BiLevel machines - how & why they vary so much.

I posted this in another cpap forum but decided it was a topic of general interest here as well.

I hope it explains why some brands of BiLevel behave like they do & why what is great for one person can be awful to another.

Please feel free to question or expand on any of the points made ..


DSM

BiLevel can take some getting used to & different brands of BiLevel behave differently enough that one can wonder how they can be so different when appearing to do the same job.

But there is one issue I have come up against that I have seen very little discussion on & this is when someone who has any sinus or nasal congestion gets put of BiLevels. The brand of BiLevel for such people can be crucial.

1) Puritan Bennett BiLevels - designed & (apart from one Mexican batch) built by god - wonderful machines - very adjustable

2) Resmed Vpaps - possibly the best machines for data collection on the market but can appear 'aggressive' to some users (explained later) these have a wide variety of adjustments compared say to a Respironics BiPap. The Vpap Adapt SV is possibly the most advanced xPAP machine in the world today but it is still very new & intolerant of air leaks.

3) Respironics BiPaps. Least amount of adjustment but the classic models are built like panzer tanks - works of art but, the Bipaps with the Auto-Trak feature don't work well with people who have constant nasal airflow restrictions of any sort such as sinus problems & regular nasal congestion or generally restricted nasal breathing. From my evaluations of most BiPap models, the Auto-trak keeps assuming your slow breathing is a leak and will flip the machine from ipap to epap while you are only halfway through breathing in. Older Respironics Bipaps without auto-trak will not behave like this. They work as any other brand except they don't tolerate leaks (what Auto-Trak tries to do). Again I add the caveat that this only happens to people with nasal airflow restrictions due to sinus, shape, etc: etc:

Back to Resmed Vpap IIIs ... (& a mention of the Vpap Adapt SV) ...
These machines use a varying speed brushless motor that can accelerate pretty well to change pressure but still has some degree of inertia to overcome & sustain & thus tend to do what is known as 'overshoot' which to the poor xpap users translates into 'aggressive' response. The older PB Bilevels did this too (the PB425 has such a tiny blower it manages to minimise this). But, the new Vpap Adapt SV has an entirely new and revolutionary blower still built around a brushless motor and varying the speed but it uses dual fan impellers (one fan at each end of the motor) thus has wonderful acceleration (no overshoot), is quieter than the Vpap IIIs (no 2-tone whine as the motor changes speed), this motor is in the best harmonic balance of any on the market and the fans are so lightweight they can accelerate & slow so fast that this machine can track a patients breathing in real time.

More on the Respironics 'Classic Bipap models' ...
The 'classic box' machines (apart from the new M series Bipaps which have gone down the same path as Resmed & Puritan Bennett & use a varying speed brushless motor) use an 'air-valve' to change airflow - this is possibly one of the best techniques in use but is super expensive to manufacture & thus is being phased out. The air-valve uses the same principles as a loudspeaker to move a valve backward & forward in a magnetic field such that it can minutely control the flow of air. These 'classic' BiLevels use a constant speed brushless motor to pump air & feed this to the air-valve which directs a percentage of air back into the input to the blower & the other percentage to the air circuit linked to the patient. The internal microprocessor can control this air-valve to direct air flow back to the blower or out to the user and vary this change of direction at great speed and with great precision. It is an impressive design & sadly being lost due to cost. A nice feature of the classic Bipap was the consistency of the motor noise which was very tolerable.

#2 But!, the air-valve is being used in the new Respironics BipapSV which suggests to me that this machine will be very smooth in its operation & if they improve on the Auto-trak leak sensing for people with restricted nasal flow, it could be as good as the Vpap Adapt SV.

Hope this info provides some perspective & clarity to what you as a user have been 'feeling'

Cheers

DSM
#3 further qualified the 'Classic Bipap' details

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