FREQUENCY-RESPONSE OF VARIABLE ORIFICE TYPE PEAK FLOW METERS - REQUIREMENTS AND TESTING

Little is known about the response of variable orifice peak flow meter s to high frequency flow input, The purpose of this study was to defin e and test dynamic requirements for such peak flow meters. In a popula tion sample we measured peak expiratory flow (PEF), rise time (tr), fr om 10-90% PEF and the duration of the flow in excess of 97.5, 95 and 9 0% of PEP, by use of a carefully calibrated Fleisch pneumotachograph w ith known and adequate frequency response. Three peak flow meters (Min i Wright, Vitalograph and Ferraris) were tested with an explosive deco mpression calibrator adjusted to values for PEF and tr as close as pos sible to the 95th and 5th percentile values, respectively, both for ma les and females, and with peak durations between 5 and more than 100 m s, The 95th percentile values of PEF were 597 L . min(-1) for females and 894 L . min(-1) for males, The 5th percentile values of tr were, r espectively 55 and 45 ms. The duration of flow in excess of 95% PEF wa s longer than 10 ms in 99% of the subjects, For all meters, the deviat ion of PEF corrected for alinearity were less than 5% at a peak durati on of 10 ms, We conclude that PEF, rise time, and peak duration can be used for description of dynamic properties of variable orifice meters , and that the tested meters had a satisfactory frequency response for recording PEF in mostly normal subjects.