A-phases consist of transient cortical events that normally occur during NREM sleep and can be observed directly in the EEG signals. One particular kind of A-phases, namely, A3-phases are related to arousals from sleep during which increased activity in other systems (such as the cardiovascular and respiratory systems) can also be observed. This study aims to characterize disruptions in the oscillations of the airflow signal during A3-phases of sleep. Spectral entropy was used to quantify the bandwidth of the airflow signal, which under baseline conditions (prior to an A3-phase) resembles a sinusoidal wave with a frequency of about 0.25 Hz and has low spectral entropy values. It was found that during most A3-phases the spectral entropy increases significantly in 70% of the test subjects. These changes occur with higher probability during A3-phases that are longer than 10s, suggesting a delay between the onset of an A3-phase and the effect it has on the respiratory system.
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