The real reason some users feel like they're suffocating.

[scotter]

This post will probably step on a lot of professional toes, but it had to be said.

The real reason some users (me included) feel like they're suffocating is... wait for it... Because they're suffocating!

Before I ever had a sleep study done, I tried using a CPAP machine to see if it helped. I couldn't tolerate it at all. I felt like I had a plastic bag over my head and that I wasn't getting good air.

After examining how the machine worked, I figured out that there was cyclonic flow going on in the mask, and bi-directional flow in the hose. Gas flows in the hose in both directions simultaneously.

The mask contains a flap valve that operates when the machine is off. Inhale, and air comes from the hose, but on exhale, it goes out side vents in the mask.

However, when the machine is running, that valve stays open to the hose and closed to the mask side vents. Virtually all of the exhalate goes down the hose and into the water canister.

When I had my first sleep consultation, I tried explaining this to the doctor. His response was stern and aggressive to put it mildly. He practically slammed his hand on the table in my direction and in a tone as tough I had insulted his mother, practically yelled "Air does NOT go back down the hose! It is POSITIVE PRESSURE!"

Great, I thought, yet another guy who thinks an MD makes him smarter than everyone else. No sense arguing with him. He was an internist with an undergrad from an m liberal arts college that did not even offer an engineering math curriculum (like my dad). I have two engineering degrees and have a couple of years working with fluid mechanics on my resume. While I by no means call myself an expert in fluid mechanics, between me and him, if there's anything approaching an expert, it wasn't him.

I could have told him that a very simple experiment would prove what I was saying beyond question, but he appeared to be the type who wouldn't believe his own eyes if it contradicted his prior position.

Light a cigarette, take a puff, and exhale into theask with the machine running. Then watch the hose and water canister fill up with smoke. Then watch it STAY THERE!

Then inhale from the mask and watch it disappears. Take the mask off and exhale in front of a mirror, and see practically the full puff of smoke come out of your mouth.

Now try another experiment. Disconnect the mask from the hose. With the machine off, put the hose in your mouth and see how long you can stand breathing through it. If the machine has a water canister, I'll water not very long before you feel like you're suffocating. You're rebreathing well over a liter of your own air every breath. Each repetition depletes over 25 percent of the oxygen, and adds 4000 ppm CO2.

Now try another experiment. With the machine off, put the mask on with the hose connected and see how long you can stand it. You should find that you can tolerate it indefinitely, because in that circumstance all of your exhalate except the mask volume is vented out. When you inhale again, most of it is fresh air.

Why this happens:

Pressure and flow are two different things. Fluid statics and fluid Dynamics are also two different things. Analyzed statically, the flap valve in the mask should activate before it allows air to flow back down the hose. However, with flow extablished coming from the machine, the mask valve stays open to the hose even during exhale, when *net* static flow in the hose is in the direction moving toward the machine.

I say *net* flow because while nearly all of your exhalate
es.flows down the hose, some fresh air continues to
pinholes flow UP the hose, keeping the aysymmetrically shaped mask valve open, and flows straight out the capillary vents in the mask.

I barely understand the principles behind why this happens myself, so I don't have much of a shot at explaining it to a non-fluid engineer or scientist. But that it does happen is easily proved with just a little bit of smoke. Seeing is believing.

Briefly, the pinhole vents in the mask set up a continuous flow from the machine up the hose and out the pinholes. But the flow through the pinholes is based on the critical flow effect, such that flow rate increases only incrementally as upstream pressure increases exponentially. So when the upstream pressure in the mask more than doubles due to exhale, the flow out the pinholes increases only a little bit. The rest has nowhere too go but back down the hose.
The water canister
Again for reasons I barely understand myself, what fluid (air) does exit the pinholes during increased upstream pressure due to exhalation is almost purely the fresh air flow from the machine. The fresh air continues to flow up the hose while the exhale flows down it at the same time, ships passing in the night style.

Okay, you say, If this is right, why doesn't everybody have the same problem?

I'd be willing to bet that the vast majority of people who have this problem have larger than average lung capacity, which means it's mostly men. Men have on average 60 percent more lung capacity than women. A bigger guy has yet more on top of that.

Due to the race condition between the (low) rate at which the system is purged with fresh air due to flow through the pinholes, the less volume one exhales per the unit of time, the fresher the air in the system will be on average.

This a smaller female might not have any problem, while a larger male will experience oxygen depletion and CO2 buildup resulting in suffocation.

Once you're asleep, respiration decreases, and the pinholes have a better chance of winning the race. This is how most users deal with the problem: tough it out til they fall asleep. But that doesn't work for all of us.

So. How do you fix this?

The first thing is to minimize the volume of air stored in the system. The water canister is the biggest offender. If
to the hose going to the machineyouu can live, without it, bypass it. The second biggest passive storage tank is the fan chamber insidev the machine. Not much you can do about that. Third is the hose itself. Use the shortest, narrowest hose to minimize volume.

If that isn't enough, a $15.00 circular check valve rom a CPAP supply site, a second hose, and some electrical tape will do the trick.


