inspiratory muscle function calculated as the area under the curve produced by sampling maximal inspiratory pressure at 16 Hz during a sustained inspiratory manoeuvre. The reliability of this measure has previously been established in normal subjects, but no published data are available for COPD patients.Methods: Forty-three COPD patients attended for data collection on two occasions, 48 hours apart. Anthropometric data were collected on the first visit, pulmonary function, inspiratory muscle and peripheral muscle function (hand grip) data were collected during both visits. Calculated reliability estimates included the intraclass correlation coefficient (ICC), coefficient of variation (CV) and Bland & Altman 95% limits of agreement.Results: Within-day reliability was consistently higher than between-day reliability. Between-day results generated an ICC of 0.92, a CV of 10% and 95% limits of agreement of - 58 to + 71 pressure time units. Hand grip data generated an ICC of 0.92 and a CV of 8%.Conclusion: In this study group PMIP area was found to be a reproducible measure of inspiratory muscle function, generating comparable levels of reliability to those found in other effort-dependent tests of skeletal muscle function