The Hoffrichter II of TREND BILEVEL ST20 generates two levels of pressure in the S-, ST- or T-way via an electrically controlled blower. Changing of a level of pressure to another is realized via a fast change of the revolutions of the fit high-performance blower to maintain the tension for the patient when down so possible. Time respiration with prescribed, time of inspiration of the group. If the function of trigger is deactivated the patient is ventilated as the parameters of group. If the function of trigger is activated the device accepts only signals of spontaneous trigger in the expiration phase.