Does the amount of air change with pressure?

[digitaleagle]

I have my machine on a very low pressure from my titrate test of only 6. Sometimes I feel like I'm not getting enough air - especially the first couple of hours I have the mask on. I feel like I am having to suck in a lot more air than what is natural. I'm very conscious of this and it makes falling asleep difficult. It's almost like I'm listening to myself on a respirator. My AHI has been averaging about 3.5 for the last three nights so it is doing a pretty good job I guess.

Does increasing the air pressure deliver more air to your nose? Or is the amount of air always the same and only the pressure is changing? I was just wondering if I increased the pressure a notch or two would my perception of not getting enough air go away?

I'm currently on an auto setting range of 6-10 with Aflex setting of 1. I tried a setting of 2 but it made it worse.

[digitaleagle]

Also - how do you yawn with a nasal mask on? When I get tired and I try to yawn I get a mouthful of air pressure which is pretty uncomfortable. Not a huge deal - but was wondering if there was a way to deal with it.

[kempo]

Try it with the Aflex turned off.

[Julie]

Yawning is a symptom of not enough air/oxygen, and not something you should be doing in a mask (presuming the machine's on). I still think you could move your 6 to at least a 7 for a few nights and stop making your life so hard for lack of air.

[dtsm]

I am not familiar with aflex but assume same as EPR on a ResMed machine. Most folks agree that for every 1 point setting of aflex/epr, a corresponding bump in the cpap pressure should be made. So if you're pressure setting is 6 and you turn apex to 1, then increase pressure setting to 7.

[cflame1]

FLEX... either AFLEX, CFLEX or BiFLEX doesn't work the same as EPR... it's not a 1 to 1 correlation.

[Janknitz]

I am not familiar with aflex but assume same as EPR on a ResMed machine. Most folks agree that for every 1 point setting of aflex/epr, a corresponding bump in the cpap pressure should be made. So if you're pressure setting is 6 and you turn apex to 1, then increase pressure setting to 7.

I think there is a difference between Flex in Respironics machines and EPR in ResMEd machines having to do with when the pressure changes back to full pressure. It seems that people with EPR have more problems with this than those with Flex.

Don't forget that during exhalation your body is passively pushing air out at the same time , the theory is that the pressure in your airway won't decrease significantly with the EPR/Flex pressure relief--your airway will remain open. But because of when the pressure switches back in the cycle it may make a difference.

Digiteagle, you can always test it out by turning the Flex settings down or off to see if you feel any more comfortable.

[GumbyCT]

I do know that Aflex may not work at a pressure of 6 or below because it can't/won't reduce the pressure anymore. Check the literature that came with you machine for proper operation.

[digitaleagle]

OK - thanks for the replies - I seem to be starving for air when the Aflex is on with a setting 6. I will bump up the minimum pressure to 7 tonight and see if that helps.

So - am I right in thinking that higher pressure also means more O2 into your system when you breath in?

It's also possible that a reading of say "6" is not exactly the same from machine to machine. In other words, perhaps the machine they used for the Titrate had a little more pressure. I suppose this is possible.

[HoseCrusher]

Digitaleagle, here is something else that will help.

Just before you put your mask on, take several deep breaths then put the mask on. This will build up your O2 levels and you will have less tendency to gasp as you start out for the night.

[idamtnboy]

OK - thanks for the replies - I seem to be starving for air when the Aflex is on with a setting 6. I will bump up the minimum pressure to 7 tonight and see if that helps.

So - am I right in thinking that higher pressure also means more O2 into your system when you breath in?

It's also possible that a reading of say "6" is not exactly the same from machine to machine. In other words, perhaps the machine they used for the Titrate had a little more pressure. I suppose this is possible.

As long as the system an air pump is connected to does not change, higher pressure from the pump will move more fluid into the system. Also, since air is compressible higher pressure will squeeze more mass of air into the same volume. So yes, higher pressure will move more air, hence O2, into your body.

A pressure reading of 6 should be the same among all machines, in theory but probably not in reality. 6 means 6 cm of water column pressure, and 6 cm is 6 cm regardless of what is generating it. Since xPAPs are medical devices there is a lot of regulatory control over them so I would expect everyone's machine would be pretty close to everyone else's. Just throwing a quess out but 6 might mean anything from 5.9 to 6.1. Not enough for you to notice I wouldn't think.

