Frequency response of variable orifice type peak flow meters: requirements and testing.

Little is known about the response of variable orifice peak flow meters to high frequency flow input. The purpose of this study was to define and test dynamic requirements for such peak flow meters. In a population sample we measured peak expiratory flow (PEF), rise time (tr), from 10-90% PEF and the duration of the flow in excess of 97.5, 95 and 90% of PEF, by use of a carefully calibrated Fleisch pneumotachograph with known and adequate frequency response. Three peak flow meters (Mini Wright, Vitalograph and Ferraris) were tested with an explosive decompression calibrator adjusted to values for PEF and tr as close as possible to the 95th and 5th percentile values, respectively, both for males and females, and with peak durations between 5 and more than 100 ms. 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, respectively 55 and 45 ms. The duration of flow in excess of 95% PEF was longer than 10 ms in 99% of the subjects. For all meters, the deviation of PEF corrected for alinearity were less than 5% at a peak duration 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.