On the relationship of arousals and artifacts in respiratory effort signals

Arousals are vital and thus very important for healthy sleep. Physiologically they manifest in cardiorespiratory signals or body movements. Generally, the acquisition of such signals is much easier than with the standard electroencephalogram (EEG). In this work we visually analyzed respiratory effort (RE) signals acquired with a respiratory induction plethysmography sensor (RIP) during whole-night polysomnography (including sleep stage and arousal annotations done with EEG) and annotated the artifacts. Artifacts are present when a change or distortion of the respiratory signal occurs. In total, the data from 15 subjects were acquired in two different sleep laboratories. The performance of detecting arousals only with the use of artifacts was evaluated. Since arousal and artifact sections are not always aligned in time, arousals have been widened by detection windows of 15 s and 30 s around it. If one artifact is present within this window the arousal was marked as detected. Median detection rates using this new approach of 69.81%, 77.36%and 83.02% were achieved for the original arousals on 15 s and 30 s window expansion, respectively. It is shown that in average 40.7% of the artifacts belong to the wake state, reducing the capability of detecting arousals that occur by definition only during sleep. During sleep, much more artifacts than arousals are present in the rapid eye movement (REM) stage, which is related to the fact that respiration is much more irregular during REM than during non-REM sleep and thus leading to increased artifacts.