Sleep apnea is a sleep disorder that causes breathing difficulties during sleep. The condition ranges in severity from a mild decrease in airflow to airflow completely stopping, which can be life-threatening.
Sleep apnea has multiple causes, including the tongue or tissues in the airways blocking the air or challenges related to the signals sent from the brain to control breathing during sleep.
The apnea-hypopnea index (AHI) is a scale to measure the symptoms of sleep apnea. It is used with sleep testing to diagnose the condition and determine how severe it is.
Learn more about sleep apnea, the apnea-hypopnea index, other tests for sleep apnea, and treatment options.
Table of Contents
What Is the Apnea-Hypopnea Index?
The apnea-hypopnea index (AHI) measures how many times per hour, on average, a person partially or fully stops breathing during sleep. AHI is measured during a sleep study, an overnight test used to diagnose sleep apnea and other sleep disorders.
A pause in breathing must last 10 seconds or more to be counted. Apnea is when breathing is reduced to 10% of normal or less, including when breathing completely stops. Hypopnea is when breathing is reduced to 70% or less.
Respiratory Event Index (REI) is a measure that is sometimes used instead of the AHI in sleep testing that is done at home. It includes all the apnea and hypopnea events during the sleep study, not just the events that happen while the person is sleeping.
The AHI is the total number of times a person experiences apneas and hypopneas in one night divided by the total number of hours of sleep. The result is the average number per hour.
For example, a person with an AHI of 12 experiences an average of 12 episodes of apneas or hypopneas for each hour of sleep. This means that their breathing was either reduced by at least 30% or stopped completely for at least 10 seconds, 12 times per hour.
Interpreting AHI Results
A lower AHI number means fewer episodes of breathing difficulty. Here are the AHI score ranges and what they mean:
- Less than five events per hour (<5): This is considered normal or no sleep apnea. It means a person had fewer than five episodes of difficulty breathing per hour that lasted at least 10 seconds.
- Five to 15 events per hour (5-15): This is considered mild sleep apnea. It means a person had between five and 15 episodes of difficulty breathing per hour that lasted at least 10 seconds.
- 15 to 30 events per hour (15-30): This is considered moderate sleep apnea. It means a person had between 15 and 30 episodes of difficulty breathing per hour that lasted at least 10 seconds.
- More than 30 events per hour (>30): This is considered severe sleep apnea. It means a person had more than 30 episodes of difficulty breathing per hour that lasted at least 10 seconds.
The AHI is not necessarily an accurate way to measure the severity of sleep apnea because it does not differentiate between apneas and hypopneas, or how much the airflow is reduced.
For example, two people may have the same AHI, but one person may completely stop breathing while the other may only experience airflow that is reduced by 30% and is less severe.
Other Sleep Apnea Tests
AHI alone is not enough to diagnose sleep apnea or show the severity of the condition. It is just one of the measures that are assessed during a sleep study (an overnight test used to diagnose sleep apnea and other sleep disorders).
Two other measures used are the respiratory disturbance index (RDI) and the oxygen desaturation index (ODI). In addition to AHI, RDI, and ODI, the symptoms of sleep apnea and how a patient feels are also considered.
Respiratory Disturbance Index (RDI)
The respiratory disturbance index (RDI) is similar to the AHI because it includes both apneas and hypopneas. Unlike the AHI, the RDI also includes the number of times per hour a person is awakened or shifts to a more awake stage of sleep because they are having breathing difficulties.
This makes RDI a more sensitive measure of assessing breathing difficulties during sleep.
Oxygen Desaturation Index (ODI)
One role of blood cells is to carry oxygen to organs, which is required to live. Oxygen desaturation is when there is a decrease in oxygen in the blood.
The oxygen desaturation index (ODI) measures oxygen desaturation during sleep. This measure is important because oxygen desaturation during sleep is linked to an increased risk of sleep apnea complications such as heart conditions.
Sleep apnea is treatable. The most common treatment for sleep apnea is positive airway pressure ( PAP) which uses a machine to push air into the lungs through the nose or through the mouth and nose together.
Continuous positive airway pressure (CPAP) is a type of PAP treatment for sleep apnea. It uses a device that pushes air into the lungs through the nose and mouth together at the same pressure level for the entire night.
