Breath Stacking

I asked this forum about rapid breathing in a previous post (C-Flex and rapid breathing) and have since talked with a resp. therapist who has given me some insight. I commented to the resp. therapist that when I use the C-Flex function, it seems as though I don't get each breath fully exhaled before the machine starts blowing full pressure at me again and, that my rate of breathing speeds up.

I've been told that what may be happening to me is that I am having "breath stacking." Because I'm not getting all of each exhalation fully out before the machine starts blowing at the full prescribed pressure for the next inhalation, my breaths get smaller in volumn and, cycle more rapidly. There is potential that this can lead to carbon dioxide build-up due to inefficient blow-off during exhalation.

I've tried using the different C-Flex levels, but I do best with the RemStar when I turn off the C-Flex feature all together and use it as a straight CPAP. Too bad that I spent all the coin for the C-Flex feature.

This post is NOT to bash Respironics or C-Flex in any way. I just found myself feeling worried about the way I was breathing with C-Flex and did not notice others on this forum posting any similar concerns. I have learned, however, that lots of us keep our concerns/fears to ourselves and feel isolated. I just wanted to share my concerns, and what I have learned, in case anyone else on this forum has had similar concerns but found no answers.

Happy to hear you have found something that works for you. I have been using the Cflex and am having trouble with my breathing so after reading your comments I will try and see if maybe I should try it without my Cflex to see if this works. Thank you.

It's too bad that some of us feel we have to excuse ourselves for any questions we have since most of us are new at this, are extremely tired and have no where to turn.

I also have noticed lately that if you say the wrong thing or ask the wrong question, or say something negative about some equipment someone out there is jumping all over people.

Yes, you are almost afraid to ask questions on this site, how sad.

I personally haven't delved into C-Flex. However, my guess is that it is an algorithmically based (versus purely mechanical) breathing comfort feature that relies on precise inspiration and expiration detection toward delivering unique IPAP and EPAP pressures---- a "relative" versus precise EPAP pressure, and with certain latency and rise parameters toward comfort.

With that said, my understanding is that mouth and mask leaks are perhaps the biggest breath-sycncronization impediments for traditional spontaeous BiLevel. So... please be sure that you are not experiencing excessive leaks anywhere in your circuit, including losing air through your mouth or mask seal. Good luck!

I think your observation is a good one in that leaks can make a huge difference. I'm very lucky to have found an interface that does not leak so I think that leak is not the issue in may case.

You have commented that C-FLEX may be algorithmically-driven which may well be the case. Even if it is mechanically driven, given that the sensor is in the machine, rather than being up at your face, measurement of the patient's tidal volumn is actually being done 6 feet away (if you are using a 6 foot long hose) from where your mouth/nose are.

The RemStar does not allow the patient to adjust the sensitivity of the C-FLEX triggering mechanism (it only allows the patient to adjust how much it flexes) so the machine has to decide when the patient has stopped exhaling so that it can increase flow. Or, the machine decides when the patient starts inhaling, and increases flow. In either event, I suspect that there is some measurement lag because of the length of hose between the patient and the machine.

Example:
If you were to put one end of a 6 INCH tube in your mouth, place you hand loosely at the other end of the tube, and did a full exhalation through the tube, you would feel lots of air (tidal volumn) exiting at the open end of the tube. If you do the same thing with your 6 FOOT tube, the tidal volumn that you will feel at the end of the long tube will be alot less --the air that you are exhaling has to move through 6 FEET of tube before it gets to the flow sensor (your hand, in this case).

So, it just seems that for me, and the way I breath, the sensor in the RemStar seems to think that I have finished exhaling when, in fact, I have not. I'm sure that there are many people for whom C-FLEX is the answer, sadly, I'm not one of them.

WillSucceed:

I don't believe all of our exhaled air has to reach the end of the tube for the sensors to pick it up, since the tube is remaining constantly pressurized. I presume the sensors are able to pick up the slightest
return pressure from exhalation.

Also, it should be noted that our exhaled air is not being completely returned to the end of the 6 foot tube. It is supposed to be properly vented through the mask, or in some connections, through a seperate air vent. Otherwise we would be rebreathing too high a percentage of exhaled air all night.

With that in mind, I'm no engineer. Just my limited understanding of how the thing works.

I discovered last night that I too might have problems with C-Flex (first night), especially with higher pressures. (I normally start at 4 and go up to 9). I woke up at around 1:30 having trouble breathing and a pounding heart, and felt like the machine was trying to blow me up like a balloon before I had fully exhaled. With it in Auto mode, I could control my breaths very easily. With C-Flex, it's basically forcing me to take a breath, even when I'm not ready. Not the best feeling in the world..I certainly feel like I've had way too much CO2 this morning !

I tried it on the highest setting, so tonight I'll try the lowest. If I have the same problem, I'll be disabling the feature.

Funny how some people love it, and others say it's no good. Just goes to show that we need to try it for ouselves to see if it works, rather than relying totally on others experiences.

Regards

I'm sure that you are right in that the machine does need to be sensitive to slight air movement as the hose is pressurized at all times when the machine is generating flow. I realize that my explanation was simplistic; you are quite right that all of our exhalation is not getting to the machine.

Somehow, the machine has to figure out when we are done exhaling and are ready to inhale. Just seems that the method that it uses can contribute to some of us breathing too rapidly and having a racing heart (I had the racing heart as well -woke me up a few times.)

I've used the RemStar in CPAP mode for the last few nights and have not had the rapid breathing/can't get all the air out/racing heart stuff at all.

Thanks for your observation and comments.
Best...

I did take a quick peek at the C-Flex documents and patent. It uses a flow based trigger, not a pressure based trigger. Specifically it will reference or trigger on the two times that IPAP is near zero flow (not to say that it will immediately commence pressure changes at those reference points). A highly stable leak rate will thus be algorithmically compensated for with a newly calculated patient-flow baseline rather well. Irratic leak rates, highly irregular and/or shallow breathing can easily fool any BiLevel's "near-zero-flow" reference triggering. C-Flex strives for EPAP pressure relief, but it also strives to have higher IPAP pressures restored by the tail end of expiration where apneas tend to be incipient. That is why Respironics will officially say that C-Flex does not require a separate titration from a previously attained fixed-pressure CPAP value that is known to be valid.

Traditional BiLevels (non-C-Flex) would definitely require a dedicated re-titration for anyone switching from fixed pressure CPAP----since sustained (lower) EPAP pressures at the tail end of expiration may not be enough to address some apneas that are already well under way.

SWS:
Thanks for the explanation!
P