Assessment of Obstructive Sleep Apnea Syndrome by spectral analysis of physiological parameters
Obstructive Sleep Apnea Syndrome (OSAS) is a very common sleep disorder that is associated with cardiovascular and neurocognitive impairments. The present study aims to assess the electroencephalographic (EEG) power before, during and after obstructive apnea episodes, in four frequency bands: delta (δ), theta (θ), alpha α and beta (β). Furthermore, Autonomic Nervous System (ANS) activity was assessed through the spectral analysis of heart rate variability (HRV) components in the three mentioned periods. For that purpose, continuous wavelet transform was applied to the EEG and RR (obtained from the ECG signal) signals. A new approach was carried out for assessing EEG power changes during an OSA episode: topographic EEG brain mapping. This technique was found to be a powerful tool to better visualize spectral changes during OSA episodes across the whole brain. The results demonstrate that there is a significant decrease in the EEG δ power during OSA, that is not totally recovered immediately after the episode. Since δ waves are linked to learning and synaptic plasticity processes, it is hypothesized that decreased δ power during OSA may contribute to the cognitive deterioration in patients with OSAS. The HRV analysis results show the presence of a pattern during OSA episodes, which is related to an impaired autonomic control of the heart in these patients.