(04-21-2016, 04:02 PM)FrankNichols Wrote:
It's a ResMed CPAP mode no EPR, no RAMP, nothing. Just CPAP. And Imgur is overload - lol...
That machine is NOT a CPAP: It's got to be a ResMed VPAP running in straight VPAP mode with IPAP = 18 cm and EPAP = 13 and a PS = 5. And here's why:
From top to bottom the graphs in this image are:
- Flow rate (or wave flow): The rate air is going into or out of the lungs measured in L/min
- Mask pressure: The actual pressure delivered at the mask itself, measured in cmH2O
- Expiration Set Pressure: The fixed EPAP pressure the machine is set to use, measured in cmH20
- Inspiration Set Pressure: The fixed IPAP pressure the machine is set to use, measured in cmH2O.
- Leak: The excess leak recorded by the machine
- Minute Ventilation: The (estimated) total amount of air inhaled by the patient in a one minute period measured in L/min obviously.
- Tidal Volume: The amount of air inhaled in one inhalation measured in Liters.
We know this is a NOT a Resmed CPAP because the set EPAP is NOT equal to the set IPAP: Look at those two curves closely: The IPAP is about 18cm. The EPAP is about 13cm. (The trick is to look at the scales
on these two graphs--they're not the same.) So is machine is NOT a CPAP: It's got to be a ResMed VPAP running in straight VPAP mode with IPAP = 18 cm and EPAP = 13 and PS = 5.
The Mask Pressure curve lets us see how bilevel really works. Here's a marked up version of the relevant graph from the original image:
The part of the Mask Pressure curve before
EasyBreathe is turned on shows how bilevel works in its most primitive form: If you look at the inhalations and exhalations that are trapped between the added vertical lines, you can easily see that when the flow rate graph is above 0, the mask pressure is at 18, and when the flow rate graph is below 0, the mask pressure is at 13. There is a sharp sudden drop in the pressure at the end of each inhalation and an equally sharp jump in pressure at the beginning of each inhalation. That's basically what my PR System One's transitions look like since I have Flex turned off: When I'm inhaling, the pressure is constant at my (current) IPAP setting and when I'm exhaling, the pressure is constant at my (current) EPAP setting. And there are sharp transitions between the two pressure settings.
Turning EasyBreathe on controls the transition between IPAP and EPAP. That's all it does, but it controls the transition in a major way. Now look at the inhalations and exhalations in the "EasyBreathe" part of the graph: When the beginning of the inhalation is detected, the machine gradually
increases the pressure until the IPAP setting is reached and ideally the IPAP pressure is reached just as the inhalation is finishing and the exhalation is starting. Once the exhalation starts, the pressure is dropped down more quickly than it was increased, but more slowly than the sudden drop from IPAP to EPAP that occurs without EasyBreathe. Once the pressure has dropped all the way to EPAP, it stays there until the beginning of the next inhalation starts.
It's also worth noting that on a Resmed VPAP there is no "EPR" because the "EPR" is built into the IPAP and EPAP settings. (EPR = IPAP - EPAP). The Resmed CPAP/APAPs need an EPR setting in order to use a slightly modified EasyBreathe algorithm. Here's a (old) image that I stole once upon a time for another post several years ago that shows the affect of EPR/EasyBreathe on the pressure curve for an S9 CPAP:
As this image shows, on a Resmed CPAP/APAP with EPR and EasyBreathe turned on, the therapeutic pressure setting is reached only at the end of every inhalation. At the beginning of the exhalation, the pressure then drops by a fixed amount that corresponds to the EPR setting. The drop in pressure looks sort of like the EasyBreathe drop on a VPAP. But on the CPAP/APAPs, as soon as "minimum" pressure is reached, the machine starts to slowly increase the pressure until the next inhalation is detected. At that point the rate of the pressure increased becomes more rapid and looks similar to the pressure increase on the VPAP. The difference, however, is that there is no "corner" in the mask pressure graph on a Resmed CPAP/APAP at the end of each exhalation. On the VPAP there is a small, but distinct corner at the end of each exhalation.
I'm not sure anybody ever uses EPR without EasyBreath on a Resmed CPAP, but for those who are interested, this is what it looks like:
The dotted pressure curve is EPR without EasyBreathe. The transition to the therapeutic pressure setting is "faster" and happens earlier in the inhalation than the traditional EPR+EasyBreathe combo. The EPR+EasyBreathe combo is the default setting if you use EPR on a Resmed machine.
Finally it's worth noting that BiFlex affects the EPAP-IPAP transitions in different way than EasyBreathe does. Unfortunately we don't have the ability to get Mask Pressure graphs off the PR machines because they don't record it. From an ancient post on another forum we can look at this figure however, that provides a snapshot of Flex vs EPR+EasyBreathe:
The three vertical lines were added by a poster on the other forum. They are relevant to the discussion however.
All Flexes increase the pressure at the blue line, which is when exhalation has dropped significantly, but well before the next inhalation actually starts. The EPR+Easybreathe used on the Resmed APAPs and CPAPs start increasing the pressure at the red line: Later in the exhalation, but still before the inhalation really starts. VPAPs and BiPAPs increase the pressure at the green line---at the start of the inhalation proper. Even with BiFlex turned on, the BiPAPs increase the pressure "faster" than the VPAPs with EasyBreathe turned on.