Diagnostic Tests for Sleep Disorders
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. These may include the following:
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 worn on the finger or earlobe that 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.
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 the 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 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 brief, the technician will gradually increase CPAP pressure (pressurized room air, not oxygen), delivered through the 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 his CPAP or bilevel. As the person goes to sleep, he will be monitored for disruptions in his breathing. Any hypopneas, apneic events, or snoring will prompt the sleep technician to adjust the pressure of their CPAP machine remotely. Again, the person will be monitored at this higher pressure. The goal is to minimize apnea and hypopnea events and eliminate snoring.
It is also ideal for the 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 farther. This will allow the reviewing physician to make comparisons among the various pressures and may reveal changes that need to be made in the pressures for the most effective management of the person’s sleep apnea.