a) to evaluate the contribution of a new coefficient –FEF50/0.5 FVC ratio –from the maximal expiratory flow-volume (MEFV) curve in the differential diagnosis of ventilatory disorders; b) to evaluate the FEF50 / 0.5 FVC ratio in the separation of groups (Normal, Obstructive and Restrictive) of patients; c) to determine cut-off points for each functional diagnosis and the probability of a diagnosis from an individual value and to test the correlation between the FEV1 / FVC ratio and FEF50 / 0.5 FVC ratio.
After evaluating the MEFV curves of the groups (Normal, Obstructive and Restrictive), we calculated the FEF50 / 0.5 FVC ratio and its differences. The whole sample was then divided in two groups: obstructive and non-obstructive and the analysis of the likelihood ratio (LR) of the FEF50 / 0.5 FVC ratio between them was done.
There were 621 forced expiratory maneuvers performed by adults with a broad range of pulmonary abnormalities and normal subjects. The FEF50 / 0.5 FVC ratio was different between the groups Normal (2.10±0.82), Restrictive (2.55±1.47) and Obstructive (0.56±0.29) (p<0,001). It also showed a positive correlation with FEV1 / FVC ratio in the obstructive group (r=0.83). The analysis of the likelihood ratios for the FEF50 / 0.5 FVC showed that values below 0.79 are strong indications of obstructive disorders and above 1.33 almost exclude this diagnosis.
The FEF50 / 0.5 FVC ratio is a useful parameter in the differential diagnosis of ventilatory disorders and has positive correlation with the FEV1 / FVC ratio.
Spirometry can provide information in order to make the diagnosis of a ventilatory disorder. Sometimes, however, the conventional approach cannot be used, and more sophisticated resources are necessary, not always available. The FEF50 / 0.5 FVC ratio can help in the differential diagnosis of ventilatory disorders.
Marcelo Rodrigues, None.