It is true that I have to stop using my CPAC machine 4 days or so before taking another polygraphe. I was told to stop using my CPAC machine when I do my 2nd test. Why so, it won't show in my polygraphe.

Who told you this and why? A polygraph is called a lie detector test. It works because most people cannot control bodily fluctuations when they lie. So the polygraph can measure these.

It's possible the use of a CPAC can either magnify the reactions or vice versa. But I couldn't find any research that indicates a connection.

Sorry, I am French so I guess I did not express myself with the right word. It is not a polygraphe test, it is a test for Apnea (a machine that is connect to you for a whole night during your sleep).

I have to pass a second test and was told to stop using my CPAC machine 4 days ahead.

When you use the CPAP (Continuous Positive Airway Pressure) machine, your body functions correctly. The doctor or sleep clinic wants you to stop getting artificial help for your body (the CPAP machine) and see how well your body works without any help.

Ahh, yes, if you are taking another sleep apnea test they will want you to stop using the machine to get a better reading on the new test.