Loss of sleep spindle frequency deceleration in Obstructive Sleep Apnea

• This study makes use of a novel approach to systematically address non-stationarity in sleep spindle oscillatory frequency: quantification of internal frequency modulation or chirp rate.
• Study suggests that Obstructive Sleep Apnea (OSA) not only slows down sleep spindle frequency, but also disrupts spindle internal frequency modulation.
• Loss of physiological sleep spindle deceleration may signal disruption of the thalamo-cortical loops involved in learning and memory.

ObjectiveSleep spindles have been suggested as surrogates of thalamo-cortical activity. Internal frequency modulation within a spindle’s time frame has been demonstrated in healthy subjects, showing that spindles tend to decelerate their frequency before termination. We investigated internal frequency modulation of slow and fast spindles according to Obstructive Sleep Apnea (OSA) severity and brain topography.MethodsSeven non-OSA subjects and 21 patients with OSA contributed with 30 min of Non-REM sleep stage 2, subjected to a Matching pursuit procedure with Gabor chirplet functions for automatic detection of sleep spindles and quantification of sleep spindle internal frequency modulation (chirp rate).ResultsModerate OSA patients showed an inferior percentage of slow spindles with deceleration when compared to Mild and Non-OSA groups in frontal and parietal regions. In parietal regions, the percentage of slow spindles with deceleration was negatively correlated with global apnea-hypopnea index (rs = −0.519, p = 0.005).DiscussionLoss of physiological sleep spindle deceleration may either represent a disruption of thalamo-cortical loops generating spindle oscillations or some compensatory mechanism, an interesting venue for future research in the context of cognitive dysfunction in OSA.SignificanceQuantification of internal frequency modulation (chirp rate) is proposed as a promising approach to advance description of sleep spindle dynamics in brain pathology.