Quantitative HRCT Characteristics In Asthmatic Patients,Patients With COPD And Asthma-COPD Overlap And Their Relationships With Pulmonary Function

ObjectiveWe sought to compare pulmonary function indices and quantitative CT parameters of airway remodeling,air trapping,and emphysema in asthmatic patients and patients with COPD and asthma-COPD overlap(ACO)and explore their relationships with airflow limitation.To evaluate the value of impulse oscillometry(IOS)and quantitative HRCT parameters for differentiating ACO in COPD patients.MethodsWe continuously enrolled asthma,COPD,ACO patients and controls who visited the respiratory clinic of our hospital from August 2017 to December 2021.All subjects completed pulmonary function test and HRCT scans were performed within 24 hours.Quantitative CT analysis software was employed for the assessment of emphysema,airway wall dimensions and air trapping:emphysema parameter(the%area of low attenuation(LAA%);bronchial parameters((wall area(WA),luminal area(LA),wall area percentage(WA%))of the 4th-6th generation in the right upper lobe apical segmental bronchus(RB1);air trapping parameters(relative volume change-860 HU to-950 HU(RVC-860 to-950),the expiration to inspiration ratio of mean lung density(MLDE/I)).The differences of pulmonary function indices and HRCT parameters were compared among the four groups.Spearman correlation analysis and regression analysis were utilized to explore structure-function relationships in asthmatic patients and patients with COPD and ACO.Furthermore,according to the diagnostic criteria,patients with COPD were divided into pure COPD group and ACO group.Multivariate logistic regression analysis was performed to analyze the associations between the different parameters and the risk of ACO.Receiver operating characteristic(ROC)curves were employed to identify the optimal cutoff and assess the diagnostic value of RVC-860 to-950,decrease in the resistance from 5 Hz to 20 Hz(R5-R20)and their combination in predicting ACO.Bootstrapping validation was used to evaluate the internal validation.The concordance index(C-index)and calibration plot were calculated to assess the discrimination and calibration of the prediction model.Results1.FEV1pred、FEV1/FVC and MEF50,MEF25,MMEF in asthma group.were significantly higher than those in COPD and ACO group.R5、R5-R20、X5 和 AX in patients with ACO were significantly higher than those in patients with asthma and COPD.2.The LAA%in both patients with COPD and ACO were significantly higher than asthmatic patients and controls,with comparable values in asthmatic patients and controls.The WA%and WA in patients with COPD and ACO were larger than those in controls,with LA were not.The differences of WA%and LA between asthmatic patients and controls reach statistical significance while WA did not.MLDE/I in asthmatic patients and patients with COPD and ACO were significantly higher than those in controls.RVC-860 to-950 decreased in order of ACO,COPD and asthmatic patients.3.RVC-860 to-950 can independently predict FEV1%pred in asthmatic patients;LAA%and MLDE/I in patients with COPD;LAA%,WA%and RVC-860 to-950 in patients with ACO.Statistically significant positive correlations were observed between IOS parameters(R5pred,R20pred,R5-R20)and WA%in patients with asthma and ACO.4.The areas under ROC curves of RVC-860 to-950 and R5-R20 in diagnosing ACO were 0.803 and 0.775,respectively.The area under ROC curve of ACO diagnosed by RVC-860 to-950 combined R5-R20 was significantly higher than that of single parameter.RVC-860 to-950>-0.62 and R5-R20>0.09 strongly predicted ACO(sensitivity:76.19%,specificity:95.12%,PPV:88.6%,NPV:88.9%).Internal validation in the model shows that the C-index is 0.892,and the calibration curve coincides well with the ideal curve.Conclusions1.Airflow limitation in patients with ACO and COPD are more severe compared with that in asthmatic patients.ACO has more serious small airway disfunction than patients with COPD and asthmatic patients.2.Emphysema is seen in patients with COPD and ACO,with comparable LAA%values and similar distribution between them,however,emphysema has not yet developed in asthmatic patients.Patients with asthma,COPD,and ACO all occur proximal airway remodeling.The bronchi are thickened outward with the WA increased in patients with COPD and ACO.In contrast,the bronchi are thickened inward with the LA decreased in asthmatic patients.Furthermore,air trapping in patients with ACO is more severe compared with that in asthmatic patients and patients with COPD.3.The indirect lung densitometry measurements might be more predictive of the degree of airflow limitation than the direct airway measurements in obstructive airway diseases.Airway remodeling was more obvious in patients with asthma and ACO with the increase of large and small airway oscillometric resistance.4.Combining RVC-860 to-950>-0.62 and R5-R20>0.09 can strongly predicted ACO and the model has good differentiation.