High HI affecting AHI rating. Should I be worried?

[ChrisC]

I posted this in my own progress thread, but wanted to specifically address one aspect. Hope you guys don't mind another thread about it. My HI ratings have been >10 and this has, of course, brought up my AHI. I've read RestedGal's posts about Resmed machines over-reporting HI's, and that one should take that number and divide it in half to get a better representation of your HI readings. The only issue is that doing so still gives me AHIs over 5. They're close to 5, but they're still over.

Last night, I put my pressure up slightly to 10.6 from 10 to see if that would help address my HI readings. Unfortunately, it seems to have had the opposite effect (both AI and HI's went up). I wonder if I should be trying to put my pressure DOWN a bit instead of up? Or, should I just be relaxing and not worrying about all this so early in my therapy?

Here are my readings so far:

Date Usage Leak AHI AI HI
26-Mar 7:25 .28L/s 12.9 0.8 12.1
27-Mar 6:14 .32L/s 8.9 1.2 7.7
28-Mar 8:37 .08L/s 11 1.1 9.9
29-Mar 6:51 0.00L/s 12.8 1.7 11.1

[ozij]

Chris,
You also said on the other thread that were ill - had a cold. When I suggested moving the pressure up slowly, I hadn't registered that you were so close to your first night.
I think you should relax, take the machine back to 10 - and stay there for a week after your cold finishes. Adapting to the therapy may take some of us time, even when we don't have colds.

Too many new things at once - and you can't figure out what causes what.

O.

[ChrisC]

Sounds good - I figured I was walking a fine line between being involved and being OCD

[rested gal]

I've read RestedGal's posts about Resmed machines over-reporting HI's, and that one should take that number and divide it in half to get a better representation of your HI readings.

One small clarification...

While it's easier/quicker to say... "ResMed machines over report hypopneas"... that's not quite what I've been saying. Or if I've ever put it like that in an old post, I shouldn't have.

What I've been saying (I hope!) is that each manufacturer uses their own definition of what they will regard as an hypopnea, for the purpose of designing the algorithms for their machines. Velbor posted a chart about the different definitions ResMed and Respironics use:

viewtopic.php?p=353046#p353046

The different definitions the manufacturers use doesn't mean that one manufacturer over reports events or that another manufacturer under reports them. Nor does it mean that one manufacturer is "right" and another "wrong" about what's an hypopnea. Nor does it mean one misses something another gets right. Nor does it mean one is overly sensitive to "hypopneas" or that another is not sensitive enough to identify them.

None of the manufacturers use the definition that most sleep labs use for "hypopnea." A sleep lab is taking into account drops in O2 and/or arousals to define an event. Our treatment machines do not see O2 sats and EEG arousals (thus cannot measure) two of the things that play into a full PSG sleep study's view of when to score a certain amount of flow limitation as an hypopnea.

From our machines' point of view, an hypopnea is an arbitrary line drawn in the sand (different for each manufacturer) for when to quit calling a certain degree of flow limitation "flow limitation" and start calling it "hypopnea."

Again, that doesn't mean that one manufacturer is correct or another is not. Doesn't mean one manufacturer's machines are overly sensitive to "hypopneas" or that another is missing them. Doesn't mean one manufacturer over reports them or that another under reports them. It's purely a matter of algorithmic definitions used by the machine's designer to make each manufacturer's machine go about what the designer intends it to do.

There are two reasons I've talked so often about "cut the HI from ResMed S8 machines in half":

1. If you were to use a Respironics machine and then a ResMed S8 machine, back and forth, you'd probably see quite a difference in the reported AHI...mainly due to a difference in the reported HI number. That doesn't mean one brand "treats" better than another. It's purely a difference in the definition of hypopnea each manufacturer uses. It's an arbitrary line drawn in the sand.... Respironics saying "this flow limitation is still regarded a flow limitation" or ResMed saying "this flow limitation is now regarded a hypopnea" purely for the purpose of what the designer wants the machine to do next.

2. We often speak on the message board of how it's good to get our AHI below 5. We talk about how "under 5" means "effective treatment." That could be very discouraging to users of ResMed S8 machines who see AHI more than 5, mainly because of the reported "hypopneas." They could think they were not getting effective treatment when they really were. So, I encourage people using a ResMed S8 machine to mentally cut the Hypopnea Index (HI) in half, then add that to the Apnea Index (AI) to see an AHI that's COMPARABLE to what they'd see if they were using another brand of machine.

