Sleep Electroencephalographic Response to Respiratory Events in Patients With Moderate Sleep Apnea-Hypopnea Syndrome

Abstract

Sleep apnea-hypopnea syndrome is a common breathing disorder that can lead to organic brain injury, prevent memory consolidation, and cause other adverse mental-related complications. Brain activity while sleeping during respiratory events is related to these dysfunctions. In this study, we analyzed variations in electroencephalography (EEG) signals before, during, and after such events. Absolute and relative powers, as well as symbolic transfer entropy (STE) of scalp EEG signals, were calculated to unveil the activity of brain regions and information interactions between them, respectively. During the respiratory events, only low-frequency power increased during rapid eye movement (REM) stage (δ-band absolute and relative power) and N1 (δ- and θ-band absolute power, δ-band relative power) sleep. But absolute power increased in low- and medium-frequency bands (δ, θ, α, and σ bands), and relative power increased mainly in the medium-frequency band (α and σ bands) during stage N2 sleep. After the respiratory events, absolute power increased in all frequency bands and sleep stages, but relative power increased in medium and high frequencies. Regarding information interactions, the β-band STE decreased during and after events. In the γ band, the intrahemispheric STE increased during events and decreased afterward. Moreover, the interhemisphere STE increased after events during REM and stage N1 sleep. The EEG changes throughout respiratory events are supporting evidence for previous EEG knowledge of the impact of sleep apnea on the brain. These findings may provide insights into the influence of the sleep apnea-hypopnea syndrome on cognitive function and neuropsychiatric defects.

Keywords: effective connectivity; electroencephalography; respiratory events; sleep apnea–hypopnea syndrome; symbolic transfer entropy.

FIGURE 1

Electroencephalography data segments used for event analysis. B1 and B2 indicate segments before respiratory apnea–hypopnea events; D1 and D2 indicate segments during apnea–hypopnea events; A1 and A2 indicate segments immediately after apnea–hypopnea termination. The duration of each segment is 5 s.

FIGURE 2

Flow diagram of EEG data processing. RLS, recursive least squares; WTD, wavelet threshold denoising; PSD, power spectral density; STE, symbolic transfer entropy; PAR, posterior-to-anterior ratio; IF, information flow.

FIGURE 3

Significant changes in spectral power across respiratory events. (A) Absolute and (B) relative power. Red and blue dots indicate a significant increase and decrease compared to B1, respectively.

FIGURE 4

Significant changes in STE across respiratory events. The red and blue arrows indicate STE significantly higher and lower than that during B1, respectively.

FIGURE 5

Changes in interhemisphere and intrahemisphere average information flow in gamma band across respiratory events. IF, information flow. *p < 0.05/$C_6^2$, **p < 0.01/$C_6^2$, ***p < 0.001/$C_6^2$, Friedman test with Bonferroni correction.

FIGURE 6

Changes in posterior-to-anterior information flow across respiratory events. *p < 0.05/$C_6^2$, **p < 0.01/$C_6^2$, ***p < 0.001/$C_6^2$, Friedman test with Bonferroni correction.