Daytime Fatique Studies

Multiple sleep latency test (MSLT)

A multiple sleep latency test or MSLT is a key study in the diagnosis of abnormal daytime fatigue and excessive sleepiness diseases (narcolepsy and hypersomnia). It can also be used to monitor the effect of therapy on a diagnosed sleep disorder such as sleep apnoea.

During the two weeks preceding an MSLT examination, the patient keeps a sleep diary. Also, in many cases, an actigraphy is performed. The patient should sleep for at least six hours the night preceding the examination and, in many cases, this is ensured with sleep registration or extensive polysomnography (link) performed at home.

Before the test begins, the patient should be awake for at least 1.5 hours. The referring physician may provide some instructions regarding the gradual ending of some pharmaceuticals affecting alertness. Since consumption of coffee during the examination day is forbidden, heavy intake of coffee should be reduced during the week preceding the examination.

The examination includes four partial registrations every two hours during the working day. These measure the EEG or electrical activity of the brain, eye movements, muscle tone, respiration and ECG. The examination is painless. The patient is placed in a dark, quiet room in a recumbent position and is asked to close his or her eyes and try to fall asleep. A partial registration takes 20 to 40 minutes.

The examination monitors sleep latency, occurrence of different sleep phases and possible respiratory disturbances. In the case of excessive sleepiness diseases, the average sleep latency is shortened and the patient can fall very quickly into rapid eye movement (REM) sleep. There are no contraindications for the examination, but careful adherence to the instructions is crucial for the success of the study.

Maintenance of wakefulness test (MWT)

A maintenance of wakefulness test or MWT is a key study in determining the work capacity of a person and, in particular, the driving capacity of a professional driver suffering from daytime fatigue. It can also be used to monitor the effect of therapy in sleep apnoea, for instance.

During the two weeks preceding the MWT, the patient keeps a sleep diary and makes an attempt to sleep normally. Before the test begins, the patient should be awake for at least 1.5 hours in the morning. The referring physician may give some instructions regarding the gradual reduction of some pharmaceuticals affecting alertness. Since consumption of coffee during the examination day is forbidden, heavy intake of coffee should be reduced during the week preceding the examination.

The examination includes four partial registrations every two hours during the working day. These measure the EEG or electrical activity of the brain, eye movements, muscle tone, respiration and ECG. The examination is painless. The patient is placed in a dark, quiet room in a semi-sedentary position and is asked to keep his or her eyes open and try and stay awake as long as possible. A partial registration takes 40 minutes at most.

In addition to possible respiratory disturbances, the test monitors the decrease in alertness and sleep latency. In connection with the abnormal daytime fatigue, the patient’s average sleep latency is shortened. There are no contraindications for the examination, but careful adherence to the instructions is crucial for the success of the study.
 

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