Pole-Zero Modeling and Classification of Phonocardiograms

Phonocardiography, the analysis of heart sounds, is a noninvasive diagnostic method useful in studying heart valve function. Phonocardiograms (PCG's) of porcine prosthetic heart valves in the aortic position were analyzed by a parametric signal modeling method in order to derive frequency domain features suitable for the classification of the valve state.     

Comments on "Pole-zero modeling and classification of phonocardiograms"

Recently,1 the Steiglitz-McBride method was used to identify the two most dominant frequencies in aortic heart sounds from porcine prosthetic heart valves. A quadratic classifier was developed to evaluate valve sounds in a test set. We have corrected computational errors, recomputed their results, and interchanged the training and test sets to yield new results.     

Spectral composition of heart sounds before and after mechanicalheart valve implantation using a modified forward-backward Prony'smethod

This paper investigates the impact of the lung-thorax and heart-valve system on the overall spectral composition of the externally recorded heart sounds. The study concentrates on the case of the first and the second heart sounds for normal patients and patients before and after implantation of a mechanical valve in the mitral or aortic position. The analysis is performed using a modified forward-backward overdetermined Prony's method (MFBPM) which uses a forward-backward mean filter and a modified procedure for estimating the position of the signal poles. In terms of the normalized cross-correlation coefficient, this method has an average modeling accuracy of 99.62% for representing the first and second heart sounds and an average least square time-domain error of 0.43%. Results obtained from 40 subjects show that the condition of the native mitral or aortic valve affects mostly the distribution of the amplitudes of the spectral components, whereas the number of the spectral components or their respective relative energy remains more or less unchanged. It has been found that the amplitudes of frequency components in the range 120-250 Hz are more affected by abnormalities of native mitral valves. Furthermore, in the case of the second heart sound the region 250-400 Hz has been found to be more affected by abnormalities in the aortic valve. It has also been found that the mechanical prosthetic heart valve affects mostly the spectrum beyond 400 Hz. A clear difference has been observed in the frequency spectrum above 400 Hz between both normally and abnormally functioning native valves and normally functioning mechanical valves. Preliminary results in some malfunctioning cases of mechanical prosthesis suggest that spectral components beyond 400 Hz can be used to monitor the condition of these prostheses     

Control of an air pressure actuated disposable bioreactor for cultivating heart valves

A disposable injection molded bioreactor for growing tissue-engineered heart valves is controlled to mimic the physiological heart cycle. Tissue-engineered heart valves, cultured from human stem cells, are a possible alternative for replacing failing aortic heart valves, where nowadays biological and mechanical heart valves are used. Growing and conditioning is done by mechanically stimulating the tissue in a bioreactor. The disposable injection molded bioreactor uses flexible membranes and steering valves to mimic a physiological heart cycle. In this work, an air pressure actuation control system for this bioreactor is designed. One membrane is position controlled to achieve a desired flow through the heart valve, while another membrane controls the aortic pressure. A third actuator controls a steering valve used to impose a resistance on the flow back to the first membrane, in order to control the heart valve closing pressure. Due to the repetitive character of the setpoints, repetitive controllers are designed and implemented. A high position tracking performance is achieved and pressure setpoints are mimicked successfully, while preventing large pressure oscillations and suppressing disturbances that could be damaging for the tissue heart valve. The control system allows full adjustability of operating conditions needed for the growing, conditioning and testing phases of tissue engineered heart valves.     

A Study of Prosthetic Heart Valve Sounds

In this paper a new mechanism is proposed for the generation of phonocardiogram (PCG) sounds from implanted mechanical prosthetic heart valves. The structures in the chest, the heart, its partitions, and major vessels, constitute a frequency selective system excited by the rapidly decelerating valve occluder. It is shown that the source, the rapidly decelerating valve, has a wide and flat power spectrum and hence is an impulsive excitation that couples energy to the resonance modes specified by the structures in the chest. Consequently, the PCG signal is composed of decaying sinusoids. The parameters of the decaying sinusoids are estimated, and it is observed that the power spectra of the PCG signals have two dominant peaks in the frequency band of 200-500 Hz. The energy coupled to these two modes depends on the state of the valve. With thrombus the decelerating occluder slows down and becomes a broader pulse concentrating the energy to the lower resonance mode. This is verified by experiments on 30 patients during postoperative time course. However, no significant change in the resonance frequencies are observed which is an evidence for their anatomical and not valvular dependence.     

