Clinical Characteristics Of Small Airway Dysfunction In Asthma Children

Background:Bronchial asthma（hereafter referred to as"asthma"）is a heterogeneous disease characterized by chronic inflammation of the airways and is a common chronic respiratory disease in children.In recent years,as the understanding of small airways has gradually increased,more and more studies have been conducted on the relationship between small airway dysfunction（SAD）and asthma.Studies have concluded that SAD is closely related to poorly controlled asthma and frequent exacerbations.Objectives:To explore the differences between pulmonary ventilation function and exhaled nitric oxide tests in the assessment of SAD,to analyze the correlation between SAD diagnosed by both and the level of asthma control,and to analyze the consistency of their diagnosis of SAD.Also,an attempt was made to explore more effective treatment options for SAD by retrospectively analyzing the efficacy of different drug regimens after treating children with SAD.Methods:1)The study was divided into two parts;the first part was correlation analysis between SAD and asthma control level evaluated by different testing methods.Consecutive children with asthma who attended the pediatric asthma center at the First Affiliated Hospital of Air Force Medical University from April 2022 to October 2022 were included,and the included children were distinguished into a well-controlled group,a partially controlled group,and an uncontrolled group based on the criteria for determining the level of asthma control in the Guidelines for the Diagnosis and Prevention of Bronchial Asthma in Children（2016 Edition）（hereinafter referred to as"the Guidelines"）.The correlation between SAD and asthma control level under two different testing methods was analyzed,and the consistency between them in the diagnosis of SAD was tested.2)The second part was to evaluate the efficacy of different treatment regimens for SAD in children with asthma.Five hundred and sixty-six children with asthma who attended the pediatric asthma center of the First Affiliated Hospital of Air Force Medical University from June 2019 to December 2021 and whose pulmonary function tests suggested the presence of SAD were included.Among them,191 cases were treated by the guideline stepⅡregimen,289 cases were treated by the stepⅢregimen,and 86 cases were treated by the stepⅣregimen.Accordingly,they were divided into three major groups,namely,the stepⅡgroup,the stepⅢgroup and the stepⅣgroup,and within each regimen group,they were further divided into two subgroups according to the preferred regimen in the guidelines and other regimens.The improvement of small airway function parameters after treatment in different groups was observed.The children with SAD were also followed up in the following six months to observe their pulmonary function and perform correlation analysis.The study also had other groupings based on high or low eosinophil levels.Results:1)In the first part,among the 370 asthmatic children included,SAD assessed by pulmonary function accounted for 35.7%and SAD assessed by pulmonary alveolar nitric oxide（Ca NO）accounted for 15.9%.Logistic regression analysis showed that SAD assessed by pulmonary function was correlated with the level of asthma control（some P value<0.05）,while SAD assessed by Ca NO was not correlated with the level of asthma control（all P values>0.05）.In a concordance analysis performed,a weak concordance was found between pulmonary function and Ca NO in assessing SAD（Kappa=0.127,P=0.002）.2)In the second part,the study finally included 566 children with SAD asthma.In the comparison between the stepⅡ,stepⅢ,stepⅣregimens treated,it was found that the small airway function indexes FEF_50,FEF₇₅and FEF_25-75were able to improve after treatment（all P values<0.05）,with statistical differences between the groups（some P values<0.05）,and no statistical differences were found in the comparison between subgroups（all P values>0.05）.Logistic regression analysis showed a correlation between the sensitivity of SAD to medications and the recurrence of pulmonary function impairment（some P value<0.05）.Conclusion:1)This study found that the proportion of SAD in children with asthma differed between the two different tests of pulmonary function and Ca NO,and that pulmonary function may be more sensitive to the diagnosis of SAD compared to Ca NO.SAD assessed by lung function correlated with the level of asthma control,whereas no correlation was found in SAD assessed by Ca NO with the level of asthma control.The two methods were in a weak concordance for the diagnosis of SAD.2)This study concluded that conventional asthma control medications are effective in improving SAD,and that small airway function can be further improved by increasing the grade of control medication or by combination.There was no significant difference in improvement of SAD between the preferred and other regimens at the same step of treatment.When SAD develops in children with asthma,early intervention is warranted,and eosinophil levels should also be monitored so that the efficacy can be readily assessed to achieve the goal of long-term asthma control.