Significance of intraindividual changes in maximum expiratory flow volume and peak expiratory flow measurements.

To examine criteria to assess significant changes of measurements derived from the forced expiratory vital capacity (FVC), and to examine changes in the peak expiratory flow (PEF) maneuvers, ten subjects were tested on approximately 30 occasions. Since mini Wright peak flow meters are increasingly used for clinical and research purposes, peak flow intraindividual variability and relations to FVC peak flow were examined, each set of tests consisting of five FVC maneuvers and one peak flow. Measurements on a pneumotachograph included FVC, (FEV1), maximum mid-expiratory flow (MMF or FEF25-75%), and instantaneous maximum expiratory flow after 50 and 75 percent expiration of the FVC. PEF measurements were derived using the mini Wright peak flow meter and the pneumotachograph. The coefficients of variation for the FVC measurements were greatest for maximum expiratory flow measurements and least for the FVC and FEV1. Maximum values from each set of tests reduced the variability. From these values, criteria and estimates were derived to evaluate significant intraindividual change. The PEF measurements were evaluated also to determine intraindividual changes. The coefficients of variation were only 2 percent to 14 percent. The peak flows obtained were shown to correlate well with the PVC peak flow.