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Review
. 2014 Jan;35(1):R1-57.
doi: 10.1088/0967-3334/35/1/R1. Epub 2013 Dec 17.

A Review of Signals Used in Sleep Analysis

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Free PMC article
Review

A Review of Signals Used in Sleep Analysis

A Roebuck et al. Physiol Meas. .
Free PMC article

Abstract

This article presents a review of signals used for measuring physiology and activity during sleep and techniques for extracting information from these signals. We examine both clinical needs and biomedical signal processing approaches across a range of sensor types. Issues with recording and analysing the signals are discussed, together with their applicability to various clinical disorders. Both univariate and data fusion (exploiting the diverse characteristics of the primary recorded signals) approaches are discussed, together with a comparison of automated methods for analysing sleep.

Figures

Figure 1
Figure 1
Excerpt of synchronous oxygen saturation (SpO2), heart rate (HR), electrocardiogram (ECG), photoplethysmogram (PPG) and impedance pneumogram (IP) tracings during an apnoeic event from a neonatal subject from the MIMIC II database (Saeed et al. 2011, Goldberger et al. 2000b). A cessation of respiration can be observed in IP at t = 10 s, followed by bradycardia (drop in HR) around 20 s later and by an abrupt drop in oxygen saturation starting around t = 36 s.
Figure 2
Figure 2
Excerpt of audio for an apnoeic patient over 4 min. There are corresponding reductions in airflow, changes in HR and PPG as well as oxygen desaturations that are out of phase with the cessation of breathing. AU = arbitrary units.
Figure 3
Figure 3
Excerpt of body movement over the course of three days, with corresponding light levels.
Figure 4
Figure 4
Simultaneous rest-activity and ambient light exposure (yellow, in lux) patterns derived from 3 weeks wrist activity monitoring of a 35 year old woman during ordinary home/work conditions. The actogram shows clear entrainment to the day-night cycle but with early morning awakenings. Actigraphic data are 48-hour double plotted with successive days on vertical axis. Activity recorded with a 1-minute epoch using Actiwatch-L with integrated light sensor. (unpublished data of K. Wulff)
Figure 5
Figure 5
Excerpt of the ECG of a healthy subject over 25 s. The R peaks have been calculated, along with the corresponding HR and EDR.
Figure 6
Figure 6
Spectrogram of EDR-RSA coherence (upper plot), and equivalent wavelet cross spectral coherence (lower plot) for the same overnight RR tachogram for a chronic heart failure patient. Note both signals are normalised to the interval [0 1] and frequencies ≥ 0.5 Hz are not considered because the average HR is ~60bpm (1 Hz). The wavelet approach also includes a bounding region inside which significant coupling is detected, and arrows to indicate phase of the coupling, with EDR leading RSA for right pointing arrows.
Figure 7
Figure 7
Three axis measuring tilt. Adapted from (K. Tuck 2007).

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