Possible To Have Too Good Of A Seal/Leak Rate Too Low?

Is it possible to have too good of a seal, for a leak rate to be too low?

Lately, as my machine has needed higher pressure to keep my airway patent, I have been experiencing orbital crepitus (air bubbles trapped under my eyelid, encircling my upper eye). Pre-APAP I used to get this maybe once or twice a year, no physician I have ever seen has had a decent explanation, and I'm at sort of a loss as well since I've never experienced any orbital trauma (it's usually associated with orbital bone fractures). In idiotpathic cases (meaning no known cause) it usually involves some kind of congential (something you're born with) sinus malformation where there is a fistula (an inappropriate connection between two spaces in the body) between the sinus space and the orbit. Despite having had more than one head MRI, nothing like that has ever been seen, but MRI, despite it being a true marvel, has limits to its resolution, it would be unable to pick up very small holes that could still be causing this.

However, I think the etiology (root cause) of my orbital crepitus may actually be my tear duct! It is really unusual, but that is one of the few anatomical openings that does indeed connect to the upper respiratory system. With an excellent mask seal, the pressure would really have no where else it could escape, my tympanic membranes are intact so the ears are a no go, the mouth and nose are covered by the mask, so the last opening that would allow pressure to escape would indeed be the tear duct.

For some reason it seems to be only the tear duct of the left eye, I'm not quite sure why that one is different from the right tear duct. I ran a few experiments on myself and it seems to be true. When my eye was closed the air bubble would start building up on the nasal side, as it grew larger it would expand around my eye, until it reached the other side of the eyelid, where I assume the gas escaped. With my eyes even slightly parted, there was no air bubble buildup, so that would seem to rule out a fistula in the upper orbit/direct communication with the sinus as is usually seen. If I closed my upper eyelid completely, but everted my lower lid just a little so the tear duct was pointing outward, it also wouldn't happen.

All very weird, right? So, what do you guys suggest? I can't seem to find anything on the internet where this has happened to anyone else. I'm hoping someone here has either experienced it or knows someone that has. Do you think loosening my mask to increase the leak rate will help, or will my machine just up the pressure to compensate for the leak? Is there a sort of leak rate "sweet spot" where enough pressure is lost to properly contain any force inside the upper respiratory tract without the machine trying to up the pressure in response to it?

Your machine will likely just try to compensate for any minor leaking so I don't know if it would help your issue or not.
If it were me I would maybe try to figure out if there was a certain pressure limit where this happens and maybe try to limit the apap from going to that pressure if at all possible.

Has anyone ever talked to you about tear duct plugs?

Any pressure above 13 or so seem to trigger it, but if I limit my maximum pressure, I potentially compromise my machines ability to control my OSA, right?

I am thinking about mentioning the tear duct plug to my sleep medicine physician, but I don't know how much pressure they're meant to withstand. I don't even know if that has ever been tested. The first time this happened it could very well go shooting right out of my eye due to the pressure.

Paralel wrote:Is it possible to have too good of a seal, for a leak rate to be too low?
Do you think loosening my mask to increase the leak rate will help, or will my machine just up the pressure to compensate for the leak? Is there a sort of leak rate "sweet spot" where enough pressure is lost to properly contain any force inside the upper respiratory tract without the machine trying to up the pressure in response to it?

the only thing having too low a leak rate will cause is death by asphyxiation.

your mask has a built in leak rate (most are around 20-50lpm depending on pressure), so the only way you can get *too low* a rate is to plug up the vent on the mask.

as to the rest of your question, you need to realize that cpaps are about *pressure* not *flow*, they are pressure regulated, not flow regulated. the impellers in the blower are constantly being adjusted in speed to provide a desired *pressure* at the mask face no matter how much leak there is, up to the point where the machine can no longer go any faster. put your ear up against the machine and you can hear the motor speed changing, even as you breath in and out, otherwise, the pressure would drop when you inhaled and increase when you exhaled.

so, in other words, "no".

Limiting the maximum pressure isn't necessarily a bad thing unless you have a truck load of apnea events if you don't let the machine go higher.