First, wrap electrical tape completely around the corner cylindrical part of the body of the check valve to close off it's exhaust vents. Next, use a copious amount of tape to couple the larger diameter port on the valve to the hose going to the machine. Last, connect the mask hose to the smaller diameter port.

This setup almost completely prevents air from going down the hose. The smoke test will confirm it.

Now you can lose the anxiety once and for all.

[palerider]

Like all the best lies and bullcrap, the above post has just enough bits of fact to seem plausible, but it's still bullcrap.

This post will probably step on a lot of professional toes, but it had to be said.

Nonsense rarely, if ever, 'has' to be said.

The real reason some users (me included) feel like they're suffocating is... wait for it... Because they're suffocating!

Um, no.
There is a huge difference in actually suffocating and simply 'feeling' like it, If people were actually suffocating, those that forced themselves to stick with it, in spite of the feeling, would be dead in the morning.

After examining how the machine worked, I figured out that there was cyclonic flow going on in the mask,

Nonsense.

and bi-directional flow in the hose. Gas flows in the hose in both directions simultaneously.

The british have a word for this... it's "rubbish".

The mask contains a flap valve that operates when the machine is off. Inhale, and air comes from the hose, but on exhale, it goes out side vents in the mask.

No, when the machine is off, the Anti-Asphyxiation valve opens, and you breathe IN and OUT through the open valve,

However, when the machine is running, that valve stays open to the hose and closed to the mask side vents. Virtually all of the exhalate goes down the hose and into the water canister.

You continue to be wrong. The exhalation goes part way into the hose, and is then flushed out by the stream of air out the vents, before you inhale again.

Light a cigarette, take a puff, and exhale into theask with the machine running. Then watch the hose and water canister fill up with smoke. Then watch it STAY THERE!

There's between twenty and FIFTY liters of air venting out the mask vents, depending on pressure, anything that actually makes it all the way up the hose isn't going to "stay there".

Now try another experiment. Disconnect the mask from the hose. With the machine off, put the hose in your mouth and see how long you can stand breathing through it. If the machine has a water canister, I'll water not very long before you feel like you're suffocating. You're rebreathing well over a liter of your own air every breath. Each repetition depletes over 25 percent of the oxygen, and adds 4000 ppm CO2.

Why would a rational person even consider doing that?

Now try another experiment. With the machine off, put the mask on with the hose connected and see how long you can stand it. You should find that you can tolerate it indefinitely, because in that circumstance all of your exhalate except the mask volume is vented out. When you inhale again, most of it is fresh air.

This is nonsensical, cpap masks aren't meant to be used when the machine is off, however, that's why there's an AA valve in full face masks, so that you can breathe if the power goes off at night.

Pressure and flow are two different things. Fluid statics and fluid Dynamics are also two different things. Analyzed statically, the flap valve in the mask should activate before it allows air to flow back down the hose.

NO, that's not what the AA valve is for. nasal and pillow masks don't even HAVE an AA valve

I barely understand the principles behind why this happens myself,

That's patently obvious to even the most casual of observers.

Briefly, the pinhole vents in the mask set up a continuous flow from the machine up the hose and out the pinholes. But the flow through the pinholes is based on the critical flow effect, such that flow rate increases only incrementally as upstream pressure increases exponentially. So when the upstream pressure in the mask more than doubles due to exhale, the flow out the pinholes increases only a little bit. The rest has nowhere too go but back down the hose.

Pressure doesn't increase in the mask when you exhale, in fact, for most people, it *DECREASES* (exhale relief, standard on most machines these days), and the pressure *INCREASES* when you inhale.

What's that noise? glub glub glub? that's your "theory" sinking.

Again for reasons I barely understand myself, what fluid (air) does exit the pinholes during increased upstream pressure due to exhalation is almost purely the fresh air flow from the machine. The fresh air continues to flow up the hose while the exhale flows down it at the same time, ships passing in the night style.

You don't understand *ANYTHING*, that's very obvious. What your fevered mind has concocted is poorly observed data, and false conclusions. in other words, you're full of it.

Okay, you say, If this is right, why doesn't everybody have the same problem?

Because they raise their pressure above the minimum of 4, which is too little for most people.

I'd be willing to bet that the vast majority of people who have this problem have larger than average lung capacity, which means it's mostly men. Men have on average 60 percent more lung capacity than women. A bigger guy has yet more on top of that.

How much do you want to lose on that bet?

Due to the race condition between the (low) rate at which the system is purged with fresh air due to flow through the pinholes, the less volume one exhales per the unit of time, the fresher the air in the system will be on average.

20-50lpm @ 4-20cmh2o, on average, check the manual of your mask for exact vent rates. That's not "low flow rate".

This a smaller female might not have any problem, while a larger male will experience oxygen depletion and CO2 buildup resulting in suffocation.

Once you're asleep, respiration decreases, and the pinholes have a better chance of winning the race. This is how most users deal with the problem: tough it out til they fall asleep. But that doesn't work for all of us.

Again, wrong.

So. How do you fix this?

The first thing is to minimize the volume of air stored in the system. The water canister is the biggest offender. If
to the hose going to the machineyouu can live, without it, bypass it. The second biggest passive storage tank is the fan chamber insidev the machine. Not much you can do about that. Third is the hose itself. Use the shortest, narrowest hose to minimize volume.

