A bi-directional flow sensor is adapted for reducing pneumatic noise during pressure sensing with a flow passing through the flow sensor. The flow sensor comprises a hollow, tubular member having a throat section disposed between a ventilator end and a patient end. A flow restrictor is disposed in the throat section and is adapted to measure differential pressure in the flow. A baffle is mounted at the ventilator end and is adapted to minimize non-axial flow at pressure taps located on opposing ends of the flow restrictor. The patient end includes a flow obstruction configured to promote uniform velocity across the flow at the pressure taps during exhalation flow from the patient end to the ventilator end. The flow sensor minimizes pneumatic noise to less than 0.1 LPM to allow accurate patient flow measurement and triggering of inhalation and exhalation phases at flow rates of 0.2 LPM.
