Understanding AI, HI and AHI results

Although I've been a CPAP user for two years, I only recently got interested in learning about my nightly sleep eficacy since I changed from a Respironics M Series CPAP to the Resmed S8 Autoset II. I've been reading and trying to sort out the differences between the Apnea Index, the Hypopnea Index and the Apnea/Hypopnea Index.

If I understand it correctly, the Apnea Index is the number of time I quit breathing for at least 10 seconds per hour. The Hypopnea Index represents the number of times per hour my breathing became shallow (less than half of the normal level) for 10 seconds or more. The Apnea/Hypopnea Index is the combined number of apnea and hypopnea events per hour.

Where I think I am getting confused is the purpose of measuring the apnea and hypopnea events separately rather than just looking at the AHI. What are the "normal" levels for the AI and HI? I know the AHI "normals" and I have found those posted in various messages threads on the site. I don't know what the normals are for the other two indexes, however.

Also, what is an acceptable leak level?

Thanks for any help anyone can offer.

You want to see your AI and your HI separately so you know what type of events are making up your AHI and how many of each. Since AI are the worst events you want to know that you are at a pressure(s) that will keep that AI number as low as possible.

You also want keep your HI as low as possible so it's good to see how many of those you are having as well. Resmed machines register more HI than other brands of machine, so on a Resmed the HI will probaly be higher.

You want to try to keep the AHI at least at or below 5. Most people do better when it is below 3. The sleep medicine profession is happy if the AHI is 5 or below.

The acceptalve leak rate depends upon which mask you are using. On the Resmed, you need to tell the machine which mask you are using for it to adjust to show the leak rate. For Resmeds it is measured in litres per second - I think. I'm not very familiar with Resmed machines. You want 0.0 for your leak rate. A very little bit above that is acceptable but not much. Someone who uses a Resmed can tell you what that very little bit above 0.0 would be.

Thanks. I checked my data for the past week and here was the readout:

Used: 43 hours; 7 of 7 days
Pressure: 12
AHI: 6.5
AI: 1.4
HI: 4.6

That looks very good, mdbarthe. I mentally cut the HI (hypopnea index) in half when I'm using a ResMed S8 machine, but that's just me.

If that were my data from a ResMed S8 machine, I'd figure I had gotten this:

AI 1.4
HI 2.3 (by cutting the 4.6 in half)

for an overall AHI of 3.7

I'd be pleased with that.

Hawthorne wrote:The acceptalve leak rate depends upon which mask you are using. On the Resmed, you need to tell the machine which mask you are using for it to adjust to show the leak rate. For Resmed machines it is measured in litres per second - I think. I'm not very familiar with ResMed machines. You want 0.0 for your leak rate. A very little bit above that is acceptable but not much.

Right...regarding "S8" machines.

I think the acceptable leak rate with ResMed S8 machines is supposed to not get over .40 l/s. Zero is ideal with a ResMed S8 machine.

My edit: Added "S8" to all my references to ResMed machines in this old post, since the definition of hypopnea was changed by ResMed in the later S9 series machines.

Hi -

I'm curious whether anyone knows the background behind ResMed over-reading HI. I've never used another machine. Is it a matter of being over-sensitive - reporting a hypopnea event for every irregularity in my breathing rhythm? As long as it's not under-report apneas, I suppose I'll keep using the machine....

Also, does anyone know whether AI and HI, being similar events of different severity, have different causes?

My Autoset measures leakage in liters / second, but I believe the units can be set somewhere in the clinical menu, so it's worth checking. Still, being near 0.0 will mean about the same in any likely unit system.

Thanks to all of you who replied. I really appreciate your information. As for the reason Resmed measures the HI so high, I have no idea but I have heard nearly everyone on this site say that at one time or another.