title: Critical aspects of the function of inspiratory flow driven inhalers.
abstract: Powder inhalers rely on the patient's inspiratory flow for delivery and aerosolization of the medicament.  Different inhalers offer different resistances to inspiration through the device.  The flow rate attained by a patient depends on the effort expended and on the air flow resistance of the device; flow rate is thus a device-dependent variable.  A comparison between powder inhalers should therefore take their air flow resistances into account.  An empirical relation between the peak inspiratory flow rate through a device and the flow resistance of the device has been developed using results from healthy subjects and verified to a limited extent using data from asthmatic patients.  The flow resistance was measured as the pressure drop at a fixed flow rate.  The empirical relation can be used to predict the change in peak inspiratory flow rate resulting from a change in flow resistance.  Matching flow rates, representing equal inspiratory efforts, may thus be calculated for different inhalation devices.
authors.affiliation: Astra Draco AB, Lund, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Olsson
authors.forename: L
authors.initials: L
authors.lastname: Asking
mesh_terms: D000336:Aerosols / Q000008:administration & dosage; D001249:Asthma / Q000188:drug therapy / Q000503:physiopathology; D004734:Energy Metabolism; D004867:Equipment Design; D006801:Humans; D009330:Nebulizers and Vaporizers; D010316:Particle Size; D011208:Powders / Q000008:administration & dosage*; D012123:Pulmonary Ventilation