低矫顽力GMR磁传感器及其单畴模型的研究

在硅片上制备结构为Ta/NiFeCr/NiFe/CoFe/Cu/CoFe/IrMn/Ta的IrMn顶钉扎自旋阀薄膜,并最终制成了一组基于此自旋阀结构的GMR磁传感器芯片。利用弱磁场下的退火工艺,改变薄膜易磁化轴的方向,当退火温度为150℃、外加磁场为120Oe时,GMR芯片的矫顽力可以降至0.2Oe以下。同时建立了一种自旋阀自由层的单畴模型,用以解释这一退火效应。利用Mat-lab计算GMR芯片的Meff-H曲线,所得到的计算结果与实验结果一致。所以,自旋阀自由层易磁化轴的方向与GMR磁传感器的性能有着密切的关系。     

衬底温度对机械瓣膜上沉积的类金刚石薄膜的影响

为掌握机械瓣膜衬底温度对类金刚石薄膜的影响规律,在实验中保持其它实验参数不变,机械瓣膜衬底温度分别取室温和150℃时,用脉冲激光沉积法在机械瓣膜上制备类金刚石薄膜。用Raman光谱仪对薄膜的微观结构进行检测;用原子力显微镜对薄膜的表面形貌和粗糙度进行检测。结果表明：当其它实验参数不变时,机械瓣膜衬底温度从室温升高到150℃时,薄膜的微观结构没有发生明显改变;薄膜表面的粗糙度减小。类金刚石薄膜和机械瓣膜衬底之间具有很好的黏附性。     

Comparison of pattern recognition methods for computer-assistedclassification of spectra of heart sounds in patients with a porcinebioprosthetic valve implanted in the mitral position

The diagnostic performance of two pattern recognition methods (or classifiers) to detect valvular degeneration was evaluated in 48 patients with a porcine bioprosthetic heart valve inserted in the mitral position. Twenty patients had a normal porcine bioprosthetic valve and 28 patients had a degenerated bioprosthetic valve. One method was based on the Gaussian-Bayes model and the second on the "nearest neighbor" algorithm using three distance measurements. Eighteen diagnostic features were extracted from the sound spectrum of each patient and, for each method, a two-class supervised learning approach was used to determine the most discriminant diagnostic patterns composed of 6 features or less. The probability of error of the classifiers was estimated with the leave-one-out approach. The performance of each method to discriminate between normal and degenerated bioprosthetic valves was verified by clinical evaluation of the valves. The best performance in evaluation of the sound spectrum (98% correct classifications) was obtained with the Bayes classifier and two patterns of six features each. The percentage of false positive classifications of valve degeneration was 0% and the percentage of false negative classifications was 4%. Sensitivity for the detection of valve degeneration was 96%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 95%. The best performance of the nearest neighbor method (94% correct classifications) was obtained by using the Mahalanobis distance and five patterns composed of three, four, five, or six diagnostic features. Using a pattern composed of only three features, the percentage of false positive classifications for degeneration was 10% and the percentage of false negative classifications was 4%.(ABSTRACT TRUNCATED AT 250 WORDS)     

激光共聚焦扫描显微系统在心血管支架表面内皮化分析研究中的应用

目的:观察内皮细胞(ECs)在植入的心血管支架表面的分布与生长状态,探讨支架材料表面的内皮化情况,并对支架表面内皮化程度的影响因素进行了初步探究.方法:在对内皮细胞不同结构进行特异性染色标记的情况下,利用激光共聚焦扫描显微系统连续扫描观察荧光标记的内皮细胞在植入体内一个月后的支架材料表面的表达程度.结果:在无任何促内皮...     

压电执行器及其在液压阀中的应用

以压电执行器为核心的高速开关阀及伺服阀等压电式液压阀具有频响高,微动性能好,结构紧凑等优点,是新型阀控类型之一,受到国内外研究者的持续关注。首先,该文介绍了阀用压电执行器的分类和特点,根据工作原理分为直推式和步进式2类4种形式;其次,对先导型、直动型、喷嘴挡板型和开关型4种典型压电阀的研究进展进行了梳理,分析了各自的代表性结构、性能特点。结果表明,随着未来对液压阀精密化、智能化需求的提升,压电液压阀的应用前景更广。因此,除高性能介电材料开发外,如微位移放大、迟滞补偿控制等关键压电驱动与控制技术仍有待深入研究。     

