Effect of positive expiratory pressure on breathing pattern in healthy subjects.

The purpose of this study was to register breathing patterns, in healthy subjects, during breathing with a positive expiratory pressure. Integrated electromyographic (IEMG) activity of the following muscles was assessed: scalene muscle, parasternal muscle and abdominal muscles, using surface electrodes. Inspiration time, expiration time, total breathing cycle time, tidal volume and breathing frequency were measured using a water-sealed spirometer. Functional residual capacity was measured using a body plethysmograph. Oxygen uptake and carbon dioxide output were measured using an automatized ergometry set-up. All measurements were performed during undisturbed breathing and during breathing with positive expiratory pressures of 5 and 15 cmH2O. Phasic activity, but not tonic activity, of the scalene muscles and the abdominal muscles increased significantly during breathing with the expiratory pressures. No significant change was observed in phasic or tonic activity of the parasternal muscle. Mean (SD) tidal volume increased significantly from 0.8(0.2) l during undisturbed breathing to 1.1(0.3) l and 1.5(0.7) l during breathing with the expiratory pressures of 5 cmH2O and of 15 cmH2O, respectively. Respiration times, breathing frequency, oxygen uptake, carbon dioxide output and functional residual capacity remained unchanged. It can be concluded that, in healthy subjects, positive expiratory pressure increases tidal volume by activity of both expiratory and inspiratory muscles, while functional residual capacity remains unchanged. The changes appeared to be pressure dependent.