REPRODUCIBILITY OF PEAK EXPIRATORY FLOW MEASUREMENTS

The measurement of peak expiratory flow (PEF) has been applied in a nu mber of different settings since Wright developed a convenient measuri ng device.22 Although it has not proved as reliable as forced expirato ry volume in 1 second (FEV1) measured by spirometry, the ease of PEF m easurement and the current availability of inexpensive, portable instr uments have led to increasing use of this measure in clinical evaluati ons of ambulatory patients and in population studies to assess environ mental and occupational hazards. In addition, patterns determined from serial measurements of PEF are now accepted as the least invasive met hod to identify individuals with airway reactivity associated with occ upational exposures in both clinical and epidemiologic settings.3 As t he application of PEF becomes more widespread, the need arises for sta ndardization of the testing protocol and interpretation of test result s. The American Thoracic Society (ATS) has published extensive informa tion regarding the standardization of the FEV1 and forced vital capaci ty (FVC) measured on a spirometer.1,2 These ATS recommendations are ba sed on an extensive literature on spirometry testing, including studie s of learning effects, instrument error, and sources of intrasubject v ariation due to diurnal, day-to-day, and within-test session differenc es. For these pulmonary function tests, the ATS statements provide det ailed recommendations concerning equipment specifications and validati on, testing protocol, and interpretation of test results. These statem ents also include recommendations for the number of efforts that ought to be performed at a test session, specification of an ''acceptable'' effort, and criteria for judging the reproducibility of the measureme nt. By contrast, there is relatively little in the literature addressi ng how best to measure PEF. No studies comparable to the Epidemiology Standardization Project8 have examined the optimal frequency, instrume nt precision, and appropriate standards of reproducibility of the test . It is current practice for measuring PEF in both field and clinical settings to record three blows and report the maximum. There is sporad ic application of a reproducibility criterion of 20 L/min (see Burge, pp 279-294 in this issue).18 Because PEF, particularly serial measures of PEF, are likely to see a far broader application in the assessment of acute respiratory hazards, a closer examination of the measurement characteristics of PEF is warranted. A review of the literature was u nder-taken to identify what is known concerning the variance of repeat ed trials of PEF within a single test session (precision) for the PEF meters in common use. Although we found frequent reference to the peak flow as a more variable measurement than other pulmonary function par ameters, e.g., FEV1, this conclusion was generally based on comparison s of diurnal variation. There was also a literature addressing the acc uracy of various PEF meters relative to measurements on the pneumotach ograph. There was virtually no literature, however, describing the var iability within a test session (precision). Although knowing that inst ruments measure maximum flow achieved during a forced expiratory effor t without systematic error is important, documenting precision is also important. This is particularly true since short-term changes in PEF over time have become the most interesting applications of PEF, making relatively small differences in flow rates important to measure preci sely (see Eisen et al., pp 265-277, in this issue). The absence of a l iterature relevant to precision led us to examine data from one of our own large worker population studies with repeated trials recorded at each test session. Here, we present a summary of the limited literatur e on precision along with results from that study.