The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

MIS-TIMING BETWEEN ACTUATION OF A METERED-DOSE INHALER (pMDI) AND INHALATION: EXPERIENCE WITH A VALVED HOLDING CHAMBER (VHC) COMPARED WITH A SPACER

J.P. Mitchell, M.W. Nagel and A. Archer. Trudell Medical International, London, Canada.

Add-on devices, such as spacers and VHCs, have the advantage of reducing losses if a patient fails to have perfect coordination between actuation of a pMDI and inhalation of the delivered medication. This study compared the performance of 5 VHCs (AeroChamber(r), Monaghan Medical Corp., Plattsburgh, NY) with 5 spacers (MicroChamber^{TM}, Respiratory Delivery Systems Inc., Chelmsford, MA) using Flovent(r) (110 µg/dose fluticasone propionate (FP), GlaxoWellcome (Canada) Inc.). Each device was tested using a breathing simulator that was based on a mechanical ventilator connected to the master side of a test lung. The mouthpiece of the device on test was connected via an aerosol filter to the slave side of the test lung. A rigid bar was placed between the two compartments of the test lung, so that inflation of the master compartment also inflated the slave side. Measurements were made at a tidal volume of 500 ml, I/E ratio of l/l, rate of 10/min, with the peak inspiratory flow rate close to 28 l/min. In the first part of the study, pMDI actuation was timed to concide with the onset of inhalation (optimum use), whereas in the second part, actuation coincided with the onset of exhalation. 5 doses of medication were delivered at 30 s intervals, and aerosol collected on the filter was assayed by HPLC-UV spectrophotometry for FP. The AeroChamber(r) VHCs provided 58.9 ± 5.1 µg FP compared with 39.4 ± 7.6 µg from the Microchamber^{TM} spacers when actuation occurred at the same time as inhalation. The output from the VHCs declined to 35.6 ± 5.4 µg FP when actuation coincided with exhalation, due largely to gravitational settling of the aerosol during the 3 s delay (each breathing cycle lasted 6 s). However, the mass of FP delivered by the spacer declined to 4.7 ± 7.7 µg under these conditions. It appears that the inhalation valve of each VHC substantially protected the aerosol retained within the device from mixing with exhaled air. The open-ended geometry of the spacer allowed mixing and consequent dilution, so that the amount of drug inhaled with the next breath was greatly reduced.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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