If that isn't enough, a $15.00 circular check valve rom a CPAP supply site, a second hose, and some electrical tape will do the trick.


First, wrap electrical tape completely around the corner cylindrical part of the body of the check valve to close off it's exhaust vents. Next, use a copious amount of tape to couple the larger diameter port on the valve to the hose going to the machine. Last, connect the mask hose to the smaller diameter port.

This setup almost completely prevents air from going down the hose. The smoke test will confirm it.

Now you can lose the anxiety once and for all.

This is such utter rubbish.

A modern CPAP/bilevel is a highly computerized precision piece of equipment, with the flow rates, and resistances of each piece carefully modeled in the software, even down to the flow resistance of various types of masks, lengths and diameters of STANDARD hoses, presence of absence of the humidifier, and (with Resmeds) Antibacterial filters.

Pressure is measured many dozen times a *second* and the flow rate adjusted to maintain exacting pressues *at the mask*.

Don't anybody listen to this crackpot.

If you feel you're not getting enough air, raise your minimum pressure, if you feel you're getting too much air (the other kind of 'suffocation' that mr genius here is ignorant of) look into exhale pressure relief.

This kind of idiotic garbage should never have been approved. :sigh:

[zoocrewphoto]

Welcome to the group.

You might want to consider reading some posts before you post. You are likely to get a lot of negative responses simply because you are wrong and started with an air of superiority while apparently quite new to cpap. Not the best way to introduce yourself.

You will find that most people here are cpap users, not doctors or DMEs. Most of us have learned that the feeling of suffocation is due to the pressure being too low. Raising the starting pressure will remove that sensation.

As palerider mentioned, the valve on the full face mask is an anti-asphyxiation valve. It is open when the machine is off so that you can breathe if the power goes off. It closes when the machine is going on so that you get the pressure provided by the machine. All masks have to be tested before they approved for use with cpap. They will not suffocate you.

[LSAT]

I got about a quarter of he way through the post and realized it was pointless to go any farther...

[Jas_williams]

Seems to me like a troll posting delete it before someone believes it

[tyrinryan]

If I were a smoker, I would immediately try to duplicate the experiment. The experiment seems pretty easy to do!!

We should at least give credit to a member of the forum (1 &1/2 years of membership!), who has put himself (herself) out there on such a contentious issue, for doing this experiment and for trying to explain it to us on a first principle basis. It's his or her first post.

If the experiment can be duplicated, we should be giving more thought to the cleaning of the hose and humidifier container.

[LSAT]

bah-humbugidiom.jpg

[Stephaniedp3]

I’ve had my APAP for just over a week and I have to say I disagree. Even without my machine on I can breathe just fine albeit a little restricted. I have a full face mask that has vents on the front and the top. I’ve also had zero problems with leaks. As others have said the pressure and vents are placed and tested to work properly. So yeah I disagree.

[D.H.]

In most cases, I think that the pressure is too, high, too low, or the patient needs some form of exhalation relief.

If there are additional diagnosis beyond Obstructive Sleep Apnea (i.e. Central or "mixed" Sleep Apnea, emphysema, COPD, asthma, then those could als be contributory. Some might also perceive claustrophobia as asphyxia.

[JayDee]

If I were a smoker...

You don't have to be a "smoker" to perform the test - go buy a pack or bum one from a buddy and let us know how your test goes.
There's another test running at the same time and It seems you may not be aware of it. It's a check for gullibility.

Good Luck!
-JD

[JayDee]

This post will probably step on a lot of professional toes, but it had to be said.

Troll_06_sm.jpg (20.91 KiB) Viewed 735 times

[Dog Slobber]

He practically slammed his hand on the table in my direction and in a tone as tough I had insulted his mother, practically yelled "Air does NOT go back down the hose! It is POSITIVE PRESSURE!"

So he practically slammed his fist, and practically yelled.

How does one practically slam one's fist, and practically yell? Sounds more like you're projecting.

Light a cigarette, take a puff, and exhale into theask with the machine running. Then watch the hose and water canister fill up with smoke. Then watch it STAY THERE!


Then inhale from the mask and watch it disappears. Take the mask off and exhale in front of a mirror, and see practically the full puff of smoke come out of your mouth.

Video tape your experiment, and post it"

You're the "engineer", you should understand the concept of supporting your claims with evidence.

[Pugsy]

Unfortunately garbage isn’t listed in the terms of agreement prohibited list which is used to filter posts.

Education and debunking of poor ideas is still probably the best way to handle those kinds of thoughts.
Extra work I know.

[babydinosnoreless]

bah-humbugidiom.jpg

I like your picture. .

[Stephaniedp3]

If I were a smoker...

You don't have to be a "smoker" to perform the test - go buy a pack or bum one from a buddy and let us know how your test goes.
There's another test running at the same time and It seems you may not be aware of it. It's a check for gullibility.

Good Luck!
-JD

Sorry as an ex smoker and someone who just lost their dad to lung cancer I’m gonna be the person. Please don’t smoke and please don’t put smoke purposely in your machine.