Body position influences the maximum inspiratory and expiratory mouth pressures of young healthy subjects

Objective The purpose of this study was to determine the effects of body position on respiratory muscle strength of young healthy subjects. Participants Sixty-three (50 female, mean age 19.7 ± 1.5 years) healthy subjects participated in the study. Design Participants were measured in the sitting position, semi-upright sitting position, and in the supine position. The order of the three conditions was randomly determined. Outcome Measures Maximal inspiratory and expiratory mouth pressures (PImax, PEmax) and lung function. Results A significant effect of body position was observed on PEmax values, controlling for gender. PImax in the sitting position (92.8 ± 20.05 cm H2O) was significantly higher than in the supine (84.1 ± 15.1 cm H2O; mean difference: 8.70, 95% CI [5.95, 12.45], p < 0.001) and semi-upright sitting positions (84.4 ± 17.5 cm H2O; mean difference: 8.43, 95% CI [5.78, 11.07], p < 0.001). PEmax was also significantly higher in the sitting position (125.4 ± 34.2 cm H2O) than in the supine (115.8 ± 29.0 cm H2O; mean difference: 9.59, 95% CI [4.86, 14.32], p < 0.001) and semi-upright sitting positions (120.2 ± 33.9 cm H2O; mean difference: 5.21, 95% CI [0.87, 9.54], p = 0.013). Conclusions Body position influences respiratory muscle strength of young healthy subjects. PImax and PEmax are higher in the sitting position than in the supine or semi-upright sitting positions. © 2014 Published by Elsevier Ltd on behalf of The Chartered Society of Physiotherapy.