Have you actually tested it to see what might happen? Tis no different from someone with aerophagia above so and so pressure.
Sometimes we make little compromises and it isn't the end of the world if a couple of apnea events slip past the defenses. Now if a truckload of them slips past the defenses...different story.

Good point. I'll try limiting the upper pressure limit and see how that helps.

There are two leak rates associated with a mask and affected by the instantanious pressure.
The first is the design leakage that takes care of the extraction of CO2 from the exhaled gases. The second is the unintentional leak rate that covers leaks due to mask fit issues. You want the first to be what the manufacturer designed into the mask and the second to be as close to zero as you can comfortably get.

Increasing either or both will just cause the CPAP to compensate.

'Nuff said about that.

However if the problem originates in the nasal passage as you speculate, then a solution potentially exists. Reduce the pressure in the nasal passage by either limiting the overall pressure as has been suggested or eliminating the pressure entirely by the use of an oral mask with the training to not need nasal clips or plugs.

It has been suggested that the following experiment be conducted. Practice blowing up a balloon to exercise the throat structures to seal off the nasal passages from oral pressure. If you can learn to do that while asleep, the nasal pressure will be zero above ambient and the problem may be solved.

A ductal plug might work without risking it popping it out. Remember that the pressure from the CPAP is minuscule compared to what would be generated by blowing up a balloon. If you can get a plug installed by your local friendly ophthalmologist, then pinch your nose and blow. If it doesn't come out under those circumstances, it won't come out at night.

Of course, there will be the issue of excess tears that now have no drainage path.

Another thought about getting to a diagnosis (or eliminating a possible one.)

At the nasal side of the eye are two ducts that drain tears from the eye directly into the nasal cavity.
Off to your local friendly ophthalmologist together with your CPAP. Get it hooked up and running at pressure and your mask on. Then the doctor inserts some flourescein dye and observes for air bubbles. If they are there, you've got a diagnosis and the plug or plugs can be installed. If not, you're back to square one.

A really interesting diagnostic problem.

Paralel wrote:Any pressure above 13 or so seem to trigger it, but if I limit my maximum pressure, I potentially compromise my machines ability to control my OSA, right?

I am thinking about mentioning the tear duct plug to my sleep medicine physician, but I don't know how much pressure they're meant to withstand. I don't even know if that has ever been tested. The first time this happened it could very well go shooting right out of my eye due to the pressure.

Regarding tear duct plugs, I've had them in both eyes for years. I am on APAP now & my pressure climbs to around 18-19 nightly. Also, prior to getting an auto machine I was on straight CPAP at 19. This has never dislodged any of my plugs. You usually see an Optometrist or Opthalmologist for this. You can discuss this with your sleep Dr but he will probably refer you to your current eye Dr.

Jen

The thoughtful replies were very helpful, thank you all.

I have an optho appt. at the end of Oct, different kind of optho than usual (neuro-optho), but I think he should still be able to handle this issue.

I'm glad to hear the TDPs are more resilient than I thought they might be. I figured that was probably the case, but that is an area of medicine where my knowledge is quite limited.

Try an Oracle Oral mask. You put it in your mouth like a SCUBA mouthpiece.

The trick is to learn to use it without nose plugs. The soft palate at the back of your mouth can close off and prevent air from going up your nose. It's the "valve" that closes off when you blow up a balloon.

If you don't use nose plugs, there is no pressure in your nose, and no pressure trying to go up the nasolacrimal ducts.

It is a bit tough to use. It dries out your mouth and throat, and the lack of airflow through the nose is uncomfortable for some, but it will fix the nasolacrimal duct leakage. Not everyone can learn to sleep without the nose plugs, though.

What I did was put the mask on, pretend I was blowing a balloon, and then I'd sort of freeze up, and relax while leaving the palate closed. Then I'd start breathing. The CPAP pressure tends to hold the valve closed. I found I could sleep with it, but the dryness and discomfort of the nose being closed of made me stop using it.

JDS74 wrote:A ductal plug might work without risking it popping it out. Remember that the pressure from the CPAP is minuscule compared to what would be generated by blowing up a balloon.

There's no pressure in the nose when you blow up a balloon, the soft palate seals off your nose, or air would come out your nostrils.