FLOW EARLY IN THE INSPIRATORY MANEUVER AFFECTS THE AEROSOL-PARTICLE SIZE DISTRIBUTION FROM A TURBUHALER

Several in vitro and in vivo studies have emphasized the importance of generating a high inspiratory flow when using a dry powder inhaler. L ittle attention has been paid to the influence of the inspiratory flow profile on the particle size distribution contained in aerosols gener ated by these devices. The internal volume of a device such as the Tur buhaler is small compared with a vital capacity breath and it is possi ble that all the powder has been drawn from the device before peak ins piratory flow has been achieved, particularly if the time to peak insp iratory flow is prolonged. A series of experiments were performed to a ssess the effect of different flow profiles through the Turbuhaler, ea ch with a peak flow of 60 l min(-1). A 400 mu g budesonide Turbuhaler was enclosed in a chamber allowing air to pass unimpeded through the d osing channels and entrainment ports. A large three-way tap was used t o blow powder from the device across a Malvern Mastersizer laser parti cle sizer which produced a profile of the particle size distribution w ithin the aerosol. The rate of increase in flow through the Turbuhaler was determined by the rate at which the three-way tap was turned, and recorded by means of a pneumotachograph. The rate of increase in flow was found to significantly affect the particle size distribution with in the aerosol. Failure to attain a flow of 30 l min(-1) before 150 ml of air had passed through the device resulted in the aerosol volume m edian diameter increasing from less than 6.6 mu m to greater than 45.3 mu m. These results indicate that flow during the initial part of the inspiratory effort may be important in determining the characteristic s of the aerosol generated by a dry powder inhaler. With more sophisti cated equipment, it might be possible to explore the relationship betw een flow profile and particle size distribution generated by dry powde r devices in more detail.