Sleep apnea is measured by the number of times you stop or reduce your breathing each hour. Together, these events are counted and known as the Apnea-Hypopnea Index (AHI). A sleep study will measure your AHI as well as the drop in your blood-oxygen levels to help determine the severity of the disease. If you have sleep apnea, your sleep study results will indicate mild, moderate, or severe sleep apnea.
There are two main types of this disorder: central sleep apnea, which occurs when the brain fails to send important signals to the breathing muscles and the more common obstructive sleep apnea, which occurs when air cannot flow through the nose or mouth even though the body is still trying to breathe.