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Understanding Flow Limitations and Flow Rate Shape
RE: Understanding Flow Limitations and Flow Rate Shape
Based on your symptoms I believe that you have UARS and need/should advance your treatment.

I see two options

1. Traditional approach is to get a BiLevel without Backup (your breathing is not stopping) and IMHO the BiLevel that you should get is the ResMed VAuto.  Treatment would basically be increasing your PS (currently at 3 (EPR))

2. By a few very well respected sleep doctors an ASV is being used.   This would be in AutoASV mode with minor adjustments to EPAP Min and PS range.  This is the more expensive option.  Read this post. http://www.apneaboard.com/forums/Thread-...ed-PAP-ASV

ASV is without question more expensive and qualifying for ASV is not easy, especially with UARS.

Your thoughts please.
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RE: Understanding Flow Limitations and Flow Rate Shape
I have read a post by Dr. Krakow before about bilevel and did read the abstract about his use of ASV in complex insomnia patients. I think it's compelling and asked my doctor about bilevel PAP, but he very much seemed against the idea, so I'll probably end up trying a second-hand bilevel first and if I feel I want to then try ASV...I'll have to work to get a prescription for one of those as they're probably harder to find.

I am interested in trying it out for sure.

Krakow, in the interview you linked, mentioned subjective and objective expiratory pressure intolerance (EPI). I feel like don't have subjective EPI and I don't fully know what to look for in regards to objective EPI, so unless you or someone else has a good idea of what that looks like, I'll probably be going solely on ease of my symptoms. Also, it sounds like Krakow overrides the standard ASV algorithm when he uses it on patients. Do you know anyone who knows how to do that, or would this just be another setting you can fiddle with.

I hope that there is research in the future that can help definitive prove and convince more doctors of some of Krakow's experience.
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RE: Understanding Flow Limitations and Flow Rate Shape
On ASV, I think what Krakow does is nothing special; he just tweaks the handful of EPAP and PS settings to, as he says, best "normalize the airflow curve" and ensure good sleep architecture. One can always do that oneself, using insights from OSCAR.

Getting a used VAuto to try would be a good option, per Fred. I think standard auto bilevel is sufficient for most people with UARS. The exception is if you happen to need high enough PS to cause central apneas.

Do note that Krakow compares in interviews like the one in that linked thread between ASV and CPAP; not ASV and standard bilevel.
Caveats: I'm just a patient, with no medical training.
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RE: Understanding Flow Limitations and Flow Rate Shape
I strongly concur with bonjour and slowriter and was pleased to see bonjour's recent post and Wiki item dealing with UARS and flow limits, both of which seem to be in a Sleep Medicine/Insurance blind spot. Getting AHI down near zero is great, but UARS-like FL effects on sleep remain to impair sleep for many. 

There is more than one online bidding site where VAutos, many with low hours, typically run $400-700. Mine was just over $300 nearly 2 years ago for one with a couple hundred hours. I may be permitted to PM you info on the one site I'm surprised is little mentioned. 

Looking at your first zoomed-in OSCAR view, with those "bimodal" inspiratory waves, is very much like seeing my own improved FR curve, but thanks to my switching to the VAuto I have far fewer and mostly smaller flow limits than you show (or that I experienced with my AutoSet). Sleeping much better now, but pressure, leak and CA averse, I have not yet tried higher pressures and pressure support (now 95% 12.00, PS 4) in an effort to smooth and make FR peaks more rounded and, quite possibly, reduce my number of what are apparently arousals and micro arousals.

I refer to those bimodals as "M-tips" and researchers (and a 2018 Resmed patent application's emphasis) have pegged them as one of the more serious among 47 shapes of airflow restriction level indicators. I see many of those and other culprits, but the M-tip in my curve is the one of those 47 most often accompanied by a FL in the next breath. Largely, the M-tip and lesser shapes are in the blind spot, not only as mentioned about care above, but also in not being flagged by our machines. Many of the other tip deformities occur and are not flagged in any way, except, possibly, in the form of some hypopneas the restrictions may cause. 

We can see the deformities in our FR curves and unrested sleepers with low AHI should note and understand them. That will help keep us away from care/DME rabbit trails, help us pursue an MD's letter of medical necessity if needed, and their frequencies can help us assess the efficacy of any life changes we may make in trying to get more restful sleep.

Your zoomed-out view is also similar to mine with the AutoSet, which had more spikes--though I still have many with the VAuto. Your FL there in that view are about like my better AutoSet nights when I had a lower than average level of FL. 

Regarding cardiogenic effects showing in your zoomed -n FR curve, I see a continuous lot of that as my exhalations end, particularly in right-side sleep.
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RE: Understanding Flow Limitations and Flow Rate Shape
I like the description "M-top." I always think of those wave-forms as looking like the silhouette of a fedora.

I got my lightly used VAuto from a private seller, and it has greatly reduced my FLs. I'd like to reduce them further, but when I try raising PS beyond 4.8, I get an uptick in CAs. I'm going to try again soon, though.

Did the PS help me sleep better? Well, the reduction in FLs did produce some improvement in the quality of my sleep, though at present night-time pain is a limiting factor.
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