THE EFFICACY OF FILTERS USED IN RESPIRATORY-FUNCTION APPARATUS

The ability of two low resistance barrier filters (Collins DC-1 and Pa ll Pf 305) to remove bacteria from expired air was assessed. A special ly designed coupling device was used to hold each filter or a disposab le plain cardboard mouthpiece a fixed distance (4.5 cm) from a blood a gar plate. Volunteers performed maximal forced vital capacity manoeuvr es through the assembled apparatus and bacteria impinged on to the aga r plate were enumerated. Both filters allowed the transmission of appr oximately one-third of expired colony forming units. The efficacy of t hese filters for reducing the likelihood of cross-infection during spi rometry is not supported by this study.