Constant positive airway pressure (cPAP) is the predominant noninvasive therapy for the obstructive sleep apnea syndrome (OSAS). The average pressure thereby applied can be reduced by online-identification of respiratory events. Oscillatory impedance measurement as an indicator for airway patency can identify central and obstructive apneas and hypopneas. Our goal was to reduce the sensors needed, to auto-calibrate the signals to each individual patient and to rule out patient induced artifacts.