Low pressures: Suffocation, rebreathing, etc.

i wonder if the docs simply missed the vent rate issues?

ThisIsMyUserName wrote:I am a little tired today, but I can definitely blame that on monday Night Football.

Especially if you are a Patriots' fan...

Sheriff

PS: It was definitely pass interference...

I am having a hard time understanding the vent rate issue. I do have a physics Ph.D., so if there is a paper or text that goes through the topic in detail I'd be happy to read through it. In the meantime, I upped the presure to 6, so far so good; I still feel like I can't get enough air when I first put the mask on (though it doesn't wake me up or anything), but I still can't see how I'm rebreathing much CO2, given the level of pressure. I guess the most obvious way to think about it would be just do a quick caluclation of the vent rate (which I can estimate as the leak rate on sleepyhead) and the volume of the mask, and then use that to estimate the time to repopulate the air in the mask; of course, this is an upper bound seeing as some of the vented air never makes it to the mask...

In other news, this is a little off the CPAP topic, but check out ESPN's physics analysis of the call: http://espn.go.com/blog/new-england-pat ... nding-call

Sometimes is just the simple fact that at the lower pressures we feel like we are being suffocated because there's just not enough air moving....we aren't but it feels that way.
A while back I did a little screening for OSA on my sister with my machine and I attempted to start her out at the minimum pressure of 4 and it only took her about 30 seconds before she ripped the mask off saying I was trying to kill her by suffocation. At 6 cm starting pressure she was comfortable.
There are some people who are quite comfortable at those lower pressures but most people simply need more air movement to be comfortable.
It's common and doesn't mean that we are actually rebreathing too much old air and causing a problem with O2 and CO2O...it just means we need a little more air moving to feel comfortable.

Masks are designed to vent the proper amount of CO2. Trust that your vent rate is correct.

Sheriff

ThisIsMyUserName wrote:I am having a hard time understanding the vent rate issue. I do have a physics Ph.D., so if there is a paper or text that goes through the topic in detail I'd be happy to read through it. In the meantime, I upped the presure to 6, so far so good; I still feel like I can't get enough air when I first put the mask on (though it doesn't wake me up or anything), but I still can't see how I'm rebreathing much CO2, given the level of pressure. I guess the most obvious way to think about it would be just do a quick caluclation of the vent rate (which I can estimate as the leak rate on sleepyhead) and the volume of the mask, and then use that to estimate the time to repopulate the air in the mask; of course, this is an upper bound seeing as some of the vented air never makes it to the mask...

In other news, this is a little off the CPAP topic, but check out ESPN's physics analysis of the call: http://espn.go.com/blog/new-england-pat ... nding-call

Look at your SleepyHead flow data waveforms (note that you can see extreme detail by simply dragging across any section) and imagine a line drawn at your leak rate (vent rate) level into the exhale cycle. Past that line you are sending air down the CPAP hose. On the other side of that line you are venting air in the CPAP hose. At that line the air is contained in the CPAP hose (this is during exhale).