Angle β of greater than 80° at the start of spirometry may identify high‐quality flow volume curves. Issue 3 (29th November 2016) - Lian, Ningfang
ABSTRACT: Background and objective: The American Thoracic Society (ATS) and European Respiratory Society (ERS) emphasize a satisfactory start in maximal expiratory flow–volume (MEFV) curves and highlight subjective parameters: performance without hesitation and expiration with maximum force. We described a new parameter, angle β for characterization of the start to the MEFV curve. Methods: Subjects completed the MEFV curve at least three times and at least two curves met ATS/ERS quality. Subjects were divided into normal, restrictive and obstructive groups according to pulmonary function test results. The tangent line was drawn at the start of the MEFV curve's ascending limb to the x‐axis and the angle β between the tangent line and x‐axis was obtained. The relationships between tangent of β, pulmonary function parameters (PFPs) and anthropometric data were assessed. The MEFV curves with insufficient explosion at the start were considered as poor‐quality MEFV curves. Results: In 998 subjects with high‐quality spirometry, although PFP varied in relation to the three aspects: the angle β and its tangent were similar ( P > 0.05), the tangent of β did not correlate with PFP or anthropometric measurements ( P > 0.05) and the lower limit of normal (LLN) of the angle β was 80° in the group with high‐quality spirometry ( P < 0.05). Angle β derived from poor‐quality MEFV curves was smaller than that from good quality one ( P < 0.05). Conclusion: Angle β may function as a parameter to assess the expiratory efforts, which can be used to assess the quality of the MEFV curve start. Abstract : Angle β, a simple parameter at the ascending limb of a flow volume curve, is a constant which does not depend on anthropometric or pulmonary function data. In high‐quality flow volume curves, the angle is greater than 80°. This angle may be used to identify high‐quality flow volume curves at the beginning of test in real time.