Apnoea characteristics across the night in severe obstructive sleep apnoea: influence of body posture

Several studies have reported changes in apnoea characteristics across the night in patients with obstructive sleep apnoea (OSA). However, the effect of body posture on these changes has not been evaluated. The purpose of this study was to assess how body posture influences sleep apnoea characteristics across the night in severe OSA. Polysomnograms of 30 patients with severe OSA who had > or = 30 apnoeic episodes in the lateral position and 30 in the supine position during Stage 2 sleep, in the early, middle and late sleep periods were analysed. For each of the 30 events in each body position, the following variables were evaluated: apnoea duration; minimum saturation; change in saturation; duration of arousal; maximum snoring loudness and change in cardiac frequency. Although at any time during the night, apnoeas in the supine posture were more severe than those in the lateral position, a time effect across the night was found only for apnoea duration, change in cardiac frequency and duration of arousal. Body position did not affect the time trend for these variables across the night. The best fit for the changes of these three variables across the night was a quadratic time trend. It was concluded that in severe obstructive sleep apnoea during Stage 2 sleep, body position does not significantly affect the time trends of apnoea characteristics across the night. These data provide support for the participation of sleep-dependent mechanisms (homeostatic and circadian) in the determination of apnoea characteristics across the night.

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 in the supine posture vs the severity of sleep apneic events occurring in the 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 sleep disorders unit.

PATIENTS

Thirty patients with severe OSA (respiratory disturbance index [RDI] = 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+/-11.7, lateral RDI = 64.8+/-17.3), and who had > or =30 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 (MinDes), Delta desaturation (Delta-Des), duration of arousal (DurArous), maximum snoring loudness (MaxSL), and Delta heart rate (Delta-HR). In addition, three other variables assessed as a ratio of ApDur (Rate-D = Delta-Des/ApDur, R-HR =Delta-HR/ApDur, and R-Arous = DurArous/ApDur) were also calculated.

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 correlated significantly with DurArous, Delta-HR, and MaxSL, but not with Delta-Des and MinDes. ApDur correlated linearly with DurArous for both postures. The slopes of the two regression lines were similar (p = 0.578) but the regression line intercept for the supine apneas was significantly higher than that of lateral apneas (p<0.0001). In addition, the average number of supine apneic events that did not end with an arousal was smaller than the 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 (0.44%) 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 have a high number of apneic events in the supine and lateral posture, the apneic events occurring in the supine position are more severe than those occurring while sleeping in the lateral position. Thus, it is not only the number of apneic events that worsen in the supine sleep position but, probably no less important, the nature of the apneic events themselves.