I could just as easily have said, "Hey, users of Respironics and Puritan Bennett and DeVilbiss machines... double your HI and add that to your AI to get your AHI." But then I'd have had to add, "Oh, by the way, forget about trying to get an AHI under 5. Shoot for an AHI under 10, because if your AHI consists almost entirely of those "mentally doubled" hypopneas that's good treatment. And it would be.

Some people will do better (I'm not talking about "better AHI"...I'm talking about actual "treatment better") on one brand or another. However, I think most (not "all"...most) people will get equally good treatment from any brand. I think that's so, even if one person sees an apnea index of 0 and a hypopnea index of 8 when using a ResMed S8 machine (giving a total AHI of 8 ) but sees an apnea index of 0 and a hypopnea index of 4 (giving a total AHI of 4) when using a Respironics machine.

Just my opinion, but I'm not a doctor, and I'm certainly not an expert about machines or how they work.

All that said, it's perfectly understandable why you phrased what RG sez the way you did, Chris. I just wanted to say it a little differently. I would keep cutting that ResMed S8 HI in half mentally, though.

Good advice from ozij! Her post is much more important and useful for you than this lonnnng one of mine.

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.

[track]

Rested gal...I will soon be able to test the difference out between a resmed and a M series. My AHI for the last year with the resmed auto spirit has hovered around 5. It will be interesting to see where it comes out on the M series machine...and if I notice any difference in treatment. After one 90 minute nap I can say that A flex is awesome. It sure beats a constant hurricane of wind blowing in my face.

[rested gal]

Rested gal...I will soon be able to test the difference out between a resmed and a M series. My AHI for the last year with the resmed auto spirit has hovered around 5. It will be interesting to see where it comes out on the M series machine...and if I notice any difference in treatment.

Cool, track! Do be sure that a couple of the comparison nights with the Respironics machine are done at exactly the same settings you used with your Spirit..which means not turning on C-Flex or A-Flex. And with the same mask.

After one 90 minute nap I can say that A flex is awesome. It sure beats a constant hurricane of wind blowing in my face.

Ain't that the truth!

[JoyD.]

The different definitions the manufacturers use doesn't mean that one manufacturer over reports events or that another manufacturer under reports them. Nor does it mean that one manufacturer is "right" and another "wrong" about what's an hypopnea. Nor does it mean one misses something another gets right. Nor does it mean one is overly sensitive to "hypopneas" or that another is not sensitive enough to identify them.

None of the manufacturers use the definition that most sleep labs use for "hypopnea." A sleep lab is taking into account drops in O2 and/or arousals to define an event. Our treatment machines do not see O2 sats and EEG arousals (thus cannot measure) two of the things that play into a full PSG sleep study's view of when to score a certain amount of flow limitation as an hypopnea.

From our machines' point of view, an hypopnea is an arbitrary line drawn in the sand (different for each manufacturer) for when to quit calling a certain degree of flow limitation "flow limitation" and start calling it "hypopnea."

Again, that doesn't mean that one manufacturer is correct or another is not. Doesn't mean one manufacturer's machines are overly sensitive to "hypopneas" or that another is missing them. Doesn't mean one manufacturer over reports them or that another under reports them. It's purely a matter of algorithmic definitions used by the machine's designer to make each manufacturer's machine go about what the designer intends it to do.

Rested Gal,

This was very helpful to me to put things in perspective . . . and to get a better feel for what a CPAP machine "is", and is designed to do . . . thanks for your lengthy explanation!

Joy

[Hermit]

'This was very helpful to me to put things in perspective . . . and to get a better feel for what a CPAP machine "is", and is designed to do . . . thanks for your lengthy explanation!'

can I second that??great explanation..
hermit

[Uncle_Bob]

Thanks rested fal thats very reassuring
Given that i got these readings last night
Leak 0.0
AI 0.3
AHI 8.7
Usage 7.46 hrs
Halving my HI puts my AHI under 5, which is even better. At this point its going to be tough getting my anti APAP doc to let me switch.

[ChrisC]

RG: Just wanted to say sorry for paraphrasing, and to thank-you for the thorough explanation! The rumours are true - you DO rock!!