Please click on the test that you would like to read about:

EEG (Electroencephalography)
Evoked Potentials (SEP, SSEP, AEP, BAEP, AER, VEP, VER, PVEP, FVEP)
EMG and/or NCS (Electromyography, Nerve Conduction Study, NCV, Nerve Conduction Velocity Testing
Sleep Study (Polysomnography; other studies include MSLT, Nap Study, CPAP Titration) 

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Sleep Study, Polysomnography, MSLT, NAP Study, CPAP, CPAP Titration

What is an Sleep Study?
What does it measure?
Is there any preparation?
How is it done?
Is it painful?
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What is a Sleep Study?

A sleep study is a test to monitor the body's function during sleep.  As with EEG, you cannot tell what a person is dreaming, or thinking, but we can tell that a person is dreaming and/or sleeping. 

There are different types of sleep studies, also known as polysomnography.  A standard overnight study is commonly used to determine the presence of absence of sleep apnea or hypopnea.  (These are disorders of breathing)  Overnight testing may also be used to check for the possible presence of several types of parasomnias (sleep abnormalities), including nocturnal seizures, possible causes of insomnia, etc. 

MSLT, or multiple sleep latency test, is a test specifically designed to assess for the diagnosis of narcolepsy (sometimes referred to as "sleeping disease".) 

The term "nap study" is usually reserved for a test which occurs during the daytime.  While some laboratories utilize this type of testing as a front line test for sleep apnea, it is widely considered to be of limited usefulness.  This is because a person with a borderline or normal daytime nap study may actually have an abnormal overnight study.  The one exception to daytime recording, however, is a person who routinely works the night shift, and has done so for  number of years. 

A so called sleep study with CPAP testing is a study done specifically for sleep apnea / sleep hypopnea. 

CPAP stands for "continuous positive airway pressure".  During this procedure, air is literally blown up the patient's nose, continuously.  A close relative of this procedure, known as Bi-PAP is a procedure which controls inhalation and exhalation.  This gives more complete control over the respiratory input/output processes, but it's use is not nearly as common, since it is unneeded in most cases. 

After ascertaining whether the condition exists, it is used to counter-act the sleep apnea.  It is only truly effective on purely obstructive apnea or hypopnea, but is also useful in cases of "mixed" apnea - in which not all of the apnea / hypopneas are caused by the collapsing of the throat. 

Titration is a term which is used to mean the adjusting of medication.  CPAP titration in this context means to adjust the pressure of the air in order to obtain the most beneficial results. 

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What Does a Sleep Study Measure?

 A sleep study shows the function of person as they sleep.  This is done by looking at several different parameters at the same time.  These parameters are:

  • EEG, or brain waves (electroencephalogram).  Brain waves show the function of the brain.  Whatever a person is thinking or dreaming cannot be told, but this does tell the technologist / physician what stage of sleep the person is in.  This is important because a particular pattern occurring at the wrong stage of sleep would be considered abnormal.
  • ECG, or EKG (electrocardiogram)  This is a reflection of the electrical function of the heart - some people think of them as "heart waves".  This shows the heart rate, as well as any abnormal beats of the heart, or irregularities that should be known about.
  • EMG (electromyography)  Myo meaning muscle, this is literally a way to look at the electrical function of certain muscles.  Are they being used, and if so, when and how hard?  Usually, the chin and legs are measured.
  • Pulse Oxymetry / Oxymetry  This measures the amount of oxygen in the blood stream.
  • EOG (electro-oculogram)  The amount and direction of eye movement are measured.  This helps to assess the stage of sleep; and is very crucial for trying to judge Rapid Eye Movement sleep (R.E.M.), which should happen only during sleep.
  • Nasal/Oral Respiration: This measures the amount of airflow through the nose and mouth.
  • Abdominal/Thoracic Respiration: Also known as abndominal/thoracid respiratory effort, this shows the amount of "effort" by the patient in breathing.  This is used in assessing the respiration patterns during sleep.
  • CO2  Considered very important in neonates and infants only, this measures the amount of carbon dioxide in the blood stream.  Customarily this is not done in adults.

