Concerned over their patients getting adequate sleep, medical professionals have developed an arsenal of tests to help them fine-tune sleep disorder diagnoses.
One example is the multiple sleep latency test (MSLT), which tests for excessive daytime sleepiness. Other sleep studies doctors often order include:
- polysomnography (PSG), an overnight test that monitors sleep cycles and sleep stages
- CPAP titration, an overnight test to determine proper CPAP pressure for people using a continuous positive airway pressure (CPAP) unit
- split night study, which combines PSG and CPAP titration tests to look for severe obstructive sleep apnea
- maintenance of wakefulness test (MWT), a full-day test to measure how alert and awake a person is in a stimulation-free environment.
Usually performed directly following a PSG, an MSLT — often referred to as a nap study — measures how long it takes you to fall asleep in a quiet environment during the day.
Testing lasts all day and includes five naps scheduled two hours apart.
If you fall asleep, you’ll be awakened after you sleep for 15 minutes. If you don’t fall asleep within 20 minutes, that nap will be ended.
To monitor when you are asleep, awake, and in REM (rapid eye movement) sleep, you will have sensors placed on your head and face.
Commonly, video and audio of your naps will be recorded and the following monitored:
- your heart’s electrical activity via electrocardiogram (EKG)
- your brain’s electrical activity via electroencephalogram (EEG)
- oxygen levels
- eye movements
- extremity movements
If you’re sleepy during the day for no apparent reason or you find yourself sleepy in situations when others are alert — such as at work or while driving — you could be a good candidate for an MSLT.
Your doctor might recommend an MSLT if they suspect you have narcolepsy (a neurologic condition resulting in excessive daytime sleepiness) or idiopathic hypersomnia (excessive sleepiness without cause).
In each of your five opportunities to sleep, how fast you fall asleep (latency) will be measured. How quickly you reach REM sleep will also be measured.
A mean latency below eight minutes and REM sleep achieved in only one nap could potentially indicate idiopathic hypersomnia.
A mean latency below eight minutes and REM sleep achieved in only two naps could potentially be due to narcolepsy.
Falling asleep when you should be alert has obvious negative consequences. If you can’t stay awake at work or while driving a car, there could be serious repercussions.
If you find yourself excessively sleepy when you should be awake and alert, contact your doctor. If they feel it’s appropriate, they will recommend a sleep specialist to conduct and interpret a sleep study that might include a PSG and an MSLT.