Resistance of DPIs

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

The difference in inhalation flow can also influence the degree of oropharyngeal deposition as has been shown for pMDIs (33). When a high inhalation flow is being used, more of the drug will deposit in the oropharynx as compared with a low inhalation flow, which is more optimal with regard to this parameter. 

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For nebulizers and MDIs, the external resistance (Re) is quite low. Different approaches have been made to describe the external airflow resistance of DPIs. Olsson and Asking [99] derived an empirical relationship between flow rate () and pressure drop (AR), AR = for a number of inhalers (such as Rotahaler , Spinhaler and Turbuhaler ) in which they define the proportionality coefficient (C) as the airflow resistance. This relationship differs only slightly from the general (theoretical) equation for orifice types of flow constrictions ... 

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