[digitaleagle]

As long as the system an air pump is connected to does not change, higher pressure from the pump will move more fluid into the system. Also, since air is compressible higher pressure will squeeze more mass of air into the same volume. So yes, higher pressure will move more air, hence O2, into your body.

Thank you for this information - that's what I thought.

Last night I put the pressure up to 7 (from 6) as some others suggested and changed the Auto mode to a straight CPAP ith Cflex+ WOW!!!!! What a difference.

There is something really good about CFlex + I never breathed more naturally. I also think upping the pressure a bit helped. I slept like a baby for over 8 hours. Also - I took the Zest mask apart for the first time to clean it. After putting it back together again I didn't have that annoying air whistling sound anymore. There must have been something not put together just right when I received the mask.

Overall my average AHI for 4 days is now 3. It has slowly been coming down each and every day. Coming from a sleep study average of 27-67, (on back) I'd say that is pretty good progress for just 4 days.

A big thanks goes to all of you on this forum who are helping me. I really appreciate the helpful advice.

[mayondair]

Good to hear you are getting everything dialed in . IMHO 6 is to low to be comfortable, the pressure raise probably helped a lot. flex or EPR seems to be a very individual thing, glad you are sleeping well.p

[GumbyCT]

The first place to look for any whistling noises is the exhaust holes. Esp. if you tend to drool, stuff will clog the holes. Use the stem of a q-tip to open the holes back up.

Good Luck

[Velbor]

There are at least three concepts which are often confused, and are confused in the discussion here. Imprecise words lead to imprecise thinking.

VOLUME. The volume of air we inhale is determined by our lungs. Sometimes we breathe in deeper (e.g. a yawn) and sometimes less so. The "compressability" of air at CPAP pressures is irrelvevantly small. And CPAP is not a ventilator (the pressures are far too low); it does not "force" air into our lungs. All the effort, and all the control of volume, is dependent only on the body, not on the machinery. As long as the airway is open, no one breathes any more, or less, deeply, because of CPAP.

FLOW RATE. When we inhale (or exhale), the rate at which air moves into (or out of) our lungs is controlled by our bodies. On inhalation, the increased volume of our thoracic cavity, due to rib-cage expansion and/or to diaphragm movement, decreases pressure in our chest, and outside air moves in to equalize the pressure difference. CPAP, even at the lowest possible pressure settings, will ALWAYS present to our airway a higher outside pressure than normal atmospheric room air. The "pump" for any major machine brand will ALWAYS maintain an adequate flow rate to provide sufficient air volume to maintain the positive pressure. Even at the lowest settings, there is no way in which we can "not get enough air." The feeling is perhaps psychological, never physiological.

PRESSURE. CPAP machines maintain a positive pressure by pushing more air into our mask than the vents let out. But this pressure, regardless of how it feels, is quite small. Think of a drinking straw. Put about 8 inches (that's about 20cm) into a glass of water. Blow bubbles. That's the highest pressure provided by most CPAP's. Not very much. Certainly not enough to "force" air into your lungs.

A higher pressure DOES result in a higher flow rate of air into the mask. But ANY CPAP flow rate at ANY pressure still provides more air than you lungs "suck in" on their own. The VOLUME of air available for you to breathe in is ALWAYS sufficient with CPAP to let you lungs suck in as much as they otherwise would from room air. But you breathe in NO MORE air than you would without the CPAP (assuming an open airway).

Do you get more oxygen into your system than you would without CPAP? As a matter of fact, you do! But that's not because there's any more oxygen in the air, or because there's more air. Oxygen passively diffuses across your alveoli into your red blood cells. When the pressure in your alveoli is higher than normal atmospheric pressure, the "partial pressure" of the oxygen in your inhaled air is higher. And that means that diffusion of oxygen into your bloodstream has a bit of an extra "push" to it. That's one reason EMS systems are now often using CPAP for a variety of patients: CPAP is a relatively safe way to increase blood oxygen levels without actually adding oxygen, which carries its own risks.

In summary, beware of simplistic answers, be attentive to terminology and to the basic physics of fluid flow, and be careful to distinguish between what you think you feel (which is admittedly important in its own right) and what is actually happening. Be attentive to your comfort, but be even more attentive to reality. If you have to choose between sensations and reality, going with reality is always a much better bet!

Blessings, Velbor