Sleep disorder centers and sleep labs use subjective tools such as patient interviews, questionnaires, and sleep diaries, as well as a range of objective tests, including:
PSG is a diagnostic test that requires the patient to sleep in the lab overnight while their sleep behavior is monitored via sensors placed on their body. The sessions are monitored by a technician and usually are recorded on video. PSG monitors a number of physiologic variables during both sleep and wakefulness, including:
- Brain electrical activity, measured by electroencephalogram (EEG)
- Eye movements, measured by electrooculogram (EOG)
- Chin muscle tonus, measured by electromyogram (EMG)
- Leg movements, to assess periodic limb movements (PLM)
Respiration, to assess breathing abnormalities during sleep, including:
- Chest and abdominal movements
- Airflow through nose and mouth
- Oxygen saturation
- Snoring sounds
- Heart rate, measured by electrocardiogram (EKG)
- Behavior, monitored by infrared recording.
If nocturnal epilepsy or another sleep disorder is being assessed, a full clinical EEG montage of at least 16 EEG channels may be recorded.
Multiple Sleep Latency Test (MSLT)2, 3
In an MSLT is a “napping” test, in which the individual’s brain electrical activity, eye movements, and changes in chin muscle tonus are recorded during 4-5 daytime rest periods, each lasting 20 minutes, spaced 2 hours apart. Both sleep latency (how fast a person falls asleep) and types of sleep are recorded to measure the patient’s degree of daytime sleepiness and the presence or absence of rapid eye movement (REM) periods at sleep onset.
Normally-alert adults take an average of 12 minutes to fall asleep on the MSLT. A patient that consistently falls asleep in less than 5 minutes is deemed to be “pathologically sleepy.” This sleepiness may be stem from the patient lacking time to sleep or from disturbed sleep (i.e., due to restless legs syndrome or disordered breathing).
Maintenance of Wakefulness Test (MWT)
The MWT is a variant of the MSLT; it measures the individual’s ability to stay awake under conditions that would usually cause sleepiness. For the MWT, patients typically sit in the dark for 20 or 40 minutes in 2-hour increments throughout the day. To be deemed to be “adequately alert,” an individual must be able to stay awake for an average of at least 11 minutes during the MWT. More than 75 percent of normal adults can stay awake for the MWT’s entire 40 minutes.
The MWT helps assess whether an individual’s inability to stay awake risks compromising either his or her safety or someone else’s (i.e., inability to stay awake while driving). The MWT is also used to assess treatment for excessive sleepiness, like the use of stimulant medications.
A wrist actigraph is a small watch-like device that monitors wrist movements throughout the patient’s routine daily activities over a one- to two-week period. The wrist actigraph stores the frequency of the person’s arm movements per minute, and then analyzes the movements to estimate time spent sleep vs. awake. (It uses the fact that we move less when we are asleep than when we are awake.) Wrist actigraphy provides a fair (although not exact) measurement of when, and for how long, a patient sleeps. (See Figure 1.9.)
Figure 1.9: Characteristic wrist actigraph summary5
- Kushida CA, Littner MR, Morgenthaler T, et al. Practice parameters for the indications for polysomnography and related procedures: An update for 2005. Sleep. 2005;28:499-521.
- Arand D, Bonnet M, Hurwitz T, Mitler M, Rosa R, Sangal RB. The clinical use of the MSLT and MWT. Sleep. 2005;28:123-144.
- Littner MR, Kushida C, Wise M, et al. Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test. Sleep. 2005;28:113-121.
- Sadeh A, Sharkey KM, Carskadon MA. Activity-based sleep-wake identification: an empirical test of methodological issues. Sleep. 1994;17:201-207.
- Hauri P. Current concepts: the sleep disorders. 2nd ed. Kalamazoo, MI: The Upjohn Company; 1982.