A computerized system for video analysis of the aortic valve

A novel technique was developed to study the dynamic behavior of the porcine aortic valve in an isolated heart preparation. Under the control of a personal computer, a video frame grabber board continuously acquired and digitized images of the aortic valve, and an analog-to-digital (A/D) converter read four channels of physiological data (flow rate, aortic and ventricular pressure, and aortic root diameter). The valve was illuminated with a strobe light synchronized to fire at the field acquisition rate of the CCD video camera. Using the overlay bits in the video board, the measured parameters were super-imposed over the live video as graphical tracing, and the resultant composite images were recorded on-line to video tape. The overlaying of the valve images with the graphical tracings of acquired data enabled the data tracings to be precisely synchronized with the video images of the aortic valve. This technique enabled us to observe the relationship between aortic root expansion and valve function.     

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.     

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     

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.      

High-gain observer-based pump/valve combined control for heavy vehicle electro-hydraulic servo steering system

Electro-hydraulic servo steering system (EHSSS) has been widely used in multi-axle heavy vehicles. Noteworthy, the traditional EHSSS controlled only by servo solenoid valve has amounts of energy loss in throttling orifice. Although the steering control accuracy is ensured, it leads to low energy efficiency. In this paper, a novel pump/valve combined control (PVCC) EHSSS is proposed to increase the energy efficiency, which only uses one servo motor pump and one servo solenoid valve to drive the steering trapezoid mechanism. Based on the control objectives of low pressure difference in valve orifice and high steering tracking performance, a dual-input-dual-output control strategy is proposed. To guarantee the high steering tracking performance of PVCC steering system, a high-gain observer based sliding mode controller (HGO-SMC) is designed for controlling the spool displacement of servo solenoid valve. During the steering process, the servo motor pump is controlled by a simple speed feedforward and PID controller, so that the pressure difference in throttling orifice is kept at a low value to reduce the energy wasted. The experimental comparison results show that the proposed method can achieve the same tracking performance as valve control EHSSS with less energy consumption.     

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.     

Dynamic behavior of an electrohydraulic valve: Typology of characteristic curves

The majority of off-road vehicles employed in agriculture are equipped with a hydraulic steering. An efficient way of automating the steering mechanism of these vehicles is by controlling the electrohydraulic valve that operates the steering cylinder. Electronically-controlled hydraulic valves often behave nonlinearly and, consequently, they introduce certain complexities in the analysis of the hydraulic system. Therefore, it is necessary to understand their behavior before designing a control system that is able to auto-steer an agricultural machine safely and efficiently. The objective of this work was to characterize the performance of an electrohydraulic valve with the aid of a set of experiments conducted on a hardware-in-the-loop electrohydraulic simulator. The operation of the valve was classified in four types (I, II, III, and IV) according to the valve characteristic curves and the properties of the input signal. The phenomena of deadband, hysteresis, and saturation helped to discriminate between types. The input signal, especially its frequency, was crucial in studying the functioning of the valve. The hardware-in-the-loop simulator was fed with signals that imitated the auto-steering action. The outcomes obtained from this research provide some critically supporting information for designing high performance steering controllers for agricultural vehicles.     

Modeling and control of a novel pneumatic two-stage piezoelectric-actuated valve

In manufacturing automation, there is a strong need for highly integrated intelligent components and subsystems. In this context, a novel two-stage pneumatic piezoelectric-actuated valve has recently been developed. It covers a wide range of pneumatic products and functions in one compact component and enables flexible and adaptive plant operation. The valve consists of four poppet main-stage valves that are driven by piezoelectrically actuated pre-stage valves and includes pressure sensors as well as a powerful computational unit. This work presents the systematic development of a model-based position control algorithm including modeling, identification, and controller design. The control concept comprises a hysteresis compensation based on the Prandtl–Ishlinskii operator theory, a flatness-based feedforward controller, and a PI feedback controller with appropriate anti-windup measures. Measurement results from a test bench demonstrate the performance of the proposed concept.     

Relations between the timing of the second heart sound and aortic blood pressure

The second heart sound (S2) is triggered by an aortic valve closure as a result of the ventricular-arterial interaction of the cardiovascular system. The objective of this paper is to investigate the timing of S2 in response to the changes in hemodynamic parameters and its relation to aortic blood pressure (BP). An improved model of the left ventricular-arterial interaction was proposed based on the combination of the newly established pressure source model of the ventricle and the nonlinear pressure-dependent compliance model of the arterial system. The time delay from the onset of left ventricular pressure rise to the onset of S2 (RS2) was used to measure the timing of S2. The results revealed that RS2 bears a strong negative correlation with both systolic blood pressure and diastolic blood pressure under the effect of changing peripheral resistance, heart rate, and contractility. The results were further validated by a series of measurements of 16 normal subjects submitted to dynamic exercise. This study helps understand the relationship between the timing of S2 and aortic BP under various physiological and pathological conditions.     

浅谈水力平衡带来的空调能耗及解决措施

在暖通空调系统的设计中,变流量系统有着定流量系统无法比拟的节能优势,所以日益受到人们的关注,并被广泛的接受和采用。简单使用静态平衡阀作为变流量系统的平衡措施,就会造成一系列的水力平衡问题,增大空调能耗。具体分析水力平衡带来的空调能耗问题,并介绍了丹佛斯阀门集团有限公司研制的动态压差平衡型电动调节阀门,能很好地解决采用静态平衡阀产生的水力平衡问题。     

数据中心制冷的鸡肋——动态平衡阀

在现有的数据中心空调设计中,稍微大一些的水冷系统,在末端每个精密空调的支管处均会设置一动态平衡阀,以保证系统水系统的水力平衡.本文将介绍数据中心动态平衡阀的类型及其作用,通过与民用项目中动态平衡阀作用的对比,探索设置动态平衡阀的原理,最终探讨设置动态平衡阀的必须性.     

