The Apnea-Hypopnea Index, or AHI, is a measurement used to diagnose and classify the severity of sleep apnea. It represents the average number of breathing disruptions per hour of sleep. These disruptions are categorized into two types: an apnea is a complete pause in breathing, while a hypopnea is a period of shallow breathing. For an event to be counted, it must last for at least 10 seconds.
How the AHI Score is Calculated
An individual’s AHI score is determined during a sleep study, known as polysomnography. This can be conducted overnight in a sleep laboratory or with a simplified testing apparatus at home. During the study, sensors monitor bodily functions to detect breathing interruptions. Airflow is measured by a nasal cannula, blood oxygen levels are tracked by a pulse oximeter, and bands around the chest and abdomen record respiratory effort.
The calculation is straightforward: the total number of apneas and hypopneas recorded is divided by the total hours the person was asleep. For instance, if a person experiences 40 combined events over eight hours of sleep, their AHI would be 5. This number provides an objective measure of how often a patient’s breathing is compromised.
Understanding Your AHI Score
For adults, AHI scores are categorized into specific levels of severity. An AHI of less than 5 events per hour is considered normal and does not require treatment. This range indicates minimal breathing disruptions and that sleep is largely uninterrupted.
A score of 5 to 15 events per hour is classified as mild sleep apnea. Individuals may experience subtle symptoms, such as light snoring, occasional daytime fatigue, or minor concentration lapses. While the immediate health impacts may not be significant, it is often seen as an early stage that can be addressed to prevent progression.
An AHI between 15 and 30 signifies moderate sleep apnea. At this level, breathing disruptions are more frequent and can lead to noticeable symptoms like persistent daytime sleepiness, morning headaches, and difficulty with concentration. The sleep fragmentation and drops in blood oxygen are more pronounced, increasing the strain on the cardiovascular system.
An AHI greater than 30 events per hour indicates severe sleep apnea. This means breathing is interrupted more than 30 times each hour, leading to significant sleep fragmentation and repeated drops in blood oxygen. People with severe sleep apnea are at a higher risk for serious health complications, including high blood pressure, heart disease, and stroke.
Treatment Approaches Based on AHI Severity
Treatment plans for sleep apnea are linked to the AHI score. For mild sleep apnea (AHI 5-15), initial recommendations focus on behavioral changes. These can include weight management, as a 10% reduction in body weight can decrease the AHI, and positional therapy to avoid sleeping on the back. Avoiding alcohol and sedatives before bed is also advised.
For moderate to severe sleep apnea (AHI 15 or higher), more direct interventions are required. Continuous Positive Airway Pressure (CPAP) therapy is the most common treatment. A CPAP machine delivers a constant stream of pressurized air through a mask, acting as a splint to keep the airway open. This prevents apneas and hypopneas, often reducing the AHI score to a normal level.
Other options are available, particularly for those with mild to moderate cases or who cannot tolerate CPAP. Oral appliances, similar to mouthguards, are designed to reposition the jaw or tongue to maintain an open airway. In some situations, surgical procedures to modify the airway may be considered if other treatments are unsuccessful.
Factors That Can Influence AHI Scores
An AHI score from a single night’s study is a snapshot, as various factors can influence the results. Sleeping position is a prominent variable, and AHI scores are often higher when sleeping on the back (supine) due to gravity’s effect on the tongue and soft palate. Shifting to a side-sleeping position can lower the number of events.
The stages of sleep also play a part, as breathing events can become more frequent and severe during rapid eye movement (REM) sleep. This is because the body experiences a natural state of muscle relaxation (atonia) during REM, making the upper airway more susceptible to collapse.
External substances like alcohol and sedatives can have a substantial impact on an AHI score. These substances relax the muscles in the throat, making airway obstruction more likely. They can also blunt the brain’s arousal response to a breathing pause, potentially prolonging the duration of apnea or hypopnea events. A sleep specialist considers these factors when interpreting AHI results.