Advantages of late expiratory relaxation during maximal forced expiratory maneuver

A modification of the maneuver for the maximal expiratory flow volume (MEFV) curve was described recently to improve the rate of achieving the acceptability criteria of the American Thoracic Society. The maneuver allows the subject to relax in the later part of expiration. The present study was carried out to determine if the modified spirometry technique offered any advantages over the standard FVC maneuver in asthma patients with a wide range of airways obstruction. MEFV curves were obtained in seventy-two subjects with standard and modified procedures in a randomized, crossover design. The patients were divided into four groups depending on the degree of airways obstruction-normal spirometry, mild, moderate and severe airways obstruction. The spirometric parameters (FVC, FEV1, FEV/FVC ratio, FET, PEFR and F25-75) were compared in each group. The modified technique gave a higher FVC measurement especially in patients with moderate and severe airways obstruction along with increased FET. PEFR and FEV1 were not different between the techniques. FEV1/FVC ratio was significantly decreased in patients with moderate and severe airways obstruction. Both the techniques gave equally acceptable and reproducible results with similar variability for FEV1 and FVC. It was concluded that the modification of the standard FVC maneuver by allowing the subject to relax in the later part of expiration is advantageous as it yields a lower FEV1/FVC ratio without affecting the FEV1, has the same within-session variability and is less strenuous.