The Apnea Hypopnea Index (AHI) is the primary measure used to diagnose and determine the severity of sleep-disordered breathing, particularly obstructive sleep apnea. AHI is derived from data collected during an overnight monitoring session, providing a standardized score that reflects the frequency of abnormal breathing events. This index is a fundamental component of a sleep study report, informing the diagnosis and treatment plan.
Defining Apnea and Hypopnea Events
The AHI score is a combined count of two distinct types of breathing disruptions: apneas and hypopneas. An apnea represents a near-complete or total cessation of airflow. For an event to be scored as an apnea, this pause in breathing must last for a minimum of ten seconds.
A hypopnea involves a partial reduction in airflow, which is less severe than a complete stoppage. This partial reduction must be 30% or more, enduring for at least ten seconds. A hypopnea is also characterized by an associated physiological consequence, such as a drop in the blood oxygen saturation level or an arousal from sleep. Both apneas and hypopneas fragment sleep and decrease the body’s oxygen levels.
How AHI is Calculated and Measured
The methodology for calculating the AHI score is a straightforward mathematical formula based on the data collected during a sleep study. This specialized monitoring test, known as a polysomnography or a home sleep test, records various physiological parameters during the night.
The calculation involves summing the total number of scored apnea events and the total number of scored hypopnea events. This combined total is then divided by the total number of hours the individual was actually asleep. The resulting figure is reported as the Apnea Hypopnea Index, expressed as “events per hour.”
Understanding the AHI Severity Scale
The numerical value of the AHI is used to classify the severity of sleep apnea in adults, providing a clear reference for diagnosis and clinical discussion. An AHI score of fewer than five events per hour is considered normal, indicating that significant breathing disruption is not present.
The classification for a mild diagnosis is applied when the AHI ranges from five to fewer than fifteen events per hour. Individuals in this category experience between five and fourteen breathing interruptions every hour of sleep. A moderate diagnosis is given for an AHI score of fifteen to fewer than thirty events per hour.
This moderate range, where a person experiences fifteen to twenty-nine events hourly, signals more recognizable sleep disturbances and an increased risk for associated health issues. The severe classification is assigned when the AHI is thirty or more events per hour. This high frequency of breathing disruptions correlates with a greater risk of experiencing negative health outcomes.
AHI’s Role in Guiding Treatment Options
The AHI score is instrumental in determining the appropriate course of treatment, as interventions are scaled to the severity of the condition. For a mild AHI score, physicians first recommend conservative measures, such as lifestyle modifications. These changes can include positional therapy to encourage sleeping on one’s side or targeted weight loss to reduce tissue around the airway.
When the AHI falls into the moderate or severe ranges, a direct intervention is required to manage the frequent breathing events. The primary treatment is a positive airway pressure (PAP) device, such as a Continuous Positive Airway Pressure (CPAP) machine. These devices deliver pressurized air through a mask to mechanically keep the airway open during sleep, aiming to reduce the AHI to below five events per hour. Other options, such as oral appliances that reposition the jaw or surgical procedures, are considered based on the severity of the AHI and the individual’s specific anatomical factors.