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.