Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 257

CHAPTER 10
Quantitative Sleep Monitoring

Paul R. Carney, Nicholas K. Fisher, William Ditto, and James D. Geyer

Sleep is a major part of everyone's life and has been studied thoroughly. Sleep is
made up of nonrapid eye movement (NREM) sleep and rapid eye movement (REM)
sleep. NREM sleep is further broken down into four stages. In this chapter, we dis-
cuss much of the terminology used in polysomnography as well as some of the tech-
niques and issues involved in recording polysomnographic data. The physiological
characteristics measured by the polysomnograph as well as how they differ
throughout the various sleep stages are explained as well. In addition, some of the
quantitative characteristics of the polysomnograph are discussed. Techniques that
try to automatically detect the sleep stage based on these quantitative characteristics
are also expounded upon. Finally, we delve into examples of sleep-related disorders
and their causes.

10.1 Overview of Sleep Stages and Cycles

Sleep is not homogeneous and is characterized by sleep stages based on EEG or elec-
trical brain wave activity, EOG or eye movements, and EMG or muscle electrical
activity [1-3]. The basic terminology and methods involved with monitoring each
of these types of activity are discussed below. Sleep is composed of NREM and
REM sleep. NREM sleep is further divided into stages 1, 2, and 3/4. Stages 1 and 2
are called light sleep , and stages 3 and 4 are called deep or slow-wave sleep . During
the night there are usually four or five cycles of sleep, each composed of a segment
of NREM sleep followed by REM sleep. Periods of wake may also interrupt sleep.
As the night progresses, the length of REM sleep in each cycle usually increases. The
hypnogram (Figure 10.1) is a convenient method of graphically displaying the orga-
nization of sleep during the night. Each stage of sleep is characterized by a level on
the vertical axis of the graph, with time of night on the horizontal axis. REM sleep is
often highlighted by a dark bar.
Most sleep recording is performed digitally, but the convention of scoring sleep
in 30-second epochs or windows is still the standard. If there is a shift in sleep stage

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