Continuous positive airway pressure (CPAP) is a prescribed breathing device to treat sleep apnea . The goal of CPAP is to improve nighttime breathing. But how do you know if a treatment is working well enough?
The apnea-hypopnea index (AHI) is a useful way to measure the severity of sleep apnea. It can also help you see how well your body is responding to treatment.
This article explains how to use AHI to optimize your CPAP machine. It also answers questions like:
- What does an AHI reading mean on a sleep study or CPAP machine?
- What is considered an event?
- If the AHI number is higher than usual, how can the CPAP machine be configured?
What is AHI?
First, it is important to understand what the value of the apnea-hypopnea index (AHI) means.
The AHI is the average number of cases of apnea or hypopnea in your body during one hour of sleep.
Apnea is the interruption of breathing during sleep. The pause may be due to the tongue or soft palate at the back of the mouth blocking the airway.
Whenever apnea occurs, you may wake up briefly. It can also cause a decrease in the amount of oxygen in the blood. When air stops flowing through your nose and mouth, apnea begins, even if your chest and abdomen move when you try to breathe.
Hypopnea refers to the period of shallow breathing. Considered less serious than sleep apnea. Researchers define hypopnea as a 30% decrease in the amount of air that passes through the airways.
If you inhale shallowly, you may be hypoventilating, which means you are not breathing enough air to meet your body's oxygen needs. Hypoventilation can also occur if you have an unusually low respiratory rate. Your breathing rate is the number of breaths you take in one minute.
Some researchers argue that hypopnea and apnea are almost identical phenomena.
To qualify as apnea or hypopnea, the change in breathing must last at least 10 seconds.
The AHI takes into account both types of respiratory disorders. The number is used to estimate the severity of sleep apnea. It is also used to measure how well procedures like CPAP machines work.
The AHI is the average number of times your airflow decreases or your breathing stops during an hour of sleep. It can be used to assess the severity of sleep apnea and evaluate the effectiveness of treatment.
Where your AHI is measured first: sleep research
The first place you can see the AHI is in the Sleep Study Report.
To diagnose sleep apnea, specialists use a sleep test, also called a polysomnogram. These tests are usually done in a sleep center. Sleep apnea is sometimes diagnosed with a home sleep apnea test .
These studies track your breathing at night. They depend on sensors like this:
- A nasal cannula (or thermistor) with plastic tips that are inserted into the nostrils.
- Breathing straps that extend over the chest and / or abdomen.
- An oximeter clip that continuously measures oxygen and pulse rate by directing a laser beam through the fingertip.
The sensors show how many times you stopped breathing or took shallow breaths during the night. They can also detect changes in blood oxygen levels.
Some bedrooms use measures other than IAH. The Respiratory Distress Index (RDI) takes into account the occurrence of apnea and hypopnea, as well as less severe respiratory interruptions.
The oxygen desaturation index (ODI) only takes into account the number of cases of apnea or hypopnea per hour that cause a drop in oxygen content of at least 3%. This drop in oxygen can increase the risk of long-term cardiovascular problems, such as high blood pressure, heart attack, and heart failure. A drop in oxygen can also lead to a stroke, dementia, or other neurological problems.
If your sleep study doesn't include these more specific metrics, there's nothing to worry about.
What is a good goal for AHI?
Your breathing can change from night to night. For this reason, trying to hit a certain daily number is probably useless. Sleep apnea can be made worse by:
Since these factors can affect your AHI, it is best to calculate your average results over 30 to 90 days. The best goal for you may depend on the severity of your condition. Your goal may also depend on the cause of your breathing problems.
Ideal AHI: less than five events per hour. This indicator is within the normal range. Some sleep professionals aim for one or two sessions per hour to help you sleep better. If the AHI in sleep research is high, say 100 events per hour, even lowering it to 10 events per hour can be a big improvement.
Children's sleep is analyzed according to stricter criteria. More than one event per hour of sleep is considered abnormal.
What is the AHI used for?
