CPAPtalk.com

Then you get into calculations involving inverse squares--something best assigned to computers.

ChicagoGranny wrote:

CapnLoki wrote: By my napkin calculation its only reduced 0.06% at 6500 feet.

It's reduced by around 20%. You can check your calculations here - https://www.mide.com/pages/air-pressure ... calculator

I'm talking about gravity. Pressure is reduced 20% but gravity is only reduced .06%. That's why gravity is only a tiny part of the pressure difference.

ChicagoGranny wrote:

CapnLoki wrote:It does make the rather laughable mistake that the pressure difference is because of reduced gravity at altitude.

Actually, that is part of the reason for lower pressure at higher altitude:

1. The gravitational attraction(*) between the earth and air molecules is greater for those molecules nearer to earth than those further away - they have more weight - dragging them closer together and increasing the pressure (force per unit area) between them.

2. Molecules further away from the earth have less weight (because gravitational attraction is less) but they are also 'standing' on the molecules below them, causing compression. Those lower down have to support more molecules above them and are further compressed (pressurised) in the process.

http://www.npl.co.uk/reference/faqs/why ... -pressure)

Yes - "supporting the molecules above" is the dominant affect.

chunkyfrog wrote:Then you get into calculations involving inverse squares--something best assigned to computers.

Yes, its the inverse square law, but the math is quite simple:

radius of Earth 6400 km; at altitude about 6402. (6402/6400) squared = 1.0006

CapnLoki wrote:... While modern cpaps can correct for the pressure, do they actually make up completely for the deficit of oxygen? People who live at altitude develop increased lung capacity; does the cpap do this? ...

For the occasional high altitude visitor the acclimatization is about hemoglobin levels and other metabolic changes that will occur over days or weeks. Lung capacity I would think is not much of a factor if you're "just visiting". Efficiency of your blood and metabolism enabling it to to absorb more of the scarcer oxygen in roughly the same volume. It would probably take weeks at altitude to normalize.

You people remind me of the fools at the Viet Nam peace talks in Paris, ..arguing about the shape of the Table. If you are so worried about little things like the machines ability to adjust for alt, why don't you consider staying home.

All the machine has to do is apply more pressure to your airway to keep it open. If it takes 10 cm to do that, it will take 10 cm, regardless of the outside air pressure, it will still take 10 cm to hold the airway open. As long as the XPAP can provide the boost, you are covered. APAP, would be a even better solution. Jim

And NO you don't need to change your pressure to cover weather changes, for the same reason.

Goofproof wrote:You people remind me of the fools at the Viet Nam peace talks in Paris, ..arguing about the shape of the Table. If you are so worried about little things like the machines ability to adjust for alt, why don't you consider staying home.

All the machine has to do is apply more pressure to your airway to keep it open. If it takes 10 cm to do that, it will take 10 cm, regardless of the outside air pressure, it will still take 10 cm to hold the airway open. As long as the XPAP can provide the boost, you are covered. APAP, would be a even better solution. Jim

And NO you don't need to change your pressure to cover weather changes, for the same reason.

Worried??? No, I said I was curious about the physics. I'm sure there were some furniture designers very interested in the peace tables.

CapnLoki wrote:

Goofproof wrote:You people remind me of the fools at the Viet Nam peace talks in Paris, ..arguing about the shape of the Table. If you are so worried about little things like the machines ability to adjust for alt, why don't you consider staying home.

All the machine has to do is apply more pressure to your airway to keep it open. If it takes 10 cm to do that, it will take 10 cm, regardless of the outside air pressure, it will still take 10 cm to hold the airway open. As long as the XPAP can provide the boost, you are covered. APAP, would be a even better solution. Jim

And NO you don't need to change your pressure to cover weather changes, for the same reason.

Worried??? No, I said I was curious about the physics. I'm sure there were some furniture designers very interested in the peace tables.

I guess so, I never met any where I was the Agent Orange killed most of our wood. Jim