Abstract: In an apparatus and method for determining an optimal opening pressure of a lung system a regulating unit delivers an inspiration pulse having an end pressure which is higher than the start pressure to the lung system. During the delivery of this inspiration pulse respiratory gas flow and pressure are measured by a measuring unit having a flow meter and a pressure gauge. The measured values are supplied to a control unit, in which measured flow and pressure are correlated and inflection points or regions in the flow-pressure-relation are identified. The highest pressure value related to an inflection point or region is defined as an interim opening pressure. By applying several different inspiration pulses, several interim opening pressures can be determined.