A Model for the Effect of Inhalation Device Flow Resistance on the Peak Inspiratory Flow Rate and Its Application in Pharmaceutical Testing

ABSTRACT An empirical relation between the peak inspiratory flow 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 empirical relation can be used to predict the change in peak inspiratory flow resulting from a change in flow resistance. Matching flow rates, representing equal inspiratory force, may thus be calculated for different inhalation devices. The fine particle dose generated by a variety of commercial powder inhalers was tested in-vitro at flow rates representing, for each device, a weak, a medium and a forceful inspiration. It was found that both the level of the fine particle dose and its flow rate dependence varied for the products.