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ASV versus Bi-PAP for RERAs
ASV versus Bi-PAP for RERAs
It was just a few months ago that I started Positive Airway Pressure (PAP) therapy for the first time. An in-lab sleep study showed that I suffered almost exclusively from a choked off airway (RERA) with a couple obstructed apneas - where I simply could get a breath at all for around 10 seconds. I don’t have central apneas (CA) where my brain simply stops sending out a signal to breath. Nor do I suffer from irregular breathing patterns where I fluctuate from drawing in a good volume of air with each breath to taking micro-breaths that don’t keep my blood oxygenated.

As a newbie, it was really confusing trying to figure out what the best possible machine would be. I knew that statistically around 50% of people don’t continue with PAP therapy because they couldn’t get used to it. And yet, it’s vitally important to breathe well while you’re sleeping and your body is making repairs. I wanted a machine that would be absolutely as comfortable as possible and still be able to keep my airway open.

After reading product literature and many threads in forums, I wrote synopsis of what I’d learned up to that point in ASV Versus Other PAP Machines. At that time, I was under the impression the more advanced the machine was, the better it would follow my natural breathing pattern and consequently be the most comfortable. I was wrong.

To help explain this, I need to let you know that a couple months after buying my expensive Dreamstation Bi-PAP AutoSV, I also purchased a used Resmed VPAP (S) standard Bi-PAP machine as a backup – no auto adjusting features. This was based upon the helpful recommendations from this board. Given that I also have chemical sensitivities, the machine was a challenge to clean up. Using the Inside View of a ResMed S9 CPAP Machine help found on this board, I was able to disassembly the used Resmed without any problems. The biggest challenges were cleaning the motor with mini Q-tips dipped in alcohol and getting the fabric softener smell off the silicone parts. I eventually found that straight ammonia that was then neutralized with vinegar and followed by bleach neutralized with hydrogen peroxide got the smell out.

Getting back to comfort and the actual felt experience, I was surprised to learn that regardless of complexity of the machine that they all basically only have two pressures to work with – inhalation pressure (IPAP) and exhalation pressure (EPAP). In other words, even though the more sophisticated Dreamstation BiPAP AutoSV monitors the tidal volume of each breath and adjusts pressures accordingly, there are only two pressures to work with. During normal and mild obstructed breathing, both machines simply apply EPAP during exhalation and IPAP during inhalation. If the machine can auto adjust like the Dreamstation, then when there is a more serious event, the machine also has the ability to vary EPAP and IPAP over a range. For examples, during a central apnea (CA), pressure (PS) support is increased while keeping EPAP low and when the airway is being choked off, EPAP is increased with much lower pressure swings (PS) changes. In any case, there is only two pressures to work with.

Granted there are settings like Trigger, Cycle, and Rise time that influence how quickly the machine transitions from the lower EPAP pressure to the higher IPAP pressure and visa versa. In terms of comfort, these are very helpful settings to prevent feeling like air was being jammed in during inhalation or air being sucked out during exhalation. There is also a Bi-Flex comfort setting on the Dreamsation but I experienced the Bi-Flex pressure drop at the end of inhalation as the machine trying to speed up or force an exhalation. When I disabled Bi-Flex, I was then given the option to adjust Rise time which is similar to Trigger on the Resmed.

It turns out that I found the auto adjusting feature to be a real annoyance and subsequently disabled it. For those that have central apneas (CA) or irregular breath volume like Cheyne Stokes, this isn’t an option. You really need the machine to be able to increase pressures so you don’t suffocate. However, in my case, I mistakenly thought that the more sophisticated Adaptive Servo Ventilation (ASV) technology that monitored tidal volume would mean that the felt experience would be more comfortable – that I’d be given a volume of air consistent with my latest breathing. This is not the case.

Both of these machines are “spontaneously triggered”. This means that if you hold your breath, the machine will sit and wait at the constant lower EPAP pressure. The moment you inhale, pressure jumps up to the IPAP pressure albeit at a transition rate you can control using Trigger or Rise Time. If you keep inhaling for way longer than you normally would, the pressure remains constant at the higher IPAP pressure. It’s only when inflow ceases and there is a slight amount of out-breath that the machine will quickly drop down to the EPAP pressure with a transition rate you can tweak using the Cycle setting on the Resmed only. In the end, the felt experience on both machines is that of having one of two pressures alternately applied. That’s it.

