Role of the Sleep Laboratory in Clinical Sleep Disorders

Role of the Sleep Laboratory in Clinical Sleep Disorders

Psychiatrists can usually diagnose most sleep disorders by tra-ditional, simple but systematic clinical methods. Referral to a specialized sleep disorders center, however, should be consid-ered in patients suspected of having severe intractable insomnia, persistent excessive daytime sleepiness and sleep disorders due to a general medical condition (such as narcolepsy, REM sleep behavior disorder, sleep apnea, periodic limb movements in sleep [PLMS], or sleep-related epilepsy). Specialists in sleep disorders medicine will evaluate the patient and, if necessary, arrange for sleep laboratory or ambulatory diagnostic procedures.

One of the most important and common laboratory exami-nations is all-night polysomnography, which typically records the EEG activity’s eye movements with the electrooculogram, and muscle tone with the electromyogram from the chin (submental) muscles. These measures are used to determine sleep stages visu-ally scored as 20- or 30-second epochs by a sleep technician. To evaluate sleep-related respiration and cardiovascular function, measures are made of nasal and oral air flow with a thermistor; of sounds of breathing and snoring with a small microphone near the mouth; of respiratory movements of the chest and abdominal walls; of heart rate with the electrocardiogram; and of blood-oxy-gen saturation with finger oximetry. To evaluate PLMS, an elec-tromyogram from the shin (anterior tibial) muscles is obtained. Other more specialized tests include intraesophageal pressures, which increase during the upper airway resistance syndrome if respiration is impeded, nocturnal penile tumescence in the evalu-ation of impotence and core body temperature (usually rectal or tympanic membrane).

Daytime sleepiness can be evaluated in the sleep labora-tory with the Multiple Sleep Latency Test, which measures sleep latency during opportunities for napping during the day (see Table 59.4). In addition, subjective sleepiness can be assessed by

a questionnaire, the Stanford Sleepiness Scale, in which the sub-ject rates sleepiness on a 7-point scale at set intervals throughout the day

.Two research laboratory procedures have been developed for experimental measurement of circadian phase in humans: the constant routine method for temperature and neuroendocrine secretions, and the dim light melatonin onset method for mela-tonin (see Table 59.2).

According to DSM-IV-TR definitions (American Psychiat-ric Association, 1994), primary sleep disorders are presumed to arise from endogenous abnormalities in sleep–wake-generating mechanisms, timing mechanisms, sleep hygiene, or conditioning, rather than occurring secondary to medical or psychiatric disor-ders. Two types of primary sleep disorders are defined: dyssom-nias (abnormalities in the amount, quality, or timing of sleep) and parasomnias (abnormal behaviors associated with sleep, such as nightmares or sleepwalking). In addition, sleep disorders may be related to other mental disorders, general medical conditions, and substance abuse.