In its 1991revision, the American Thorax Society (ATS) recommended that each region should define its own equations to determine the theoretical, or predicted values of the spirometric parameters that best represent the pulmonary functional reality of the local population. At that time, the United States already had various equations of its own as well as the European Community, specially Poland. In 1992, Pereira et al., analysing 4,200 spirograms on healthy Brazilians, found predicted values (PV) of forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and middle expiratory flow (MEF) different from those reported by American and European authors. The purpose of the present study was to compare the equations developed by Pereira et al., using a Brazilian sample population, with those determined by Knudson et al. for American populations, that are the most used by Brazilian specialists. This study included 1,070 spirograms performed in patients of both genders (389 males and 681 females) who came to our service for routine functional assessment. No pathology was excluded and the smoking status of the patients was not taken into account. For each patient the PV of FVC, FEV1 and MEF were calculated accordingly to the equations of Pereira et al. (PV-P) and Knudsen et al. (PV-K). Subsequently, the means, standard deviations and reports obtained by both methods were compared. Among females, the PV-K of FVC were 4,01% (p < 0.005) greater, leading to a higher rate of restrictive impairment whereas among males there was no significant difference. Regarding FEV1, PV-P were higher in both males (4.76%; p < 0.005) and females (5.04%; p < 0.05) resulting in a greater sensitivity in the identification of respiratory obstructions. No significant difference was observed between PV-P and PV-K as to FEF25-75 regardless of gender.

Keywords: Spirometry. Reference values. Forced expiratory flow rates.