Cracked ribs

archangle wrote:This made sense at first, but I think it's a little more complicated. After playing with a ziploc bag and 4 cm pressure I realized what's wrong.

Right, plastic bags and air mattress don't stretch (much) and we're not trying to compress the air inside. Therefore, to inflate them takes very little pressure. Only an amount of air equal to the volume of bag or mattress has to be pumped into them and it doesn't take much pressure differential to do that. Typically, air mattresses are probably inflated to less than one psi. Air mattress pumps tend to be high volume low psi, while tire pumps tend to be high psi, low volume.

Paxton did try it: https://www.youtube.com/watch?v=PNeZr2jiR9I Which does show a cpap could be handy for inflating a mattress, but I don't think the experiment proves anything about "cracking ribs" with one.

Your ribs don't hold the air in, your muscles do and they are much more powerful then the cpap. A healthy human can produce much more pressure then 20cm H2O. We can inflate a balloon, causing it to stretch and even explode, we do this with our muscles. Your muscles are so powerful that spasms of muscles can break bones - any of your bones. BUT it takes some really powerful ones to break bones.

You also have to remember that the initial cpap was developed using a reversed vacuum cleaner for premature babies. None of them exploded either.

BlackSpinner wrote:

archangle wrote:
However, to be sure, we really do need someone to try it with real air mattresses and CPAP machines.

No we don't - our bodies are not made of the same materials. We leak air from both ends. We breathe in and out. You can tell this by the fact that people who have CA's on cpap machines do not inflate. Their throats are open but they are not breathing.

Well, you do need to try it if you want to figure out what happens on an air mattress if you inflate it with a CPAP machine.

You are misunderstanding the physics of lung inflation. CPAP machines deliver constant pressure, not constant airflow. Once the pressure in your lungs equals the pressure in the mask, the inflation stops. Put a balloon over then end of your CPAP hose. It will inflate up to the point where it's full enough that the pressure inside equals the CPAP pressure and then it stops.

CPAP pressure DOES inflate your lungs, but since the pressure is constant, it inflates your lungs to the point where the elasticity of your muscles and other body parts equalizes the pressure. Consider a hospital ventilator, which works much the same as a CPAP, but it raises and lowers the pressure to inflate and deflate your lungs. Hospital ventilators may use a higher pressure, up to 50 cmH2O, if needed, but they do mechanically inflate and deflate your lungs, and will actually breathe for you if you've stopped breathing on your own.

BlackSpinner wrote: You can tell this by the fact that people who have CA's on cpap machines do not inflate. Their throats are open but they are not breathing.

People with CA's DO inflate to some extent. It's just that unless the CPAP pressure goes up and down, their lungs will fill up to some extent and then the airflow stops. Consider how an ASV or S/T mode bilevel machine works. They use on/off pressure to cause breathing in CA sufferers.

BlackSpinner wrote:We leak air from both ends.

Not sure what you mean by "leak from both ends." Air going down your windpipe pretty much has to come back out the same way in the same volume, although you do exchange O2 for CO2 and add H2O. You may have mask or mouth leaks.

Jay Aitchsee wrote:Paxton did try it: https://www.youtube.com/watch?v=PNeZr2jiR9I Which does show a cpap could be handy for inflating a mattress, but I don't think the experiment proves anything about "cracking ribs" with one.

Yes, it inflated it, but did it create enough pressure to sleep on the mattress? I suspect it did, however, that doesn't mean it's dangerous pressure. A small amount of pressure over a large area creates a pretty large amount of force.

It would also be nice for someone else to confirm it and comment.

When I filled up the trash bag with 4 cm pressure, it felt like similar pressure to what I'd put into my air mattress when I had it.

It would be really interesting if someone with a manometer would inflate an air mattress with a CPAP, then measure the pressure with and without someone laying on it.

Paxton05 wrote: When I rolled over to get up I was so bloated with air in my stomach I felt my ribs crack.

By experience, I know farting eliminates the chance of broken ribs.

DeadlySleep wrote:

Paxton05 wrote: When I rolled over to get up I was so bloated with air in my stomach I felt my ribs crack.

By experience, I know farting eliminates the chance of broken ribs.

