Spectral oscillations of RR intervals in sleep apnoea/hypopnoea syndrome patients.

A recent study has shown that daytime heart rate variability is reduced in obstructive sleep apnoea/hypopnoea syndrome (OSAHS) patients. In the present study, the hypothesis was that sympathovagal balance around apnoeas/hypopnoeas and nocturnal autonomic activity are altered in OSAHS patients. Frequency- and time-domain analyses of RR intervals were performed to monitor sympathovagal activity noninvasively. Fourteen untreated OSAHS patients and seven healthy subjects underwent overnight polysomnography. Low (LF) and total (TF) frequency power increased 2 min around the end of apnoeas/hypopnoeas (LF 229+/-38 ms2 TF 345+/-45 ms2) compared with undisturbed sleep (LF 106+/-18 ms2, TF 203+/-23 ms2). The increase in high frequency (HF) power was not significant. LF increase was proportionally higher than the HF increase (normalised LF (LFn) 67+/-1 units, normalised HF (HFn) 33+/-1 units) compared with undisturbed sleep (LFn 52+/-2 units, HFn 48+/-2 units). RR duration did not change around apnoeas/hypopnoeas (RR 904+/-28 ms). The LF and TF power increase was greater around arousal-inducing (LF 260+/-45 ms2 TF 390+/-65 ms2) compared with self-terminating (LF 161+/-31 ms2, TF 249+/-40 ms2) apnoeas/hypopnoeas; the LF and LFn increases were significant in both groups compared with undisturbed sleep and HF power differences were nonsignificant. RR intervals were longer around self-terminating apnoeas/hypopnoeas (RR 914+/-29 ms); the differences were not significant compared with undisturbed sleep. RR interval spectral power was not influenced by the event type. RR duration decreased (912+/-28 ms) and LF, HF and TF power increased (LF 111+/-16 ms2 , HF 62+/-6 ms , TF 173+/-21 ms2) across patients, compared with healthy controls (RR 1138+/-91 ms, LF 57+/-3 ms2, HF 35+/-3 ms2, TF 91+/-6 ms2). LFn and HFn did not change significantly. Sympathetic activity increases around apnoeas/hypopnoeas. The recurrent nocturnal fluctuations of sympathovagal balance and the overall increase of nocturnal autonomic activity may be of importance in the development of cardiovascular disease in sleep apnoea patients.

Electroencephalographic spectral analysis: detection of cortical activity changes in sleep apnoea patients.

There are no visible electroencephalographic (EEG) changes at the termination of some apnoeas and hypopnoeas. This study tests the hypothesis that cortical activity fluctuates at apnoea/hypopnoea termination, despite the lack of visible changes. To detect these changes, EEG spectral analysis was performed and centred around the end of apnoeas/hypopnoeas in 15 sleepy patients. Ten second windows were applied and comparisons were conducted between the normalised power of the same frequency bands before and after termination of each apnoea/hypopnoea. Comparisons were performed within patients between apnoeas/hypopnoeas and periods of undisturbed sleep as well as between patients and healthy subjects during sleep. Normalised theta power (4-8 Hz) decreased significantly at apnoea/hypopnoea termination. No significant changes were found between consecutive periods of undisturbed sleep across the 15 patients. During nonrapid eye movement sleep, changes were detected irrespective of arousal visibility. During rapid eye movement sleep, nonarousal apnoeas/hypopnoeas were not accompanied by any significant spectral power changes. Theta power was significantly lower across patients compared to healthy subjects (p=0.03) and was correlated to the apnoea/hypopnoea index (rho=0.6, p=0.008). The authors conclude that electroencephalographic spectral analysis improves detection of changes at apnoea/hypopnoea termination. Further validation is needed to determine whether it improves correlation between nocturnal measures and daytime symptoms.

Arousability in sleep apnoea/hypopnoea syndrome patients.

Sleep disruption and daytime sleepiness in obstructive sleep apnoea/hypopnoea syndrome (OSAHS) patients result from recurrent apnoeas/hypopnoeas and arousals from sleep. Around 30% of apnoeas/hypopnoeas are not terminated by visible cortical arousals. The current authors tested the hypotheses that arousal induction is linked to sleep stage, oxygen desaturation, event type, event duration and time of occurrence during the night. Fifteen patients with OSAHS of varying severity were studied and all their apnoeas/hypopnoeas were evaluated. Eight of 15 patients had apnoeas/hypopnoeas in all sleep stages, and all their 610 apnoeas/hypopnoeas were analysed in the between stages comparison; data from all 15 patients were included in other comparisons. Thirty-four per cent of apnoeas/hypopnoeas during slow wave sleep (SWS) were associated with arousal, significantly less than the 77% during nonrapid eye movement (NREM) 1 and 2 and 62% during rapid eye movement (REM) sleep. Arousal induction was not affected by oxygen desaturation, event type, duration or time of the night. The apnoeal/hypopnoea index was 39 x h(-1) in REM 1 and 2, significantly higher compared to 17 x h(-1) in REM or to 11 x h(-1) in SWS sleep. In conclusion, apnoeas/hypopnoeas in slow wave sleep are associated with fewer cortically apparent, visually detected arousals.