A Continuous Positive Airway Pressure (CPAP) machine is a device that uses room air delivered through a mask system to keep the airway open of the person using the machine. A CPAP is generally used to treat mild obstructive sleep apnea by preventing the airway from collapsing on itself during times of sleep. CPAPs are generally used with a heated humidifier that uses heat to turn water into a mist delivered with the air to prevent nasal passages and the mouth from getting dried out due to the airflow. Distilled water must be used in the humidifier to prevent mineral build up and deposits on the metal tank in the humidifier. Another comfort feature on CPAPs is called ramp. This means the pressure will start lower and slowly build, or ramp, up to the prescribed level. A CPAP can either be a standard CPAP set at a single pressure or an Auto that has a range of pressures that adjust automatically based on the breathing of the user. All pressures or ranges must be set according to a prescription from a doctor and can not be adjusted without a prescription. Resmed, Respironics and Fisher & Paykel are the major manufacturers of CPAP machines and the masks that are used with them to deliver the air. Resmed’s newest line of CPAPs is the S9 series, and the models include the Escape, Elite, Escape Auto and Autoset. Respironics has the System One line, and the models include the Remstar, Remstar Pro, Remstar Plus and Remstar Auto. Fisher & Paykel has the Sleepstyle and Icon lines of machines, and the models include the 234, 242, Novo, Premo and Auto.