Changes And Clinical Application Value Of Small Airway Parameters In Subjects With Preserved Pulmonary Function And Chronic Respiratory Symptoms

BackgroundChronic obstructive pulmonary disease(COPD)and asthma are the main chronic respiratory diseases,characterized by irreversible or reversible airflow limitation.Typical chronic symptoms can be manifested as cough,sputum,wheeze and dyspnea.Some individuals with preserved pulmonary function have similar chronic respiratory symptoms,reduced quality of life,accelerated lung function decline,and increased risk of respiratory hospitalisations and death,which are difficult to distinguish from obstructive pulmonary disease especially early onset of COPD.Small airway dysfunction(SAD)is considered a precursor to COPD and asthma,and can also be found in people without airflow restriction.The prevalence of SAD in Chinese adults aged 20 years and older without airflow restriction is 25.5%,and the prevalence is higher in the group with preserved pulmonary function and chronic respiratory symptoms.In view of the heavy burden of SAD,it is of practical clinical significance to explore the characteristics of small airway function in this group and recognize SAD early based on the guidance of clinical symptoms.ObjectiveTo analyze the characteristics of symptoms and small airway function in subjects with preserved pulmonary function and chronic respiratory symptoms,and to further explore the diagnostic value of impulse oscillometry in identifying small airway dysfunction in this group.MethodA total of 135 subjects who met both inclusion and exclusion criteria and visited the outpatient clinic of Zhujiang Hospital of Southern Medical University from September 2021 to December 2022 due to chronic respiratory symptoms were included as the preserved pulmonary function group,healthy subjects who had no smoking history and COPD patients during the same period were also included.Demographic characteristics,qualitative and quantitative assessment of symptoms,impulse oscillometry and spirometric parameters were collected for the groups.The differences of characteristics between the PPF group,the COPD group and the healthy control group were compared.Subgroup analysis was performed on the PPF group to explore the influence of smoking and small airway dysfunction defined by spirometry.The relationship between symptoms and lung function parameters was further evaluated qualitatively and quantitatively.And the diagnostic value of IOS parameters in detecting SAD of this group was discussed by using the receiver operator characteristic curves.Results1.The spirometric parameters FVC,FEV1,MEF75 and MEF50 in PPF group were decreased compared with healthy control group,while the IOS parameters Z5,Z5(%pred),Fres,R5,R5(%pred),R20,R20(%pred)and AX were increased.The COPD group was older than the PPF group,and spirometer parameters were decreased except FVC(%pred),while the IOS parameters except R20(%pred)showed no difference.2.The IOS parameters in the PPF group were correlated with specific symptoms,symptom severity and spirometer parameters.3.The proportion of smokers with SAD in PPF group was higher than that of non-smokers;The spirometric parameters FEV1,FEV1/FVC,MEF75,MEF50,MEF25 and MMEF were decreased compared with healthy control group and non-smoking group.The IOS parameters Z5(%pred),Fres,R5,R5(%pred),R5-R20 and AX were higher than those of healthy control group,and Fres,R5-R20 were higher than those of non-smoking group.4.The spirometric parameters except FVC in SAD group were decreased compared with those in non-SAD group,while the IOS parameters Fres,R5,R5-R20 and AX were increased.5.IOS parameters had certain diagnostic value for SAD in PPF group.The optimal cutoff value of Fres was 12.13Hz,R5 was 0.420kPa/L s,R5-R20 was 0.030kPa/L s,and AX was 0.320kPa/L.Fres had the largest area under the curve,whose AUC was 0.698(95%CI 0.608-0.788),sensitivity was 75.5%,and specificity was 62.2%.R5-R20 had the highest sensitivity of 79.2%and R5 had the highest specificity of 78.0%.Fres,R5-R20 and AX all detected more SAD in PPF group,and R5-R20 had the highest positive rate of 76.3%in diagnosing SAD.Conclusions1.Subjects with preserved pulmonary function and chronic respiratory symptoms showed decreased pulmonary ventilation function and increased small airway resistance compared with healthy subjects.Even without airflow obstruction,the increase in small airway resistance is close to mild COPD.2.Small airway dysfunction is often associated with Subjects with preserved pulmonary function and chronic respiratory symptoms,especially smokers,who have poorer pulmonary ventilation function and higher small airway resistance than those without small airway dysfunction.3.The change of IOS parameters were related to specific symptoms and severity of symptoms in subjects with preserved pulmonary function and chronic respiratory symptoms,and the sensitivity to detect small airway dysfunction in this group was also higher.Fres,R5,R5-R20 and AX all have certain diagnostic value.Fres has the highest value in diagnosing small airway dysfunction,and R5-R20 is more suitable for screening small airway dysfunction.