Association of body position with severity of apneic events in patients with severe nonpositional obstructive sleep apnea

Study objective: To compare the severity of sleep apneic events occurring i n the supine posture vs the severity of sleep apneic events occurring in th e lateral posture in patients with severe obstructive sleep apnea (OSA). Design: A retrospective analysis of apneic event variables in a group of 30 OSA patients who underwent a complete polysomnographic evaluation in our s leep disorders unit. Patients: Thirty patients with severe OSA (respiratory disturbance index [R DI] = 70.1 +/- 18.2) who were nonpositional patients (NPP), ie, in whom the ratio of the supine RDI to the lateral RDI is < 2 (supine RDI = 85.7 +/- 1 1.7, lateral RDI = 64.8 +/- 17.3), and who had <greater than or equal to> 3 0 apneic events in the lateral position and 30 apneic events in the supine position during sleep stage 2 were included in the study. Measurements: For the 30 apneic events in each body position, the following variables were evaluated: apnea duration (ApDur), minimum desaturation (Mi nDes), Delta desaturation (Delta -Des), duration of arousal (DurArous), max imum snoring loudness (MaxSL), and Delta heart rate (Delta -HR). In additio n, three other variables assessed as a ratio of ApDur (Rate-D = Delta -Des/ ApDur, R-WR = Delta -HR/ApDur, and R-Arous = DurArous/ApDur) were also calc ulated. Results: For all variables evaluated, apneic events occurring in the supine posture were significantly more severe than those apneic events occurring in the lateral posture during sleep stage 2. ApDur of both body postures co rrelated significantly with DurArous, Delta -HR, and MaxSL, but not with De lta -Des and MinDes. ApDur correlated linearly with DurArous for both postu res. The slopes of the two regression lines were similar (p = 0.578) but th e regression line intercept for the supine apneas was significantly higher than that of lateral apneas (p < 0.0001), in addition, the average number o f supine apneic events that did not end with an arousal was smaller than th e average number of lateral apneic events not ending with an arousal (4.4 /- 6.0 vs 10.5 +/- 6.7, respectively; p < 0.0001). Also, only 4 of 900 (0.4 4%) apneic events analyzed in the lateral posture ended with an awakening ( > 15 s), whereas in the supine posture, there were 37 (4.1%) such events (p < 0.001). Conclusions: These results show that even in patients with severe OSA who h ave a high number of apneic events in the supine and lateral posture, the a pneic events occurring in the supine position are more severe than those oc curring while sleeping in the lateral position. Thus, it is not only the nu mber of apneic events that worsen in the supine sleep position but, probabl y no less important, the nature of the apneic events themselves.