An auto lets the pressure fluctuate, depending on the breathing disruptions it finds. The pressure will fluctuate regardless of whether you are inhaling or exhaling. Therefore, on an auto you may find yourself exhaling against the highest pressure in the range you gave it. Respironcs added an exhale relief option to its autos, which will drop the pressure, just a little bit when you exhale, but you may still find yourself exhaling at a pressure that it pretty close to the max.
On a bi-level machine, you inform the machine ahead of time which pressure you want for inhaling and which for exhaling. The difference between these two can be very big - much bigger than what can be achieved with the flex options. Therefore, on a bi-level machine, you will never find yourself trying to exhale against the maximum pressure that was set for
inhale. Your maximum exhale pressure will not be enough to keep you airway open when you
inhale - so you can't keep that as the top of the range. A good reason to create a separate machine.
On a bi-pap
auto, you can separate pressure
ranges for inhale and exhale. For instance: you need a higher inhale pressure on your back, and less on the side - and auto bi-pap will supply the higher pressure when needed, and lower it when it's unnecessary. Same for exhale - you do fine at a lower pressure for exhaling till you start dreaming. Then you need higher exhale pressure. An auto bi-pap can handle that, and change your lower pressure.
The changes in inhale pressure and exhale pressure on an auto bi-pap occur independently.
O.
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CPAPopedia Keywords Contained In This Post (Click For Definition):
auto,
Bi-Level Machine