Reliability of plethysmography, the single breath oxygen test, and spirometry in population studies.

Three thousand five hundred and twenty-eight residents of a census tract in Los Angeles, California underwent pulmonary function testing in a mobile laboratory (the Breathmobile). Tests included respiratory questionnaire, electronic spirometry, the single breath O2 test and body plethysmography. The reliability and sensitivity of the tests performed in the Breathmobile was measured by repeating the same tests and others on a 3% probability sample at the University of California at Los Angeles Pulmonary Function Laboratory. The reliability of the FVC and FEV1 was excellent; of the FEF 25-75% and the FEF 50-75% -- good; and of the VTG, RA and delta N2 -- reasonably good. As yet the reliability of the closing volume fraction is inadequate in our study. Grouping by individual reported symptom complexes identified different groups of people. The questionnaire and the forced expiratory flow rates identified the most people as having decreased respiratory function. Selection of the best breath or average of the two best breaths affected results of spirometry very little.