Bagno Andrea, Anzil Federico, Tarzia Vincenzo, Pengo Vittorio, Ruggeri Alfredo, Gerosa Gino
Department of Chemical Process Engineering, University of Padua, Padua - Italy.
Int J Artif Organs. 2009 Mar;32(3):166-72. doi: 10.1177/039139880903200307.
Heart valve disorders, caused by congenital defects, rheumatic fever, calcification, myocardial infarction and other cardiovascular diseases, often require native valves to be replaced by bio-prosthetic devices or mechanical heart valves (MHVs). Among MHVs, bileaflet valves are usually preferred for their hemodynamic features, similar to physiological ones, and their durability, but they are prone to complications due to thromboembolic events. Due to the asynchronous closure of the leaflets, bileaflet MHVs are also known to produce closing sounds typically characterized by the presence of two peaks in the time domain. The detection of this "double click" in the signal may be useful for the early diagnosis of bileaflet MHV malfunction. The closing sound is actually a non-stationary signal that can be properly explored by means of time-frequency analysis. This paper describes a preliminary approach to the investigation of bileaflet MHV closing sounds performed by Continuous Wavelet Transform (CWT) analysis. Signals were collected from 3 patients immediately after surgery by means of the Myotis 3C, which is a traditional phonocardiographic apparatus. Signals were analyzed by two algorithms: one embedded in the Myotis 3C, based on the Fast Fourier Transform (FFT); and one specifically created for the purposes of the present study, based on CWT. The performance of these algorithms was compared and the results showed that the proposed CWT technique correctly classifies as ''double'' a large number of clicks that are recognized as ''single'' by the Myotis 3C.
心脏瓣膜疾病由先天性缺陷、风湿热、钙化、心肌梗死及其他心血管疾病引起，通常需要用生物假体装置或机械心脏瓣膜（MHV）替换天然瓣膜。在MHV中，双叶瓣膜通常因其血流动力学特征（类似于生理特征）及其耐用性而更受青睐，但它们容易因血栓栓塞事件而引发并发症。由于瓣叶异步关闭，双叶MHV还会产生典型的在时域中具有两个峰值特征的关闭声音。检测信号中的这种“双击”可能有助于双叶MHV故障的早期诊断。关闭声音实际上是一个非平稳信号，可以通过时频分析进行适当探究。本文描述了一种通过连续小波变换（CWT）分析对双叶MHV关闭声音进行研究的初步方法。信号是通过传统的心音图设备Myotis 3C在3名患者术后立即采集的。信号由两种算法进行分析：一种嵌入在Myotis 3C中，基于快速傅里叶变换（FFT）；另一种是为本研究专门创建的，基于CWT。对这些算法的性能进行了比较，结果表明，所提出的CWT技术能将大量被Myotis 3C识别为“单”的点击正确分类为“双”。
