Strong coincidence between slow wave sleep and low AHI is explainable by the high instability of slow wave sleep to obstructive apnea exposure.

It is well known that in patients with obstructive sleep apnea syndrome (OSAS) the apnea-hypopnea index (AHI) is significantly decreased during slow wave sleep (SWS). It used to be explained by the ability of SWS to stabilize the upper airways against collapse. Another explanation, which is the focus of the current study, is that it is just a result of high instability of SWS to obstructive apnea exposure, i.e. high susceptibility of SWS to transition into lighter sleep stages during exposure to obstructive apneas. A retrospective chart review was performed on 560 males who underwent an overnight polysomnography. Two hundred and eighty-seven patients were eligible for the study. They were divided into 3 groups according to different AHI level. All three groups had a higher SWS occurrence in the lateral position than in the supine position. A special fourth group of patients was created with severe OSAS in the supine position but with very mild OSAS in the lateral position. This group had, in the lateral position, (A) higher AHI in NREM sleep (4.1+/-3.1/h vs. 0.7+/-1.2/h, p<0.001) as well as (B) higher SWS occurrence (27.7+/-15.0 % vs. 21.4+/-16.2 % of NREM sleep, p<0.05), than the group with the lowest AHI in the study, i.e. AHI<5/h in NREM sleep. These data suggest that strong coincidence between SWS and low AHI is the result of the high instability of SWS to obstructive apnea exposure. The data also support the presence of SWS-rebound in OSAS patients in the lateral body position.

Does obstructive sleep apnea worsen during REM sleep?

Although it is thought that obstructive sleep apnea (OSA) is worse during rapid eye movement (REM) sleep than in non-REM (NREM) sleep there are some uncertainties, especially about apnoe-hypopnoe-index (AHI). Several studies found no significant difference in AHI between both sleep stages. However, REM sleep is associated more with side sleeping compared to NREM sleep, which suggests that body position is a possible confounding factor. The main purpose of this study was to compare the AHI in REM and NREM sleep in both supine and lateral body position. A retrospective study was performed on 422 consecutive patients who underwent an overnight polysomnography. Women had higher AHI in REM sleep than NREM sleep in both supine (46.05+/-26.26 vs. 23.91+/-30.96, P<0.01) and lateral (18.16+/-27.68 vs. 11.30+/-21.09, P<0.01) body position. Men had higher AHI in REM sleep than NREM sleep in lateral body position (28.94+/-28.44 vs. 23.58+/-27.31, P<0.01), however, they did not reach statistical significance in supine position (49.12+/-32.03 in REM sleep vs. 45.78+/-34.02 in NREM sleep, P=0.50). In conclusion, our data suggest that REM sleep is a contributing factor for OSA in women as well as in men, at least in lateral position.