You're original post asked for input from someone who had been through the switch from CPAP to BiPAP to explain something about how the differences between the two feel in use. I started PAP therapy using an S9 AutoSet set first in CPAP mode with EPR = 3 and then APAP mode with EPR = 3. I was switched to bi-level after three months due to severe problems with tolerating CPAP/APAP therapy. My problems were severe aerophagia and growing insomnia caused in part by the fact that the sensory stimuli from the S9 was driving me crazy and waking me up when I would go to bed while feeling like I was falling asleep on my feet.
My comments concern the differences between the Resmed S9 AutoSet with EPR compared to a bi-level machine---either the PR System One BiPAP (which I now use) or the Resmed VPAP.
Let me start with the most obvious difference between therapy using a CPAP/APAP machine and therapy using a bi-level machine (BiPAP or VPAP): On a bi-level, the difference between EPAP and IPAP is not limited to 3cm
. This affects how the therapy actually feel in many ways. Two of the most important are:
- For some people a larger difference between the two pressures is simply much more comfortable to breathe with. At low pressures, this not (usually) enough to medically justify the use of a bi-level machine, but it's also not something to be completely ignored when someone is having serious adjustment problems. But many people have very serious problems exhaling against pressure once their titrated pressure reaches 15cm or more of pressure. And so for people with very high pressure, a switch to bi-level can make a difference in the ability to tolerate the machine.
- The overall average pressure needed to properly manage the OSA may be reduced, and that can increase comfort, and hence compliance in a subset of sensitive patients. Patients with minor problems with pressure indued centrals may find that the switch to bi-level is just enough to keep the pressure induced centrals from becoming a serious problem and hence prevent the need to move the patient to an even more expensive and possibly more difficult machine to adjust to. Another group of patients who may do better with a reduced average pressure are patients dealing with serious problems with aerophagia.
You specifically asked in your original post:
Quote:As an example: Is there a difference in the pressure 12 on a CPAP vs. the pressure 12 on a BIPAP (for inhale)? I ask because I was told that there was a difference.
I'm going to assume that you mean "Is there a difference between using a BiPAP with IPAP = 12 and an S9 AutoSet with pressure = 12 and the Resmed EPR system since that's the machine you have in your profile.
There is a more subtle, but very real difference between the S9 CPAP/APAPs and bi-levels: The transition between the EPAP pressure and the IPAP pressure is subtly different. Although most people like to think of EPR as a "poor man's bi-level", it's just not quite true.
The S9 CPAP/APAP with EPR starts to subtly raise the pressure earlier in the breath cycle than the S9 VPAP (or the PR BiPAP) does
. The S9 AutoSet pressure transition is supposedly much smoother (with the so-called "easy breath" pattern and the default "medium" transition pattern, but the fact remains, the pressure starts to go up during the flat part of the wave flow---a part of the breathing cycle that is a brief pause between the exhalation and the inhalation; for some people(like me) this pause psychologically feels like the end of the "exhalation", and that subtle pressure increase can make it feel as though the S9 is trying to rush you to inhale before you are ready to. This figure illustrates what I'm talking about:
The pressure curve is on top and the patient's airflow is on the bottom. The part of the wave flow under the red slanted line is the part of the pressure curve that corresponds to the brief pause between the exhalation and the inhalation. The period between the red vertical line and the green vertical line represents a period where the pressure is distinctly going up, but the wave flow is still in that pause between the exhalation and the inhalation.
(NOTE: The Flex system on the PR CPAPs and APAPs increases the pressure even earlier than EPR does and the increase during this pause between the exhalation and the inhalation is even more pronounced than the increase in the Resmed EPR system)
The S9 VPAP waits until the inhalation has clearly begun to raise the pressure
. The following figure shows the pressure curve for the S9 VPAP Auto. Note how the transition to IPAP (the tops of the waves) is much sharper and and has a V-shaped notch rather than a smooth u-shaped bottom at the beginning of the pressure increase. The red slanted lines indicate where that pause between the active exhalation and the active inhalation occurs in the pressure curve. Unlike the S9 AutoSet's Easy Breathe with EPR curve, there is no pressure increase during that time period indicated by the red slanted line until the "sharp" jump upwards right at the end of the time period, which is when the inhalation actually starts:
It's a subtle difference in feel and most people probably would not be able to pick up on it if they were comparing an S9 APAP/CPAP with EPR set to 3 to an S9 VPAP with the PS set to 3. (On the S9 VPAP, the PS setting controls the difference between IPAP and EPAP: At all times, IPAP = EPAP + PS.)
The differences between the PR System One BiPAP and the S9 APAP/CPAP with EPR are even greater than the differences between the S9 APAP/CPAP with EPR and the S9 VPAP
. The System One BiPAP has a more square shaped pressure transition curve than either the S9 VPAP or the S9 CPAP/APAP with EPR. And if you turn on Bi-Flex, then there's also the fact that you get a bit of additional
pressure relief right at the start of the exhalation with the PR System One BiPAP. When Bi-Flex is turned on, the pressure curve and the patient's wave flow look like this:
The blue vertical line indicates the end of the "active" part of the exhalation and the beginning of the brief pause between the exhalation and the inhalation (that to me feels like it's part of my exhalation). Note how the dip in pressure triggered by the start of the exhalation has been increased back to the full EPAP setting by the time the active part of the exhalation is over. The red vertical line has been added to indicate where the Resmed EPR system kicks in its subtle pressure increase. Also note how the PR System One basically increases the pressure from EPAP to IPAP more or less in one giant leap with only the smallest bit of rounding based on the Flex setting.
