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For Patients - Sleep Studies

Following is a list of sleep studies performed by the experts at Desert Pulmonary and Sleep Consultants.


Polysomnography is the medical term for a sleep study. The purpose of the test is to determine what, if anything, is abnormal with a person’s sleep. In order to monitor the sleep, small metal cups connected to wires are affixed to the patient’s scalp, face and chin. These cups (called electrodes) conduct signals from the body to a series of filters and amplifiers, and a computer then displays graphic waves that represent these body signals. Technologists with years of training are able to interpret these signals to determine if you are awake, drowsy, or in dreaming or deep sleep. The signals are monitored throughout the study (which typically takes 7 to 8 hours), and the technologist (either during the study or after it is completed) will mark the sleep “stage” every thirty seconds on the recording as well as any disruptions from normal sleep.

At the same time, several different sensors monitor your breathing. A small wire or tube placed in front of the nose senses air movement, while elastic belts around the stomach and chest sense expansion, indicating breathing effort. A tiny flat microphone or vibration sensor taped to the neck detects snoring, and a plastic finger clip or wrap around the finger determines oxygen levels by measuring light absorbed by the blood vessels.

Small sticky plastic patches are placed below the shoulders and on the ribcage to monitor heart rate and rhythm (EKG). Another set of patches is placed on each of the lower legs to detect muscle twitches or foot/leg movements. All of these sensors are amplified, filtered and displayed the same as those for detecting sleep. A video camera and microphone/speaker is also installed so the technologist can observe your movements and communicate with you. The technologist will examine the signals from every one of these monitors throughout the study and mark or notate anything out of the ordinary.

(The sensors and electrodes are attached in such a manner that you can still move around, and even get up without removing everything, but it is best to ask the technologist to assist you to prevent injury or equipment damage.)

It is important to understand that a polysomnogram is a medical procedure, and you will probably not experience a completely normal night’s sleep. The technologists and physicians recognize this, and are only looking for things that are irregular – they have studied many people without sleep problems and know what is “normal” for the sleep laboratory.

Once the study is completed, the technologist will prepare a summary of the findings. A physician trained and certified in sleep medicine will then review the entire study and the technologist’s notes and summary before making a final diagnosis. This physician will also recommend treatment if any is necessary, but it is usually up to your own doctor to actually provide this treatment.

Polysomnography is almost always covered by private insurance, as long as your doctor has documented an appropriate need for testing. This might include obstructive sleep apnea, nocturnal hypoventilation (insufficient breathing), low oxygen levels at night, narcolepsy, unexplained daytime sleepiness, violent or excessive body movements while asleep, nocturnal chest pain or arrhythmias (unusual heart rhythms), or waking up choking or gasping. The procedure is usually not covered to test for insomnia, sleep talking or nightmares

 Continuous Positive Airway Pressure

CPAP stands for Continuous Positive Airway Pressure. It is the most effective treatment for obstructed breathing during sleep. Small amounts of air are applied to the nose by a mask strapped over the head or a forked tube in the nostrils. The air is supplied through a plastic hose connected to a book-sized blower at the bedside. The air does not contain any more oxygen than normal air, but it is at slightly higher pressure (about 1/30th that of an aquarium pump.) For those who cannot breathe through their mouth, or can only breathe through nose and mouth, larger masks are available.

Since breathing control is very sensitive, it is important to determine the correct amount of pressure to relieve the obstruction. Too little, and the airway will close off, resulting in lower oxygen levels, heart strain and other serious complications. Too much pressure can affect the body’s chemical sensors and actually produce more pauses in breathing. The technologist will generally start the pressure at the lowest comfortable setting and increase it gradually while you are asleep. Besides correcting oxygen levels and breathing pauses, the optimum pressure will help restore normal sleep patterns and decrease disruptions. This technique may require some trial and error, so it is important that the technologist has adequate time to perform this procedure.

Once the ideal pressure has been determined (and reviewed by a doctor), a prescription can be written for a home device to be used while sleeping. A large number of mask types are readily available, and they are all interchangeable with any machine. Your own doctor can help you find a company that provides and maintains these devices.

 Bilevel PAP

Bilevel PAP (Positive Airway Pressure) is similar to CPAP. It uses the same masks and hoses, and the machines look similar as well. With bilevel PAP, the pressure you breathe in is higher than the pressure when you exhale.

