Apnea Hypopnea Index (AHI) is the number of times per hour of sleep that your upper airway partially or completely collapses, leading to a brief arousal (or awakening) from sleep or a drop in blood oxygen levels. The partial collapse of the airway is called a hypopnea. The complete absence of airflow through the nose and mouth, despite an effort to breathe as measured at the chest and abdomen, is called an apnea event.

The AHI is used to classify the severity of sleep apnea. This same classification is used to assess how well the CPAP machine is working.

The following guidelines are used in adults:

• Normal:
• Fewer than 5 events per hour of sleep
• Mild sleep apnea:
• 5 to 15 events per hour of sleep
• Moderate sleep apnea:
• 15 to 30 events per hour of sleep
• Severe sleep apnea:
• Greater than 30 events per hour of sleep