Oral airway resistance during wakefulness in patients with obstructive sleep apnoea.

BACKGROUND: Patients with obstructive sleep apnoea (OSA) have a number of upper airway structural abnormalities which may influence the resistance of the oral airway to airflow. There have been no systematic studies of the flow dynamics of the oral cavity in such patients.

METHODS: Inspiratory oral airway resistance to airflow (RO) was measured in 13 awake patients with OSA in both the upright and supine positions (neck position constant). Each subject breathed via a mouthpiece while the nasal airway was occluded with a nasal mask.

RESULTS: In the upright position the mean (SE) RO was 1.26 (0. 19) cm H2O/l/s (at 0.4 l/s) which increased to 2.01 (0.43) cm H2O/l/s when supine (p<0.05, paired t test). The magnitude of this change correlated negatively with the respiratory disturbance index (r = -0.60, p = 0.03).

CONCLUSION: In awake patients with OSA RO is normal when upright but abnormally raised when in the supine position.