To measure an Apnea Hypopnea Index score, doctors count the number of apneas or hypopneas a patient experiences in an hour, states Harvard Medical School. An apnea event occurs when a blocked airway restricts breathing, and a hypopnea occurs when a partial airway blockage occurs.
Doctors use the AHI to determine the severity of a patient’s obstructive sleep apnea, according to Harvard Medical School. If there are less than five events per hour, then the severity is to minimal. Mild suffers have a score greater than or equal to five but less than 15, moderate sufferers have a score greater than or equal to 15 but less than 30, and severe sufferers have a score greater than or equal to 30.