BTW, there is no "S10" model. ResMed says "AirSense 10" or "Air 10," but most of us say "A10."
ResMed uses what's called FOT Forced Oscillation Technique to try to distinguish central apnea from obstructive. Google it.
When you stop breathing, after 4 seconds or so, the machine starts sending little pulses of air down the hose to try and see if your airway is open.
Put on your machine, breathe for a while and then stop breathing. After about 4 seconds, it will start sending little pulses. You may or may not hear or feel the pulses. Depending on how the hose is lying, it may or may not move a bit.
Make a note of the time when you hear this sound. It will show up on your SleepyHead graphs as some "fuzz" on the mask pressure graph.