Many individuals who have only recently been diagnosed with sleep apnea or who think that they may have sleep apnea may be confused by the words ‘apnea hypopnea index’. This is a common phrase that you’ll find on pretty much every piece of apnea information and it may be confusing for people new to this information. I talk you through the apnea hypopnea index and how it relates to you and your sleep apnea.
Overview
Sleep apnea is characterized by lack of airflow, causing you to stop breathing literally hundreds of times a night. The word apnea is the Greek word for ‘without breath’ and is characterized by an approximate reduction in airflow of 80%. Hypopnea is a less severe episode and is characterized by a reduction in airflow of around 50%.
In an apnea episode, you may stop breathing for ten seconds or longer, whereas in a hypopnea episode, you may have abnormally shallow breathing for ten seconds or longer.
You’ll be given a scale number after either a sleep study done at a clinic or a sleep study done at home.
What is the Apnea Hypopnea Index?
The apnea hypopnea index, or the AHI, is an index that’s used to categorise the severity of sleep apnea episodes. It counts how many times you have apnea or hypopnea episodes per night, the number of which is then divided by the total amount of hours you’ve slept which gives you an average number of apnea or hypopnea episodes per hour.
The AHI scale for adults is as follows:
- Fewer than 5 episodes of abnormal sleep episodes per hour is considered normal = AHI under 5
- Between 5 and 15 episodes of abnormal sleep episodes per hour is considered mild = AHI between 5 and 15
- Between 15 and 30 episodes of abnormal sleep episodes per hour is considered moderate = AHI between 15 and 30
- Over 30 episodes of abnormal sleep episodes per hour is considered severe = AHI over 30
In some cases, a disorder called Upper Airway Respiratory Syndrome is taken into account when counting abnormal sleep episodes. In this disorder, the airflow meets resistance in the mouth which causes the sleeper to waken. The American Academy of Sleep Medicine takes into accounts apnea, hypopnea, and episodes of flow limitation in UARS for their sleep scale – the Respiratory Disturbance Index or RDI.
The RDI scale is calculated in the same way as the AHI – the number of abnormal sleep episodes over the night are counted and then divided by the number of total hours of sleep.
The RDI scale for adults is as follows:
- Fewer than 5 (including 5) episodes of abnormal sleep episodes per hour is considered normal = RDI of 0 – 5
- Between 6 and 20 episodes of abnormal sleep episodes per hour is considered mild = RDI of 6 – 20
- Between 21 and 40 episodes of abnormal sleep episodes per hour is considered moderate = RDI of 21 – 40
- Over 40 episodes of abnormal sleep episodes per hour is considered severe = RDI of over 40
Remember that this scale could change depending on your doctor and sleep clinic. Generally, anything over 10 episodes of abnormal sleep per hour, on both the AHI scale and the RDI scale will get your doctor to begin to explore the options of treatment with you.
You should also remember that your AHI/RDI number is an average. If your number is 30 or 40, that doesn’t mean that you will have 30 or 40 episodes of wakefulness during every single hour of sleep. What is more likely is that you’ll have two or three hours of uninterrupted sleep, followed by a few hours of lots of abnormal sleep episodes – these episodes are more likely to happen during REM sleep, so you may find that when you drop off you’re okay and early in the morning as you’re waking up you’re okay.