Postural changes in respiratory airflow pressure and resistance in nasal, hypopharyngeal, and pharyngeal airway in normal subjects.

We investigated the effect of posture on nasal and pharyngeal resistance in 12 healthy subjects studied during wakefulness. Airway pressure and airflow were measured with subjects seated and in dorsal and left lateral recumbency, during inspiration and expiration. We found that pharyngeal resistance was approximately four to six times lower than the nasal resistance. Only pharyngeal resistance was significantly increased upon assumption of a supine posture, from 0.02 +/- 0.01 Pa/mL per second when seated to 0.06 +/- 0.05 Pa/mL per second in dorsal recumbency and to 0.05 +/- 0.04 Pa/mL per second in left lateral recumbency. Mean nasal and pharyngeal resistances doubled upon assumption of a supine posture, but this difference was not statistically significant. There was no significant difference in pharyngeal resistance between inspiration and expiration. Finally, there was a strong linear relationship between pharyngeal pressure and pharyngeal resistance (r = .98, p<.0001). We concluded that in normal awake subjects 1) pharyngeal resistance increases with assumption of a supine posture, 2) the walls of the pharynx are not compliant enough to alter their resistance in response to inspiratory and expiratory pressure changes, and 3) it may be possible to infer pharyngeal resistance from measurements of pressure alone, without measurement of airflow.