The effect of body position on maximal expiratory pressure and flow

Positioning combined with coughing and huffing is frequently used to promote secretion clearance. Maximum expiratory pressure (MEP) and peak expiratory flow rate (PEFR) have been used as surrogate measures of cough and huff strength. This study investigated the effect of body position on MEP and PEFR. Repeated measures of MEP and PEFR were performed across seven randomised positions (standing, chair sitting, sitting in bed with backrest vertical, sitting in bed with backrest at 45 degrees, supine, side lying, and side lying with head down tilt 20 degrees) on 25 adults with normal respiratory function (NRF) and 11 adults with chronic airflow limitation (CAL). For the NRF group, MEP in standing (143 ± 10cmH2O, mean ± SEM) was significantly higher than MEP in chair sitting (133 ± 10cmH2O) which in turn was significantly higher than in the remaining positions. The MEP in head down tilt (108 ± 9cmH2O) was significantly lower than in all other positions. The PEFR in standing (571 ± 24ml/s) was significantly higher and head down tilt (486 ± 23ml/s) was significantly lower than in all other positions. For the CAL group, MEP in standing (134 ± 18cmH2O) was significantly higher, while in head down tilt (96 ± 15cmH2O) was significantly lower, than in most other positions. For the CAL group, PEFR in standing (284 ± 40ml/s) was significantly higher, while in head down tilt (219 ± 38ml/s) was significantly lower, than in most other positions. Body position has a significant effect on MEP and PEFR in NRF and CAL subjects, with the lowest values in the head down position. Thus, to maximise the strength of expiratory manoeuvres during treatments that use the head down position, patients should be encouraged to adopt a more upright position when coughing or huffing