How does the machine know to adjust pressure in AutoSet mode?

AutoSet devices automatically increase pressure as airway blockage starts to occur.

After you fall asleep and your pressure needs begin to vary, your AutoSet device responds to three separate parameters, based on the degree of airway blockage caused by your sleep apnea: inspiratory flow limitation, snore, and apnea. AutoSet devices automatically increase pressure as airway blockage starts to occur in order to minimise the chances of it developing into apneas.