Curvilinearity of a Maximum Expiratory Flow-Volume Curve: A Useful Indicator for Assessing Airway Obstruction in Children With Asthma

Abstract

BACKGROUND: Lung function parameters are used as signs in the diagnosis and evaluation of asthma; however, their sensitivity and specificity are not ideal. We calculated and combined angle ␤ with lung function parameters to identify the ideal indicator. OBJECTIVE: We aimed to identify an ideal indicator for evaluating the severity of airway obstruction in children with asthma. METHODS: In total, 151 school-age children diagnosed with asthma were selected as the asthma group, and 106 healthy children were selected as the control group. The subjects were divided into the exacerbation group, chronic persistent group, and clinical remission group. Furthermore, the subjects were classified into mild and moderate groups or severe and critical groups. Angle ␤ was calculated in each group. A receiver operating characteristic curve analysis was performed to determine the cutoff values of angle ␤ and lung function parameters that together provided high sensitivity and specificity for airway obstruction evaluation in children with asthma. RESULTS: The mean value of angle ␤ in the asthma group was significantly smaller than that in the control group (178.18°and 196.72°, respectively, P < .001). More exacerbations or greater severity corresponded to smaller angle ␤ values (P < .001). The best cutoff value of angle ␤ was 189.43°, and the area under the receiver operating characteristic curve of angle ␤ was 0.877, which is greater than the area under the receiver operating characteristic curve of FEV 1 , forced expiratory flow (FEF) at 75% vital capacity (FEF 25%), and FEF at 50% vital capacity (FEF 50%), but smaller than the area under the receiver operating characteristic curve of FEF 75% and FEV 1 /FVC%. Interestingly, combining these measures can enhance the sensitivity and specificity in assessing airway obstruction. CONCLUSIONS: Angle ␤ was a useful indicator for assessing airway obstruction. Furthermore, angle ␤ combined with FEV 1 , FEV 1 /FVC%, FEF 25% , FEF 50% , and FEF 75% can enhance the sensitivity and specificity of airway obstruction evaluations.

Assessment of bronchial obstruction and its reversibility by shape indexes of the flow‐volume loop in asthmatic children

“…The specificity was the same for zβ‐angle and zFEF50/PEF or zFEV1 (Table 2). A recent report in school‐aged asthmatics found large AUC and sensitivity for β‐angle and, in contrast to our study, FEV1 sensitivity was also high while β‐angle and FEV1's specificities were very low 18 . The different patterns of sensitivity—specificity at baseline indicate that a significant proportion of false diagnosis of asthma would result if solely shape indexes would be taken in consideration to identify airway obstruction.…”

“…β‐angle, constructed to transcribe the curvature of the FVL into a single numerical value, 16 is the angle between the first and second half of the FVL at the point of maximum flow point at mid pulmonary volume. β‐angle and its simplified estimate, FEF50/PEF, in absolute values or z ‐scores, were significantly lower at baseline in our school‐aged asthmatic children compared to healthy subjects, in keeping with previous reports, demonstrating more concave FVL configuration measured by smaller β‐angle in asthmatic preschoolers 17 or schoolers 18,19,26 …”

“…To improve the diagnostic ability of spirometric parameters to detect asthma in children, we investigated whether the combination of shape indexes with “usual” spirometric parameters will improve their discriminating power. AUC's improved and the best sensitivity was obtained when shape indexes were associated with zFEV1 and the best specificity when they were associated with zFEV1/FVC (Table 2), in agreement with recent reports demonstrating that the association of quantitative and qualitative parameters may enhance the diagnosis accuracy 18,26 …”

“…Its value indicates the FVL's upward convexity or concavity respectively when it is greater or smaller than 180° 16 . β‐angle has been shown to be a robust variable with good reproducibility and feasibility in adults, 16 preschool, 17 and school children 18,19 . A simplified approach to estimate β‐angle is FEF50/PEF ratio, easily computed in routine practice, though, as previously shown, it does not replace β‐angle, the results yielded by the two parametres being sometimes different 17 …”

“…16 β-angle has been shown to be a robust variable with good reproducibility and feasibility in adults, 16 preschool, 17 and school children. 18,19 A simplified approach to estimate β-angle is FEF50/PEF ratio, easily computed in routine practice, though, as previously shown, it does not replace β-angle, the results yielded by the two parametres being sometimes different. 17 To overcome the difficulty of interpreting a FVL in children based on a single parameter, that is, FEV1 that lacks sensitivity, we hypothesized that shape indexes, β-angle and FEF50/PEF, might be considered in routinely clinical practice to ameliorate the sensitivity/ specificity of spirometry in identifying the presence of an airway obstruction and its BD reversibility.…”