ApneuHypopneuIndex

Apneuhypopneuindex, known in English as the apnea–hypopnea index (AHI), is a standard metric in sleep medicine used to quantify the severity of sleep-disordered breathing. It is defined as the average number of apneas (complete or near-complete cessations of airflow) and hypopneas (partial reductions in airflow with associated oxygen desaturation or arousal) per hour of sleep.

Calculation is based on overnight sleep recording, typically polysomnography in a laboratory or validated home sleep apnea testing. Events are counted and divided by total sleep time (in hours) to yield the AHI. Some scoring rules distinguish obstructive, central, or mixed events; others focus specifically on obstructive events. In home testing, the denominator may be total recording time rather than true sleep time, which can affect the value.

Severity thresholds for adults commonly used are: AHI 0–4.9 normal, 5–14.9 mild, 15–29.9 moderate, and 30 or more severe sleep apnea. Pediatric thresholds are lower and interpretation differs by guideline, reflecting age-related changes in sleep and breathing.

Clinical use and interpretation: The AHI guides the diagnosis and grading of obstructive sleep apnea and helps inform treatment decisions, including continuous positive airway pressure (CPAP) therapy, oral appliances, lifestyle modifications, or surgical options. It is also used to monitor treatment efficacy, with reductions in AHI indicating improvement.

Limitations: AHI is an aggregate measure and does not capture all physiologic consequences of sleep-disordered breathing, such as intermittent hypoxemia or arousals that occur without a counted event. Scoring criteria can vary (for example, American Academy of Sleep Medicine vs. other guidelines), and measurements may differ between in-lab studies and home testing. AHI is often complemented by indices such as the respiratory disturbance index (RDI) or oxygen desaturation index (ODI).