Repeatability of sites of sleep-induced upper airway obstruction. A 2-night study based on recordings of airway pressure and flow

Objectives: To evaluate repeatability of overnight continuous airway pressu re and flow recordings for assessment of obstructive sites and their distri bution in patients with obstructive sleep apnea (OSA). Study design: Open, prospective study of 30 men with sleep-induced obstructive events (apnea an d hypopnea). Methods: Repeated ambulatory sleep recordings of airway pressu re and flow to assess the localization of sites of obstructive events were compared. Obstructive sites were divided into upper (transpalatal) or lower (subpalatal). The exact distribution of obstructive sites was expressed as percentage upper obstructive events. A cut-off at apnea index (Al) = 5 was used for comparison between frequent and infrequent obstructers. Results: Eighty-two percent (14/17) of patients with frequent, and 58% of those with infrequent apneic events maintained their predominant site of obstructive events classified as upper (transpalatal) or lower (subpalatal) [72% (21/29 ) in the entire group]. We found a significant correlation between recordin gs for the percentage upper apneic (R = 0.54, P = 0.024, n = 17) and hypopn eic (R = 0.59, P = 0.012, n = 17) events in patients with frequent, but not in those with infrequent apneic events. Patients who had the vast majority of obstructive events located at a single site were more stable than those with more evenly distributed obstructive events. Conclusion: Repeatability of sites of obstructive events is influenced by the severity of illness an d the degree of upper or lower obstructive predominance. The distribution o f sites of obstructive events (classified as mainly "upper"/"lower" or as p ercent upper obstructive events of all) can be identified with relative con fidence in patients who have frequent apneic events (AI ! 5) or a high degr ee of upper or lower obstructive predominance and especially in those who h ave a combination of these two criteria.