Time-frequency and time-scale techniques for the classification ofnative and bioprosthetic heart valve sounds

The determination of diagnostic features in recorded heart sounds was investigated with Carpentier-Edwards (CE) bioprosthetic valves. Morphological features, extracted using the Choi-Williams distribution, achieved between 96 and 61% correct classification. The time-scale wavelet-transform feature set achieved 100% correct classification with native valve populations, and 87% with the CE replacements     

Programmed Shape‐Morphing Scaffolds Enabling Facile 3D Endothelialization

Rapid formation of a confluent endothelial monolayer is the key to the success of small‐diameter vascular grafts, which is significantly important for treating dangerous and even sometimes deadly vascular disorders. However, the difficulty to homogenously locate endothelial cells onto the lumen of small‐diameter tubular scaffolds makes 3D endothelialization greatly challenging. Here, novel shape‐morphing scaffolds enabling programmed deformation from planar shapes to small‐diameter tubular shapes are designed and developed by combining biocompatible shape memory polymer and electrospun nanofibrous membrane. Endothelial cells can be conveniently seeded and attached on the 2D surface of the scaffolds and subsequently self‐rolled into 3D organization at physiological temperature. Endothelial cell responses and functions are varied on the shape‐morphing scaffolds with different nanofibrous electrospun membranes as the inner layer, arisen from the inducement of scaffolds with different morphological, physical, and biochemical characteristics. Owing to excellent properties of the nanofibrous membrane fabricated by the coelectrospinning of poly‐ε‐caprolactone (PCL) and gelatin methacrylate (GelMA), the shape‐morphing scaffolds with a nanofibrous PCL/GelMA inner layer support desirable homogeneous endothelial cell attachment as well as the rapid formation of biomimetic cell–scaffold interaction and cell–cell interaction under the 3D cell culture condition, therefore offering a visible approach for facile 3D endothelialization.     

Development of a new fully flexible hydraulic variable valve actuation system for engines using rotary spool valves

In this paper, a new hydraulic variable valve actuation (VVA) system is proposed and designed. The VVA system can significantly improve the engine performance in terms of the power density, volumetric efficiency, emission, and fuel consumption. In this system, each engine valve is actuated by a hydraulic cylinder which is charged and discharged using two rotary spool valves. The rotary spool valves are rotated by the engine crankshaft while their phases are controlled by hydraulic or electric phase shifters. Similar to camless valvetrains, the new engine valve system is capable of flexible engine valve timing and lift at any engine speed without the drawbacks of existing camless valvetrains including high control complexity, low reliability, and slow actuator response. The mathematical model of the system is derived and verified by comparing simulation and experimental results. Two feedback controllers are designed and implemented for precise valve opening and closing timing and valve lift control. Experiments are performed to validate the mathematical model and evaluate the proposed system's performance. The results show excellent system repeatability and controllability at different operating conditions.     

Effects of Unphysiological Factors on Cardiac Output Regulation During Artificial Heart Pumping

Several Factors affecting artificial heart output were studied employing two mathematical models of prosthetic hearts, i.e., sac and diaphragm heart models. The stroke volume sensitivity to changes in venous pressure was analyzed by numerical computations. Increased inflow valve resistance, increased pump vacuum pressure, decreased elasticity of the ventricular sac or diaphragm and decreased size of the ventricle were shown to depress artificial heart function. In total prosthetic heart replacement experiments in calves, the resistance at the junction of the right heart to the natural atrium was measured by varying the pump vacuum pressure. When the vacuum pressure exceeded ?20 mmHg, the orifice resistance to flow increased approximately 4 times. Optimizing the above factors, a prosthetic heart should be designed that provides sufficient flow with a pump vacuum pressure not greater than ?20 mmHg.     

Video-Based Measuring of Quality Parameters for Tricuspid Xenograft Heart Valve Implants

Defective heart valves are often replaced by implants in open-heart surgery. Both mechanical and biological implants are available. Among biological implants, xenograft ones—i.e., valves grafted from animals such as pigs, are widely used. Good implants should exhibit certain typical anatomical and functional characteristics to successfully replace the native tissue. Here, we describe a video-based system for measuring quality parameters of xenograft heart valve implants, including the area of the orifice and the fluttering of the valves' leaflets, i.e., their flaps (or cusps). Our system employs automatic methods that provide a precise and reproducible way to infer the quality of an implant. The automatic analysis of both a valve's orifice and the fluttering of its leaflets offers a more comprehensive quality assessment than current, mostly manual methods. We focus on valves with three leaflets, i.e., aortic, pulmonary, and tricuspid valves.      

