Understanding the AHI Sleep Apnea Index
Obstructive sleep apnea causes breathing difficulties when sleeping due to blocked or partially blocked airways. Without diagnosis and treatment, sleep apnea increases your risk of heart disease, stroke, and diabetes.
A sleep study is generally recommended if sleep apnea is suspected. Data recorded during a sleep study helps produce one of the main tools used in diagnosing this sleep disorder. This diagnostic tool is the AHI sleep apnea index.
What Is the AHI Sleep Apnea Index?
AHI stands for the apnea-hypopnea index. This sleep apnea index is used to assist in the diagnosis of sleep disorders like sleep apnea. The index relates to the average number of breathing disturbances experienced for every hour of sleep.
This could be when your breathing fully stops (termed apnea) or when your breathing is partially reduced (hypopnea).
How Is Your Sleep Apnea Index Calculated?
An AHI score is calculated by adding the number of apneas and hypopneas experienced during a sleep study and dividing them by the total amount of sleep.
To be registered as an episode, an apnea and hypopnea must last at least 10 seconds. A reduction of airflow of 90% is classed as apnea, while hypopnea is usually signaled by a 30% drop in airflow.
Let’s look at an example of someone who experiences 20 apneas and 40 hypopneas during the night, and sleeps for a total time of six hours. The AHI score is calculated as follows:
- 20 + 40 = 60 / 6 = AHI score of 10
Using AHI to Diagnose Obstructive Sleep Apnea
An AHI score below five indicates normal breathing patterns. However, a score of five or above may indicate sleep apnea.
A sleep apnea index between five and 14 together with symptoms like daytime fatigue, snoring, and morning headaches means a likely diagnosis of sleep apnea. An AHI above 15 is likely to be diagnosed as a more severe degree of obstructive sleep apnea.
The severity of sleep apnea is relevant when considering treatment plans. The higher your AHI, the worse your sleep apnea symptoms are likely to be.
As weight is a major contributing risk factor for obstructive sleep apnea, a mild degree of the disorder may be addressed through lifestyle changes that result in weight loss.
A more severe degree of the sleep disorder may be treated using CPAP. Your AHI score helps determine the air pressure settings on the CPAP device required to keep your airways free from obstruction.
The severity of sleep apnea is classified using the sleep apnea index as shown below.
- AHI 5 to 15: Mild
- AHI 15 to 29: Moderate
- AHI 30 and above: Severe
While your sleep apnea index is an important diagnostic tool, your healthcare provider will also ask questions about your health history and review your symptoms before offering a diagnosis.
A sleep study may also provide further data of interest to a healthcare provider to help with a diagnosis. This includes sleep quality and how long you stay in the different stages of sleep.
Another set of data recorded during a sleep study may show oxygen levels in the blood. This could include how often you are in a state of hypoxemia while sleeping. This is when you have low levels of oxygen in the blood.
At-Home Tests
The sleep study used to obtain an AHI score is called a polysomnography and is a multi-parameter study. Therefore, it provides the most thorough examination of your sleep patterns to supply your healthcare provider with data to better inform their diagnosis.
It is also possible to receive an AHI score from an at-home test. However, these tests do not produce such detailed reports and may not detect milder degrees of obstructive sleep apnea. Therefore, an at-home test is only usually recommended for someone suspected of having moderate to severe sleep apnea.
An at-home test generally involves wearing a clip on your finger while you sleep that is attached to a monitor. The data recorded may include breathing patterns, heart rate, oxygen levels, and even body movement.
At-home tests are not viewed as reliable as a sleep study, but they can be an indicator of obstructive sleep apnea, from which your doctor can make a diagnosis with your health history and symptoms.
The test may also confirm the possibility of sleep apnea before a sleep study is used to provide more detailed data about the relationship between your breathing patterns during different stages of sleep.
Continued Monitoring of AHI
Your AHI score will continue to be used to determine how well you are responding to treatment for obstructive sleep apnea.
CPAP is a leading treatment for moderate to severe obstructive sleep apnea. Modern CPAP devices can record the number of breathing episodes you experience during sleep, which can then be used to evaluate your AHI score.
CPAP is effective in reducing sleep apnea symptoms but may not eliminate them. Therefore, you cannot automatically expect an AHI score of zero when using CPAP.
Someone with a severe case of the disorder and a previous AHI score over 30 could aim to reduce this to 10 or below. Each reduction in your AHI score should equate to fewer breathing episodes and an improved quality of sleep.
As well as using CPAP, further ways to reduce your AHI score include:
- lifestyle changes such as exercise and a healthier diet to promote weight loss
- quitting smoking and limiting alcohol consumption
- sleeping on your side rather than on your back to prevent gravity from pulling throat tissue down to block the airways
- wearing an oral appliance to help keep the airways open when you sleep if you struggle to tolerate CPAP
- surgery to remove obstructions to the airways
An AHI score is important in helping your healthcare provider diagnose sleep apnea. Ongoing monitoring of this score will help to evaluate the success of your treatment plan in reducing the number of breathing episodes experienced during sleep.
