Is Measurement of Beta Angle in Flow Volume Loop Useful for Diagnosis of Airways Obstruction?


Department of Pulmonary Medicine, Iran University of Medical Sciences and Health services, TEHRAN-IRAN


Background: Spirometry is the most common method for evaluation of lung function, and the shape of flow-volume loop is very helpful for recognition of pulmonary disease pattern particularly, the site and severity of airway obstruction. The slope of descending arch of expiratory curve is one of the criteria which determine the severity of lower airways obstruction. Measurement of Beta angle is one of the methods for determination of this slope. Beta-angle is characterized by determination of three points on the flow-volume loop. Its vertex is maximum flow in the middle of vital capacity (V.max 50%). Its other points are the outset of residual volume (RV) on the volume axis and the peak flow on the flow axis. Materials and Methods: This is a cross-sectional descriptive study. To determine the measurement of Beta- angle, the flowvolume curve was examined in 325 patients, (smokers and non-smokers) randomly. These patients were referred for pulmonary function tests to our hospital. All the patients underwent standard spirometry and used SPSS package for calculating the results. Results: Following results were obtained: The size of Beta-angle decreased with the increase of age, from the third decade of life and onward. There was a significant difference in the mean Beta-angle between the smokers that consumed more than 20 pack-year and the non-smokers. The size of Beta-angle decreased with obstruction of peripheral airways, but it had no correlation with restrictive lesions. The size of this angle decreased with the reduction of different pulmonary measures such as FEV1, FEV1/FVC, and FEF25-75%. Conclusion: The size of Beta-angle is useful for detecting patient with obstructive lung disease. (Tanaffos 2003; 2(5): 37- 42) Abbreviations: FEV1= forced expiratory volume in second one FVC= forced vital capacity FEF25-75= forced expiratory flow in mid-portion of vital capacity