If you compare the pressure increase on the System One BiPAP to the S9 VPAP, you'll see that both increase the pressure from EPAP to IPAP pretty quickly and pretty steeply at the beginning of the active stage of the inhalation. The S9 starts to drop the pressure as the inhalation starts to slow down (that's the characteristic "peak" in the pressure wave), while the System One maintains the pressure at full IPAP until the end of the exhalation.
Bi-Flex is an option on the PR System One BiPAP and not everybody likes it. (I really dislike it---it makes me feel like the machine is rushing me to inhale.) When you turn Bi-Flex off, you get a different option called Rise time. There is no additional decrease in pressure at the start of the exhalation, and the Rise Time setting controls how long it takes for the pressure to increase:
- Rise time = 1 means it takes the System One 0.2 seconds to increase the pressure from EPAP to IPAP.
- Rise time = 2 means it takes the System One 0.3 seconds to increase the pressure from EPAP to IPAP.
- Rise time = 3 means it takes the System One 0.4 seconds to increase the pressure from EPAP to IPAP.
At this point I've probably overwhelmed you with technical information. So now I'll give you my subjective opinion.
I started out with the S9 AutoSet in CPAP mode at a pressure setting of 9 cm with EPR set to 3. I found it difficult to exhale and I felt like the machine was constantly rushing me to inhale before I was ready to take my next inhalation. But if I turned EPR down to 2 (or 1 or or off), I found it even harder to exhale against the pressure. In short, I felt like I was running a marathon in my sleep every night trying to keep up with all the air the S9 was "forcing" me to breath. And it triggered really severe aerophagia.
After a mere two weeks I could not stand the aerophagia any more and I looked like the walking dead. The PA in the sleep doc's office kindly switched me to APAP for a week or two of autotitriation which showed that 8cm was probably enough to manage my OSA. The aerophagia was more tolerable on APAP and I begged to not be switched back to full time CPAP. Hence she left me running in APAP with a tight range of 4-8 cm. Aerophagia continued to plague me and my AHI started to bounce around a bit and snoring became an intermittent problem. And the insomnia continued to grow worse. Two months later, after yet another meeting with me talking about how much worse I still felt, how hard it was for me to fall asleep and stay asleep, and how often I was still waking up in the middle of the night with a seriously bad stomach ache and a visibly bloated, rock hard abdomen, the PA said she and the doc had talked and all they could come up with was to swtich me to bi-level.
Back to the lab for a bilevel titration. The test showed rampant insomnia---far worse than I thought. I self reported that I thought I'd slept for about 3 1/2 or 4 hours during the test; the EEG data said I slept for 110 minutes. But at least my stomach was much more comfortable with the bilevel---no rock hard, bloated tummy that night. And a titration level of IPAP = 8; EPAP = 6. The S9 VPAP was not yet on the market and after a month of agonizing over whether to the the S8 VPAP or the PR System One BiPAP, I finally opted for the System One BiPAP.
I turned Bi-Flex off the first night: It made me feel like the machine was trying to make me inhale before I was ready to. I'm really, really sensitive to pressure increases when I am not actively inhaling
. But when I switched the machine to Rise Time, for the first time in three long months, I actually felt sort of semi comfortable breathing with the damn machine. I still had trouble exhaling against the pressure when I was awake and hence I used the ramp alot while I was awake. And I still was waking up with aerophagia alot, but at least it no longer looked or felt like I'd swallowed a basketball. After six weeks of being on BiPAP, the PA sent me back to the lab for another titration study and my pressure was reduced to 7/4, which felt like heaven. I could finally breathe with the machine in comfort. Unfortunately, that was not enough pressure to really control the apnea on a nightly basis. And hence I was finally changed to the tight Auto BiPAP range I now use.
I occasionally self titrate to see if an increase in pressure would make me sleep any better. So far, the answer seems to be either,and empahtic "NO!" or "nor really." It sort of depends on how high the EPAP pressure goes during the autotitration period. If the EPAP spends any appreciable time above 6cm, my stomach objects. If the IPAP spends any appreciable time above 10 cm, my stomach may object. I sort of wish I had one of he newer Series 60 BiPAP Autos that allow you to set a minimum PS
setting since that would allow me to let the IPAP go up to 9 or 10 cm while still restricting the max EPAP to 6 cm.
I personally find the fact that my BiPAP keeps the pressure at EPAP all the way through the entire exhalation and that pause between the active exhalation and the active inhalation very important. That's what makes it possible for me to be able to breathe in a fashion that feels mostly normal to me when I'm trying to get to sleep at the beginning of the night or when I'm trying to get back to sleep after one of my many wakes.