How the Bipap Auto works

I have added this thread to explain how the Bipap Auto works as I had it completely wrong (it is a complex topic) and didn't realise this until I got one of the machines and could actually see the settings on it.

I had always incorectly assumed it was a normal Bilevel that allowed the user to set the regular Ipap CMS the regular Epap CMS and a minimum gap between them and that the machine would during the night adjust ipap and adjust epap independantly but always maintain the minimum gap between them. This I now know, is mostly wrong.

In another post I mentioned discovering how on most cpap machines (except the Puritan Bennet models) I seem to be able to show that there is a 1 CMS discrepancy between the real pressure in the mask & what most cpaps record (excepting the PB range). See ...
viewtopic/t17117/Respironics-Bipap-Auto ... e-use.html

In this other post I was trying to explain how the Bipap Auto worked & realised how hard it is to explain because it is not a simple process. It was then I decided to add this post in an attempt to do a better job.

If it is still unclear I am sure other Auto Bipap users can add their own explanations but please do think carefully what you add as it is easy to complicate the topic into oblivion

In this post I will only talk about Auto Bipap Mode & won't even try to add the complexity of using BiFlex as well. That can come later. Also this is the Bipap Auto Std model (not the 'M').

The following are taken directly from the LCD as I type. I am also using example settings as shown below.

A) In AbPAP mode you are allowed to set these parameters

1> Mode = AbPAP
2> Min Epap = (e.g. 5) (minimum epap the machine will run at)
3> Max Ipap = (e.g. 15) (maximum ipap the machine will rise to)
4> ps = 4 (this is the max pressure seperation allowed between epap and ipap and the most it can ever be set to is = Max Ipap minus Min Epap i.e. 15 - 5 = 10 in this example)
#2 Other info suggests that on top of the above rule is an absolute max
for ps of 8 (8 is the highest value the machine will accept beyond the MaxIpap minus MinEpap rule). Also it seems the minimum ps can be set to is 3.
5> rise = 2 (0,1,2,3) The speed the machine switches from epap to ipap.

These are all the relevent settings for this mode.

The Min Epap is the epap that the machine starts with and the current Ipap is going to be this min epap + 2 (that +2 is built into the machine and can't be changed).

Initial settings
So the machine starts off running at min epap and with ipap set 2 cms above the min epap. If the machine detects no obstructions or snores or flow limitations, it will remain all night at these settings.

Nightly auto adjustments
During the night the machine may detect epap breathing disturbances (breathing out) and decide to increase the min epap to a higher setting.
Also, during the night the machine may detect ipap breathing disturbances (breathing in) and decide to increase the curretn Ipap to a higher setting.

Ipap increase
If the machine is in the process of increasing the Ipap CMS, when the Ipap has been increased such that the gap between current epap and the current ipap is now about to exceed the 'ps' gap setting, the Epap will get increased as well.
#2 other data suggests that if max ps has been reached, Ipap will not get increased any further

Epap increase
If during the night the Epap gets increased due to any problems & there has been no Ipap disturbances, the Epap will be increased and the Ipap will also be increased if the machine needs to maintain the minimum built-in gap of 2 CMS between Epap and Ipap. However, if the Ipap has already gone up by any amount, then Epap will be increased on its own as long as there is still a difference gap of 2 or more CMS to the current Ipap setting.

Restated the machine will always maintain a minimum gap of 2 CMS between Epap and Ipap and will also always maintain a maximum gap between current Epap & current Ipap that is no more than the ps setting.

If you are still confused, don't worry, it is a complex equation & compounded even further when we add the effects of BiFlex.

The main point is it is pretty clever & it works for a lot of users

DSM


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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, CPAP, auto

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, CPAP, auto

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, CPAP, auto

dsm,

Sounds like a good explanation to me! I never use my auto bipap unit without biflex, and the "rise time" setting is not an option with biflex. Can you explain what rise time means?

Moogy

Moogy,

Rise time is how fast (usually stated in milliseconds) the air pressure changes when switching from epap pressure to ipap pressure.

This is a crude attempt to show this ...

Ipap ____xxxxx_____xxxxx_____xxxxx (assume Ipap = 14)


Epap xxxx_____xxxxx_____xxxxx_____ (assume Epap = 10)

-----------^________^________^_____
__

If we assume the x's represent the actual pressure coming from the
machine, it is clear that the pressure has to rise from 10 CMS to 14 when
the machine switches from Epap mode to Ipap mode. (I have attempted to put up arrows where the flip from epap to ipap occurs but they may look odd depending on what browser & font are used).

If the rise time is 0, the pressure will jump up very quickly (under 25 millisecs IIRC). If we set max risetime, the jump in pressure will be much
slower (I can't recall the actual risetime value for 3 but lest say it is 350 milisecs or 1/3 of a second).

If the rise time is short, the volume of air pumped will be noticably higher than if the rise time is at its slowest. The risetime when slow, means less air is pumped by the machine during the rise period (the period the switch starts & ends).

This reduction in air volume (minute ventilation) can have side effects reulting in less effective therapy but if the rise time is too fast, it can disturb some people & thus have an equally detrimental effect.

This is a very simple attempt at describing this - I know there is a SAG chart (I'll go look for it) that describes it in more clinical detail.

DSM

#2

This Sleepy Dave post shows the waveform representing risetime & how increasing the rise time puts a curve in the waveform. This curve illustrates how much less air gets pumped as risetime increases.
http://www.apneasupport.org/viewtopic.php?p=24770

D