Respiratory muscle activity and pulmonary function during acutely induced airways obstruction

BACKGROUND: Patients with airway obstruction may spontaneously breathe with a positive expiratory pressure by pursing their lips during expiration, especially in case of dyspnea. Dyspnea seems to be related to increased activity of the respiratory muscles. A potential explanation for the use of pursed lips breathing (PLB) is that this type of breathing leads to a reduction of respiratory muscle activity. The purpose of this study was to assess the effect of breathing with a positive expiratory pressure of 5 cm H2O, simulating pursed lips breathing (SPLB), on respiratory muscle activity and pulmonary function during induced airway obstruction.

METHODS: In twelve asthmatic patients, tonic and phasic electromyographic (EMG) activity of the following muscles was obtained: scalene muscle, parasternal muscle, and abdominal muscles. Pulmonary function and EMG measurements were performed before and after propranolol induced airway obstruction.

RESULTS: Simulated pursed lips breathing resulted in a significant increase of functional residual capacity and tidal volume both at baseline and during airway obstruction. Phasic respiratory muscle activity during PEP breathing increased especially at baseline. We conclude that beneficial effects of breathing with a positive expiratory pressure of 5 cm H2O, which is similar to pursed lips breathing, cannot be explained by changes in respiratory muscle activity or pulmonary function.