Murray W Johns, Chapter 2 In: Sleep Deprivation: Causes, Effects and Treatment ISBN: 978-1-60741-974-7 Editors: Pedr Fulke and Sior Vaughan
Introduction
It is commonly recognized that sleep deprivation causes an increased tendency to fall asleep; that is, it causes an increase in the sleep-deprived person’s sleep propensity. Their increased sleep propensity may reach a level that causes excessive daytime sleepiness (EDS).
According to one current definition, EDS is “sleepiness in a situation when an individual would be expected to be awake and alert” [1] . EDS is not a disorder. It is a symptom that can have many different causes, not only sleep deprivation. EDS is a very common symptom among patients who present to sleep clinics around the world. Unfortunately, the concepts of “sleepiness” and EDS have not been well developed and the methods used for their measurement, including both subjective and objective methods, remain a matter of contention [2].
Before we can define what EDS is, we must be able to say what “sleepiness” is and how we can measure it. What follows in this Chapter is an attempt to answer the question “what is excessive daytime sleepiness?” This requires an examination of the basic assumptions behind the current view of EDS, many of which are implicit rather than explicit. There is evidently a need for some new definitions and a broader frame of reference within which to consider “sleepiness” before we can define EDS. A new conceptual model of sleep and wakefulness is outlined that recognizes major influences on “sleepiness” derived from the combined effects of sensory inputs to the central nervous system [3]. They have not been included in other models. The methods that are commonly used, and several others that have been proposed for measuring “sleepiness” are then described within this new conceptual framework As others have commented, it is very difficult to discuss EDS meaningfully without a clear understanding of what it is and how it can be measured [2]. Our first task therefore is to clarify those issues. We shall not be concerned here with the epidemiology of EDS or the disorders that cause it. The contents of this Chapter are based largely, but not exclusively, on the published work of the present author. This involves several terms and concepts that are new to sleep medicine, some of which may still be considered hypothetical.
