[Equipment] Fabrication of an Enhanced Expiratory Rebreathing Space (EERS)

[sherwoga]

EERS stands for Enhanced Expiratory Breathing Space.  

It is a small dead volume (between the mask and line vent) that contains used air rich in carbon dioxide at the end of an exhalation.  That air does not get swept from the line by air coming from the CPAP pump because it is upstream of the new line vent position.  Hence the CPAP user will breathe in that carbon dioxide in the next inhalation.  The operational theory here is that for some patients and some CPAP machines settings the treatment can so efficiently remove carbon dioxide from the blood that the body's mechanism for controlling the next breath gets messed up.  The brain fails to send the "breathe" command to the diaphragm until the carbon dioxide level in the blood builds back to the threshold required for the mechanism to work.  If so, the patient is believed to have treatment emergent central apnea.  These periods without breathing due to this mechanism are detrimental as are Obstructive Apnea Events.  The EERS with the "Rebreathing" of some carbon dioxide is supposed to lower the efficiency of the carbon dioxide removal, but not eliminate it of course, at least that is how I understand it at this point.

I had been using my CPAP for about 2 years when I joined the Apnea Board Forum mid October of 2019.  I had for the previous year been using a Pressure range between 8 and 18 and an EPR setting of 3.  I not infrequently saw AHI's as high as 20 or 1/3rd of my original diagnosis.  I was really frustrated that my treatment wasn't working well at all.  I did not have access to the wealth of data available from the CPAP because my sleep doctor prescribed the CPAP without a flash card and the only feedback I got was from software that reported the AHI with no breakdown into types of apnea events.  OSCAR software and the Apnea Board Forum has been a real eye opening experience for me.  

The very first daily image from OSCAR that I shared resulted in an immediate recommendation to lower the EPR to 1.  I saw an immediate lowering of the number of Central Apnea Events, and in turn the AHI went down, too.  It became apparent that my obstructive event counts have been low all along.  I turned the EPR off completely, at which point I had trouble exhaling against the high pressure.  (The EPR setting lowers the line pressure on the exhalation half of the breath cycle and I wan't getting that help.) The second recommendation from the Gurus on the forum was to begin lowering the Max Pressure.  Currently I'm being told that I need the EPR to be 3 and to have an EERS in line so that I get both the best benefit of the obstructive sleep apnea treatment and don't turn on the Central Apnea events by fouling up my bodies breathing control mechanism.  It remains to be seen what my operational pressure will be with the EERS.  

I've communicated with various people on the forum and one of them (Slowriter) has helped me obtain equipment for the EERS.  Multiple participants gave me information.  My purpose in starting this thread is to document my "fabrication of my EERS" so others will be able to learn from my experience.  

Please, don't expect expertise on the front end of this thread either with the fabrication or with the forum.  I'm just telling you what I'm doing and hope you will benefit from my learning experience.  At times, I may look like I don't know what I'm doing.  That's because I don't.  

Later in the thread I will share more information about sources and part information for the equipment needed.  But I do have to observe the rules of the forum and not endorse any particular manufacturer.  So to start with, I am going to share two pictures.  

The first is my air line equipment as it was.  Click on the picture to make it larger so you can see the detail.  

   

The second is my equipment altered by plugging the vent holes on my original elbow connector and the hose and vented straight connector inserted in series in the line.  

   

I plan to use this arrangement tonight and will report results tomorrow.  

I will post additional articles to the thread.  In particular a couple of questions came up in my discussions with others that I don't think are addressed yet.  1) What happens if I lose power.  Will I be able to breathe?  I think the check valve on my elbow connector is still functional, but absent air flow in the line, I also think I would be re-breathing a lot more used air.  I do have a gas generator that will turn on in less than a minute if I lose electricity so I fully expect to wake up tomorrow.  But that is not the correct design if this is in fact a problem.  2) Also, will I have condensation in the EERS hose segment?  (My line hose is heated and my air supply humidified.) The line segment is only six inches long.  Will water form and get back into my CPAP?  I don't think so, because there will be low spots in the line where it would accumulate.  But it could run into my face.  3)  An additional question that occurs to me has to do with the size of the vents.  The holes I plugged with silicone were very big in comparison to the holes I can't even really see on the straight vented connector.  I suspect there is some interplay between the algorithms that control the pump flow and the size of those vents.  The two vents are from two different manufacturers. So that needs some consideration also.  

