The CPAP (Continuous Positive Airway Pressure) therapy is the most common therapy to treat the obstructive sleep apnoea syndrome. If the upper respiratory tracts collapse, it may lead to breathing interrupts during sleep. The CPAP-device provides a positive pressure to splint the airways. The influence on the pressure is different from patient to patient and their medical condition. It has been shown that many CPAP-devices can not maintain the required pressure set points, because the mask pressure is seriously influenced by the patient's breathing. In this work the electromechanic part and pneumatic part of the breathing therapy system is modeled to provide an opportunity for a model-based control approach. Based on the physical chain of effect an existing control strategy is extended. In the end some control results are shown and a conclusion is made.