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Is There Any Preparation for This Test?

Yes.  The person being tested should wash their hair, and leave it clean and dry, putting NO CHEMICALS back into the hair or scalp.  Also, don't use vaseline, lotion, or oil on the face, hands, and legs.  Make sure that any fingernail polish  has been removed!

Some laboratories have a VCR in them, and invite their patients to bring movies.  The person being tested should wear something comfortable to sleep in.  Remember you will be on camera while in the laboratory, and sound in the room will also be recorded.  Children may want to bring their favorite snuggling toy, such as a "teddy bear." 

If the person being tested is coming for to check on a possible diagnosis of narcolepsy, this person may be in the laboratory for 18 hours.  This test also requires staying awake for different periods of time.  Most laboratories has a TV, but in any case, bring something to do that will not make yourself bored or sleepy.

You should also bring things to aid in personal hygiene, to use before departing the laboratory: shampoo, toothbrush, special facial soap, etc.

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How is a Sleep Study Performed?

A number of electrodes are either or pasted or glued to the scalp.  The number is variable, depending on the laboratory protocol, the laboratory director, and the purpose of the test.  Before applying the electrodes, the technologist may or may not measure the patient's head and mark it.  Before applying the electrodes, though, a gritty solution will be rubbed on various points on the scalp, where the electrodes are to be placed.  

Other electrodes / wires will also be placed.  The number and placement of these vary somewhat from laboratory to laboratory.

In order to monitor eye movement, there will be more than one electrode placed next to the eyes.  There will be at least 1 next to each eye. 

Leads will also be placed on the chin, usually just underneath.  The exact placement may vary from this.  These measure the muscle tension in the chin muscles.  Leg muscles will also be monitored; 1 or 2 leads will be placed, usually using both legs.

For monitoring the heart, two electrodes will be placed on the chest.

A sensory will be wrapped around the tip of one of the fingers, or slipped over the end of one of the fingers, depending on what type of sensor is being used.

A sensor will be placed to monitor the person's nasal / oral airflow, there will also be belts placed around the (usually) the thorax, and another around the abdomen.

For certain procedures, and mask may be placed, usually over the nose (although there may be cases where one is placed over the nose and mouth.)  A mask placed only over the nose is referred to as a CPAP mask (Continuous Positive Airway Pressure).  This may happen either at the very beginning of the test, or part way through, or not at all.  Some people tolerate this mask better than others.  It is advised that each person being tested try it, at least for several hours.

A further note about CPAP masks.  Occasionally, the person being tested may hear the word "Bi-PAP".  This referrs to the way the mask operates.  In CPAP, the air pressure goes only one way - toward the patient.  In Bi-PAP, pressure support is used for both inhalation and exhalation.

Below are specifics for each type of test.

Routine Overnight Polysomnography (Sleep Study)
All the electrodes / sensors listed above will be used, esxcept the mask noted.  The test usually lasts about 8 hours, after the set-up, and not including "take down."  It may be that the person being tested has a breathing problem, in which case the following test may be performed.

Split-Night Sleep Study With CPAP
This test is the same as the one above, but has the following difference.  If the person being tested has a breathing problem when they go to sleep, the mask noted above may be placed over the nose; but this would happen after at about 1 - 2 hours..  Air then flows through the mask into the patient's nose.  The air will be started at a very gentle flow, and then will be gradually increased during the test.  

Overnight Test Sleep Study With CPAP Titration
This is actually the same as a split night, except that the CPAP mask (the mask which blows air into the patient's nasal passage) will be used from the beginning.  The air pressure will be adjusted throughout the night.  The physician will determine from this test what pressure should be used to best help the patient breathe during regualar use.