The Apnea-Hypopnea Index
Q. What is the Apnea-Hypopnea Index?
A. In severe sleep apnea cases, people are briefly awakened hundreds of times every night due to oxygen deprivation (imagine someone sitting at your bedside, tapping you on the shoulder every minute or so to awaken you), leading to poor sleep and extreme fatigue during the day. The number of these episodes per hour of sleep—as measured with an at-home WatchPAT sleep study or a sleep-laboratory study—is called the Apnea-Hypopnea index, or the AHI. This index specifically calculates sleep apnea severity based on the total number of complete cessations (apnea) and partial obstructions (hypopneas) of breathing per hour of sleep.
Some patients have 50 or more episodes per hour; most sleep experts use a cutoff of 10 events or more per hour before considering treatment with a continuous positive airway pressure (CPAP) device or some other sleep apnea therapy.