How to Lower AHI while using BiPAP?

[bisyonary]

First time user here with severe apnea. I always thought being sleepy was normal for me until my wife urged me to get checked. I got a sleep study and titration with results below.
Before titration: AHI 79, O2 74 (lowest)
After titration: AHI 58, O2 89 (lowest) using pressure 15/11

My doctor requests on getting me another sleep study but I asked for a CPAP machine prescription as I noticed great improvements on myself on the day after that sleep study. 

AHI (26) is still severe on my current prescription so I'm still in queue for that next sleep study 3 weeks from now.
My current prescription is: BiPAP machine, IPAP=16, EPAP=12, PS=4

Any thoughts on how to improve my AHI? Thank you for looking into this.

[Sleeprider]

Your events are entirely obstructive and clustered. We typically find this is related to a positional apnea caused by tucking the chin which cuts off the airway. We have examples of charts like your in the Optimizing Therapy wiki, and how they resolved to near zero AHI with the use of a soft cervical collar. This link will take you to the postional apnea section of that wiki, but it's worth reading the whole thing http://www.apneaboard.com/wiki/index.php...onal_Apnea Another one for you is Flow Limitation. http://www.apneaboard.com/wiki/index.php...Limitation

Welcome to Apnea Board. I'm certain your results are going to improve very quickly, then we can get you on Vauto mode and lower pressures.

[Gideon]

Welcome to the forum.

You have a very good machine and I have some setting changes to suggest but first,  I think your problem is positional Apnea and your charts look remarkably like those in this WIKI article.

Positional_Apnea

I strongly suggest a loose fitting soft cervical collar or an anti-snoring collar like the Dr Dakota to keep your chin from tucking and severely restricting your breathing.
Before changing your settings I would suggest the collar.   YMMV but look at the results of someone else in the article.

Fred

[bisyonary]

Thank you @bonjour, @Sleeprider for pointing out the Positional_Apnea wiki. I can say that I fully relate to it, as I observe airway obstruction during both relaxed chin and light pressure on chin tissue test. 

I used a large size soft collar last night but I got higher AHI result (41.66) on first use, sleepyhead screenshot attached here. I'm guessing I don't have the right size of collar as I tend to lift my chin up slightly while wearing it. How do I find the right size of soft cervical collar for me?

[cate1898]

Welcome to the forum bisyonary! Glad you found us and glad you are getting the help you need. You're well on the way to better health!!

[Gideon]

I would try a smaller collar but a question, is the collar too tight, is it applying pressure to the front of the throat?    We do not want that and this chart looks like the problem is slightly aggravated over your previous chart.

[Sleeprider]

The ideal collar applies pressure to the back of the jaw, and supports the chin without pressing anywhere on the throat. The biggest challenge seems to be getting a loose fit in circumference while providing the needed support. Wish I could be more specific.

[bisyonary]

You are right @bonjour, the smaller collar definitely increased my AHI to 60.00 last night. 
I'm seeing a problem with my neck and chin, as they are not in ideal 90 deg angle but the extra neck tissue is looking more like a double chin. I gained weight in the last year or so.

@Sleeprider, I'll probably try to cut away some portion of the collar to conform to my chin and support the jaw. 
But my relaxed chin also goes downward and inward which probably makes the standard collar not easy to deal with. What do you think about the chin strap, would it somehow work?

Thank you @cate1898, I definitely feel welcome on this forum.

[Gideon]

Try setting your IPAP Max to 20, let's see if pressure can help as well.