There are apparently adapters to address the first two questions.  The third one might be addressable by just increasing pressure.  Food for thought and future contributions to this thread.  

I will appreciate any feedback I get from anyone to this first installment.  

Enough for tonight.  It's time for sweet, sweet sleep.  Wish me luck!

[SarcasticDave94]

Great article there EERS guy sherwoga. IMO your anti-asphyxiation valve should still protect you. Condensate shouldn't make it back to your machine. Keep rolling out your reports.

[Hydrangea]

Color me clueless. Are trying to make yourself re-breathe your carbon dioxide?

[Gideon]

NOT a lot, but that is the concept.

[SarcasticDave94]

It's a way to manipulate the low CO2 that's causing CA in some. It's a method of intentionally pushing CO2 levels up a bit and force the pulmonary breath signal that the xPAP has corrupted the missing balance, so to speak.

[Hydrangea]

Ah, ok.

[jaswilliams]

Stupid question as your using the quiet elbow, have you blocked the holes under the diffuser ring as it is unclear from the picture, it looks like you have just blocked the antiaphyixiation valve

[SarcasticDave94]

After Jaswilliams comment, I had another look at that images. Yep that's the holes you've blocked. Best to open those anti-asphyxiation openings I'd think.

[slowriter]

A couple things:

1. While I didn't myself use the anti-asphyxiation valve, and so wasn't sure exactly how best to integrate that (and hence suggested you post this thread), in general, the only vent holes you plug are on the original mask (including the elbow vent if you're using that)).
   
2. I found I did get condensation the first night. The second night, and last in my EERS experiment, I tried a suggestion someone else made on another thread to place the hose under the cover to keep it warmer. That worked.
   

On 1, that valve came as part of a kit where it was attached to a length or hose and the elbow vent. I did not myself construct that. I wasn't sure if best to adapt that somehow directly, or remove the valve.

[sherwoga]

Color me clueless. Are trying to make yourself re-breathe your carbon dioxide?

Others have adequately answered your question, which is very definitely a good one, and what I'm about to share has already been shared elsewhere in the forum.  But in the interest of keeping the issue covered coherently in this thread it is worth sharing again. 

My CPAP reports median, 95%, and maximum tidal volume.  The Apnea Board Forum Glossary of Terms reports that tidal volume is

The amount of air that passes in and out of the lungs in an ordinary breath. Usually expressed in liters.

Since Oct 19 when I first use a flash card in my CPAP,  my median tidal volume range has been reported between 480 and 600 mL.  

The section of tubing that I am attempting to use to create "dead" volume (or re-breathing space) can be considered to be a cylinder of length 6 inch and radius 11 millimeters.  The volume of a cylinder is given as

V = πr²l.

This works out to about 58 mL.  And there is a bit of additional dead volume associated with the connectors.  But this inserted dead volume is still only between 10 and maybe 15 % of the volume of one of my median breaths.  So as a simple approximation, I would get about 10% used air mixed with 90% fresh air in each breath with this arrangement.

Further the concept has been tested in at least one controlled lab study conducted in a polysomnography lab (sleep study lab) using 6, 12, and 18 -inch lengths of inserted tube.  The very technical report of that study can be found on the web at:

EERS Lab Study

I have not attempted a detailed reading of the same, but have looked it over enough to augment my understanding of the theory behind the EERS.  It is worth at least a perusal. 

A second report of a similar study is at:

Effect of Zolpidem and Enhanced Expiratory Rebreathing Space on Complex Sleep Apnea

So the simple answer to your question is YES: I'm trying to re breathe carbon dioxide.  It isn't very much, but enough to lower the efficiency of the removal of carbon dioxide by my lungs as assisted by my CPAP.  If it works successfully it will be because the level of carbon dioxide in my blood will not fall below that threshold that my brain is looking for to know that I need another breath to continue the carbon dioxide removal. And my brain will send the "breathe now" command to my diaphragm in a regular fashion, i.e. one less altered by the CPAP treatment of my Obstructive Sleep Apnea.  And the number of central apnea events will be curtailed even though I'm using the EPR setting to assist with exhalation at high line pressure (max pressure setting). And the high max pressure will maintain suppression of obstructive events.