Severity of obstructive sleep apnoea/hypopnoea syndrome and subsequent waking EEG spectral power

Abstract

It is well known that most patients with obstructive sleep apnoea/hypopnoea syndrome (OSAHS) suffer sleepiness, although the underlying mechanisms of this relationship remain unclear. The present study examined the relationship between nocturnal variables and the subsequent waking electroencephalogram (EEG), in order to determine if sleepiness was related to OSAHS severity and due to sleep fragmentation or to nocturnal hypoxaemia.In total, 12 moderate-to-severe OSAHS patients underwent a total sleep night followed by a 24-h period of sustained wakefulness where the waking EEG was measured every hour.The results showed that alpha (7.9-12.6 Hz) and beta (12.7-29.2 Hz) activities were strongly related to OSAHS severity, mainly reflected by the apnoea index. Moreover, spectral power in most of the waking EEG components was significantly correlated with nocturnal hypoxaemia indices, namely alpha and beta activity when hypoxaemia becomes severe. However, no correlation was found between the waking EEG and sleep fragmentation parameters.In conclusion, the present results suggest that the difficulty in maintaining an optimal level of alertness, reflected by a higher activity in awake alpha and beta bands (7.9-29.2 Hz) in obstructive sleep apnoea/hypopnoea syndrome, was better explained by: 1) the apnoea as opposed to the hypopnoea index; and 2) nocturnal hypoxaemia as opposed to sleep fragmentation.

Improvement of EEG slowing in OSAS after CPAP treatment

“…In a 40-hour sleep deprivation study, theta power was increased as wake time was prolonged and the increase of theta power paralleled the increase of subjective sleepiness [27]. Also, correlations between EEG spectral power and sleepiness were reported in healthy subjects during 24-hour sustained wakefulness [24]. In the current study, a relatively high correlation was observed between changes of EEG slowing and daytime sleepiness measured by ESS.…”

“…Nocturnal hypoxia, rather than daytime sleepiness has been suggested as an underlying mechanism of EEG slowing in OSAS [24]. In conditions other than OSAS, such as hypobaric and hypoxic conditions generated by a low pressure chamber, hypobaric hypoxia induced an increase in relative delta and theta activity and a decrease in relative alpha activity [25,26].…”

Aberrant Awake Spontaneous Brain Activity in Obstructive Sleep Apnea: A Review Focused on Resting-State EEG and Resting-State fMRI

“…Not only the slowing ratio, some researchers even found that AHI and α power were positively correlated in OSA patients, and oxygen desaturation index (ODI) was positively correlated with θ and α power. In addition, they found that daytime alertness efforts were related to ArI, and daytime sleepiness was related to ODI (49). Other studies found no significant correlation between OSA severity and any rsEEG rhythm (26,27,49,50).…”

“…In addition, they found that daytime alertness efforts were related to ArI, and daytime sleepiness was related to ODI (49). Other studies found no significant correlation between OSA severity and any rsEEG rhythm (26,27,49,50). Only two studies found a significant correlation between subjective sleepiness and rsEEG power.…”

“…A Korean group found that the slowing ratio in the whole-brain area decreased after treatment (53). Several studies have pointed out that the main finding on the rsEEG is the reduction of θ power (27,30,49). For δ power, a study led by Xiromeritis et al (30) found a significant increase in δ power after treatment, whereas another study found the contrary conclusion (27).…”