When you visit a sleep clinic for a sleep study, your doctor may arrange for you to have a Multiple Sleep Latency Test (MSLT) the following day.
This test is used to measure the level of sleepiness you are experiencing.
What to Expect
A MSLT is usually done following a normal sleep study. This is convenient since you will already be at the clinic, wired up and ready to go. The same measurements that are taken during a sleep study are also recorded during the latency test.
This test will take a good part of the day since you will have 4 or 5 naps at 2 hour intervals during the day. When you are not in the nap period you are disconnected from the computer and can wander about, read, watch TV, etc.
But when nap time comes you are reconnected to the recording computer and settle in for a 20 minute nap.
You will also be asked to fill out a survey before and after the nap period to describe how you feel.
What is Sleep Latency?
A mulitple sleep latency test is measuring sleep onset latency (or sleep latency). This is a measure of the time between lying down to sleep and actually falling asleep. The lower this time is, the higher your fatigue level.
A sleep latency of more than 15 minutes is considered excellent (20 minutes is fully alert). If your latency is under 10 then you are considered to be fatigued. Under 5 minutes is severe.
When I had my first MSLT I was asleep in under 1 minute for all 4 rest periods. It was a confirmation of how I had been feeling for years.
Variation of the Test
The sleep clinic where I was originally diagnosed had a variation of the multiple sleep latency test that I also underwent. This was on a second day following a second sleep study.
In this variation rather than lying in bed and trying to nap, I was sitting in a chair while trying to stay awake. The room was darkened and no distractions were allowed. Once again, there were 4 tests of 20 minutes each that were spaced every 2 hours. It should be no problem to stay awake for the 20 minutes for a person who is not fatigued.
The idea of this test was to see how well I could stay awake without any stimulation. You probably won’t be surprised to hear that I managed to stay awake for almost 5 minutes on the last test (it was under 2 for the other 3 tests).
Not all sleep clinics will use this variation, but it can be useful to test how well you are able to keep yourself awake in a low stimulus situation. That is also a good indication of your fatigue level.
If you want to get an idea of your fatigue level, you can try this at home. Obviously you won’t be able to monitor the activity of your brain, heart, etc. like a sleep lab could. But you can determine your sleep onset latency.
Set yourself up in bed comfortably where you can see a clock. Hold a spoon or similar object in your hand and dangle it over the side of the bed. You can put something under the spoon so that it will make a loud noise when it falls (a pot would be good).
Note the time that you start trying to sleep. When you do sleep the spoon should fall from your hand and wake you up. Look at the clock and see how much time has elapsed.
Once again, this is not a substitute for a proper sleep study and MSLT, but it allows you to assess your fatigue levels.