The Maximal Expiratory-to-Inspiratory Pressure Ratio and Supine Vital Capacity as Screening Tests for Diaphragm Dysfunction

Purpose The change in vital capacity from the seated to supine position (∆VC-supine) is used to screen for diaphragm dysfunction (DD), but some individuals are unable to tolerate the supine position. Since expiratory muscle function is often preserved in patients with isolated DD and inspiratory strength is reduced, the purpose of this study was to examine if the ratio of maximal expiratory pressure to maximal inspiratory pressure (MEP/MIP) may provide an alternative to ∆VC-supine when screening patients for DD. Methods We performed a cross-sectional analysis on 76 patients referred for evaluation of unexplained dyspnea and possible DD. MEP and MIP were measured in the seated position as well as the percent change in VC from the seated to supine position (∆VC-supine %). The presence of unilateral diaphragm paralysis (UDP), bilateral diaphragm paralysis (BDP), or normal diaphragm function (N) was confirmed by ultrasound. Results Of the 76 patients, 23 had N, 40 had UDP, and 13 had BDP. MEP/MIP was significantly greater for UDP compared to N (2.1(1.2–5.7) and 1.5(0.7–2.2), respectively) (median and interquartile range) and for BDP compared to UDP (4.3(2.3–7.5) and 2.1(1.2–5.7), respectively) ( p