Evaluation of the upper airway cross-sectional area changes in different degrees of severity of obstructive sleep apnea syndrome: cephalometric and dynamic CT study.

BACKGROUND AND PURPOSE: The upper airway lumen is narrower in patients with obstructive sleep apnea syndrome (OSAS) than normal subjects. In this study, we examined changes of the upper airway cross-sectional area in each phase of respiration in different degrees of severity of OSAS with dynamic CT and investigated whether these changes have any correlation with sleep apnea severity parameters, including polysomnography (PSG) and cephalometry. MATERIALS AND METHODS: Between May and November 2004, 47 patients who had at least 2 of 3 major symptoms of snoring, daytime somnolence, and apnea with witness were included in this prospective study. As control group, 24 habitual snorers were studied. All patients underwent PSG and upper airway CT. The average number of episodes of apnea and hypopnea per hour of sleep (the apnea-hypopnea index, AHI) was calculated. An AHI of 5 -29 represented mild/moderate OSAS and an AHI > or = 30 represented severe OSAS. Cross-sectional area of the airway at the level of oropharynx and hypopharynx were obtained in each phase of quiet tidal breathing and at the end of both the forced inspiration and expiration. Six standard cephalometric measurements were made on the lateral scout view. All parameters were compared between controls and mild/moderate and severe OSAS groups. RESULTS: Twenty-seven patients had mild/moderate OSAS, and 20 patients had severe OSAS. Patients with severe OSAS had significantly narrower cross-sectional area at the level of uvula in expiration, more inferiorly positioned hyoid bone, and thicker soft palate compared with patients with mild/moderate OSAS (P < .05) and the control group (P < .05). In addition, severe OSAS patients had bigger neck circumference than those in the control group (P < .05). CONCLUSION: Patients with severe OSAS had significant differences in the parameters. Measurement of the cross-sectional area of oropharynx in expiration can especially be useful for diagnosis of severe OSAS as a new key point.