Obstructive and Central Sleep Apnea (cont.)
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Exams and Tests
Evaluation of sleep apnea usually begins with taking a detailed and comprehensive medical history. Other medical conditions (most importantly, heart and lung diseases), a complete list of medications, history of drug and alcohol use, smoking history, and a review of symptoms pertinent to sleep apnea are typically included in the history.
A complete physical examination by the doctor is also an important part of the evaluation. Particular attention may be given to the examination of the heart and lungs, body weight and height, evaluation of the neck circumference, and examination of the oral cavity, pharynx, tonsils, and nasal passages.
The patient's family members and bed partners also need to be questioned about the patient's sleep patterns, snoring, breathing problems during sleep, witnessed apnea during sleep, and symptoms of sleep apnea.
Polysomnography is the best available test (gold standard) used to diagnose or rule out sleep apnea. Based on the medical history and physical exam, if the doctor suspects sleep apnea, he or she may then refer the patient to a sleep specialist to perform this study.
Polysomnography (sleep apnea test) typically requires an overnight stay at a sleep center designed for this purpose. The individual is hooked up to monitors while they sleep during the night. Several parameters are detected by these monitors including heart rate, blood oxygenation, rate of breathing, electrocardiogram (ECG or heart monitor), electroencephalogram (or EEG, to monitor brain activity and sleep stages), limb movements, eye movements, and airflow.
Many useful data are generated from an overnight sleep study, which are then analyzed by the doctor to make a diagnosis of sleep apnea. An apnea-hypopnea index (AHI) is calculated using the data by dividing the total number of episodes of apnea and hypopnea by the number of hours of sleep. An index of 15 or more is suggestive of sleep apnea (roughly one episode of apnea or hypopnea every four minutes).
Respiratory disturbance index (RDI) is another measurement of breathing-related sleep problems, which includes milder impairments to air flow in addition to apnea and hypopnea episodes.
Other information is also obtained from the sleep study including limb movements, snoring, oxygen saturation, total sleep time, and sleep disturbances. These additional data can be used to further support the diagnosis of sleep apnea or to diagnose other sleep-related disorders.
Another advantage of the overnight sleep study is that once the information suggests sleep apnea, then treatment with a special breathing machine called a CPAP (continuous positive airway pressure) can be initiated and a rough comparison of the quality of sleep with and without the device can be made. This is called a split study.
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