Extensive medical interview and physical examinations were undertaken to identify a healthy population. Spirometry was performed using two calibrated instruments. The methodological guidelines of the American Thoracic Society were observed when performing spirometry. Measurements were analyzed and underwent multiple regression to process prediction equations for each spirometric parameter. Thus, a pulmonary function measurement that is below 'normal' with respect to one published reference sample may well be above 'normal' with respect to a different published model.
Some variations are due to ethnic differences.
4,10 Local and native prediction equations may enhance the reliability of the performed spirometries. 11 Test quality remains the most important concern in pulmonary function testing. 4,12-14 Variability of consecutive measurements in an individual case is greater in pulmonary function tests than in most other clinical laboratory tests, because of the inconsistency of effort by the patients. Any of the 2552 participants who had respiratory complaints, history of ever regular smoking, serious cardiopulmonary disease or evident chest deformity were excluded from the study. The subjects heights were measured in stocking feet against a wall with a right angle.