An endotracheal tube (ETT) is provided with a built-in pressure differential flow sensor at the end closest to the lungs. The airway of the ETT (4) has a fixed diameter throughout, with the exception of a section located within the pressure differential flow sensor (8), within which the diameter of the airway increases relative to the fixed diameter. The flow sensor functions by sensing the difference in air flow between the airway portion (102) where the diameter is fixed and the airway portion (104) where the diameter is relatively larger. The pressure differential flow sensor is configured to communicate with a monitor (10) capable of determining lung flow from measurements provided by the flow sensor.
