Coincidentally, right before getting my first therapy machine a few weeks ago, I happened to acquire an older model Respironics machine at an auction of obsolete medical equipment most of which comes from a nearby Vet hospital.
That machine was not useable for therapy....so I used it as a learning experience and a possible source of parts for my many hobby development projects.
In other words, I took it apart and analyzed it.
What is a CPAP machine? (also APAP, BiPAP, etc. - they all have the same basic guts)
IT'S A BLOWER. That's it....it's just a blower.
The blower is based on a very high quality precision motor which can be finely controlled in terms of its speed and therefore its airflow output.
There are also several high precision pressure sensors that monitor the output and also the back pressure imposed by the user's breathing pattern.
The processor inside simply regulates the speed of the blower motor according to its software programming using the pressure readings as compared to time to adjust the motor speed to maintain the pressure level.
To be effective, the pressure delivered needs to be just enough to overcome the difference between your diaphragm's attempt to decrease the pressure in your lungs (allowing air to rush in) and the blocking effect of one's soft palate closing up the airway (This according to my doc)
Humidifiers, heaters, modems, etc. are all just accessories to the basic controlled blower function.
I hope this helps to provide a bit of a look behind the curtain so you can make informed decisions in your therapy and a maintain a measure of skepticism when certain providers try to sell you a red herring or know when they are not.
Feel free to ask me more questions if you have them. I'm really just starting to delve into the details of these machines but let it be known that they are really not very complicated - precise, yes....complicated, not so much.
Hope this helps!