An evaluation of the mini-Wright peak flow meter.

The mini-Wright peak flow meter (MPFM) has been evaluated, and the results obtained from it show a strong positive correlation (r=0.970) with the Wright's peak flow meter (PFM). MPFM measurements, however, were biased to be about 38 1/min higher than PFM measurements (95% confidence limits 31.01/min to 45.01/min). Between instrument variation was found (F--ratio 3.67 with 9 and 81 degrees of freedom: P less than 0.001). In practice this did not appreciably affect individual measurements greatly as 95% confidence limits on any individual measurements were increased from +/-24 1/min to +/-27 1/min. There was no significant day-to-day variability in measurements obtained with individual instruments. The MPFM is a pocket-sized, simple, cheap, and robust instrument for following changes in ventilatory function. In clinical trails and surveys, however, both the bias in favour of the MPFM compared to the PFM and inter-machine variation must be taken into account. As the manufacturers have altered the scale to remove the bias since this study was performed, it will be important to know whether the original or the modified meter is being used in future studies.