One of the key findings in OSA is a drop in oxygen concentration. Movement of the chest wall is monitored to determine if the apnea is central or obstructive. Other types of sleep disorders are associated with leg movements, jaw clenching, and other characteristic movements. Sleep is divided into characteristic stages based on brain wave activity. This activity is monitored during the sleep study.
Sleep apnea is often more common while lying on one's back.
This allows the tongue to more easily fall back and block the airflow. The sleep study is a very complex test and all of its results must be carefully interpreted in order to properly diagnose the severity of the sleep disorder. There are, however, two measures that are often quoted in order to summarize the results. First, the number of apneas and hypopneas are summed and averaged over the nighttime to calculate the average number of respiratory disturbances per hour. Sleep apnea is generally defined in adults as an RDI of 5 or greater.