关键词: 肺疾病, 慢性阻塞性；哮喘-慢性阻塞性肺疾病重叠；深吸气量；支气管舒张试验；鉴别诊断

Abstract: Background　Bronchial dilation test is mostly used as an important step in differentiating chronic obstructive pulmonary disease（COPD） from bronchial asthma-chronic obstructive pulmonary disease overlap（ACO），but it does not identify all COPD and ACO.Studies have shown that inspiratory capacity（IC） has a good sensitivity to reflect the degree of pulmonary hyperinflation and respiratory difficulty in patients with severe COPD，so we aim to study whether IC can be used as an indicator to distinguish patients with COPD from patients with ACO.Objective　To evaluate the diagnostic value of IC in identifying COPD and ACO.Methods　Twenty patients with COPD（COPD group） and 21 patients with ACO（ACO group） who were admitted to the respiratory department of the First Hospital Affiliated to Zhejiang Chinese Medical University and met the study criteria were enrolled from March to September in 2018.All patients underwent pulmonary ventilation function test，whose data were recorded as pre bronchial dilation test data，and then bronchial dilation test.After the bronchial dilation test，the pulmonary ventilation function test was performed again，whose data were recorded as post bronchial dilation test data.The general information（including height，mass，BMI，gender and age），indicators of pulmonary ventilation function 〔forced expiratory volume in 1 second（FEV1），forced vital capacity（FVC），IC，peak expiratory flow（PEF），forced expiratory flow after 25% of FVC（FEF25），forced expiratory flow after 50% of FVC（FEF50），forced expiratory flow after 75% of FVC（FEF75），maximum mid-expiratory flow（MMEF）〕，the pre and post bronchial dilation test data and their absolute value changes（Δ），and improvement rate between patients in two groups were compared.The correlation between IC improvement rate and Δ FEV1，improvement rate of FEV1，Δ FVC，improvement rate of FVC，Δ PEF，improvement rate of PEF among patients with ACO and COPD was analyzed.The improvement rate of IC was analyzed to show its diagnostic value of ACO.Results　The age of patients in the ACO group was smaller than that in the COPD group（P<0.05）．When compared with the COPD group，the ACO group showed higher ΔFEV1 and improvement rate of FEV1，higher ΔFVC and improvement rate of FVC，higher ΔPEF and improvement rate of PEF，and improvement rate of IC（P<0.05）．There was no correlation between the improvement rate of IC and ΔFEV1，improvement rate of FEV1，ΔFVC，improvement rate of FVC，ΔPEF and improvement rate of PEF in ACO group（P>0.05）．Improvement rate of IC was positively relevant with improvement rate of FVC in the COPD group（rs=0.501，P=0.021） and was not related with ΔFEV1，improvement rate of FEV1，ΔFVC，ΔPEF and improvement rate of PEF（P>0.05）. In ROC analysis，the improvement rate of IC presented an area under the ROC curve of 0.714（P=0.019）；the optimal cutoff value was 13.11%，with a sensitivity of 61.90% and specificity of 85.00%.Conclusion　IC has a certain value in evaluating the response of bronchodilator in patients with mild-moderate COPD，but it is not as sensitive as FEV1 in a certain extent.IC does show good sensitivity and specificity in the ACO diagnosis，and has a large clinical reference value.However, whether IC can be used as an indicator to identify COPD and ACO needs further study.

Key words: Pulmonary disease, chronic obstructive；Asthma-chronic obstructive pulmonary disease overlap；Inspiratory capacity；Bronchial dilation test；Differential diagnosis