Enhanced Expiratory Rebreathing Space (EERS)

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Enhanced Expiratory Rebreathing Space (EERS) may be a solution for individuals that experience therapy onset central apnea with CPAP or bilevel therapy. The rebreathing space prevents all of the exhaled air from being vented through the CPAP mask. This increases the amount of carbon dioxide that the user inhales in the next breath. CPAP and Bilevel therapy flush most of the user's expired air out of the mask. For some sensitive individuals, this decreases the amount of carbon dioxide which leads to the appearance of central apnea. Many of these individuals find that CPAP/BPAP therapy is uncomfortable due to the central apnea and hypopnea that they experience. EERS can ensure a volume of expired air is available for rebreathing, and this can prevent these therapy onset central apnea, or Treatment-Emergent Central Apnea .

EERS is a potentially useful therapy for positive pressure CPAP and BPAP associated respiratory instability and CPAP treatment failures. Individuals that experience therapy onset central apnea seems to be particularly likely to benefit from EERS. Some patients experience hypocapnia, a state of reduced carbon dioxide in the blood. The theory is that the use of positive air pressure, especially with pressure support (PS) or exhale pressure relief (EPR) can result in a drop in carbon dioxide in the blood, which through various respiratory feedback mechanisms can result in the emergence of central apnea (CA). By adding dead-space or a larger volume of re-breathed air, the normal carbon dioxide balance can be restored, and thereby prevent the side effect of central apnea in these individuals.

EERS is accomplished by blocking the mask exhaust vents using Mack's Silicone Putty (earplugs), and adding a length of tubing to the mask that terminates in a mask exhaust vent. For safety purposes, an antiasphyxiation/safety valve is included in EERS for full-face mask setups to ensure continued airflow in the patient circuit in the event of CPAP failure. This safety valve can be omitted in nasal therapy. EERS creates a larger dead-space by moving the mask vent to a position further down the tubing toward the xPAP machine.

Fabrication of EERS

EERS can be added to nasal or full face mask interfaces. At his time there is no commercial or retail availability of the EERS circuit and they must be custom built by the user or a few knowledgeable durable medical providers or doctors. This section describes a simple method of constructing EERS using available Corr-A-Flex CPAP tubing, a mask vent / swivel and an optional antiasphixiation safety valve. To find these items for a DIY, search on Ebay, Amazon or similar site for:

  • Respironics Whisper Swivel II
  • Fisher & Paykel Oracle 452 Flexitube Kit (includes the safety valve, which I couldn't find on its own)
  • Hudson RCI CORR-A-FLEX Corrugated Tubing 72 in
  • Mack's Silicone Putty Earplugs

Without adding the Corr-a-Flex segment, the nasal mask tube (16-inches x 15 mm) provides about 70 mL of dead space. Standard Corr-a-Flex is in 6-inch (15.24 cm) segments which has about 58 mL of dead space. (The volume of the tubing is V = Pi * r squared * length and 22 mm diameter tubing has about 3.8 mL/cm with 15 mm diameter tubing being about one-half (0.7) of that volume).

Currently we know of two DMEs that work with Dr. Robert J Thomas (see references) to fabricate the EERS. This information is not provided as an endorsement, and patients may require a prescription to obtain the device. The only DMEs we are aware of that provide the EERS supplies are:

Regional Homecare
125 Tolman Avenue
Leominster MA, 01453
Phone: 978-840-0113

Reliable Respiratory
1504 Boston Providence Turnpike, Suite 11A
Norwood, MA 02062
Phone: 781-551-3335

User Experience with EERS

This section will be used to link to user experiences with EERS as they occur.

Slowriter EERS This is a fabrication of EERS using a Bleep mask and showing charts that verify a reduction in CA events as well as increases in tidal volume and minute vent. The significance of this post may be that tidal volume is increased without suppression in respiration rate resulting in real ventilation gains as well as a reduction in CA events.
Croatoan EERS This member changed from a Philips Dreamstation to Resmed Airsense 10 Autoset using a full face mask. EERS reduced mostly central AHI form 10
Sam R Squared EERS This member started a thread seeking to optimize therapy with an Airsense 10 Autoset. Events were mostly central with AHI of 6-10 per hour. After trying a lower EPR, Sam fabricated an EERS and achieved improved respiratory volume and a lower CAI.

EERS Construction with Bleep

Apnea Board user sherwoga wrote a post that this section is based on. Here is the forum article http://www.apneaboard.com/forums/Thread-Any-way-to-tackle-the-remaining-CAs-AutoSet-for-Her?pid=358256#pid358256

There are only 4 items that you need to construct an EERS system. Mask, Tubing, Putty, and the vent.


