A breathing assistance apparatus operates in alternating inhalation and expiratory phases wherein a) the control means of the apparatus comprise selection means capable of selecting a pressure parameter or a flow rate parameter to define b) the reference value for the gas source, the selection means are controlled by an automatic control unit being: I) connected to pressure and flow rate sensors situated on the inhalation duct to form a direct closed regulation loop for selecting a reference value parameter, II) associated to a program allowing the selection to be made in real time from a pressure or flow rate signal, so that the association of a direct closed regulation circuit for the selection of a reference value parameter with a valve permitting proportional operation, allows real time control of barometric and volumetric operating modes, between and during the inhalation and expiratory phases. The invention also concerns associated operating processes.