There are essentially two different reasons to use bilevel PAP instead of CPAP: Some people may find that the pressure required to keep the airway open makes it difficult to exhale. As long as the pressure is high enough while breathing in, a lower pressure can be used while exhaling. A bilevel Pap machine allows the two pressures to be different.

The more common use of the bilevel PAP machine is in treating non-obstructive breathing disorders. By breathing in more pressure than you exhale, it is sometimes possible to regulate the depth and frequency of breathing. In addition, these devices often have other settings to help control the size and regularity of each breath, both inspiration and expiration.

The bilevel PAP machines are not for everyone: they are many times more expensive than CPAP, and they are unnecessary if breathing is primarily obstructive and the pressure is well tolerated (which is usually the case.) A bilevel study is conducted the same way as a CPAP study, but it is typically much more difficult to find the correct settings. Patience, adequate time and a very experienced technologist are necessary to find optimal pressure settings. Oft times, more than one study may be necessary to provide sufficient time and exposure to all body positions and stages of sleep. In some patients, bilevel PAP alone may not be sufficient to treat all nighttime breathing problems. Your physician may need to order additional therapies to manage your breathing.

 Split Night

In order to save time (and often money), a split-night study is sometimes ordered. The first half of the test is the same as a normal polysomnogram (see above). If significant obstructive breathing (apnea) is noted during this time, a mask is applied to the nose and the test continues as a CPAP study (see above). Under ideal conditions, this takes the place of two separate tests. In reality, however, this test is often inconclusive. Regulations require that you sleep for at least two hours before the CPAP is applied, and demonstrate a large number of obstructed breathing events before beginning treatment.

Because of the strange environment and the anxiety sometimes associated with testing, it may take longer than usual to fall asleep, or you may awaken for some time. As a result, it may take a number of hours before two hours of sleep have occurred. This leaves less time to perform the CPAP procedure. After being awakened to begin the CPAP procedure, it may take some time to adjust and return to sleep, further limiting the ability to find an adequate pressure. In addition, the breathing events may only occur later in the night, during specific stages of sleep, or only in certain body positions, usually while flat on your back.

It may take the entire study before sufficient data has been documented to qualify for treatment. Because of this, many “split-night” patients have to return to the sleep center for a second night of (CPAP) therapy anyway.

 MSLT (Multiple Sleep Latency Test)

The MSLT is a test for excessive sleepiness. If left alone in a dark, comfortable, quiet bed long enough, anybody will fall asleep. A well rested person, however, will usually take a significant amount of time (more than 15 to 20 minutes) before succumbing.

After spending the night in the sleep lab and undergoing a polysomnogram to rule out any obvious sleep disturbance, the MSLT patient awakens as usual and goes about their morning routine (breakfast, usual medications, get dressed, etc.). About an hour later, the patient is asked to get back into bed (some of the sensors are left in place or reattached.) The lights are turned out and the patient is instructed to try to nap. A short time later, the patient is asked if they think they fell asleep. Their perception is recorded, as is the brain activity during the test. The patient is then asked to get up and resume normal activities. (Caffeinated coffee and other stimulants are sometimes prohibited during this test.) This procedure is repeated every two hours for four or five trials (depending on the length and depth of the patient’s sleep.) After the final trial, the sensors are removed and the patient is free to leave. The entire procedure takes nine or more hours to complete.

Falling asleep on one or more naps is not unusual, but the sleepier you are, the quicker and more often you will fall asleep. The technologist is also looking at the depth (or stage) of sleep or wake every thirty seconds. Dreaming sleep (REM) during these short trials is unusual, and may signify a disorder such as narcolepsy. (Note: You may experience dreams during sleep, but not be in REM sleep. The brain waves can distinguish the difference.)

 MWT (Maintenance of Wakefulness Test)

The MWT is designed to test the ability of a person to stay awake when all stimulation has been removed. The test is conducted by attaching the same sensors used for the MSLT test (above). The patient is then asked to sit in a comfortable lounger or sit up in bed. The lights are dimmed and the door is closed. The patient is then asked to remain awake without any stimulation for forty minutes (no reading, television, singing to yourself, wiggling your feet, etc.) The trial ends when the patient falls asleep or after forty minutes. The patient is then free to resume normal activities. This is repeated every two hours for a total of four trials.
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