  1. Some Corr-A-Flex tubing (Search Amazon). You need 3 feet. It comes in rather long lengths but is very inexpensive. The search will take you to amazon where you can buy 4 feet of the tubing for less than $7. It is molded in a manner that makes it easy to cut it into lengths that are in increments of 6-inches, that is 6, 12, 18, 24, and so on. You probably should start with a 6-inch length: I use 12 inches now but did experiment with both 6 and 18 inches. I found it a bit more work to breathe with the latter. Also, you can buy this material in many places on the web. I saw one source where you can buy 6-inches for $0.49, but the shipping would probably be prohibitive.
  2. Some Mack's Pillow Soft Silicone Putty Earplugs 6 Ct (Search Walmart). These are readily available at most any drugstore. You'll only need one package as just one plug will suffice to plug the vents on your Bleep Mask interface. If you are creative you will probably only have to do it once.
  3. A Respironics Whisper Swivel II valve or vent (Search Amazon). I think of it as a vent, because it does not have a "closed" position. It is always open. Air escapes between two concentric surfaces that are about 1 mm different in diameter. See the attached picture. This is the most expensive item you need costing about $27 at Amazon. Note that as of tonight that web page reports only 2 left in stock.
  4. An appropriate mask, this example uses a Bleep mask. If your chosen mask has a short hose connecting the mask and the CPAP hose you will need to account for the volume.
    1. All masks use a common connection to the CPAP hose (except for a few used in "Travel" machines.


  1. Plug the vents on the front of the Bleep interface using the silicone earplugs completely. This material is very pliable and long-lasting. Try to be neat and remove excess so that the appearance of your equipment does not become less pleasing, but completely plug those vents. Yes, there are warnings about NOT plugging your mask vents, we are not removing this functionality, we are relocating vents to further away from the mask. Thus this is safe.
  2. Attach a 6-inch length of Corr-A-Flex tubing to the mask.
    1. You can eliminate the section of tubing you are currently using between the Bleep Interface and the CPAP supply hose, as the Whisper Swivel II can connect directly to the latter. This will bring that supply hose closer to your face and you might find that arrangement less comfortable just because of the change in weight on your face and it might be more difficult to manage the hose. It is your choice as eliminating that section of tubing is not necessary to make this modification work. Note: If you leave it in you need to compensate for its volume.
  3. Attach the Respironics Whisper Swivel II vent to the above Corr-A-Flex tubing.
  4. Attach the above assembly of Mask, Corr-A-Flex tubing, and Respironics Whisper Swivel II vent to the CPAP hose.
  5. Test how successful you were with this effort
    1. by attaching the mask as if for a night's sleep and temporarily plug the far end of the hose before you connect it to the CPAP supply hose, probably using just the flat of your hand.
    2. Pressurize the line with air from your lungs through your nose with your mouth closed and see if it leaks.
    3. Move on quickly to attaching your pump to get a supply of fresh air from your pump after this test. Don't pass out on your own carbon dioxide.


  • One assumption I've made here is that the port on the Bleep interface has an outer diameter of 22 mm. That is a standard size for tubing and parts used by most CPAP manufacturers. If that is not the case, I can't help you. You will have to find tubing, adapters, and a vent that will work with the Bleep dimensions.
  • Another concern might be that the Corr-A-Flex tubing might fit but because the port is so short the tubing may not stay connected after a bit of distortion, i.e., it might easily slip off. Be gentle with the tubing to avoid stretching it and bringing this problem on or exasperating it. If this happens you might be able to obtain some kind of a clamp to hold the hose on the port. A clamp I used to use in the laboratory is known as a Keck Clip and designed to keep standard taper glassware joints joined. They are also available at Amazon, but you would be on your own to investigate whether they are needed and/or would work. Also, you can just renew the Corr-A-Flex tubing as needed.
  • The vent in the Whisper Swivel II will substitute for these vents, but at a greater distance from your face forcing you to "Rebreathe" about 58 CC of used air for each 6-inch section of Corr-A-Flex tubing you insert in your line. Your tidal volume is probably on the order of 600 CC, Note that this will vary by individual, sex, and size. If so, you will be reducing the amount of fresh air you breathe in each breath by about 10% for each length of tubing. Nothing I've ever seen in print used any more than 18 inches of tubing. I can't support using anything greater for that reason and because even at 18 inches I was less comfortable.
  • Note that your tidal volume may go up. I've never seen a good explanation of this phenomenon or any warnings that it is dangerous. Mine went up from the low to mid 600's to the low 800's. After months of using the 12 inches of rebreathing space, my tidal volumes run in the mid 700's. So, my body has adjusted to the EERS. I've been using it since early February and experimented before that starting in November of 2019
  • Rainout is another problem I encountered. That is moisture in my warm, exhaled breaths condensed on the cold inside surfaces of my EERS. It could actually make my face get wet. I solved this by wrapping my EERS in a small rectangular piece of quilted flannel cut to the length of the EERS and sufficiently wide to wrap the tubing about two times. My wife made this for me. She mounted Velcro strips to make it easy to secure the wrapping.

