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

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 β 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 β was calculated in each group. A receiver operating characteristic curve analysis was performed to determine the cutoff values of angle β 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 β 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 β values (P < .001). The best cutoff value of angle β was 189.43°, and the area under the receiver operating characteristic curve of angle β was 0.877, which is greater than the area under the receiver operating characteristic curve of FEV₁, 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 FEV₁/FVC%. Interestingly, combining these measures can enhance the sensitivity and specificity in assessing airway obstruction.

CONCLUSIONS: Angle β was a useful indicator for assessing airway obstruction. Furthermore, angle β combined with FEV₁, FEV₁/FVC%, FEF_25%, FEF_50%, and FEF_75% can enhance the sensitivity and specificity of airway obstruction evaluations.