So when they talk about more the complex and expensive machines being able to monitor tidal volume along with keeping track of flow rates at numerous points along the breath curve, this is for improved ability to determine when there is a breathing event. As the literature points out, it’s very important for more complex breathing issues. However, it does not mean the machine will be more comfortable – in my experience. Note: There may be some increase in comfort for those that have central apneas (CA) or irregular breathing. During these events, the machine must automatically adjust pressures to try and keep breath volume up. I would think that the more data points the machine has to determine what’s actually required more natural the felt experience would be.

In my case, where it is all about a choked off airway, I personally found the auto-adjusting feature to be a real nuance. If I rolled over to change position in bed, my breathing often was irregular enough that the Dreamstation Bi-PAP AutoSV (ASV) would start jacking up pressures andthen  hold them high for 10 minute or more. When I was sleeping, the auto increased pressures would wake me up. It was intolerable; I turned off the auto adjusting feature.

In pursuit of comfort first so I could actually tolerate PAP therapy, I also ended up dropping pressure support from 4 cm of H2O to 2 cm of H2O. The up-and-down movement of my mask from the higher PS kept me awake. It’s really the pressure swings that I find most annoying. As PS increases, the mask moves an intolerable amount, my nostrils flare, and my cheeks billow out. It was either throw the PAP machine in the garbage bin or tweak setting so I could actually use the machine.

I also dropped EPAP from 8 cm of H2O to 5 cm of H2O. I really didn’t have too except I do worry about the fact that our brain lymph system only works on 7 cm of H2O along with not wanting to instill central apneas. With all these tweaks, I now actually enjoy PAP therapy. The support is very uniform and feels natural. After having my mask on for a few minutes, I completely forget about the baseline EPAP pressure and the increase up to the IPAP pressure feels like being gently supported in my effort to inhale.

Now you may be thinking that my AHI score went to hell with all this tweaking. It didn’t. It’s perfect. Remember, I only suffer from RERA, and from what I can tell, it’s a mild case at that. My Dreamstation data did show a handful of events when viewed using EncorePro 2 software. However, I also video tape myself, record audio, and sometimes use a professional Alice PDx home sleep study device to really see what’s going on. It turns out that all of the recorded events on the Dreamstation was when I was awake shifting around in bed. The Resmed gave me an AHI score of 0 (zero) using SleepyHead software.

So maybe my breath curves aren’t as smooth as Dr. Karkow would like but I can at least use my PAP machine now. My expensive Dreamstation has had the auto feature disabled by setting the same max and min EPAP pressure and the same max and min IPAP pressure. I’ve turned down pressure support (PS) and EPAP on both machines to maximize comfort. The felt experience of the Resmed is slightly better since due to the extra Cycle setting. Both machines feel great.

I plan on using the used Resmed S9 VPAP that I bought on Craigslist for less than $200 when I travel. With the dehumidifier off, the Resmed is way quieter in terms of the sound coming through the tubing than the Dreamstation and this is another reason to take it when traveling – I don’t normally use humidification.

For what it’s worth, I’ve written several in-depth posts relaying my foray into the world of PAP therapy. If you’re interested, you may want to start with Sleep PAP Therapy – DIY as it relates to this subject material. Note: This is just my personal experience.
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RE: ASV versus Bi-PAP for RERAs
Interesting story of your journey, and an unusual one, considering you are using an Auto SV. In BiPAP-S mode I can understand how that would work. Is your RERA mainly related to flow limitation in the upper airway? That helps explain why a relatively low EPAP with some pressure support works to resolve that problem, while higher pressures actually make things worse.
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RE: ASV versus Bi-PAP for RERAs
Yes, it's an upper airway restriction - big tongue, loose soft palate.

Regarding higher pressures, they do smooth out my flow rate curve and my AHI scores are low but I sleepy miserably - lighter with frequent awakenings. 

It may be an ASV machine but with my settings it running like a standard Bi-PAP.
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