The invention relates to a breathing assistance device for a patient (P), the device including: -a source of respiratory pressurized gas (S), a gas transmission duct (31) comprising a distal end (31d) coupled to said source and a proximal end (31p) coupled to the patient, -a gas regulating valve (32, 50) interposed in the gas transmission duct at a proximal location, comprising a leakage orifice (531) and an obstruction means (54) capable of varying the opening of the leakage orifice upon signal of controlling means (35) and allowing a bidirectional gas flow through the leakage orifice in both expiration and inspiration phases.
