Fluid flow measuring apparatus

Respiratory flow rate measuring apparatus comprising a tubular stator which has oblique slots formed in its tubular wall;

• a casing within which said tubular stator is mounted and which forms a circumferential gallery around the tubular stator, a first port which communicates with the gallery at one end and which projects outwardly with respect to the stator from that end, and a second port which communicates with the interior of the tubular stator and which is in substantially coaxial alignment with the tubular stator;
• a rotor which is mounted for rotation within the stator;
• means by which a readout indication of respiratory flow rate is derived from rotation of the rotor;
• and a barrier which extends across the gallery so that substantially all respiratory flow which enters the gallery from said first port is constrained to flow around the tubular stator in one circumferential direction only, respiratory flow so circulated around the tubular stator being passed through to the interior of the tubular stator via the oblique slots and forming within the interior of the tubular stator a spirally swirling respiratory flow which drives the rotor, the location of the radially outer ends of the oblique slots and the orientation of the oblique slots with respect to said one circumferential direction being such that the angle by which the respiratory flow enters each slot from the gallery deviates from the respiratory flow path around the tubular stator is an acute angle.