If your CA's are treatment-induced you might, per the theory of how the EERS operates, experience fewer of them. I certainly do. I was having erratic CAI's (Central Apnea Index / CAI) that sometimes went above 25. I rarely go above a CAI of 1 now. I do use greater pressure support, too. I can discuss that further in other posts if you are interested.

Flow-pressure graphs available at Dreamport.com for the Bleep mask and at Respironics for the Whisper Swivel II vent are very similar. Without offering a lot of explanation I think this is a good indication that your CPAP pump will perform essentially the same with the Whisper Swivel II as it does with the open vents on the Bleep mask. Again we can discuss this at a high cut (because I don't pretend to fully understand it) in another post.

Finally, note that you will NOT be creating a new asphyxiation hazard with this arrangement. I understand that nasal masks do not include an anti asphyxiation valve anyway. Full face masks do include anti asphyxiation valves. My AirTouch F20 full face mask does. Your Bleep mask doesn't. All you have done with this arrangement is to move the vent further from your face. You will survive an electrical power loss with the new arrangement the same way you would have without the new arrangement.

I look forward to hearing about your success (or failure). I'm delighted with my use of the EERS.

EERS Construction with ResMed F20, F30 Masks

The prior article on EERS with a Bleep mask covers the general details very well. Here is how I (GuyScharf) assembled EERS for ResMed F20 and F30 masks.

Creating EERS for the F20/F30 masks is particularly easy. You need to block the vents (but not the anti-asphyxia valves) on the QuietFlow elbow, attach the desired length of Corr-A-Flex tubing, the Whisper Swivel II vent, and connect your CPAP hose.

To block the vents on the QuietFlow elbow, pry off the translucent plastic cap that covers the vent holes. This cap is glued on in the center and you need to break the glue join. This is easier on some elbows than others. Next pull out the sound filtration foam that covers the vent holes. Take a silicon earplug and roll it into a little larger than 1/8" diameter cylinder; you probably need only about half an earplug of silicon. Place this cylinder around the elbow and over the vent holes. Press down enough to make sure the vent holes have been plugged by the ear plug material. Finally, press the translucent plastic cap down over the ear plug material until it is back in its original position. You should have used enough earplug material so that some squishes out the edge of the cap. Cut away and discard the excess material (any dull object will do the job). The material is slightly sticky, so the cap will stay in place without gluing.

Do not block the anti-asphyxia valves on the elbow! These are the two flaps that are shut when the CPAP machine is producing air pressure but fall open when the machine is off. When the machine turns off, such as for a power loss, these valves open so you can still breathe.

Do clearly mark any QuietFlow elbows you have modified. You do not want to become confused about whether an elbow is modified or not and use a modified elbow without the Whisper Swivel II. This would result in your not getting any fresh air and that is likely to be dangerous to your health.

I found that the Whisper Swivel II was considerably noisier than the QuietFlow elbow. I solved that by wrapping a 3" x 6" piece of filter around the Whisper Swivel II and securing it with tape. The filter served to muffle the noise without affecting the airflow, much like the filter material on the QuietFlow elbow did. (The filter I used was a spare intake filter from a Miele vacuum cleaner we have.) The photo shows a filter than has been in place for about a year. The tape is just to hold the filter on to either side of the now-hidden Whisper Swivel II. The filter around the Whisper Swivel II's exhaust ports is intentionally left loose so airflow is just diffused but not impeded.

Titration of EERS

To titrate for EERS you need to see if the underlying condition has been eliminated. This consists of

  1. A visible decrease in CAI.
  2. A notable decrease in Central influenced Flow Limits in the Flow Rate chart. For this, you need to review a substantial portion of the Flow Rate in an expanded forum. Here is a chart made from successive popout 15-minute segments of the Flow Rate chart from OSCAR pasted together in a graphics editor. Note the waxing and waning that is the classic CO2 induced waveform, both with and without CA events. Also note the high level of Flow Limits, both diminished height/flow and flat and sloped tops to the waves. This is without EERS. See the chart below.
  3. Monitoring the "advanced" breathing stats including Breathing Rate, Tidal Volume, Minute Vent, Inspiration/Expiration times and ratios, looking for significant changes.
  4. Titration is performed by starting with the 6-inch (smallest) segment of Corr-A-Flex tubing, evaluating the above, noting the results including the subjective comfort of the user, then deciding whether or not to proceed to the next size (12-inch) and repeat. Then repeat again if indicated with the 18-inch segment.
  5. recommended interval is a minimum of 3 days/nights between steps to adjust.


Treatment of positive airway pressure treatment-associated respiratory instability with enhanced expiratory rebreathing space (EERS).

Alternative approaches to treatment of Central Sleep Apnea

end of article