The invention relates to a breathing assistance device for a patient (P), thedevice including: - a source of respiratory pressurised gas (S), a gas transmissionduct (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 thegas transmission duct at a proximal location, comprising a leakage orifice (531)and an obstruction means (54) capable of varying the opening of the leakage orificeupon signal of controlling means (35) and allowing a bidirectional gas flow throughthe leakage orifice in both expiration and inspiration phases.