Especially if a manometer has been inserted

DeadlySleep wrote:

Paxton05 wrote: When I rolled over to get up I was so bloated with air in my stomach I felt my ribs crack.

By experience, I know farting eliminates the chance of broken ribs.

It also leads to Dog Shaming! Jim

Jay Aitchsee wrote:Especially if a manometer has been inserted

Not surprisingly, anal manometry is a thing.

archangle wrote:...
It would also be nice for someone else to confirm it and comment.
...
It would be really interesting if someone with a manometer would inflate an air mattress with a CPAP, then measure the pressure with and without someone laying on it.

Ya know these small air mattresses can be blown up lung power alone, right? So, it can't take too much pressure to do it.

Here's my guess. A small air mattress is about 2 ft by 6 ft or 12 sq ft, which equals 1728 sq inches. So, if a 300 hundred pound man lies down on 1728 sq inches (ignoring any deflection or stretch in the surface), that's about 0.17lbs/sq in. So the manometer should see an increase of about 0.17psi in pressure.

What do you think?

P.S. 20cmH2o = 0.284467 PSI (see Google conversion https://www.google.com/?gws_rd=ssl#q=cmh2o+to+psi
And I still don't think a cpap is going to crack anyone's ribs

Air bags are even used to upright turned over tractor trailers, that have overturned. Not much pressure can produce big results, it all depends on surface area. Jim

Paxton05 wrote: When I rolled over to get up I was so bloated with air in my stomach I felt my ribs crack.

Well maybe, considering balloons, tractors, etc.

archangle wrote:The air in the bag is at 15 psi (absolute). If you compress the bag by 10% by lying on it, you would have about 1.5 psi pressure, even if there is 0 psi with the bag inflated with no weight.

as usual, you're full of fertilizer.

nobody talks about pressure in relation to a perfect vacuum. you talk about pressure in relation to the other side of whatever you're measuring.

it doesn't matter whether your theoretical bag is at sea level (where mean air pressure is 14.503782 psi vs vacuum) or in (denver, where it's 12.0431psi)

it's all RELATIVE. same pressure inside and out, 0psi diff, 20cm/h20 and you have 0.284466866686psi... where's your 10% more now?

Jay Aitchsee wrote:Paxton did try it: https://www.youtube.com/watch?v=PNeZr2jiR9I .

people that shoot video vertically should be banned from the internet.

Balloons are hardest to inflate if not pre-stretched. Even the balloon animal guy stretches every one out before inflation.
The mattress is not stretchy, shrunken, and needing pressure to reach its ultimate volume--it is already there.
Minimal pressure is needed to inflate. Now try to blow it up with a person lying on it. Waaaay harder! Physics.
Even a child makes it harder. Now picture a 300 pounder with a belly full of gas/air rolling over in bed.
Lucky not to break every rib!

palerider wrote:

archangle wrote:The air in the bag is at 15 psi (absolute). If you compress the bag by 10% by lying on it, you would have about 1.5 psi pressure, even if there is 0 psi with the bag inflated with no weight.

as usual, you're full of fertilizer.

nobody talks about pressure in relation to a perfect vacuum. you talk about pressure in relation to the other side of whatever you're measuring.

it doesn't matter whether your theoretical bag is at sea level (where mean air pressure is 14.503782 psi vs vacuum) or in (denver, where it's 12.0431psi)

it's all RELATIVE. same pressure inside and out, 0psi diff, 20cm/h20 and you have 0.284466866686psi... where's your 10% more now?

Sorry you didn't understand what I said. I'll try to express it more clearly.

The absolute pressure of the air in a container is important in terms of calculating the effects of compressing the container. If you want to consider what happens to the pressure inside a mattress when you lay on it, you have to consider the absolute pressure.

If the air in the mattress is at 15 PSI absolute, and you compress the volume of the bag by 50%, the pressure will go up to 30 PS1 absolute/15 gauge.

If the air was at 1 PS1 gauge/16 absolute, then if you compressed it by 50%, the pressure inside would then be 32 absolute/17 gauge.

Even if the gauge pressure inside the bag is small, it can go up fairly rapidly when you put weight on it and start compressing it.