Sleep Studies: What Are They? Why Are They Done?

Sleep studies are the only means to evaluate sleep. They are done when the doctor suspects that the patient could be suffering from a sleep disorder. The results of sleep studies are used to:

–          Identify the type of sleep disorder

–          Locate the source of the sleep problem

–          Identify the cause of the sleep disorder

–          Assess the severity of the condition

What are the different types of sleep studies? 

  1. Overnight sleep study, also called polysomnography. This is a multi-parametric diagnostic procedure that detects and records several biophysical changesthat occur during sleep. The results can diagnosis a range of sleep disorders including sleep apnea. The results, known as polysomnogram, can also help in assessing the severity of the condition. The parameters studied include:Sleep stages
    Eye movements (EOG)
    Brain activity (EEG)
    Muscle activity (EMG)
    Study of limb movements, respiratory efforts, etc.
    Oral and nasal airflow
    Heart rate (ECG)
    Oxygen levels in the blood (oximetry)
    Movements of the chest and abdomen
    CO2 levels
    Snoring volume
  2. CPAP Study: Used to set and adjust the right air pressure for CPAP therapy for sleep apnea patients.
  3. Home Sleep Test: Polysomnography can be done either at home or at a sleep clinic. The home sleep test involves using a portable-monitoring system for detecting sleep apnea in adults.
  4. Maintenance of Wakefulness Test (MWT): This test measures daytime alertness.
  5. Nap Study (MSLT or Multiple Sleep Latency Test): An objective diagnostic tool that tests sleep onset rapid eye movement sleep periods (SOREMPS), useful for diagnosing narcolepsy.  According to the American Academy of Sleep Medicine (AASM), MSLT is considered to be the de facto standard for the objective measurement of sleepiness.

Which of these sleep studies is most revealing?   

Currently, polysomnography is considered the “gold standard” diagnostic test for sleep disordered breathing (SDB) and other sleep disorders. This diagnostic procedure is usually performed by a specially trained technologist under supervision of a qualified physician (e.g., respirologist, neurologist, or psychiatrist), who later interprets the recorded results.

Which is better: testing at home or at a sleep center? 

While it is a personal choice whether the sleep studies should be done at home or at a sleep center, there are several advantages as well as limitations of both these options. Here is an overview:

–          Location problem: Sleep evaluation at a sleep center requires the patient to spend the night at a new environment which might be a problem for some patients.

–          Diagnostic limitations: Other than sleep apnea, sleep centers have the facilities to detect several other sleep disorders; home testing allows only detection of this disorder.

–          Limitations on age: Diagnosis at a sleep center can be done for patients of all age groups including older adults; home testing could be insufficient for older adults who may have other medical conditions that affect sleep.

–          Recording of sleep data: An overnight sleep center collects signals of all vital signs that are linked to sleep which are recorded in 12 separate channels (centers accredited by American Academy of Sleep Medicine); home testing can detect only those signals that help in detecting obstructive sleep apnea.

–         Accuracy of results: Overnight sleep centers have proven to provide more accurate results with low failure rate. While home testing method provides accurate data for sleep apnea, for other sleep disorders, it provides less accurate results.

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