Users of continuous positive airway pressure (CPAP) devices and apps often report feeling confused by the data they are presented with. The AHI is one such, if not the most significant measures that your CPAP machine records. In this article, we’ll discuss how to evaluate your AHI and what steps you may take to bring it down if necessary.

In CPAP terms, what does an AHI mean?

Apnea-hypopnea index is the abbreviation for this measurement. Sleep studies are the gold standard for estimating AHI. The word REI (respiratory event index) may be used instead of AHI in a home sleep apnea test result.

In CPAP terms, what does an AHI mean?

When you remove your CPAP mask in the morning, many devices may display information about your use the night before, including your AHI. To differentiate this value from the AHI that is determined by the gold standard, a sleep study, I prefer to call it the “calculated AHI” or cAHI.

With the use of a CPAP machine’s smartphone app, you may collect and analyze more data over time. You need to connect your CPAP machines to a clinical database in order to get the full range of available information. The AHI is broken down into snoring, central apneas, obstructive apneas, and hypopneas, which I, as a sleep physician, can access.

CPAP: what’s a decent AHI?

In most cases, the cAHI should be set at or below 5, as this value indicates the absence of sleep apnea as determined by a sleep study. From what I’ve seen, a cAHI of 5 or less is considered good, but a cAHI of 3 or less indicates that your sleep apnea is under excellent control. Please be aware that I have never encountered a zero AHI. No matter how well you program your system, it will always estimate a small number of breathing occurrences as a residual.

“Treat the patient, not the numbers” is a common medical maxim. Nighttime oxygen level studies are frequently checked if an AHI is high despite the patient’s report of good sleep and general well-being during the day. I will not adjust the CPAP settings if oxygen levels are within normal range. You can read about CPAP and Bi-level PAP Therapy: New and Established Roles by clicking here.

Ways the CPAP machine reports the AHI

An AHI estimate is calculated by CPAP devices using proprietary algorithms. We sleep doctors think the gadget “pings” your airway with little bursts of air to test if it is open, measuring resistance to the airflow they are trying to provide.

CPAP machine reports the AHI

For example, a CPAP machine will “ping” your airway if it detects a lack of airflow for more than 10 seconds. An obstructive apnea is detected if the air packet is reflected back to the monitor, indicating that the airway was blocked. If the air packet doesn’t come back, it indicates that your airway was clean and that this apnea was central. Hypopneas are thought to occur when there is a sudden and dramatic increase in resistance to the airflow given by the CPAP for at least 10 seconds.

Keep in mind that the cAHI should be viewed with caution because CPAP devices do not conduct diagnostic sleep studies on you on a nightly basis. Visit to read about the Guide on How to Set Up Your CPAP Pressure Correctly.

Is the CPAP AHI reliably accurate?

Not at all true. Keep in mind that the cAHI can provide you a very accurate picture of how well you’re performing overall. Moreover, it is essential to examine the data patterns, rather than relying on a single night’s worth of information, before drawing any judgments. Mask seal, alcohol consumption, drugs, body posture, altitude, and other variables can all affect AHI from one night to the next. Before evaluating whether or not a CPAP machine has to be changed based on the cAHI, we want to gather at least two weeks of continuous data.

By and large, we have found that the AHI from a sleep study done on the same patient while they were using CPAP is much greater than the cAHI from the CPAP machine. The cAHI may be grossly underestimating the true incidence of residual abnormal breathing occurrences, as we believe it does.

The cAHI can give you a ballpark figure for how many residual abnormal breathing episodes you’re averaging each hour, but it shouldn’t be seen as gospel.

How can a CPAP’s AHI be reduced?

To put it simply, high leak is the most prevalent cause of a high cAHI. Your airway will continue to collapse if air is exiting from the system rather than entering your throat. When a leak occurs, it might be one of two types: the mouth leak and the mask leak.

The most prevalent sign of a leaking mouth is a persistently dry mouth when you wake up. Wearing a full-face mask or chin strap if you’re experiencing this is highly recommended.

If your CPAP mask is leaking, you need to replace it. Those who use CPAP and sleep on their side may also require a certain type of pillow.

Complex sleep apnea, in which you have obstructive sleep apnea before starting CPAP, can also lead to a high CPAP AHI.

With this issue, there may be a need for you to adjust the pressure in your machine. Among the many possible ways to this are:

The pressure reading from your machine may be inaccurate for you due to a number of reasons, including but not limited to: your body weight; some kind medical conditions that might exacerbate sleep apnea, such as hypothyroidism, PCOS, atrial fibrillation, heart attacks, and strokes; New drugs that can impact muscle tone or the diameter of your airway, such as testosterone;

If your AHIs have been consistently high and the cause does not appear to be a leak, you should consult a sleep specialist.