Novel approach to continuous adventitious respiratory sound analysis for the assessment of bronchodilator response

Background
A thorough analysis of continuous adventitious sounds (CAS) can provide distinct and complementary information about bronchodilator response (BDR), beyond that provided by spirometry. Nevertheless, previous approaches to CAS analysis were limited by certain methodology issues. The aim of this study is to propose a new integrated approach to CAS analysis that contributes to improving the assessment of BDR in clinical practice for asthma patients.
Methods
Respiratory sounds and flow were recorded in 25 subjects, including 7 asthma patients with positive BDR (BDR+), assessed by spirometry, 13 asthma patients with negative BDR (BDR-), and 5 controls. A total of 5149 acoustic components were characterized using the Hilbert spectrum, and used to train and validate a support vector machine classifier, which distinguished acoustic components corresponding to CAS from those corresponding to other sounds. Once the method was validated, BDR was assessed in all participants by CAS analysis, and compared to BDR assessed by spirometry.
Results
BDR+ patients had a homogenous high change in the number of CAS after bronchodilation, which agreed with the positive BDR by spirometry, indicating high reversibility of airway obstruction. Nevertheless, we also found an appreciable change in the number of CAS in many BDR- patients, revealing alterations in airway obstruction that were not detected by spirometry. We propose a categorization for the change in the number of CAS, which allowed us to stratify BDR- patients into three consistent groups. From the 13 BDR- patients, 6 had a high response, similar to BDR+ patients, 4 had a noteworthy medium response, and 1 had a low response.
Conclusions
In this study, a new non-invasive and integrated approach to CAS analysis is proposed as a high-sensitive tool for assessing BDR in terms of acoustic parameters which, together with spirometry parameters, contribute to improving the stratification of BDR levels in patients with obstructive pulmonary diseases.

研究背景
对连续性附加音（continuous adventitious sounds, CAS）进行全面分析，可提供肺量测定法无法覆盖的、与支气管舒张试验反应（bronchodilator response, BDR）相关的独特且互补的信息。然而，既往的CAS分析方法受限于若干方法学缺陷。本研究旨在提出一种全新的一体化CAS分析方法，以助力哮喘患者临床实践中BDR评估的优化。
研究方法
本研究共纳入25名受试者，采集其呼吸音与呼吸流量信号，其中包括经肺量测定法确认的支气管舒张试验阳性（BDR+）哮喘患者7例、BDR阴性（BDR-）哮喘患者13例，以及健康对照5名。采用希尔伯特谱对共计5149个声学成分进行特征提取，并以此训练并验证一款支持向量机分类器，该分类器可区分CAS相关声学成分与其他声学成分。待该方法验证完成后，通过CAS分析对所有受试者的BDR进行评估，并与肺量测定法得到的BDR结果进行对比。
研究结果
BDR+患者在支气管舒张术后的CAS数量均出现显著升高，与肺量测定法确认的BDR阳性结果一致，提示气道阻塞具有较高可逆性。但我们同时发现，多数BDR-患者的CAS数量同样出现显著变化，提示存在肺量测定法未能检出的气道阻塞改变。本研究提出了CAS数量变化的分类标准，借此可将BDR-患者划分为3个特征一致的亚组。在13名BDR-患者中，6例呈现与BDR+患者相似的高反应性，4例出现显著的中度反应，1例仅表现为轻度反应。
研究结论
本研究提出的新型无创一体化CAS分析方法，可作为基于声学参数的高灵敏度BDR评估工具；该方法联合肺量测定法参数，有助于优化阻塞性肺疾病患者BDR水平的分层管理。