The contradiction in treatment for overlap syndrome is how to improve hypercapnia because of narrower difference between inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP), and meanwhile to eliminate apnea and popnea events which may easily occur at the end of expiration For ordinary Bipap ventilator. If the IPAP is set to higher, the patients may feel discomfort, if the pressure difference between IPAP and EPAP is too narrow or the expiratory positive airway pressure (EPAP) too high, hypercapnia may occur. If the EPAP is too low, redusual apnea and hypopnea event may become common.