Obstructive sleep apnea (OSA) is a sleep disorder characterized by repetitive complete (apnea) or partial (hypopnea) obstructions of the upper airway during sleep, often leading to blood oxygen desaturations and reoccurring arousals from sleep. Arousals, often visible in the electroencephalogram (EEG), constantly interrupt the normal sleep pattern, resulting in inadequate sleep and shortened sleep time. Even though arousals from sleep are identified from overnight recordings to characterize the degree of sleep interruption, only the number of arousals is often considered in daily clinical practice when assessing OSA severity. This study investigated the spectral content of EEG during different arousals caused by varying respiratory events.
In the study, high-frequency content, i.e. gamma band (30–40 Hz) power, of EEG was investigated in respiratory arousals of 869 patients with clinical suspicion of OSA. The differences were studied between arousals caused by different respiratory event types (i.e. obstructive apnea or hypopnea) and severities (i.e. in terms of event duration and the presence of oxygen desaturation). Arousals were also compared to steady sleep during different sleep stages.
As opposed to steady sleep, where gamma power decreased towards deeper stages, arousal gamma power was higher in deeper sleep. In addition, arousal gamma power was higher related to obstructive apneas compared to hypopneas, and increased alongside obstructive apnea duration, whereas hypopnea duration was not associated with significant gamma power changes. Furthermore, arousal gamma power was higher in the presence of an oxygen desaturation, regardless of the respiratory event type.
As elevated EEG gamma activity could indicate a shift towards wakefulness, the present findings demonstrate that the arousal intensity and, therefore, the magnitude of sleep disruption might vary depending on the preceding respiratory event characteristics. The present findings reinforce the importance of developing methods for more comprehensive OSA severity assessment.