PEAK EXPIRATORY FLOW AND THE RESISTANCE OF THE MINI-WRIGHT PEAK FLOW METER

The purpose of this study was to examine whether the resistance of the peak flow meter influences its recordings. One hundred and twelve sub jects, (healthy nonsmokers and smokers and subjects with lung diseases ) performed three or more peak expiratory flow (PEF) manoeuvres throug h a Fleisch pneumotachograph with and without a mini-Wright peak flow meter added in random order as a resistance in series. The results wer e as follows. In comparison with a pneumotachograph. alone, peak flow measured with an added mini-Wright meter had a smaller within-test var iation, defined as the difference between the highest and second highe st values of PEF in a series of blows. The mean (se) variation was 14 (1.3) L . min(-1) and 19 (1.5) L . min(-1) with and without meter adde d, respectively, In comparison with the pneumotachograph alone, the ad dition of the mini-Wright meter caused PEF to be underread, especially at high flows, The difference (PEF with meter minus PEF without meter ) = -0.064 (average PEF) -8 L . min(-1); R(2) = 0.13. The mean differ ence was -7.8 (1.1)%, and increased numerically for a given PEP, when maximal expiratory flow when 75% forced vital capacity remains to be e xhaled (MEF75%FVC) decreased, The reproducibility criteria for repeate d measurements of peak now are more appropriately set at 30 L . min(-1 ) than the commonly used 20 L . min(-1), because a within-test variati on of less than 30 L . min(-1) was achieved in 76% of the subjects wit hout PEF meter inserted and in 88% with meter inserted, with no differ ence between healthy untrained subjects and patients. The resistance o f the peak expiratory flow meter causes less variation in recordings b ut reduces peak expiratory flow, especially at high values and when th e peak is targe as compared with the rest of the maximal expiratory fl ow-volume curve.