Residual volume/total lung capacity ratio confers limited additive significance to lung clearance index for assessment of adults with bronchiectasis

BackgroundMosaicism and hyperinflation are common pathophysiologic features of bronchiectasis. The magnitude of ventilation heterogeneity might have been affected by the degree of hyperinflation. Some studies have evaluated the discriminative performance of lung clearance index (LCI) in bronchiectasis patients, but the additive diagnostic value of hyperinflation metrics to LCI is unknown.ObjectiveTo compare LCI and the ratio of residual volume to total lung capacity (RV/TLC), along with the LCI normalized with RV/TLC, in terms of discriminative performance, correlation and concordance with clinical variables in adults with bronchiectasis.MethodsMeasurement items included chest high-resolution computed tomography, multiple-breath nitrogen washout test, spirometry, and sputum culture. We analyzed bronchodilator responses by stratifying LCI and RV/TLC according to their median levels (LCIHigh/RV/TLCHigh, LCILow/RV/TLCHigh, LCIHigh/RV/TLCLow, and LCILow/RV/TLCLow).ResultsData from 127 adults with clinically stable bronchiectasis were analyzed. LCI had greater diagnostic value than RV/TLC in discriminating moderate-to-severe from mild bronchiectasis, had greater concordance in reflecting clinical characteristics (including the number of bronchiectatic lobes, radiological severity score, and the presence of cystic bronchiectasis). Normalization of LCI with RV/TLC did not contribute to greater discriminative performance or concordance with clinical variables. The LCI, before and after normalization with RV/TLC, correlated statistically with age, sex, HRCT score, Pseudomonas aeruginosa colonization, cystic bronchiectasis, and ventilation heterogeneity (all PConclusionLCI is superior to RV/TLC for bronchiectasis assessment. Normalization with RV/TLC is not required. Stratification of LCI and RV/TLC is not associated with significantly different bronchodilator responses.背景：支气管扩张症的常见病理生理特征为肺镶嵌征与肺过度充气。通气异质性的程度可能受肺过度充气程度的影响。已有多项研究评估了肺清除指数（lung clearance index, LCI）在支气管扩张症患者中的鉴别诊断效能，但肺过度充气指标对LCI的附加诊断价值仍未明确。 目的：比较肺清除指数（LCI）、残气量与肺总量比值（residual volume to total lung capacity, RV/TLC）以及经RV/TLC校正后的LCI，在成人支气管扩张症患者中的鉴别诊断效能、与临床变量的相关性及一致性。 方法：检测项目包括胸部高分辨率计算机断层扫描（high-resolution computed tomography, HRCT）、多次呼吸氮冲洗试验、肺量测定法及痰培养。本研究依据LCI与RV/TLC的中位数水平对其进行分层（LCI高值/RV/TLC高值、LCI低值/RV/TLC高值、LCI高值/RV/TLC低值及LCI低值/RV/TLC低值），以此分析支气管舒张剂反应性。 结果：本研究共纳入127例临床稳定的支气管扩张症成人患者并完成数据分析。相较于RV/TLC，LCI在区分中重度与轻度支气管扩张症时具备更优的诊断价值，且在反映临床特征（包括支气管扩张受累肺叶数、影像学严重程度评分及囊性支气管扩张的存在）方面一致性更高。经RV/TLC校正后的LCI并未提升其鉴别诊断效能或与临床变量的一致性。校正前后的LCI均与年龄、性别、HRCT评分、铜绿假单胞菌（Pseudomonas aeruginosa）定植、囊性支气管扩张及通气异质性存在统计学相关性（all P）。 结论：相较于RV/TLC，LCI用于支气管扩张症评估更具优势，无需经RV/TLC校正。对LCI与RV/TLC进行分层与支气管舒张剂反应性无显著关联。