Sleep Studies

The most common sleep study administered by sleep technologists at the sleep clinic is “polysomnography.” It is considered the “gold standard” test for diagnosing many sleep-related disorders. Most people normally go through four to six sleep cycles during the night, cycling between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep every 90 to 110 minutes. The purpose of polysomnography is to trace events that occur during each sleep cycle in order to detect any abnormalities that may impede the normal sleep process.

In a typical polysomnography, information is gathered in much the same way as a polygraph collects data for a lie detector test. The sleep technologist attaches various electrodes and sensors to your scalp, face, chin, chest, finger and legs to record multiple biological functions during sleep, such as brain wave activity, eye movement, leg movement, muscle tone, heart rate, airflow, breathing effort, snoring and oxygen levels in your blood. In a separate room, the sleep technologist observes you while you sleep and monitors the recording data as it is being collected. Additionally, a record of the sleep study is made via an audiovisual recording.

There are three types of polysomnographic studies:

The purpose of the initial polysomnography is to diagnose sleep-related disorders. The study is indicated for the diagnosis of sleep apnea, narcolepsy, periodic limb movement disorder, parasomnias (abnormal behaviors or movements such as sleep walking, night terrors, head banging, and enuresis), seizure-related disorders, and REM sleep behavior disorder (yelling or moving violently during REM sleep). 

During a diagnostic polysomnography, the patient is observed without interruption throughout the night. Various biological functions are monitored to detect any abnormalities that may impede sleep and characterize the sleep-related disorder.

If the results of the diagnostic polysomnography indicate that the patient has sleep apnea, then a continuous positive airway pressure (CPAP) device or oral appliance may be prescribed to effectively treat the disorder. The titration polysomnography is performed as a follow-up study to determine, by trial and error, the optimal settings on the CPAP device or oral appliance at which sleep apnea is alleviated.

The titration polysomnography is similar to the diagnostic polysomnography in that the same biological functions are monitored and recorded; however, during the second polysomnography the patient wears a CPAP device or oral appliance while sleeping.     

If CPAP therapy is prescribed, the sleep technologist fits the patient with a CPAP device prior to the sleep study. The CPAP device is designed to deliver pressurized air to the patient through a specially designed mask that fits over the nose or mouth. The pressurized airflow serves to hold the upper airway passage open during sleep. Initially the physician estimates the correct pressure settings for the CPAP device based on results of the diagnostic polysomnography. Then during the second study, the technician adjusts the airway pressure higher or lower from the prescribed setting to find the optimal pressure that eliminates the obstructive apneas and/or hypopneas, oxyhemoglobin desaturation, respiratory effort–related arousals, and snoring in all sleep stages.

If an oral appliance is prescribed, the patient arrives at the sleep clinic with the oral appliance that has been custom fabricated and fitted by his or her dentist. The oral appliance is designed to incrementally advance the mandible until a protrusive position is reached with maximal therapeutic effect.  In a process analogous to CPAP titration, the oral appliance is adjusted manually or remotely by trial and error during the night to determine the optimal degree of mandibular advancement to resolve the sleep apnea.

 In some cases, both diagnosis and treatment of a sleep-related breathing problem can be accomplished in a single night’s study, rather than two separate studies. The sleep technologist observes obvious signs of sleep apnea during the first few hours of the initial sleep study, ends the diagnostic study, and converts the study into a CPAP titration study.  Thus, in a split-night study, both the diagnostic polysomnography and titration polysomnography are done in the same night. 

For the sleep technologist to convert the diagnostic polysomnography into a titration polysomnography on the same night, sufficient data must be collected to definitely diagnose sleep apnea. Moreover, there must be enough time during the remainder of the night to effectively titrate the CPAP device.  

The advantages of the split-night study are that the test is less expensive and less disruptive for the patient. The patient is required to sleep only one night in the sleep clinic. The disadvantage of a split-night study is that there is insufficient time to diagnose obstructive sleep apnea and perform the CPAP titration. In some cases, it may take six or more titrations before the optimal CPAP setting is found. If the CPAP titration is begun with only a few hours of sleep left, the remaining time may not assure proper titration and the patient may still have to return to the sleep clinic for a second night. Also, if sleep apnea is under-diagnosed in the first part of the night, then CPAP titration is likely to be inaccurate as well. 

In certain circumstances when there is a high likelihood that the patient has moderate-to-severe obstructive sleep apnea and the patient has no significant medical conditions other than the suspected obstructive sleep apnea, the physician may order a home sleep apnea test instead of an overnight study at the sleep clinic. A home sleep study is a simplified version of an overnight, attended sleep study. It is only used though to diagnose or rule out obstructive sleep apnea.

If a home sleep apnea test is indicated, you will be given portable diagnostic equipment to take home with you to use overnight while you are sleeping.  That night, before bed, you’ll need to secure the sensors that will record information about your airflow, snoring, breathing effort, heart rate and oxygen levels. In the morning, you’ll remove the sensors and return all items and equipment to the sleep clinic so that the data can be downloaded and analyzed.

In some cases, a follow-up overnight sleep study at the sleep clinic may still be necessary if the test results are unclear; there is insufficient data to make a diagnosis; or another sleep-related disorder is suspected. If the home sleep apnea test does not find obstructive sleep apnea even though symptoms of sleep apnea are apparent, a diagnostic polysomnography at the sleep clinic will be necessary to rule out other reasons for hypersomnia.

Once your sleep study is finished, a board-certified physician will interpret the results of your study and  compile a detailed report with treatment recommendations. The report is then forwarded to the referring physician who is responsible for reviewing the results of the sleep study with you and recommending a treatment plan.