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Sleep disorders are prevalent in American society. The National Commission on Sleep Disorders Research estimates that almost 20% of adults suffer from chronic sleep disorders and that an additional 10% suffer from intermittent sleep disorders. Sleep disorders have been linked to over 100,000 automobile accidents yearly with nearly 1500 fatalities and 75,000 injuries annually. They may also be responsible for up to 30% of commercial truck driving accidents. It has been estimated that chronic sleep deprivation costs $15 billion annually in direct medical expenses and an estimated $70 billion in lost productivity.
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Although there are many disorders of sleep, this chapter deals specifically with sleep-disordered breathing because it is referable to the otolaryngologist.
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Classification of Sleep & Sleep Disorders
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Sleep is a reversible physiologic and behavioral state that manifests as decreased awareness and reaction to external stimuli. Normal sleep architecture comprises two distinct phases: NREM (non-rapid eye movement) sleep which comprises 75–80% of sleep and occurs in four stages (Stages I–IV), whereas REM (rapid eye movement) sleep which comprises 20–25% of sleep and occurs in two stages. In a normal adult, these two phases of sleep occur in semiregular cycles, which last approximately 90–120 minutes and occur three to four times per night.
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In the normal adult male, Stage I (N1) sleep, which is considered the transition to sleep, occupies 2–5% of sleep and is characterized by an increase in theta waves and a decrease in alpha waves on an electroencephalogram (EEG). Stage I sleep is also marked by a decrease in awareness and in muscle tone. Stage II (N2) sleep occupies 45–55% of sleep and is characterized by K-complexes and spindles on EEG as well as decreases in muscle tone and awareness. Stage II sleep is considered by most authorities to be the “true” onset of sleep. Stages III and IV (N3) sleep comprise deep sleep, and it occurs predominantly in the first third of the night. The hallmark of deep sleep is the abundance of delta waves on EEG. Stage III sleep occupies 3–8% of sleep, and Stage IV sleep occupies 10–15% of sleep. Stages III and IV are widely considered the most restful stages of sleep. With increasing age, deep sleep progressively occupies less and less of total sleep time.
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The remaining portion of sleep is composed of REM sleep, which is divided into tonic and phasic stages. During the tonic stage, the EEG becomes asynchronous and muscles lose tone. The phasic stage of REM sleep is characterized by rapid eye movements as well as erratic cardiac and respiratory patterns.
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Derangements in sleep are categorized by the American Sleep Disorders Association in the International Classification of Sleep Disorders (ICSD), which arranged sleep disorders into four ...