Similar to an NPSG, your brain waves, oxygen levels, heart rate and breathing, and leg movements will be monitored throughout the night, with the addition of a CPAP machine. The mask of the CPAP is fitted so that a continuous stream of air is introduced into the nose as you breathe, keeping the airway open. Your technician that will be there with you throughout the process can increase or decrease the air flow (pressure) as needed, determining which pressure is best for you.