Different ways of scoring AHI

[Cuppa]

Since changing from the Resmed S10 Autoset to the Devilbiss Intellipap 2 my AHI has changed

It changed on the first night I used the Intellipap2.

On the Resmed my AHI varied between 0.5 & 2  (over 4 weeks)
With the Devilbiss my AHI varies between  2.5 & 4.75 (over 4 weeks)

The CA's remain about the same. - averaging around 0.5
The OA's remain about the same - averaging around 0.3

The Hypops are what have have pushed up the AHI - the Devilbiss machine is recording far more hypops than the Resmed did.

The Devilbiss allows for the parameters of the 'definition' by the algorithm of hypops to be changed within certain limits. The results I am seeing is with there needing to be a flow restriction of 50% for a minimum of 10 seconds to qualify as a hypopnea.

Can anyone tell me how the Resmed machines define a hypopnea?  I'm wondering if they require a greater flow restriction before labelling an event a hypopnea?

Thanks

[xxyzx]

Since changing from the Resmed S10 Autoset to the Devilbiss Intellipap 2 my AHI has changed

It changed on the first night I used the Intellipap2.

On the Resmed my AHI varied between 0.5 & 2  (over 4 weeks)
With the Devilbiss my AHI varies between  2.5 & 4.75 (over 4 weeks)

The CA's remain about the same. - averaging around 0.5
The OA's remain about the same - averaging around 0.3

The Hypops are what have have pushed up the AHI - the Devilbiss machine is recording far more hypops than the Resmed did.

The Devilbiss allows for the parameters of the 'definition' by the algorithm of hypops to be changed within certain limits. The results I am seeing is with there needing to be a flow restriction of 50% for a minimum of 10 seconds to qualify as a hypopnea.

Can anyone tell me how the Resmed machines define a hypopnea?  I'm wondering if they require a greater flow restriction before labelling an event a hypopnea?

Thanks

i think it is in the resmed manual

it is more likely how  they think they measure it rather than the definition  

i would worry more about my o2 minimum 
all the indices do is say if its >10 seconds they count it

they dont care how long which is important to your health and safety as O2 gets lower the longer you do not breathe or breathe well

all the indicies are using a surrogate statistic to get one overall number for doctors to use as a guide

[Gideon]

I may be wrong here but. . .
I have and used the orig Devilbiss for years and I recall that they are much more sensitive to Hyponeas. I recall they used a 30% reduction in flow vs a standard 50% reduction.

[eseedhouse]

The AHI is a standard and is simply the total number of apneas plus hypopneas in a sleep session divided by the hours slept. AHI is a diagnostic tool. If your AHI is over 5 then you have sleep apnea that needs to be treated according to the medical community.

The trick is how you define an apnea or a hypopnea. This is more difficult for the machines because they don't have access to the kind of data a sleep study uses. Still, these measurements are pretty good - close enough in general for most people.

Of course AHI alone isn't a complete measurement since a 100 second apnea will count the same as a 10 second one. This is also true in the sleep clinic.

But your machine also gives the total time in apnea, and this together with the AHI is probably enough for the "normal" user. If your AHI is going down or holding steady but your Total Time in Apnea is going up this is a signal you should check more closely.

For most patients most of the time AHI is close enough. For some (me included) it isn't, but usually it is. If, say, your AHI is nice and low but you still feel lousy and especially if you feel you are deteriorating then your doctor should be consulted as you may need a different or supplementary treatment (as I did).

[Cuppa]

I may be wrong here but. . .
I have and used the orig Devilbiss  for years and I recall that they are much more sensitive to Hyponeas.  I recall they used a 30% reduction in flow vs a standard 50% reduction.

For hypopneas those reduction flow percentages on the intellipap2 can be altered with 30% reduction the most sensitive & 50% the least sensitive. Default is 40%. I set mine at 50%. Minimum time in that flow reduction can also be changed between 10 seconds & 16 seconds.  Default is 10 seconds which I left it at as that seemed to be comparable with what the hired Resmed machine I initially had did.

Last night I experimented with the machine in APAP mode again. I tried this when I first got it but changed back to fixed pressure which I've remained on since (until last night). The reason I didn't keep it on APAP before was that I experienced what I now understand to be called 'pressure runaway' over several nights.

My prescription pressure is 8cm h20.   Previously when I tried 7 to 9 (with 2 flex) resulted in the machine rising to 9 & staying there most of the night with little difference to my AHI results. So I returned to a fixed pressure of 8 as this gave me less aerophagia discomfort.

From reading here, I learned that having lower settings closer to one's prescription pressure when in APAP mode can help with reducing hypops as well as potentially helping to prevent pressure runaway with certain machines (Devilbiss included).

So last night I tried APAP again, this time set at 8 to 9.5. (& 2 flex). This mornings result has been quite remarkable (to me).  AHI dropped by almost half to 2.5. Within this figure CA's dropped to zero, & OA's dropped to zero, Hypops at 2.5. First time ever that I've had zero CA's & OA's. Of equal interest the 90th & 95th percentile for pressure were both 8.5 with an average pressure of 8.1. ....... so an improvement in events & no pressure runaway!  The overall percentage of time  in flow limitation over 8 hours was 0.5%. This spread fairly evenly through the night ..... which suggests (I think) that O2 desaturation shouldn't have been too bad at all.

So I think this is clearly a step in the right direction. It's tempting to set the minimum pressure to 8.5 to see if this drops the hypops further.... BUT I now plan on continuing with the 'new' setting for a while to see if these results remain stable first. Sound sensible to you more experienced folk??

[pholynyk]

Instead of increasing your minimum to reduce the hyponeas, you might try increasing your flex setting. I found, with my AirSense, that maximising my EPR minimised my hyponeas. I'd love to see what a Bi-level could do for me, but with a usual AHI between 2 and 3, it's not likely.

[Cuppa]

Instead of increasing your minimum to reduce the hyponeas, you might try increasing your flex setting. I found, with my AirSense, that maximising my EPR minimised my hyponeas. I'd love to see what a Bi-level could do for me, but with a usual AHI between 2 and 3, it's not likely.

By 'increasing' the flex setting do you mean

Increase from 2 to 3 (ie. greater flex/ lower flex pressure)

OR
Reduce the amount of flex (from 2 to 1) (ie less flex/ higher flex pressure) ?

I suspect yo mean the latter?

[pholynyk]

Nope, I mean go from 2 to 3. It has been shown that increasing the pressure support (EPR, flex), in the absence of CA, will decrease the hyponeas. It's not the flex pressure that increases, but rather the differential between inhaling and exhaling that increases. It works for me and several others, it may or may not work for you; you just have to try it for a few days.

[PaytonA]

If I remember correctly the definition of hypopneas is a 30-50% reduction of flow with a certain amount of desat. When Resmed went from the S8 models of machines to the S9 models they changed the flow reduction requirement for the machine to score a hypopnea. The flow limitation is defined by Resmed as a flattening of the inhalation curve, whereas a hypopnea has the normal breathing curve it is just smaller in amplitude. All I could find for flow limitation with a quick search was Expiratory flow limitation which appears to be a different animal entirely and is something that the machines are not capable of scoring directly.

Best Regards,

PaytonA

[Cuppa]

Thanks, the info has been useful. I'll trial last night's APAP setting for a week to see if the results stay similar & will then try adjusting the flex as suggested. If then the flex adjustment reduces the number of hypops further, I may return the hypop detection algorithm to the default 40% (from 50%) reduction in airflow, as I guess that potentially this could make the machine more responsive.