The AHI will be used to help you choose the best treatment for you.
- CPAP machines are suitable for treating mild, moderate, or severe sleep apnea.
- An oral device may be the best option for mild to moderate sleep apnea. An oral device is a mouth guard that your dentist makes for you. Press your tongue so it doesn't block your airway.
- Surgery may be the best option if your apnea is related to your anatomy.
- Positional therapy can be helpful if your sleep apnea worsens when you sleep on your back.
- Other treatments may be recommended based on your AHI.
To interpret your AHI, your healthcare provider will look at the big picture – your baseline sleep study, anatomy, medications, changing health conditions, and other factors.
If you have had surgery or are using oral devices, you may need another test to make sure the treatment was effective in lowering your AHI.
How CPAP Machines Detect Breathing Problems
The basic principle is that the machine expels air at a constant pressure. It can also send short bursts of extra pressure. If your airway is partially blocked, CPAP can measure how much airflow is slowing down.
In "automatic" machines, when the machine senses that something is restricting the flow of air, it increases the pressure to better support the airways.
Measurements from CPAP machines used at home are not always accurate. If the reading remains high without a good explanation, you may need a new sleep study.
How CPAP Machines Treat Sleep Apnea
Modern CPAP machines track the number of respiratory events that occur at the current pressure setting. Each event means that you either wake up briefly or have a short-term drop in your blood oxygen levels.
Using CPAP does not necessarily completely prevent sleep apnea. This depends in part on the pressure set by your sleep therapist.
Imagine trying to inflate a long, flexible tube by blowing air into it. If there is too little air, the tube will not open. It will remain collapsed. If the CPAP pressure is set too low, the upper airway can still collapse. This could mean ongoing hypopnea or apnea. Your symptoms may persist if your treatment is not long enough.
Can you have apnea even if your CPAP is working?
You may have ongoing episodes of sleep apnea and other breathing problems, even if you use a CPAP machine. New machines can track these events and report them to AHI.
The results can be viewed on the device, or you can verify them using an app or website. This information can provide you with information about the effectiveness of your treatment. When CPAP calculates AHI, your equipment supplier or doctor can also download the data and make a plan to improve your treatment.
If your AHI remains elevated, it's time to go back to a certified sleep professional for an evaluation.
Can the CPAP pressure setting change your AHI?
A certified sleep technician is the best person to decide which CPAP setting is right for you. The sleep specialist will review your average AHI score and your experience with treatment. While anyone can change the settings, your healthcare provider should make this informed decision.
AHI readings can be influenced by many factors, and a high AHI does not necessarily require a high CPAP pressure. When deciding how much pressure you need, consider your anatomy.
If you are having trouble adjusting to treatment, lower pressure settings may make you more comfortable. However, if the settings are too low, it may not work well enough to fix the problem.
Turning the device too high can cause central sleep apnea . This is when your brain doesn't tell you to breathe while you sleep.
The CPAP device can be configured to address various types of problems, including:
- Obstructive sleep apnea (collapse of the airways)
- Central apnea (episodes of holding your breath)
- Unknown issues (often associated with leaky masks)
Different problems will need to be approached in different ways. For example, it may be necessary to increase or decrease the CPAP pressure. Or the mask may need an adjustment or replacement.
The AHI is a measure of the number of cases of sleep apnea or hypopnea that you experience during one hour of sleep. The term "apnea" means a pause in breathing. Hypopnea refers to a 30% or more reduction in the amount of air delivered during breathing.
During your initial sleep study, you will receive a baseline AHI score. This information will be used in conjunction with other factors to find the best treatment options for you.
If you are using a CPAP device, it will continue to calculate AHI numbers while you sleep. Your sleep professional can use this information to make sure you are taking proper sleep procedures to protect your health.
Get the word of drug information
If you have questions about what AHI means for your condition and if your CPAP is working as expected, contact your sleep specialist to discuss your options. Regular follow-up at the clinic will help ensure the success of your treatment.