Sleep is a complicated function of the body. Most people spend about thirty percent of their lives sleeping. Sleep is primarily a function of the brain, however, several other organs function differently when we are sleeping. For example, muscle tone decreases during sleep, which can affect our breathing pattern. For this reason, studying sleep in a laboratory requires analysis of several systems and organs, including the brain, the eyes, the heart, the lungs and the muscles. A complete sleep study requires monitoring of all these systems, however, sometimes a simpler sleep study can be performed and may provide sufficient clinical information. The typical sleep study is performed in a specialized sleep laboratory where the patient spends the night. Sometimes, a follow-up test is performed during the day. Occasionally, sleep studies can be performed at home.
A polysomnogram, or sleep study, consists of an overnight test performed at a specialized sleep laboratory. The study typically starts in the evening and ends in the morning. Several bodily functions are monitored to assess the quality of sleep and look for sleep disorders. Brain waves, or EEG, muscle tone and eye movements are monitored to determine the amount and quality of sleep. Breathing is monitored by measuring the air flowing in and out of the lungs and by measuring the movements of the chest and belly. Monitoring breathing patterns helps determine if the patient suffers form sleep apnea. Oxygen saturation is also measured to help determine if the patient is receiving enough oxygen. Finally, leg movements are measured to determine if the patient suffers from a movement disorder during sleep, such as periodic limb movement of sleep or other types of movements during sleep. Once the test is completed, the sleep technologist and physician review the study and interpret the results. A polysomnogram is very safe and is not associated with any significant risk, except for the discomfort caused by sleeping in a strange bedroom with multiple wires connected to the body. Diagnostic Polysomnogram
A diagnostic plysomnogram consists of a sleep study as described above. The patient spends the night at the sleep lab and goes home in the morning, awaiting the interpretation of the study. Positive Airway Pressure Titration
If the diagnostic sleep study reveals that the patient has obstructive sleep apnea, treatment with continuous positive airway pressure (CPAP) is sometimes recommended. In this case, a repeat sleep study is necessary to determine the level of air pressure needed. The patient comes back to the sleep laboratory for a second study during which CPAP is started and the degree of air pressure is gradually increased to achieve the best results possible. The sleep technologist monitors the breathing pattern and blood oxygen level to determine the level of air pressure at which the patient achieves normal breathing and oxygen levels. At the end of the CPAP titration study, the physician and staff of the sleep laboratory help the patient obtain a CPAP machine at home and prescribe the recommended air pressure.
Occasionally, the diagnosis of sleep apnea and CPAP titration are performed in a single night. The study is called a split-night study. If the sleep technologist determines that the patient has definite obstructive sleep apnea, she/he may initiate CPAP titration and try to determine the best level of air pressure in the remaining time of the study. This usually spares the patient a second sleep study.
Multiple Sleep Latency Test
Multiple sleep latency test, or MSLT, also referred to as a "nap test", measures our tendency to fall asleep during the day. It is usually performed after an overnight sleep study. The patient stays in the sleep laboratory until late afternoon and is asked to try to nap either four or five times. The sleep technologist ensures that the room is dark and quiet and the patient is given 20 minutes to try to fall asleep. After 20 minutes, lights are turned on in the room regardless if the patient had fallen asleep or not. After a break, the process is repeated and the patient is asked to taken another nap. The naps are then analyzed to assess whether the patient had actually fallen asleep or not, and which sleep stages were reached. In general, most people are not able to fall asleep four or five times during the day, unless they are severely sleep deprived, or suffer from a sleep disorder that causes excessive sleepiness.
Maintenance of Wakefulness Test
Maintenance of wakefulness test or MWT is the opposite of the multiple sleep latency test. It measures our ability to stay awake when given the opportunity to fall asleep. It is usually performed after an overnight sleep study. The patient stays in the sleep laboratory until late afternoon and is given four opportunities to fall asleep. The sleep technologist ensures that the room is quiet and leaves a dim light on. The patient is asked to sit in bed and stay awake. Unlike MSLT, the patient is supposed to make an effort to avoid falling asleep. The study is then analyzed to assess if the patient was able to stay awake or not.
Ambulatory Sleep Study
With the advancement of technology, we are now able to perform a sleep study while the patient is at home. The study is similar to a regular polysomnogram, sometimes using a smaller number of electrodes. The study can be set up in the sleep laboratory or the doctor's office. In some cases, the technologist will go to the patient's home and set up the study. Once the study is completed, the information collected is then analyzed by the sleep technologist and the physician to determine if the patient has a sleep disorder or not. The main advantage of an ambulatory sleep study is that it is performed in the comfort of the patient's own home and bed, and replicates the natural circumstances of the patient's nightly sleep. The major problem with it is that the information recorded is not monitored continuously throughout the night and is only reviewed next day, once the study is completed.