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Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
#1
Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
Think I discovered a bug in Oscar and I've been doing some detective work on the board here to confirm. It seems many unknowingly have the same issue. 

Basically if you're using in F20 mask on an Airsense 10, your Inspiration time is going to record higher than your Exp time when that is likely not the case. Usually a insp time higher than a Ex means you have significant flow limitation, but as you can see below, I do not. 

I tried using a dreamwear full face mask and the insp time was correctly calculated. I don't know if it's just harder to pick it up with the mask or what, but something I think should be flagged for people looking out for these things. 

Below is a picture of my stats with F20 and the second is the next night with a dreamwear full face mask The difference is apparent, but had a similar AHI.


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#2
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
The inspiration times are from my understanding are recorded by the machine and just graphed by OSCAR.

What you will probably notice in your detailed data is the presence of cardiogenic oscillations or something else causing flow rate to pass over the 0 flow line multiple times per breath. This confuses the machines and ends up with them not reporting the correct inspiration times. This is a known issue for people like myself with cardiogenic oscillations.

The fact that your inspiration data appears more accurate with a different mask is interesting. You would have to look at the detailed flow rate data to try and understand why that is the case and whether or not the one mask might be more effective for you for some reason.

My guess is it is related to different venting rates but that is just a guess. The f20 has very low venting rate and may be more prone to showing fine data like cardiogenic oscillations whereas other masks with higher venting those little details may not be as present.
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#3
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
It is interesting! And it makes sense it's the machine, and not a problem with oscar. 

Below you can see the two different flow rates. The longer inspiration is obviously with the F20, the second is with the dreamwear mask. 

I felt the same with both, the venting makes a little sense. I think there just might be some sort of lag with the F20 communicating with the machine once EXP starts. I've looked through the board trying to see if others who used an f20 mask and had an Airsense 10 had similar Inspiration numbers and every single one I saw did. That's why I'm thinking it doesn't mean I'm breathing better with one mask over the other, just that the calculation is wrong.


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#4
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
In the first example you can see the longer period of near zero flow at the end of exhalation and the odd little bumps that cross 0 flow rate. Thise bumps are cardiogenic oscillations and when they cross the 0 flow rate the screw up the inspiration time by starting it too early (moment first cardiogenic oscillations crosses 0 flow rather than when the primary inspiration starts).

It is sort of interesting that your exhalation appears shorter and there isn't the same dwell at low flow rates. Part of that can be due to a different sleep stage but part appears to be the different mask and that could just be an interesting point or it may or may not indicate more effective exhalation or something along those lines. From a therapeutic sense I don't know which breath shape indicates a better exhalation cause it isn't clear if the longer near zero flow exhalation of f20 mask is due to lower exhalation efficiency drawing out the process or if the initial exhalation is that much more efficient so the body just waits until it is ready to inspire.

Either way it isn't worth worry about imo. Just worrh noting the inspiration times are often wrong due to thr simple way they calculate these times.
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#5
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
I hope I don't mess up too many theories raised in the above posts... however, the autoset models do not report I and E times; they are calculated by OSCAR for these machines.

I believe sawinglogz has looked at these calculations and was not convinced of their accuracy in all situations, but we have not been able to review them in detail.

For the moment, a detailed comparison at the zoomed in flow rates of the two masks may give some answers. Also compare the mask vent charts.
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#6
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
Thanks for confirming that pholynyk, I used to blame OSCAR but then was told it was the machine not OSCAR and have believed that ever since.

Do the vautos calculate their own I and E times? I did find it strange how my autoset never correctly determined my inspiration times but my vauto seems to do so fine. I assume because the vautos do infact record at least inspiration time since that is one of the features timing controls are used to manipulate.
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#7
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
The vAuto machines report I and E times and I:E ratio.
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#8
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
So modest811 the correct answer to your question is that OSCAR can struggle to calculate inspiration times accurately if things like cardiogenic oscillations are present but the reason you get different results with different masks is because your data/breathing is different. I am going to stick with initial guess and say this is related to the venting of the two masks as the dreamwear has noticeably more venting than F20.
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#9
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
Interesting. So you these squiggly lines on my inhale are cardiogenic? It sees these are what are what making my Insp time come up as more. I don't think they're a flow limitation, but maybe they are?


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#10
RE: Inaccurate Insp. Time and Exp. Time with Airfit F20 mask and Airsense 10
Modest, that pattern has often caused both Philips machines and the Autoset to show excessive inspiration times. There are a couple of ideas to use several increasing flow rates to indicate the start of inspiration, rather than just crossing the zero-flow to positive. It's not always an easy thing to identify as the machines are known to lose the zero-flow crossover under certain circumstances. The worst right now is the Philips machines which consistently get start of inspiration wrong. Trust me, we've been looking at this for at least two years. Getting the inspiration break to the top of the queue has been challenging with the introduction of new machines and working out other problems.
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