A Bilevel Positive Airway Pressure (BiPAP) machine is like a CPAP in that it also uses room air delivered through a mask system to keep the airway open of the person using the machine. The difference being that a BiPAP uses two different preset pressures for increased tolerance of PAP treatment. A higher pressure is set as the inhale or IPAP pressure, and a lower pressure is set for the exhale pressure or EPAP. Like CPAPs, they also use heated humidifiers and ramp to increase patient tolerance and compliance. Like a CPAP they too have Auto models that use a set range of pressures to determine how much air is needed at a given time. Resmed uses the term VPAP, or variable positive airway pressure, to describe their BiPAP machines. Resmed has the S9 line of BiPAPs, and the models are the VPAP S and VPAP Auto. Respironics also has System One BiPAP machines, and they are the BiPAP Pro and BiPAP Auto.