Objective: To explore the cutoff value for assessing small airway dysfunction in children with asthma. Methods: A total of 364 asthmatic children aged 5 to 14 years, with normal ventilatory function, followed up at the Asthma Clinic of the Children's Hospital of Capital Institute of Pediatrics from January 2017 to January 2018, were selected as the case group. Concurrently, 403 healthy children of the same age range and without any symptoms in the community were chosen as the control group, and pulmonary function tests were conducted. The values of forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), forced expiratory flow at 50% of FVC (FEF50), forced expiratory flow at 75% of FVC (FEF75) and maximum mid-expiratory flow (MMEF) were compared between case group and control group. Statistical tests such as t-test, χ2 test, or Mann-Whitney U test were used to analyze the differences between the groups. Receiver operating characteristic (ROC) curves were constructed, and the maximum Youden Index was utilized to determine the optimal cutoff values and thresholds for identifying small airway dysfunction in asthmatic children. Results: This study comprised 364 children in the case group (220 boys and 144 girls) and 403 children in the control group (198 boys and 205 girls). The small airway parameters (FEF50%pred, FEF75%pred, MMEF%pred) in the asthmatic group were significantly lower than in the control group (77% (69%, 91%) vs. 95% (83%, 109%), 67% (54%, 82%) vs. 84% (70%, 102%), 76% (66%, 90%) vs. 97% (86%, 113%), Z=12.03, 11.35, 13.66, all P<0.001). The ROC curve area under the curve for FEF50%pred, FEF75%pred, MMEF%pred was 0.75, 0.74, and 0.79, respectively. Using a cutoff value of 80% for FEF50%pred achieved a sensitivity of 56.9% and specificity of 81.4%. A cutoff value of 74% for FEF75%pred resulted in a sensitivity of 67.3% and specificity of 69.2%. Finally, using a cutoff value of 84% for MMEF%pred achieved a sensitivity of 67.9% and specificity of 77.2%. Conclusion: In the presence of normal ventilatory function, utilizing FEF50<80% predicted or MMEF<84% predicted can accurately serve as criteria for identifying small airway dysfunction in children with controlled asthma.
目的： 探讨支气管哮喘患儿小气道功能障碍的诊断界值。 方法： 诊断性试验。选择2017年1月至2018年1月在首都儿科研究所附属儿童医院哮喘门诊随诊的5~14岁且通气功能正常的哮喘控制患儿364例作为病例组。选择同时期同年龄段社区无不适症状、完成常规肺功能测定的403名健康儿童作为对照组。比较两组患儿第1秒用力呼气容积（FEV1）、用力肺活量（FVC）、FEV1/FVC、用力呼出50%肺活量时的瞬间流量（FEF50）、用力呼出75%肺活量时的瞬间流量（FEF75）、最大呼气中期流量（MMEF）等肺功能参数的差异，组间比较采用独立样本t检验、χ2检验、Mann-Whitney U检验。绘制受试者工作特征（ROC）曲线，并用最大约登指数确定哮喘患儿小气道功能障碍的最佳参数和界值。 结果： 病例组364例患儿中男220例、女144例，对照组403名儿童中男198名、女205名。病例组患儿的小气道功能参数FEF50、FEF75、MMEF实测值占预计值的百分比均低于对照组［77%（69%，91%）比95%（83%，109%），67%（54%，82%）比84%（70%，102%），76%（66%，90%）比97%（86%，113%），Z=12.03、11.35、13.66，均P<0.001］。ROC曲线显示小气道功能参数FEF50、FEF75、MMEF的曲线下面积分别为0.75、0.74、0.79。FEF50取界值80%时，灵敏度56.9%，特异度81.4%；FEF75取界值74%时，灵敏度67.3%，特异度69.2%；MMEF取界值84%时，灵敏度67.9%，特异度77.2%。 结论： 在通气功能正常的情况下，将FEF50<80%预计值或MMEF<84%预计值作为哮喘控制患儿存在小气道功能障碍的判断标准较为准确。.