Characterization of Maximal Respiratory Pressures in Healthy Children

Abstract

Background: Measurements of maximal voluntary inspiratory (P<smlcap>i</smlcap>_max) and expiratory (P<smlcap>e</smlcap>_max) pressures are used in the management of respiratory muscle disease. There is little data on the appropriate reference range, success rates, or repeatability of P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max in children or on methodological factors affecting test outcomes. Objectives: To determine P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max in healthy children and examine which published reference equations are best suited to a contemporary population. Secondary objectives were to assess within-test repeatability and the influence of lung volumes on P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max. Methods: Healthy children were prospectively recruited from the community on a volunteer basis and underwent spirometry, static lung volumes, and P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max testing. Results: Acceptable and repeatable (to within 20%) P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max were obtained in 156 children, with 105 (67%) children performing both P<smlcap>i</smlcap>_max and P<smlcap>e</smlcap>_max measurements to within 10% repeatability. The reference equations of Wilson et al. [Thorax 1984;39:535–538] best matched our healthy Caucasian children. There was an inverse relationship between P<smlcap>i</smlcap>_max and the percent of total lung capacity (TLC) at which the measurement was obtained (beta coefficient –0.96; 95% CI –1.52 to –0.39; p = 0.001), whereas at lung volumes of >80% TLC P<smlcap>e</smlcap>_max was independent of lung volume (p = 0.26). Conclusion: We demonstrated that the Wilson et al. [Thorax 1984;39:535–538] reference ranges are most suited for contemporary Caucasian Australasian children. However, robust multiethnic reference equations for maximal respiratory pressures are required. This study suggests that 10% within-test repeatability criteria are feasible in clinical practice, and that the use of lung volume measurements will improve the quality of maximal respiratory pressure measurements.