POLL: What is your TYPICAL nightly AHI?

jnk wrote:The AHI estimates don't compare well between brands, since it is only trending data. It has been said, for example, by respected equipment experts, that the HI portion of the AHI seems to run about double in ResMeds compared to others. So do you want ResMed users to convert (by taking the HI part out, cutting it in half, and adding it back in to AI to get AHI to make the number more comparable to a Respironics estimate), or do you want them to post actual estimates as reported by their machines?

Jason S. wrote:For most people HI is not much relative to AI. If my AHI is 1.5 on a Respironics machine, my HI might be 0.2. So even if my HI would change to 0.4 on a ResMed machine, it doesn't change the overall AHI that much. The poll should be accurate but could possibly be shifted to a slightly lower (definitely less than 0.5) AHI mean due to the somewhat higher numbers provided by ResMed users.

Jason S. wrote:

jnk wrote:The AHI estimates don't compare well between brands, since it is only trending data. It has been said, for example, by respected equipment experts, that the HI portion of the AHI seems to run about double in ResMeds compared to others. So do you want ResMed users to convert (by taking the HI part out, cutting it in half, and adding it back in to AI to get AHI to make the number more comparable to a Respironics estimate), or do you want them to post actual estimates as reported by their machines?

For most people HI is not much relative to AI. If my AHI is 1.5 on a Respironics machine, my HI might be 0.2. So even if my HI would change to 0.4 on a ResMed machine, it doesn't change the overall AHI that much. The poll should be accurate but could possibly be shifted to a slightly lower (definitely less than 0.5) AHI mean due to the somewhat higher numbers provided by ResMed users.

jnk wrote:My AI is consistently below 1, but my HI is generally between 5 and 8. That HI would likely be 2.5 to 4 on a Respironics.

rested gal wrote: Re: AHI question...
by rested gal on Sun Aug 02, 2009 1:09 pm

. . . trying to compare the AHI numbers from ResMed machines with the AHI numbers from other brands of machines is somewhat like trying to compare apples and oranges.

A person can be getting EXACTLY the same good, effective treatment from a ResMed machine that shows them an AHI of 9.5 (when the AHI is made up mostly of a high HI number and very low AI number) as they would be getting from a Respironics machine displaying half that AHI number.

. . . The "why" (regarding the AHI you see) has to do with where each manufacturer chooses to draw that imaginary line in the sand for calling a flow limitation a "hypopnea."

When you read "your AHI should be 5 or below" -- that statement DOESN'T APPLY TO RESMED MACHINES, in my opinion. With a ResMed machine, if the AI (apnea index) is extremely low and it's the HI (hypopnea index) making up the bulk of the AHI number, I'd say "Your AHI should be below 10 with a ResMed machine." Only then would you be really comparing AHI's between ResMed and Respironics machines, imho.

If you're going to compare AHI's between various brands of machines, you really must take into consideration that each manufacturer uses his OWN DEFINITION of "hypopnea" -- and that definition is different from one manufacturers to another. The different definitions are going to yield different identifying and reporting results. And that's perfectly ok.

I think you should either quit looking for "5", or else convince yourself to chop the HI that you see in half, then re-add your AI and HI (the new chopped one) together to see an AHI that can be more realistically compared (imho) to the AHI you'd be seeing from other brands of machines.

That doesn't mean one brand is right about the HI and another wrong.

It doesn't mean that one brand misses hypopneas that another brand sees.

It doesn't mean that one brand "over-reports" hypopneas or that another brand "under-reports" them.

It's purely a matter of definition of "hypopnea." None of the manufactures uses the same definition of "hypopnea" that is used in a full PSG sleep study anyway, so I'd not worry it.

. . . Mentally cut the ResMed HI (hypopnea index) in half and do some re-adding, if you want a more realistic comparison of your AHI to the "ought to be under 5" AHI that people who are using Respironics machines often talk about. . . .

jnk wrote:I believe it is the rule, not the exception, since brands of machines use very different definitions for what they are estimating, as often explained by rested gal and proved by Velbor's chart:

jnk wrote: My AI is consistently below 1, but my HI is generally between 5 and 8. That HI would likely be 2.5 to 4 on a Respironics.

Jason S. wrote:

jnk wrote:My AI is consistently below 1, but my HI is generally between 5 and 8. That HI would likely be 2.5 to 4 on a Respironics.

I said most people. Exceptions such as yourself would not be statistically significant in a large sample.

Jason S. wrote:

jnk wrote:I believe it is the rule, not the exception, since brands of machines use very different definitions for what they are estimating, as often explained by rested gal and proved by Velbor's chart:

You believe what is the rule, that ResMed machines register AHI differently than other machines? I don't dispute that, and I wasn't referring to that when I said "exception". What I am saying is that if you take the subset of users with ResMed machines, and then further take the subset of users with ResMed machines who have high HI indexes relative to their AI indexes, that sample of people is small relative to the total sample, and therefore statistically insignificant.