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S8 vs S9 AHI Event readings
#1
I just got my new S9 Autoset yesterday.

I been running an S8 Autoset for the past few years with AHI Events between 4 and 5.

First night on the S9 I got a 1.32 AHI.

I wonder if it was just an extra good night (although I never had a number below 3.0 AHI with the S8).

Setup is the same. Both machines running in plain CPAP mode at 12cm H20. Same mask, same bed, same pillow, same wife.

I wonder if anyone else experience lower AHI numbers with the S9 over the S8???
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#2
I've only ever had an S9, but I do notice different numbers when I swap wives. :-p

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#3
(04-18-2012, 02:23 PM)CHanlon Wrote: I've only ever had an S9, but I do notice different numbers when I swap wives. :-p

Laugh-a-lot Too-funny Bigwink

Its been said over the years that the S8 is more agressive when it comes to registering apneas and again you have seemed to add more weight to the argument. The only real way of getting proof is to wear two machines at once but this cant be done. It does seem to be though that the information is true but thats only my opinion.

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#4
Each machine having a different algorithm is going to record AHI differently, (such as the variations between the S8s and S9s which have differing algorithms). Probably more variation between two separate brands of machine as well (ResMed S9 vs. PR System One Auto).

What's important is not so much what the recorded AHI is, but rather your trend data. Most of these modern machines will accurately record the trends for you, which is what you will use to determine the most effective pressure(s) over time.

In other words, it would be inaccurate to say "since the S9 is recording my AHI at 2.0 and the S8 records it at 2.3, the S9 is doing a better job of lowering my AHI levels".

Now, some of that decrease in AHI may in fact be due to a more refined and updated algorithm and better equipment in the S9 units over the S8 units. So some of the lowering of your AHI is for real... but you can't determine that for certain unless you use two machines simultaneously (which as Dreamcatcher pointed out, is impossible).

One thing I will say, is that with a 1.32 AHI on your first night, that is AWESOME. I wouldn't change a thing at this point in your therapy. I can only wish that I could get AHI numbers at that level on a consistent basis.


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#5
All good points.

I agree the AHI Events reading is more of a relative thing. As long as the trend in numbers stays the same or goes down I am happy.

Main reason for upgrading to the S9 was for the CA detection. The older S8 would not do that.

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#6
Can any more experienced user comment on how the S9 reports CA (presumably central apnea)? In other words, could it be inferred from the marked reduction in AHI on the S9 that many of the 'AHI' recorded by the S8 were actually CA and no longer treated by the algorithm or recorded? Or are they recorded in some way but just not treated (by escalating pressure)?

I am considering the purchase of an S9 so this is not just a rhetorical question for me. The answer might have some clinical significance for Tom also.

(04-18-2012, 04:15 PM)Tom Wrote: All good points.

I agree the AHI Events reading is more of a relative thing. As long as the trend in numbers stays the same or goes down I am happy.

Main reason for upgrading to the S9 was for the CA detection. The older S8 would not do that.

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#7
CSA detection
It uses the Forced Oscillation Technique (FOT) to determine whether the airway is open or closed during an apnoea. Small oscillations in pressure are added to the current device pressure.
The CSA algorithm uses the resulting flow and pressures to measure whether the airway is open or closed.
http://www.s9morecomfort.com/s9morecomfo...toset.html

Central Sleep Apnea Detection and the Enhanced AutoSet Algorithm
http://www.resmed.com/au/assets/document...-paper.pdf
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#8
(04-19-2012, 12:43 AM)SlightlySleepy Wrote: Can any more experienced user comment on how the S9 reports CA (presumably central apnea)? In other words, could it be inferred from the marked reduction in AHI on the S9 that many of the 'AHI' recorded by the S8 were actually CA and no longer treated by the algorithm or recorded? Or are they recorded in some way but just not treated (by escalating pressure)?

I am considering the purchase of an S9 so this is not just a rhetorical question for me. The answer might have some clinical significance for Tom also.

(04-18-2012, 04:15 PM)Tom Wrote: All good points.

I agree the AHI Events reading is more of a relative thing. As long as the trend in numbers stays the same or goes down I am happy.

Main reason for upgrading to the S9 was for the CA detection. The older S8 would not do that.

(04-19-2012, 01:13 AM)zonk Wrote: CSA detection
It uses the Forced Oscillation Technique (FOT) to determine whether the airway is open or closed during an apnoea. Small oscillations in pressure are added to the current device pressure.
The CSA algorithm uses the resulting flow and pressures to measure whether the airway is open or closed.
http://www.s9morecomfort.com/s9morecomfo...toset.html

Central Sleep Apnea Detection and the Enhanced AutoSet Algorithm
http://www.resmed.com/au/assets/document...-paper.pdf

It still records them as events, and they still add to your AHI - so that doesn't explain the AHI reduction. That could be a change in the algorithm that detects them, or a "policy change" on what constitutes an event. Or even a higher success rate at preventing them. Don't think I've seen any definitive answer.
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