A simple spirometric clue to asthma: airways obstruction suggested by negative or reduced forced expiratory reserve volume despite normal FEV1-FVC ratio.

I report on 25 asthmatic patients in whom airways obstruction was not detectable by conventional spirometric indices, but was suggested by a reduced or negative forced expiratory reserve volume (FERV), that is, the ERV measured from the forced vital capacity (FVC) maneuver and preceding tidal breaths. Patients with known causes for reduced ERV were excluded. The ratio of forced expiratory volume-1 sec (FEV1) to FVC was normal or high in all 25 patients, and the forced expiratory time (FET)25-75% was normal in half (12). Using conventional spirometric algorithms, the condition of most (76%) of the patients would be interpreted as "restrictive impairment". The FERV is easily measured in a physician's office or clinic. If this simple test is to provide a clue to the presence of airways obstruction that is otherwise not demonstrable spirometrically, the FVC maneuver must be maximal and reproducible and the preceding tidal breaths, as well as the FVC, must be graphically recorded.