Why does pressure climb

[millerdq]

I use a Resmed autosense 10. Initially, it was delivered to auto adjust from 4-20 with the ramp feature turned off. After a few horrible nights, I started experimenting with different pressures and learned I could not tolerate much over 8. Long story, short--I've managed to meet compliance and lower my AHi below 3 by staying in the 4-8 range.

Still, I'm confused by how the auto pressure works. Upon dawning the mask, the pressure accelerates to 4 in a matter of seconds. (That part I understand). Then in as I fall asleep, it starts climbing to near the max or around 12, whichever is less. It seems to stay at 4 while I'm awake and breathing normally, then climb as I drift off. However, there are no apnea events driving the pressure up, so what is?

If the pressure goes much above 8, I start getting lots of CA's, OA's, and RERA's. I also wake up and difficulty exhaling keeps me awake until I push the button on the machine to start over at 4. It's hard to know for sure, but it seems like the pressure is causing the apnea events, rather than the other way around. Does that make sense?

Note, at some point I set EPR to 3, which was the breakthrough that let me get comfortable in the 4-8 range. Without that, my exhaling subsides and my chest just fills up with air. as I experience a sense of the machine taking over my breathing.

While, I'm doing OK in the 4-8 range, the machine algorithms want me around 12 and I have to assert a max to keep the pressure down where I can tolerate it. Any way to know if the machine is working right?

One more point of confusion. Before I go to sleep, the machine stays a 4 as long as I lay awake. But after I wake up, the machine stays at a high pressure--it never drops very much. Certainly not back to 4. What gives with that?

[sonicboom]

Conclusion - Your machine obviously wants you at a higher pressure to get manage therapy. Post some charts and we can look at them. I suspect SH will show high flow limitations at your pressures. If not, something else is causing your machine to want higher pressures.

If you are new to cpap then you will adjust over time to some slightly higher pressures. First, at pressure of 4-8, EPR of 3 is helping minimally. Your machine can't go below 4. At 8 pressure, EPR of 3 will give you an exhale pressure of 5. At 7 exhale pressure of 4. At 6, 4. At 5, 4. At 4, 4. I would reduce EPR to 1 or 2 for a week each - experiment and see what you like, after all it is a comfort setting.

Initially my machine was set to 4-20. Its called a wide open setting. As I began to look into my data I adjusted down to a tight range of 4-6.2 because I too found higher pressures non tolerable. Max of 6.2 left me with too many RERAs for my liking so over time I have now settled on a comfortable range of 4.6-7.6. 7.6 protects me from the machine going bonkers on the high end and 4.6 allows me to benefit from lower pressures when not needed.

[Crimson Nape]

The lowest pressure the Resmed will operate at is 4cm. Your EPR setting of 3 doesn't come into full effect until the pressure raises to 7cm (7-3=4). Below that pressure it will start a 5cm with an effective relief of 1 (5-1=4). If you have your ramp feature turned on, the Resmed's won't record any events during the ramp phase.

To be recorded, an event has to be 10 seconds or more. You need to look at the time intervals to see their magnitude in time.

While the EPR feature is basically for comfort, it can increase CA's by washing out the Co2 levels.

The way I understand your statement about the "When the pressure goes up, you start getting CA's, OA's, and REARS is just the reverse. The CPAP senses the events and tries to increase the pressure to prevent them. The CA's are common when adjusting to a higher pressure. They're referred to as "pressure induced centrals". By the way, the terms Centrals and Clear Airway can be used interchangeably for our purpose because we don't have the equipment to be to differentiate between them.

I hope I answered some of your questions.
-Red

[FrankNichols]

The machine will sense if you are experiencing Obstructive Apnea events or if there are limitations to the flow of air in your airways. If either condition is met, it will raise the pressure slightly and quickly and then wait a while to see what happens. If will continue that process until either the max pressure setting is met or the flow limitation and/or apnea events are eliminated. Once there are not Flow limitations and no obstructive apnea events occurring, it will slowly ramp the pressure back down to the min setting - I think it takes about 20 minutes for it to reduce the pressure back to the min.

If you have a problem getting to sleep with higher pressure one of comfort settings that could help is called "ramp". If you set the ramp on it will take the amount of time you set (30 minutes?). I think it ramps up to the min pressure, so say you raised the min pressure to 8 and the max to 10 and set the ramp to 30 minutes. Then you will have 30 minutes to fall to sleep before the pressure gets up to 8. From that point on it will vary between 8 and 10 - for example. I believe the lowest pressure you can set is 4, so if you have it set to 4 the ramp will do nothing, since that is as low as it can go.

Most people find 4 to be too low, it make most people feel like they are suffocating and can't get enough air. I would suggest trying a little higher - 6 or 8 for example.

[justMongo]

Flow limitation and/or snore will raise pressure to head off HAs and OAs.
The machine will not increase pressure in response to a CA.

[PaulaO2]

The muscles in your throat are voluntary, the same as the muscles in your arm. So as you go to sleep, they relax the same as your arm does. In people with sleep apnea, these relaxing muscles, along with various other tissues including the tongue, can start to collapse the airway and narrow it. This narrowing is called a hypopnea.

If the airway narrows further, it can close completely. This is called an apnea event, specifically an obstructive apnea event (OA).

You probably know all this but I'm getting to my point.

What the APAP does is it starts out at the minimum pressure it senses you need. It doesn't know if you are awake or asleep. It knows you are connected to it, that you are breathing which is basically the flow rate. Your awake pressure is different because you are awake and in control of that voluntary group of muscles. The APAP doesn't need to do anything. But as you go to sleep and it all relaxes, it may need to increase the pressure just to maintain the airway, event or not. This is why we all have individual minimum pressures. Some have 6, some have 12, others have much higher (mine is 15). It all depends on variables for each individual. Should you sleep on your side, that minimum would be lower than if you were sleeping on your back, for example.

When the flow rate changes during your sleep, the machine knows you are starting some sort of event and will increase the pressure to either prevent that event from happening or to prevent it from getting worse or prevent the next one from happening. It will increase the pressure until it senses the event is over then start to decrease it if it can. This rise and fall happens throughout the night as your needs change.

[trish6hundred]

Hi millerdq,
WELCOME! to the forum.!
Good luck to you with your CPAP therapy and hang in there for more responses to your post.

[millerdq]

Thanks all for sharing your insights. Something besides AHI or CA events definitely drives up my pressure as I fall asleep. Flow rate does tend to stabilize at the same time, so maybe that's the metric the machine reacting to.

I do notice that it takes concerted effort to exhale (even at 4cm) and my breathing gets shallow as a result. Thought that was what was affecting the flow rate. But it also makes sense that the machine would increase pressure to try and keep the flow at a sufficient level. I'll pay more attention to that and see if a pattern emerges.

[green wings]

Hi, dqmiller. If you decide that you'd like to post some screenshots of graphs from your SleepyHead software, here's a link to some tips on how to organize them. Organize Your SleepyHead Charts

Most of us upload our images to a file hosting site like imgur or Dropbox and share the link from that.