Nasal interface apparatus with air entrainment port of adjustable open area

A system for delivering gas to a patient via the patient's nostrils, comprising:

• (a) a pulse flow gas source and a gas supply line in fluid communication with a nasal interface assembly, the pulse flow gas source including a pressure sensor and configured to release a pulse of gas only when a signal pressure detected by the pressure sensor is below a trigger pressure level;
• (b) wherein the nasal interface assembly comprises a pair of nasal inserts and a hollow body manifold defining:
• (i) an internal chamber;
• (ii) at least one inlet for fluid communication from the gas supply line into the internal chamber;
• (iii) at least one outlet for fluid communication between the internal chamber and the pair of nasal inserts;
• and
• (iv) at least one air entrainment port for fluid communication between the internal chamber and a space external to the hollow body;
• and
• (v) at least one valve member movable relative to the hollow body for varying the size of an open area of the at least one air entrainment port, wherein fluid communication between the internal chamber and the space external to the hollow body via the at least one air entrainment port is permitted only via the open area of the at least one air entrainment port;
• (c) wherein the at least one valve member is positioned to create a signal pressure below the trigger pressure upon inhalation by the patient, and above the trigger pressure upon exhalation.