Why High AHI using DreamStation vs AirSense 10??

[Fixit50]

I’d like to get some guidance on a few things.  I have two machines right now, AirSense 10 autoset and DreamStation auto.  I have to give one back soon.  The ResMed always gives very low AHI scores but makes some noise on exhale that I find distracting.  I think its normal for the machine.  

• The DreamStation AHI scores seem to range from 4 to 14 and the DreamStation average pressures are normally lower than the AirSense pressures.  Don’t know if lower DreamStation pressures explain the higher scores or not?
  
• Last night I used the DreamStation for the first time in 5 days and got AHI of 14.  If I use it for a few days in a row it seems to get lower, not sure if this makes sense or if it's just coincidence.  Even though the score is not good, I don’t feel a noticeable difference in the morning depending upon the machine I used.  
  
• Why are the AHI numbers so much higher with the DreamStation?  Does this mean it’s not as good for me or does it have to do with how the two companies define events? 
  

You can find some DreamStation data here:
https://imgur.com/a/LysSZ
The top graph is the whole night followed by blow-ups of specific parts.  Note the fast breathing rate at some times. 
You can find data from the AirSense 10 in my prior thread Here in posts 1,4,9,10:
http://www.apneaboard.com/forums/Thread-...ing-apneas 
and also at these links:
https://imgur.com/a/j72rZ
https://imgur.com/a/52Upo  

All help and guidance is appreciated.  Thanks!

[Shin Ryoku]

I too find that I get higher AHI with my Dreamstation than with my Resmed Airsense 10 Autoset. I have not yet figured out whether it's a difference in how AHI is measured vs how effective the treatment is.

One clue is that I seem to get more "events" scored while awake wearing the Dreamstation than I do with the Resmed. Thus I think the Dreamstation probably has more false positives. But that is a very preliminary observation because I've only used the Resmed for a few days now.

[jaswilliams]

The resmed machine responds to apnea more aggressively than the dream station. You are running a low initial treatment pressure that does not treat you apnea the resmed gets to an effective pressure quicker than the dream station if your initial pressure was closer within 2cm of your 90% treatment pressure both machines would be as effective. An initial pressure of 8 or 9 would give lower ahi’s

Jason

[Fixit50]

Thanks for these two responses. Both make good sense.
The data shows that there are a lot of apneas during the ramp time when pressures are below therapeutic and after the minimum auto pressure is reached but while the DreamStation is (too) slowly responding to apneas. I may need decrease the ramp time or increase the ramp start pressure and increase the minimum pressure probably to at least 12. That should probably help at least as a start as long as its still comfortable to fall asleep.

[Crimson Nape]

Fixit50,
Does the Dreamstation record events during the ramp time? I know that the Resmed S9 doesn't record events during the ramp period. I am guessing the A10 may do the same.

[Fixit50]

Yes, I found recently that the A10 does not log events until the ramp has completed. The DreamStation ramp is quite different however to the ResMed ramps in its function. All it does is stay in auto titration mode but with a different minimum pressure until the ramp time has run out or the minimum auto pressure is reached, whatever comes first. That’s different that ResMed’s ramp and yes, the DreamStation does log events during the ramp. This contributes to the appearance of a higher AHI for the DreamStation because during its ramp period (I have it set to 20 mins) therapeutic pressures have not yet been reached. In my case the ResMed’s ramp runs out quickly so I don’t often have many apneas during ramp but it does happen.
Also, besides the reasons stated thus far to explain the higher AHIs with the DreamStation, I have also seen events logged in the DreamStation that are less than 10 seconds long! I don’t understand that since I thought those were not supposed to qualify as events. Maybe the DreamStation applies a different definition of Event??
There’s a lot to learn if you want to get a good night’s sleep!

[ajack]

This issues has been danced around since I joined the site. Is it too impolite to say that the DS has a dumb algorithm? Or is it a case where you shouldn't make fun of the algorithmically challenged and keep saying the DS is a bit slow to respond (is this PC now days?) and needs a pressure closer to the 95%. AKA near enough to fixed cpap. Not that fixed is bad, I think it's underrated.

[Walla Walla]

ajack,

             I'm shocked by your unbiased statement!

[ajack]

I suppose it would have helped if I put [/sarcastic] in there somewhere. You'll be even more shocked when I tell you that I run my ASV epap 1 cm under my 95% (the same as I'm bagging the DS for)..I'll put some charts up to show I'm not BS'ing.

For a new user, the philips apap isn't as plug and play as the resmed, it doesn't make it a bad machine, but it needs someone who knows how to fine tune it, this counts out most DME and doctors who set 4-20, or the ones that are a bit better and set 6-20

here's one from October, my min epap:9 and 95%:9.38
https://i.imgur.com/rP44rTk.png

[Fixit50]

ajack,
Do you have a recommendation for setting the min and max pressures for my DreamStation auto? I was thinking min of 12 maybe 13 and max of 20 (though it probably wont get there). The idea of the higher minimum in my view is to allow the algorithm to increase to a needed pressure faster since it will have less change needed to obtain the needed pressure with the higher minimum. The trade is when the higher minimum is not needed, it will hang out there possibly causing comfort issues. Am I looking at this correctly? I'm not certain I understand the theory of fine tuning the DreamStation or the importance of setting the minimum a specified distance from the 95% pressure.
With the AirSense auto, 10 to 20 gave very low AHI.