amount of oxygen in heated air

[Ghandi]

since "cold air will have more oxygen due to the density of the molecules being closer together. Warm air has less density of molecules. Thus, when you breathe in cool/cold weather, you are getting more oxygen into your lungs. Hot weather produces the feeling of "hard to breathe" due to the less amount of oxygen density."

I was wondering if the cpap machine would provide less oxygen to breath when the air is heated. with my PR the heat is at 4. that means 80 degres. I use to have it off. And i'm wondering if this could change the effect of therapy since i would get a little bit less oxygen. This would be mild i guess.

[justMongo]

The effect is so slight as to be negligible. We could go into a long exercise in physics to prove it.

The percentage of O2 at sea level is 20%. Heating the air reduces the density but not the percentage of O2.
A slightly higher tidal volume would compensate for the slight reduction in density.

[Ghandi]

I'm not an expert in physics but your eplanation makes sens to me.

Thanks a lot justMongo

[Skypilot]

If you are concerned about the density of the air in the heated hose then you also too need to look at your altitude of your residence. Many places in the US can be at quite an altitude AMSL.

Here in Oz the highest hill (they are not mountains) is only 2,228 metres.....

I would suggest the heat applied to the air in the hose would tend to increase the flow by the time it gets to the end of the hose (expanding air due to heat) and/or slightly raise the pressure. As mentioned above I doubt that would have any effect in the treatment.

The height above AMSL would be more of an issue I would imagine. I do not know if the CPAP machine compensate for altitude.

[MAPnea]

What is the percentage of O2 at 5,600' above sea level?
Thanks

[archangle]

What is the percentage of O2 at 5,600' above sea level?
Thanks

The rule of thumb is air is 1% less dense 1000 feet of altitude, so you get about 5% less O2.

The percent of oxygen in the air is roughly the same, but there's less air per breath.

The fact that the percent of O2 doesn't vary that much with height is counterintuitive. We tend to think heavier gasses concentrate near the ground. Oxygen weighs 14% more than nitrogen, but the concentration doesn't vary much with height.

[archangle]

OK, I'm bored.

The temperature of the air in your lungs is going to be pretty close to 37C/98F body temperature no matter what the temperature of the air you're breathing is. Your respiratory system goes to a lot of effort to make that happen.

The density of the air in your lungs is a function of absolute pressure in the lungs and the temperature of the air in your lungs. That won't vary with the temperature of the air in the hose.

Assuming your lungs make the same motions independent of the hose air temperature, the volume of air in your lungs won't vary. The absolute pressure in your lungs at the top and bottom of the breathing cycle equals the absolute hose pressure.

The density is the same, the volume is the same, you'll inhale/exhale the same mass of air with each breath.

However, the volume of air in the hose will vary. You'll inhale the same mass, but less volume of cold air than you will of hot air. In theory, that would increase or decrease your measured tidal volumes, but the effect is fairly minor.

Since I've already calculated it, here's calculations on the density of air at the same pressure but different temperatures. I turns out this doesn't affect the amount (mass) of air in your lungs anyway.

It would work this way if the air in your lungs didn't match body temperature.

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You do this calculation in Kelvin degrees, if you are civilized. Primitive societies like the US might use Rankine/Fahrenheit.

Kelvin=Celsius+273.

At a fixed pressure, the volume of a fixed mass of air is 1/T, with T in Kelvin. .

If room air is 27C/77F/298K, your CPAP machine heated it to 50C/122F/323K, the hose air would be 92% of the density of the room air.

I think 50C/122F air would feel really hot.

Going from 27C/77F/298K room air to 37C/98F/310K body temperature air reduces the density of air to 96% of the room air.

Assume outside air temperature is freezing, 0C/32F/273 K. Air inside your house is 25C, 77F, 298K. Air and O2 density in the house is 92% of the outside air. (273/298)

[justMongo]

You might be interested in the concept Density Altitude.
http://en.wikipedia.org/wiki/Density_altitude
As a former aviator, it is a key concept in aircraft performance.
It affects the lift generated by a fixed or rotary-wing.
And, it affects the engine's ability to generate torque; and hence thrust (which translates to lift by the airspeed of the airfoil.)

There will be a written test later!

[Skypilot]

If I could edit I would go and edit but instead of flow increasing I should have said velocity.

[Ghandi]

I'm not sure i understand it all but the part i get seems logical.

I,m living at 75 meters above the see. so there is not problem for me with altitude.
But lets see if i get this right. Less air per breath in altitude because the pressure is ligther and the density lowers per volume rigth?

For the heated air of the hose at 27C when the room temperature is 20 the the density of the air would have been aournd 96% but anyways it will have lowered the intake to 94% of the density of the room them by the time it's in the lungs.Rigth ?

My question is at 94% of density the oxygen level is still 20% ?

Would't it take the more volume of air when heated to provide our body with the same amount as cold air. Would't we have to breath a little more? Like when in altitude? Would't it midly increase our breathing?