7 Diagnostic Tests for Sleep Disorders

sleep study
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For those who suffer from the ill effects of sleep disorders, many diagnostic tests are available that may lead to a better understanding of what the problem may be. Let's discuss the options.

Overnight Oximetry

Overnight oximetry is one of the simplest and, generally, earliest sleep studies that may be conducted. It involves the use of a probe (similar to a clothespin) that is worn on the finger or earlobe which continuously measures oxygen levels and heart rate. This is accomplished with a red light and sensor that detects changes in the color of blood that may suggest desaturations (or loss of oxygen) are occurring.

This test will typically be done at home while sleeping. It may identify individuals at risk for nocturnal breathing disorders. such as sleep apnea, and may be used to identify those who need additional evaluation, such as with a polysomnogram.

Polysomnography (PSG)

This is largely regarded as the gold standard for the diagnosis of sleep disorders. It involves a visit to a sleep center, which may consist of specially designated rooms in a hospital, sleep laboratory, or even a specially equipped hotel room. These sleep studies involve an overnight stay that is monitored by a trained technician.

Various physiological parameters are monitored while an individual sleeps, including an EEG, EKG, respirations, oxygen levels, muscle tone, and eye and extremity movements. There is also a video and audio recording that provides a record of the night’s sleep. These tests can diagnose many sleep disorders—from sleep apnea to restless legs syndrome to parasomnias—and may even be useful in ruling out other causes of insomnia.

Titration Study

Titration with Continuous Positive Airway Pressure (CPAP) is commonly done during the same night as a diagnostic polysomnogram (PSG) to save waiting time, minimize cost to the patient, and treat sleep apnea as soon as possible.

Early treatment may reduce cardiovascular complications of sleep apnea. In short, a technician will gradually increase CPAP pressure (pressurized room air not oxygen) delivered through a soft mask to the level that eliminates most or all episodes of cessation of breathing. This level of CPAP pressure will be prescribed for home therapy.

The patient often begins the night on a low pressure of their CPAP or bilevel. As the person goes to sleep, they will be monitored for disruptions in breathing. Any hypopneas, apneic events, or snoring will prompt a sleep technician to adjust the pressure of the CPAP machine remotely. Again, the person will be monitored at their higher pressure. The goal is to minimize apnea and hypopnea events and eliminate snoring.

It is also ideal for a patient to be titrated to an effective pressure supine (on their back) and during periods of rapid eye movement (REM) sleep. These two conditions will often lead to worsened sleep apnea, so an effective pressure in these conditions would be most favorable.

Often towards the end of this study, the pressures may be increased even further. This will allow the reviewing physician to make comparisons among the various pressures. Also, it may reveal changes that need to be made in the pressures for the most effective management of a person’s sleep apnea.

Multiple Sleep Latency Testing (MSLT)

Multiple Sleep Latency Testing (MSLT) is also often called a nap study. It is similar in setup to the polysomnogram (PSG) described above.

These studies will typically be done after an initial overnight PSG study. After waking up, an individual will have scheduled nap times throughout the day. These typically occur every two hours. 

Generally, a patient is put to bed and allowed to lie there for 20 minutes with the goal of falling asleep. A technician will monitor for the onset of sleep and, in particular, REM sleep. After 20 minutes, the person will be awakened or told that the time for a nap has ended. Then, in two-hour intervals, this process is repeated. Typically these will occur over a 10-hour period.

These tests are useful for identifying excessive daytime sleepiness. This may be present in numerous disorders, such as sleep apnea, idiopathic hypersomnia (excessive sleepiness without a cause), and narcolepsy. In particular, the early onset of REM in these sleep periods may suggest narcolepsy.

Actigraphy

Actigraphy is the measurement of activity with the use of a small, wristwatch-sized device. This device monitors movement and can be used to assess sleep-wake cycles, or circadian rhythms, over an extended period of time. They may be worn for weeks or even months.

The devices help determine whether disruptions in the sleep-wake cycle exist, as many occur in circadian rhythm disorders such as advanced sleep phase syndrome, delayed sleep phase syndrome, or even with insomnia. These results are often correlated with a sleep diary.

Sleep Diary

The sleep diary, or sleep log, is sometimes useful for assessing circadian rhythm disorders or insomnia, especially in adjunct to actigraphic data. These may also be used to assess sleep problems among children.

In general, they are a paper record and document sleep and wakefulness over a period of weeks and months. The bedtimes and wake-times are noted. Any periods of wakefulness during the night or naps during the day are also documented. Sometimes the use of caffeine, alcohol, or medications may also be recorded.

Home Study

Most individuals recognize that they sleep far better at home than they might in a sleep center. This is certainly true, and many are pushing to develop technologies that may allow home assessment of sleep disorders. These may include limited studies that monitor basic parameters of sleep, such as oxygen levels, heart rates, and the movement of the chest and abdomen with special belts. Some titration studies can be conducted at home through the use of the CPAP machine, such as auto-titration studies.

In addition, new technologies are being researched that may lead to other monitoring. In general, these new technologies are in their infancy and the data may not be reliable as the current gold standard of diagnosis, which is the overnight polysomnogram performed in an accredited sleep center.

Sources:

Littner, M. et al. Practice parameters for clinical use of the multiple sleep latency test and the maintenance of wakefulness test. Sleep; 28:113.

Mitler, M. and Miller, J. Methods of testing for sleepiness. Behav Med; 21:171.

Stepanski, E. et al. Effects of sleep deprivation on daytime sleepiness in primary insomnia. Sleep; 23:215.