What does the apnea-hypopnea index (AHI) measure?

The apnea-hypopnea index (AHI) is a crucial measurement used in the assessment of sleep apnea. Specifically, it evaluates the severity of sleep apnea by calculating the average number of apneas and hypopneas that occur per hour of sleep. An apnea is defined as a complete cessation of airflow for a specified duration, while a hypopnea involves a partial reduction in airflow coupled with a decrease in blood oxygen saturation. By determining how many such events occur during a sleep study, clinicians can classify the severity of sleep apnea as mild, moderate, or severe, guiding treatment options and management strategies.

This metric focuses on event frequency rather than other parameters, such as heart rate or sleep architecture. It does not measure the amount of time spent in specific sleep stages nor does it directly assess treatment effectiveness. The emphasis on events per hour distinguishes AHI as a pivotal tool for diagnosing and understanding the impact of sleep apnea on an individual's overall sleep health.