Abstract
OBJECTIVE: To assess four different criteria for selecting the 'best' forced vital capacity (FVC) manoeuvre to be used for clinical diagnostic purposes.DESIGN: Criterion standard.SETTING: General population survey performed in 1980-82.PATIENTS: One thousand, two hundred and eighty-three subjects (age range eight to 64 years) were first stratified into five mutually exclusive groups according to the following criteria: simultaneous largest FVC, forced expiratory volume in 1 s (FEV1) and peak expiratory flow (PEF) (group 1; n=481); isolated largest FVC (group 2; n=223); isolated largest FEV1 (group 3; n=144); isolated largest PEF (group 4; n=299); and overlapping criteria (group 5; n=136).INTERVENTION: Subjects performed spirometry following American Thoracic Society (ATS) protocol and filled out a standardized respiratory questionnaire.MAIN OUTCOME MEASURES: Spirograms were analyzed by examining the frequency of spirometry abnormalities with regard to the presence of respiratory symptoms, first within mutually exclusive groups of subjects and then within the whole sample. The hypothesis of the role of PEF in 'best test' selection was formulated after data collection.MAIN RESULTS: When the isolated largest PEF criterion was used, the following data were obtained: the highest prevalence of spirometric abnormalities for each FVC parameter in each mutually exclusive group; the highest predictive value for mean and instantaneous expiratory flows in separating symptomatic from asymptomatic subjects; and finally, using the whole sample, higher levels of sensitivity and similar specificity to other criteria for all test parameters (all over 90%, except for PEF).CONCLUSIONS: While maintaining the current ATS criteria of acceptability and variability for FVC trials, it is proposed that the curve that better reflects maximal expiratory effort, ie, that with the largest PEF, be recorded and analyzed for spirometric variables.