I'm answering you and Jim. Pulmonary specialist should be the one to order a sleep study and follow up. BiPap pressure is set at the fitting for a machine. The accessories for both cpap and bipap need to be replaced periodically. My schedule is disposable filter every two weeks face cushion once a month headgear and water tank ( reservoir) and air hose every six months. A sleep study is necessary to determine which type of machine is needed. I can't breath through my nose while sleeping. Apnea means breath stops. BiPap pushes air through my gasping mouth. No one should on their own buy a machine without a sleep study and a trained professional assisting.