Cpap To Apap

[jobe2433]

So 6 months ago I had my sleep study and was sent on my way with a new cpap machine and a pressure setting of 8. Since that time I have switched sleep doctors and as of two days ago he has put me on an APAP machine for 3 weeks to make sure my pressure setting is accurate. The past two nights my pressure has stayed at 16 for 90% of the night., I guess my questions is , is this a normal occurrence? i would assume the sleep study would be better able to get and accurate setting for your cpap. I guess I think its crazy for 6 months I have been sleeping at an 8 and now with this new machine I am up to a 16. Is it normal for the pressure to double like this?

[Pugsy]

APAPs will increase pressure in response to leaks (as well as events) because it tries to maintain pressure. This can cause more leaks and feed the leak even more. Nasty little cycle.

While sleep study results aren't always spot on, they don't usually miss it by 100%.
My first thought would be to check leak line. Is the machine like mine in my profile? If so there is software available to see exactly what the pressure is doing and if the increases cold be related to leaks. I mention my machine because it also reports a 90% max pressure. There may be other brands that do the same.

[LSAT]

I had a similar situation...My sleep study reflected a pressure of 8.....several months later my doctor recommended an at home study with 2 weeks on an APAP. The results showed a 90% pressure of 12. I have been at 12 for 18 months. I have since purchased an APAP on CL and check my pressure with it periodically. It has remained at 12. ( I use my "brick" on a regular basis because It is quieter than my APAP and doesn't require an exhale relief.)

[Otter]

I honestly don't see why an APAP machine would increase the target pressure to maintain mask pressure when there's a leak. What would make sense would be to increase flow as much as is needed to maintain pressure. But increasing the target pressure doesn't make any sense, and though many people say that happens, I doubt it.

Yes, you can increase flow without increasing the target pressure. When there is a leak, the APAPs controller spins the blower faster to compensate, increasing flow. The increased flow adds to the mask pressure until the target pressure is reached, then, unless I'm missing something, the APAP's algorithm will stop increasing the flow. Thus pressure remains the same even though the blower is spinning faster to keep that pressure up.

I think what really happens is that the machine increases pressure in response to something else, and the leak rate goes up because higher pressure will force more air through any gap and in many cases make the gap larger. Because it's common knowledge that APAPs increase pressure in response to leaks, and you'd have to look very closely at the data to determine cause and effect, many people will assume the leaks caused the pressure increase, perpetuating the myth.

So, what does that leave us with?

One thing about a sleep lab is that you're not in your own bed. Change the mattress or pillow, and you may change your sleeping position. Change your position, and you change your airway. Also, in a one night study in a strange bed, knowing you're being watched by a stranger, you might never reach the deeper realms of sleep that cause the muscles of your throat to go slack. Other factors can change your airway too, allergies, for instance.

Often enough, apnea doesn't show up at all the first night of a study, but on the second or third night the need for CPAP becomes clear. It could be that you only needed 8cm that night in the lab back in January, but you really do need 16 at home now. This is exactly why your new doctor prescribed the APAP. Seems to me he's off to a good start.

[pjbrownva]

Wow, Otter. Thanks for the great info. Even though I'm not the OP, I learned a ton of useful information from your response.