For those who show signs of Obstructive Sleep Apnoea (OSA), it is recommended to take a sleep study or a sleep test.

The Sleep Apnoea test will confirm whether or not you have a sleep disorder by reading your AHI number.

So, what does your AHI mean, and why is it important?

What does AHI mean?

AHI stands for Apnoea Hypopnoea Index, which is the calculation of apnoeas and hypopnoeas that occur during sleep. This calculated number is then divided by the hours you sleep, resulting in your AHI.

Apnoea: When your airway is completely blocked, and you stop breathing for 10 seconds or more. 

Hypopnoea: A period of shallow breathing for ten 10 seconds or longer. Your breathing doesn’t entirely stop; however, your airflow is 30% lower than usual. 

Apnoeas and hypopnoeas are very similar and can cause you to wake up catching your breath. You may do this by waking up choking, coughing and gasping.

What is Sleep Apnoea RERA?

RERA stands for Respiratory Effort Related Arousal, a sleep disturbance that causes a decrease in oxygen but does not qualify as an apnoea or hypopnoea. 

What is the Respiratory Disturbance Index (RDI)?

Similar to AHI, your RDI is the combination of apnoeas, hypopnoeas and RERAs per hour whilst you sleep. 

What is the Oxygen Desaturation Index (ODI)?

If you have had a sleep study or sleep test, your ODI is calculated. ODI is the average number of times the oxygen levels in your blood drop by 4% or more every hour during sleep. Usually, every time your breathing has disrupted, the oxygen in your blood decreases.

Need help understanding your Sleep Apnoea test results? Contact us.

Sleep Apnoea and AHI

Your AHI is first read from a sleep test or sleep study; this determines if someone has Sleep Apnoea or not. The AHI number has to reach a certain level to confirm Sleep Apnoea. Once your OSA is confirmed, you will receive your recommended treatment plan.

If you are a CPAP machine user, you may find your CPAP readings will state your AHI in your sleep data report – your AHI should remain low, and if it does not, this could be a sign of an issue, e.g. mask leaks. 

Please note: it is usually newer CPAP devices that show this feature.

What does your AHI number mean? 

Here’s a breakdown of the AHI numbers and the correlating severity of OSA:

• Normal sleep – An AHI lower than five events per hour. CPAP machine users will find they still have a few apnoeas during sleep. 
• Mild Sleep Apnoea – An AHI of 5 to 15 events per hour.
• Moderate Sleep Apnoea – An AHI of 15 to 29 events every hour.
• Severe Sleep Apnoea – An AHI of 29 events and above per hour. 

What causes a high AHI?

Different factors can affect the severity of someone’s OSA, including:

• Weight & neck circumference – Research has found that men with a neck circumference above 17 inches and women with a neck circumference above 15 inches have a much higher risk of developing Sleep Apnoea. Many people with severe cases of OSA are overweight or obese, as excess weight puts pressure on the upper airway.
• Deviated septum – This can cause OSA or intensify the severity due to the deviation blocking the airflow, making it difficult to breathe. 
• Smoking – Smokers are at a higher risk of OSA as it causes the upper airway to inflame and causes the airway to relax, leading to blockages. 
• Alcohol – Regularly consuming a high amount of alcohol before you sleep disrupts your REM sleep, increasing the risk of OSA by 25%.
• Medications and sedatives – Certain medications can aggravate sleep disorders. It is worth checking with your doctor if your medication works in partnership with your Sleep Apnoea treatment.
• Sleeping position – Depending on the individual, certain sleeping positions can cause more apnoea events throughout the night. Sleeping on your side is generally advised for those with OSA as it comfortably opens the airway. 

Related page: CPAP masks for side sleepers

Why does my AHI change?

Many CPAP users find that their AHI changes. If your AHI alternates between the safe range of 1 to 5, there’s nothing to worry about. If the number goes above the normal range, you need to address it; read our helpful advice below.

How to improve CPAP AHI 

If you’re wondering why your AHI number has increased, all of the above factors should be considered to reduce your AHI. But you can do some extra things to get the most from your CPAP therapy.

Tips to lower your CPAP AHI:

• You must use the best CPAP mask for your OSA to prevent air leaks and stop yourself from taking your mask off. 
• Replace your mask parts when necessary to avoid wear and tear affecting your therapy. 
• Avoid alcohol before bed to control your symptoms from being heightened. 
• Consider a CPAP pillow to make sleeping on your side easier. Alternatively, you can use multiple pillows to elevate your head to comfortably sleep on your back and keep your airway open.
• If you use a nasal mask and breathe through your mouth, adding a chin strap will prevent leaks and lower your AHI.
• Clean your CPAP equipment regularly to get the most from your supplies, prevent skin irritation and get a good mask seal.
• Make sure your pressure settings are correct; if you have gained or lost weight, you may need to contact your doctor to ensure the settings are appropriate.
• Use sinus and nasal care products if you suffer from congestion; blocked sinuses prevent your therapy from working.
• Visit your doctor and ask for your CPAP data to be downloaded to create a plan to improve your treatment.
• Utilise a CPAP app; different brands have designed apps to help you easily track and troubleshoot what’s impacting your AHI. (ResMed myAir, Sefam Access) Please be aware that most apps are only compatible with the brand’s equipment.

Related page: ResMed myAir all you need to know

What is a good AHI?

Sleep specialists believe the ideal AHI for CPAP machine users should be below 5. However, it differs from person to person, and it is normal for the number to fluctuate.

Please note: If you use an oral appliance for treating your OSA, you may need additional tests by your doctor to see the change in your AHI.

What is Sleep Apnoea?

Obstructive Sleep Apnoea is a common sleep disorder affecting around 4 million people in the UK.

It causes the upper airway to become blocked during sleep, which leads to breathing interruptions or pauses. 

Symptoms of OSA:

• Morning headaches
• Choking during sleep 
• Snoring
• Irritability
• Waking up with a dry mouth and throat.
• Anxiety and depression

Untreated Sleep Apnoea can lead to the development of more severe health conditions. Such as heart disease, high blood pressure, type 2 diabetes and atrial fibrillation. That is why it is essential to take a sleep test if you think you have OSA.

In-home sleep test and AHI

If you show symptoms of OSA, you should take a sleep test.

When completing a sleep study or sleep test, your AHI is calculated.

If you choose to take a private in-home sleep test, you will receive a detailed sleep report referencing your AHI throughout the night.

Our Sleep Test experts use this data to recommend the correct treatment for your OSA. Treatment options vary, from CPAP therapy and lifestyle changes to CPAP machine alternatives. 

To Summarise

Your AHI indicates the severity of your Sleep Apnoea; treating the sleep disorder manages and controls your breathing disruptions.

If you need any help or advice, contact us.