Understanding the air flow

I have a question about what exactly the air is doing?
Supposibly when you have a blockage its because your muscles relax and actually close your air wave.

Is the air that is being pushed into actually pushing your muscles up to open the airway....?

If so then why is it that normal breathing can't do this? Is the pressure from a cpap actually that strong.....????

Yes, the air flow from the cpap is literally pushing the collapsed tissues inside the throat aside, to open the air way.

When we are asleep, most of our muscles relax completely. For some people (us!) our anatomy is such that the throat and tongue relaxation allows the tissues to touch, collapse, cut off air.

Breathing while we're awake isn't what keeps it all open. Normal "awake" muscle tension of throat and tongue are what keeps it open.

While the air flow from a cpap seems like "a LOT", this might put it into perspective...from some posts on TAS:

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Q. Hi, I am new to CPAP. Is it truly possible that the CPAP could permenately damage my diaphram and lungs?

A. (by rwguinn) No more so than standing in water up to your neck and breathing will.

The pressures are very low. 1 Cm water is .0014 psi, 20 cm water is .028 psi. You can, without trying, blow a balloon up by lung power to more than 10 times that.

Also by rwguinn:

"Remember, our pressures are really low, compared to atmospheric. 25.4 cm is 10 inches. If you stand in water up to your chin, your lungs have to draw in against about 20cm of water.

If you were hooked up to your CPAP (set at 20cm) at the same time, it would be exactly like standing on the ground and breathing without the CPAP--like normal, in other words."

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From Less Sleepy:

"To provide a little perspective. Air pressure at sea level is 760 mm of mercury. The density of water at 4 degrees Celsius is 1 gram per milliliter. The density of mercury is 13.6 times that at 13.6 grams per milliliter. So, air pressure at sea level is 760.0 mm x 13.6/10 mm/cm = 1034 cm H2O.

For CPAP, we're talking about adding at most 20 cm, which is still less than 2% of normal air pressure. Ordinary changes in weather conditions can produce changes of 5% or more, with no travel at all.

My numbers come from the CRC Handbook of Chemistry and Physics, 48th edition (okay, I know it's old, but these things don't change)."

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Here is a simple definition. The air is being forced through collapsed tissue.

CPAP Definition

But also keep in mind that when we breath we are not "pumping" air into our lungs. As our diaphragm contracts, it causes a NEGATIVE pressure in our chest cavities that if unobstructed, allows air to move into the lungs to balance out the pressure between the inside and outside of the chest. Any bit of blockage, as happens with OSA, can greatly hinder the balancing of the pressure gradient, and therefore, air cannot move into the lungs. This is especially true with the very gentle diaphragm movement during sleep. The positive pressure therapy; all of the types; helps overcome that reluctance of air to move past the obstruction by simply INCREASING the pressure OUTSIDE to lungs which in turn makes it easier for the air to move INTO the lungs!

Hope that helps to clarify things a bit!

In order to understand what is going on you need to be clear about the difference between the pressure of the air and the flow rate of the air that is being supplied to us by the machine.

If you turn on your machine without the hose attached, there is a lot of air blowing out into the room. We have all felt this and wondered how we can stand having so much air blowing into us. Well, the machine is actually trying to supply a certain amount of pressure to us and when the hose is open it blows really hard trying to increase the pressure to its setting(10 cm for example). But it is open to the air and can't do this, so it keeps blowing. But when the system is closed, such as when you put on the mask, it does not need to supply this large amount of air, since not so much is leaking out, so it blows enough air until the pressure is at its setting and then slows it down to give us just enough air to breathe.

Try this experiment: With your mask on, draw in a very long and fast breath, then draw in a very slow breath. The machine keeps up with you no matter how fast or slow you breath. How does it do this? By changing the amount of air it supplies to us all the time keeping the pressure at the setting. This is air flow.

Then try this: With your mask on and the pressure set low, say 4 cm, let the air into you mouth with your lips closed. Your cheeks blow up, right? Then change the pressure setting to a high one, say 15 cm and do the same thing. Notice that your cheeks are blown up more and harder with the high pressure than the low pressure. You can do this without actually breathing, but just letting in enough air to blow up you cheeks. This is the effect of pressure rather than air flow and this is what CPAP is supposed to do. Blow open our closed airways with pressure while supplying enough air flow so we can breath.

These are pretty sophisticated machines and for all that they do the prices are not all that high.

GoodKnight's description us true for self adjusting (automatic) Continuous Positive Air Pressure machines.

If so then why is it that normal breathing can't do this? Is the pressure from a cpap actually that strong.....????

As a matter of fact, our brain makes sure the we do start breathing, eventually - it does so by waking us up just enough to open the obstruction. The brain is an integral part of "normal breathing". The problems with this natural breathing are:
1. Our sleep is disrupted by the brain instructing our bodies to kindly wake up and unrelax that airway
2. The amount of oxygen in our blood drops
3. The negative pressure created in out chest is not good for our heart
4. Our blood pressure rises
5. Sometimes the pressure causes gastric reflux
Etc....
For more info, look at this video Understanding Sleep Disordered Breathing


So, rather than rely on our natural ability to keep ourselves from choking to death, we use an airpap, to keep outselves breathing smoothly.

It's important to remember xPAP therapy does most of its work by creating an air splint in our airways, thereby keeping the airways from collapsing. With proper therapy, obstructions rarely happen - and if they do, we need to raise the pressure, not in order to "burst through them" but in order to give those sagging tissues enough support so they remain open.

O.

It's important to remember xPAP therapy does most of its work by creating a air splint in out airways, thereby keeping the airways from collapsing. With proper therapy, obstructions rarely happen - and if they do, we need to raise the pressure, not in order to "burst throuhg them" but in order to give those sagging tissues enough support so they remain open.

You're exactly right, ozij. My description was a very poor one when I wrote of pushing already collapsed tissues open. Preventive action, just as you described, is how the machines keep our throats open...preventing the throat from collapsing in the first place. Glad you posted!!

It's important to remember xPAP therapy does most of its work by creating an air splint in our airways, thereby keeping the airways from collapsing. With proper therapy, obstructions rarely happen - and if they do, we need to raise the pressure, not in order to "burst through them" but in order to give those sagging tissues enough support so they remain open.

Talk of typos.... its "our airways" ...

O.