Acceptable alternatives for forced vital capacity in the spirometric diagnosis of bronchial asthma

BACKGROUND: In patients with advanced obstructive ventilatory disorders, expiration may last for a relatively long time until the end-of-test standards for forced vital capacity (FVC) are satisfied. This may be difficult for both the patient and the technician. The Forced expiratory volume in 3 seconds (FEV3) and Forced expiratory volume in 6 seconds (FEV6) maneuvers are simple, undemanding and easier to perform when compared with FVC; however, their reliability to be used as alternatives for FVC is controversial. AIM: To judge whether FEV3 and FEV6 can be used instead of FVC in detecting airway obstruction in asthmatic patients. SETTINGS AND DESIGN: This study was a cross-sectional case–control laboratory-based study. MATERIALS AND METHODS: The study involved 40 known asthmatic patients and 40 apparently healthy, gender- and age-matched controls. Spirometery was used for assessing pulmonary function according to the American Thoracic Society and European Respiratory Society criteria. STATISTICAL ANALYSIS: A significant difference in the means between the groups was performed using Student's t-test. The receiver operating characteristic (ROC) curves were used to compare efficiency of the studied spirometric measurements on asthma diagnosis. RESULTS: The mean of FEV3 was not significantly different when compared with the mean of FVC (P = 0.352 for asthmatic patients and P = 0.957 for control group). This was also true when the mean of FEV6 was compared with the mean of FVC (P = 0.805 for asthmatic patients and P = 0.957 for control group). The area under the ROC curves of FEV1/FVC%, FEV1/FEV3% and FEV1/FEV6% were also comparable. CONCLUSION: FEV3 and FEV6 are accurate and reliable alternatives for FVC in assessing airway obstruction of asthmatic patients.