A CEPHALOMETRIC AND ELECTROMYOGRAPHIC STUDY OF UPPER AIRWAY STRUCTURES IN THE UPRIGHT AND SUPINE POSITIONS

Obstructive sleep apnea (OSA) is characterized by recurrent upper airw ay obstruction during sleep, usually in the supine position. To invest igate the relationship between upper airway size and genioglossus (GG) muscle activity, upright and supine cephalograms were obtained in 20 OSA patients and 10 symptom-free control subjects. Tongue electromyogr aphic (EMG) recordings were obtained with surface electrodes, and pres sure transducers were placed in the 10 symptom-free controls. The tong ue cross-sectional area increased 4.3% (p < 0.05), and the oropharynge al area decreased 36.5% (p < 0.01) when the OSA patients changed their body position from upright to supine. No changes were observed in the tongue area, but soft palate thickness increased (p < 0.01) when the control subjects changed from the upright to the supine position. Furt hermore, the oropharyngeal cross-sectional area decreased 28.8% (p < 0 .01) despite a 34% increase (p < 0.05) in resting GG EMG activity. Pos terior tongue pressure increased 17% (p < 0.05) with the change from u pright to supine. On the basis of these findings, we propose that body posture has a substantial effect on upper airway structure and muscle activity. This postural effect should be taken into account when asse ssing upper airway size in the erect posture (conventional cephalograp hy) and in the supine position (computed tomography). The vertical and anteroposterior position of the tongue and its relationship to airway size may be more important than soft palate size in the pathogenesis of OSA.