A device for use in a CPAP system to assist patient breathing, the device comprising: a generator body forming: an inlet for fluid connection to a source of pressurized gas, a chamber fluidly connected to the inlet, first and second flow circuits fluidly connected to the chamber, each of the first and second_flow circuits including: first and second jets each defining an inlet end and an outlet end, the inlet end fluidly connected to the chamber, a flow director defining: a jet side fluidly connected to the outlet end, a patient side opposite the jet side for directing gas from a patient's naris, a first wall section between the jet and patient sides, the first wall section tapering in diameter toward the patient side, a second wall section between the first wall section and the patient side, characterised in that the second wall section tapers in diameter toward the jet side, and in that a transition point separates the jet side and the patient side, wherein the diameter of the flow director defines a reduced aperture of the flow director at the transition point. a generator body forming: an inlet for fluid connection to a source of pressurized gas, a chamber fluidly connected to the inlet, first and second flow circuits fluidly connected to the chamber, each of the first and second_flow circuits including: first and second jets each defining an inlet end and an outlet end, the inlet end fluidly connected to the chamber, a flow director defining: a jet side fluidly connected to the outlet end, a patient side opposite the jet side for directing gas from a patient's naris, a first wall section between the jet and patient sides, the first wall section tapering in diameter toward the patient side, a second wall section between the first wall section and the patient side, characterised in that the second wall section tapers in diameter toward the jet side, and in that a transition point separates the jet side and the patient side, wherein the diameter of the flow director defines a reduced aperture of the flow director at the transition point. an inlet for fluid connection to a source of pressurized gas, a chamber fluidly connected to the inlet, first and second flow circuits fluidly connected to the chamber, each of the first and second_flow circuits including: first and second jets each defining an inlet end and an outlet end, the inlet end fluidly connected to the chamber, a flow director defining: a jet side fluidly connected to the outlet end, a patient side opposite the jet side for directing gas from a patient's naris, a first wall section between the jet and patient sides, the first wall section tapering in diameter toward the patient side, a second wall section between the first wall section and the patient side, characterised in that the second wall section tapers in diameter toward the jet side, and in that a transition point separates the jet side and the patient side, wherein the diameter of the flow director defines a reduced aperture of the flow director at the transition point. first and second jets each defining an inlet end and an outlet end, the inlet end fluidly connected to the chamber, a flow director defining: a jet side fluidly connected to the outlet end, a patient side opposite the jet side for directing gas from a patient's naris, a first wall section between the jet and patient sides, the first wall section tapering in diameter toward the patient side, a second wall section between the first wall section and the patient side, characterised in that the second wall section tapers in diameter toward the jet side, and in that a transition point separates the jet side and the patient side, a jet side fluidly connected to the outlet end, a patient side opposite the jet side for directing gas from a patient's naris, a first wall section between the jet and patient sides, the first wall section tapering in diameter toward the patient side, a second wall section between the first wall section and the patient side, characterised in that the second wall section tapers in diameter toward the jet side, and in that a transition point separates the jet side and the patient side, wherein the diameter of the flow director defines a reduced aperture of the flow director at the transition point.