A piezoelectric driven ratchet actuator mechanism with application to automotive engine valves

Increasing demands on the performance of internal combustion engines, specifically automobile engines, require the production of more mechanical energy for a given amount of chemical fuel with reduced tailpipe emissions. Of particular interest in the development of high performance/low emission engines is the control and timing of individual engine valves. This paper investigates the design of an innovative piezoelectric ceramic (PZT) based actuator mechanism with a novel stepping motion amplifier to deliver force and displacement at higher magnitudes and operating frequencies. The target application is an engine valve train which traditionally uses cam-based lifter driven rocker arms to regulate the cylinders’ intake and exhaust valve motion. The proposed PZT-based actuator mechanism introduces a high frequency, lightweight, precise position solution for cylinder-by-cylinder variable valve timing. Numerical results are provided to demonstrate the feasibility of a PZT-based/camless valve train. The new valve train demonstrates similar cam-based performance characteristics while enabling computer controlled individual valve timing opportunities.     

Automated onboard modeling of cartridge valve flow mapping

Proportional poppet-type cartridge valves are the key elements of the energy-saving programmable valves, which have been shown to be able to achieve good motion control performance while significantly saving energy usage in our previous studies. Unlike costly conventional four-way valves, the cartridge valve has a simple structure and is easy to manufacture, but the complicated mathematical model of its flow mapping makes the controller design and implementation rather difficult. Although off-line individually calibrated or manufacturer supplied flow mappings of the cartridge valves can be used, neither method is ideal for wide industrial applications. The former method is time-consuming and needs additional flow sensors while the latter may lead to significantly degraded control performance due to the inaccuracy of the manufacturer supplied flow mappings. Furthermore, due to inevitable system worn out and/or changing working conditions, actual cartridge valve flow mapping may change significantly over the life span of the system and need to be updated periodically in order to maintain the same level of control performance. Sometime, it may be even impractical to do off-line calibrations once the valve leaves the manufacturing plant. To solve this practically significant problem, this paper focuses on the automated onboard modeling of the cartridge valve flow mappings without using any extra sensors and removing the valves from the system. The estimation of flow mappings is based on the pressure dynamics of the hydraulic cylinder with the consideration of effects of some unknown system parameters such as the effective bulk modulus of the working fluid. Localized orthogonal basis functions are proposed to bypass the lack of persistent exciting identification data over the entire domain of the flow mapping during onboard experiments. Experimental results are obtained to illustrate the effectiveness and practicality of the proposed novel automated modeling method.     

Spectral characterization and classification of Carpentier-Edwardsheart valves implanted in the aortic position

This paper demonstrates an improvement in the performance of spectral phonocardiography, combined with pattern recognition techniques for monitoring the condition of bioprosthetic heart valves. The analysis of the heart sounds is performed using a modified forward-backward overdetermined Prony's method. Results show that the condition of the bioprosthesis affects mostly the higher part of the spectrum (i.e., above 250 Hz) where no frequency components were found for malfunctioning cases. Therefore, the amplitudes of the three highest frequency components are used as the input vector of an adaptive single layer perceptron-based classifier to identify normal and malfunctioning classes. For the sample set examined, this method gives 100% correct discrimination between normal and malfunctioning Carpentier-Edwards (C-E) valves     

Design, control, and energetic characterization of a solenoid-injected monopropellant-powered actuator

This paper describes a direct-injection configuration of a monopropellant-powered actuator that is intended to provide high-energy-density actuation for a self-powered position- or force-controlled human-scale robot. The proposed actuator is pressurized by a pair of solenoid injection valves (each of which control the flow of a monopropellant through a catalyst pack and directly into the respective side of a pneumatic-type cylinder), and depressurized via a three-way hot-gas proportional exhaust valve. A controller is described that coordinates the control of the two solenoid propellant injection valves, together with the control of the proportional hot-gas exhaust valve, in order to provide actuator force tracking. Experimental results are presented that validate the effectiveness of the force-control approach. Finally, energetic performance of the proposed actuator is experimentally assessed and shown to provide an energetic figure of merit, an order of magnitude greater than that of a battery-powered servomotor approach.