Concave Pattern of a Maximal Expiratory Flow-Volume Curve: A Sign of Airflow Limitation in Adult Bronchial Asthma

Background . In patients with bronchial asthma, spirometry could identify the airflow limitation of small airways by evaluating the concave shape of the maximal expiratory flow-volume (MEFV) curve. As the concave shape of the MEFV curve is not well documented, we reevaluated the importance of this curve in adult asthmatic patients. Methods . We evaluated spirometric parameters, the MEFV curve, and its concave shape (scoop between the peak and endpoint of expiration) in 27 nonsmoking asthmatic patients with physician-confirmed wheeze and positive bronchial reversibility after a short-acting β 2-agonist inhalation. We also calculated angle β and shape factors (SF 25% and SF 50% ) to quantitate the curvilinearity of the MEFV curve. Results . The MEFV curve was concave in all patients. Along with improvements in standard spirometric parameters, curvilinear parameters, angle β , SF 25% , and SF 50% were significantly improved after bronchodilator inhalation. There were significant correlations between improvements in angle β , and FEF 50% , and FEF 25-75% , and between improvements in SF 25% , and SF 50% , and FEF 75% . Conclusions . The bronchodilator greatly affected the concave shape of the MEFV curve, correlating with spirometric parameters of small airway obstructions (FEF 50% , FEF 75% , and FEF 25-75% ). Thus, the concave shape of the MEFV curve is an important indicator of airflow limitation in adult asthmatic patients.