Maintenance of Wakefulness Test

The Maintenance of Wakefulness Test is used to measure how effective therapies are.  The result of the test is the sleep latency time.  If the therapy is trying to lower excessive daytime sleepiness, the goal is to have the sleep latency be high.  If the goal is to keep people awake when they would otherwise be sleeping (e.g. military applications, certain jobs), the goal is to keep the sleep latency high.

In a comprehensive sleep diagnostic regimen, the MWT is done the morning after the nighttime polysomnogram, although the MWT is sometimes given as a stand-alone test. The subject of the test sits upright in bed with electrodes connected to his/her body.  Measurements include any or all of: EEG (for measuring brain waves), electrooculography (for measuring activity on the retina), electromyography (for measuring muscles on the head), and electrocardiography (for measuring heart activity).  The room is kept dark.  Usually a technologist can look in through a video remote. When the subject falls asleep, the total time to get to sleep (sleep latency) is recorded, and the technologist awakens the subject usually within a couple minutes.

Medical practitioners who use the MWT generally consider 40 minutes the maximum they will measure.  If the subject does not fall asleep, the test is ended. People who can keep awake that long are considered at very low risk of becoming drowsy.  The shortest time is 8 minutes.  If sleep latency is 8 minutes or less, the person is essentially on verge of sleep.  If sleep latency is only this low a few hours after normal wake-up time, the person is considered likely to have a sleep disorder.  A doctor uses this result to make a diagnosis.

Related: sleep diaries

The Sleepdex book is now available on

Click here