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Multiple Sleep Latency Test

The Multiple Sleep Latency Test (MSLT) is a nap study. It is used to see how quickly you fall asleep in quiet situations during the day. The MSLT is the standard way to measure your level of daytime sleepiness. Excessive sleepiness is when you are sleepy at a time and place when you should be awake and alert.

The study is based on the idea that you should fall asleep in a shorter amount of time as your feeling of sleepiness increases. The MSLT charts your brain waves and heart rhythm and records your eye and chin movements. The study also measures how quickly and how often you enter the rapid-eye-movement (REM) stage of sleep, also called “dream sleep”. Results of the nap study are routinely used to detect sleep disorders.

What to Expect

The daytime nap study is taken right after you do an overnight sleep study. For the MSLT to be accurate, you should have had a total sleep time of at least six hours during the overnight sleep study.

The MSLT consists of five nap opportunities with two hours between each. A shorter four-nap study may also be used. But the five-nap version is more reliable at detecting narcolepsy. The first nap trial begins between one and a half and three hours after you wake up from the overnight sleep study. You will be given a light breakfast at least one hour before the first nap trial.

For each nap trial, you are asked to lie quietly in bed and try to go to sleep. Then the lights are turned off. Once the lights are out, the test will measure how long it takes you to fall asleep. Each trial will end if you do not fall asleep within 20 minutes. If sleep does occur, it will be allowed for 15 minutes. Then after 15 minutes, you will be awakened. Between nap trials, you will have to stay out of bed and occupy yourself so that you remain awake. A light lunch should be provided right after the end of the second (noon) trial.

After the last nap trial, you will be free to go.