The machine is connected to a hose that is attached to the face with either a mask that covers the nose and mouth or a smaller piece that sits at the openings of the nose.
Bi-level positive airway pressure (BiPAP) is a type of PAP treatment for sleep apnea. The treatment involves a device that pushes air into the lungs through the nose or through the mouth and nose together at different pressure levels during the night.
The pressure increases when the person inhales and decreases when the person exhales to allow for more breathing support when needed without such a high pressure when it is not needed. This is important because some people who are unable to tolerate CPAP are able to use BiPAP.
Adaptive servo-ventilation (ASV) is a type of PAP treatment for sleep apnea. The treatment involves a device that pushes air into the lungs through the nose or through the mouth and nose together at different pressure levels during the night. Unlike BiPAP, ASV measures the breathing of the person and automatically changes the pressure setting to respond to changes in breathing.
For example, when the machine detects that a person is struggling to breathe, the air pressure will increase. This option might be best for people who are likely to experience changes in the pressure settings they need in a short time, such as pregnant people or people who are losing weight.
ASV is also used for people who have more complicated cases with multiple types of sleep apnea and people who do not respond well to other PAP options.
In addition to PAP devices, there are other ways to treat sleep apnea, including lifestyle changes. Since being overweight can block airways and lead to sleep apnea, weight loss can be used as a treatment either instead of or along with other options.
Lifestyle changes to improve sleep apnea include:
- Exercise: Physical activity can help with weight loss and tighten the muscles in the mouth and throat to improve airflow. Myofunctional therapy is a specific type of exercise used for sleep apnea.
- Nutrition: A balanced diet can help with weight loss and may decrease inflammation or swelling that blocks airways. Eating fruits, vegetables, and healthy fats such as nuts, seeds, and olive oil, while limiting sugar, processed foods, and meats has been shown to reduce weight.
- Reduce alcohol consumption or stop drinking: Alcohol can lead to the relaxation of muscles that may contribute to or worsen sleep apnea. Decreasing or stopping alcohol use can help to treat the condition.
- Quit smoking: Smoking can disrupt sleep architecture and lead to more awakenings during the night. It can also damage the upper airway muscle function and increase mucus congestion in the upper airway. Quitting smoking can help to treat the condition.
- Weight loss: Losing weight can decrease the tissue in the airways that might be blocking them. For people with obesity or who are overweight, losing weight is the primary treatment for sleep apnea along with PAP options
Sleep apnea is a sleep disorder that causes difficulty breathing during sleep. The apnea-hypopnea index (AHI) is a number that is used to diagnose sleep apnea and determine the severity of the condition. It measures the average number of breathing difficulty events per hour of sleep.
However, AHI cannot be used alone. Other measures are also used along with assessing the symptoms each person experiences. In general, an AHI of less than five is considered to be normal, five to 15 is considered mild sleep apnea, 15 to 30 is considered moderate sleep apnea, and 30 or above is considered severe sleep apnea.
However, it's important to know the measure is just a guideline. The scores represent the average number of events per hour, not how restricted the airflow might be during those events.
A Word From Verywell
Living with sleep apnea can be challenging, especially when the symptoms are severe enough to interfere with your nightly sleep or affect your daily life. Treatment options are available, including devices to help with breathing and lifestyle changes.
If you or someone you know is dealing with sleep apnea, you can get treatment. Reach out to your healthcare provider or a specialist like a neurologist or a pulmonologist specializing in sleep medicine for support.
Frequently Asked Questions
What is a good AHI index?
The apnea-hypopnea index (AHI) measures the number of times a person experiences difficulty breathing each hour of sleep, on average. An AHI of less than five is considered normal and no sleep apnea. An AHI of five to 15 is considered mild sleep apnea.
However, the number alone cannot show the severity of sleep apnea because it does not show how much the air is blocked (e.g., partially or fully).
How can I lower my AHI index over time?
AHI can be lowered by treating sleep apnea. Treatment options for sleep apnea include machines to help with breathing, mouth appliances, medications, and lifestyle changes such as diet and exercise to lose weight.
What are the side effects of sleep apnea?
The side effects of sleep apnea include dry mouth, headache in the morning, sleepiness throughout the day, and high blood pressure. In more severe cases, sleep apnea can be life-threatening. It is important to seek medical care if you think you may have sleep apnea.