O papel da razão FEF50%/0,5CVF no diagnóstico dos distúrbios ventilatórios obstrutivos

Abstract

Objective: To evaluate the contribution of a new coefficient, the FEF 50% /0.5FVC ratio, obtained from the maximal expiratory flow-volume curve, to the diagnosis of obstructive lung disease (OLD); to test this coefficient in differentiating among patients considered normal, those with OLD and those with restrictive lung disease (RLD); and to determine cut-off points for each functional diagnosis, as well as the probability for each diagnosis based on individual values. Methods: A prospective, cross-sectional study analyzing the pulmonary function of patients referred to the Porto Alegre Hospital de Clínicas, in Porto Alegre, Brazil, between January and December of 2003. We collected demographic and spirometric data. The patients were divided into three groups: normal; OLD; and RLD. We calculated the FEV 1 /FVC and FEF 50% /0.5FVC ratios, and we compared the mean FEF 50% /0.5FVC values among the groups. We used Pearson's correlation test in order to compare FEF 50% /0.5FVC with FEV 1 /FVC. The patients were again divided into two groups: those with OLD and those without OLD. We calculated the likelihood ratio for different cut-off points. Results: The mean age of the patients was 55.8 ± 14.7 years. There were significant differences among the groups in terms of the mean FEF 50% /0.5FVC (2.10 ± 0.82, 2.55 ± 1.47 and 0.56 ± 0.29, respectively, for normal, RLD and OLD; p < 0.001). There was a positive correlation between FEF 50% /0.5FVC and FEV 1 /FVC in the OLD group (r = 0.83). We found that an FEF 50% /0.5FVC < 0.79 strongly suggests OLD, whereas an FEF 50% /0.5FVC > 1.33 practically excludes this diagnosis. Conclusions: The FEF 50% /0.5FVC ratio is a potentially useful parameter in the differential diagnosis of OLD and correlates positively with the FEV 1 /FVC ratio.Keywords: Pulmonary disease, chronic obstructive; Spirometry; Respiratory function tests. ResumoObjetivo: Avaliar a contribuição de um novo coeficiente, a razão FEF 50% /0,5CVF, medida através da curva fluxo-volume máximo expiratório, no diagnóstico dos distúrbios ventilatórios obstrutivos (DVOs); testar esse coeficiente na diferenciação entre grupos de pacientes normais, com DVO e com distúrbio ventilatório restritivo (DVR); e estabelecer pontos de corte para cada um dos diagnósticos funcionais e a probabilidade para cada diagnóstico a partir de valores individuais. Métodos: Estudo transversal, prospectivo, com a análise de testes de função pulmonar de 621 pacientes encaminhados ao Hospital de Clínicas de Porto Alegre entre janeiro a dezembro de 2003. Foram coletados dados demográficos e espirométricos. Os pacientes foram divididos conforme o diagnóstico funcional em três grupos: normal; DVO; e DVR. Foram calculadas as razões VEF 1 /CVF e FEF 50% /0,5CVF, e as médias de FEF 50% /0,5CVF foram comparadas entre os grupos. Para correlacionar FEF 50% /0,5CVF com VEF 1 /CVF, utilizou-se a correlação de Pearson. Os pacientes foram, então, divididos em dois grupos: com e sem DVO. Foram calculadas as razões de verossimilhança para diferentes pontos d...

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