Design and control of the atrio-aortic left ventricular assistdevice based on O2 consumption

The left ventricular assist device (LVAD) is used in parallel with the left ventricle to temporarily assist patients with diminished cardiac function for the purpose of minimizing heart workload and to maintain systemic arterial perfusion. The proper adjustment and timing of the pneumatic LVAD is important such that this goal is achieved. Previous investigations into the left ventricular assist device are inconclusive regarding the optimal utilization of this device. This paper documents a protocol for optimal timing of the LVAD. Timing is studied using a closed-loop analog model of the heart, vascular system, and the LVAD. The model is tested for basic representation of the physiological system. The LVAD is incorporated into the model to discover its interaction with cardiac preload and afterload. Heart workload is computed via the pressure-volume-area method. The normal and impaired heart are modeled, in each case the pump control variables are adjusted. A protocol for adjustment of the LVAD is proposed based on reduced heart oxygen consumption. It was found that the pump should begin ejection immediately after the close of the aortic valve and that the pump filling pressure should be set to a value which produces maximum filling of the pump. Although aortic pressure and flow could be improved at pump rates above the heart rate, oxygen utilization of the heart could only be minimized for synchronous pumping. The adjustment of the pump ejection pressure is a tradeoff between d/dt (LVO2) and stroke volume and mean arterial pressure. The LVAD should be designed to minimize inflow and outflow resistance and to maximize pump compliance. The process of weaning the patient from the LVAD is considered. The overall results provide quantitative guidance for the use of the AA-LVAD.     

电液控制四轮转向技术在电动搬运车中的应用研究

电液控制四轮转向技术是一种主要应用于工程车辆领域的智能控制技术,利用电液比例阀技术控制四组车轮同步转向的系统.电液四轮转向系统结合了液压系统独有的高扭矩特性以及四轮独立转向带来的小转弯半径特性,很好的解决了大吨位工程搬运车辆在狭小空间内搬运货物的难题.系统对主要部分进行建模仿真分析,验证了电液控制四轮转向技术的良好性能.     

Assessing aortic stenosis using sample entropy of the phonocardiographic signal in dogs

In aortic valve stenosis (AS), heart murmurs arise as an effect of turbulent blood flow distal to the obstructed valves. With increasing AS severity, the flow becomes more unstable, and the ensuing murmur becomes more complex. We hypothesize that these hemodynamic flow changes can be quantified based on the complexity of the phonocardiographic (PCG) signal. In this study, sample entropy (SampEn) was investigated as a measure of complexity using a dog model. Twenty-seven boxer dogs with various degrees of AS were examined with Doppler echocardiography, and the peak aortic flow velocity (V_max) was used as a reference of AS severity. SampEn correlated to V_max with R = 0.70 using logarithmic regression. In a separate analysis, significant differences were found between physiologic murmurs and murmurs caused by AS (p < 0.05), and the area under a receiver operating characteristic curve was calculated to 0.96. Comparison with previously presented PCG measures for AS assessment showed improved performance when using SampEn, especially for differentiation between physiological murmurs and murmurs caused by mild AS. Studies in patients will be needed to properly assess the technique in humans.     

微小型高压力流体电磁控制阀

用于航空航天领域微流量控制系统中的微小型阀 ,需要具有耐高压、低泄漏、高频响和高控制精度等综合性能。本文提出了一种可控高压力微流体的常闭微小型阀的设计方案用于满足该系统需要 ,其特点在于采用以较小的致动力控制较高的流体压力的结构原理 ,并以弹性材料薄膜作为阀芯的支承结构件同时作为密封件。该阀由其本体结构和外置致动器两部分构成 ,其本体结构的设计在制作工艺上适合进一步的微小型化 ,外置致动器的设计具有较大灵活性。初步研制了采用电磁致动的小型常闭阀样机既可控气体又可控液体的特性。实验测试其工作压力范围为 0～5atm ,阀的驱动响应时间小于 5ms,流量控制分辨率达到 9μL/ pulse ,无泄露     

A Pneumatic Pressure Cycling System for an Artificial Heart

Included in this paper is a discussion of the operating principle, design, construction and testing of a stroke-limited, transistorized, pneumatic pressure cycling system for a single-chambered artificial heart. The system is free of valve-stiction catastrophes, and reveals that conventional calculations of heart power based on mean blood pressure, cardiac output and kinetic energy of the aortic blood should be augmented substantially to account for turbulence, valve resistance and pneumatic feedline distensibility. Graphs are presented to illustrate the over-all performance data.     

Fault tolerant real time control system for steer-by-wire electro-hydraulic systems

A steer-by-wire (SBW) control system is presented with emphasis on safety issues. The applications are in articulated vehicles such as the wheel type loaders, articulated trucks, and others. The electro-hydraulic (EH) power circuit is controlled by two embedded electronic control modules (ECM), the primary ECM and backup ECM. The two ECMs monitor each others condition. If one detects fault in the other, it takes over the control functions. There are two main control algorithms that run in the ECMs in real-time: the steering valve control algorithm and the failure detection algorithm. The valve control algorithm basically generates command signal to the steering valve based on operator steering column signal as well as other machine condition sensors.The failure detection algorithm implements a fault detection logic for both input sensors and output drivers, and flags the corresponding warning for to the operator, and take a predefined action depending on the type of the failure detected. A unique fault strategy organization is implemented by inspecting the failure behavior on both the component and the system levels. The failure detection algorithm also determines the most likely “good” sensor signal from a set of redundant sensors for each critical measurement. Based on these good sensors data, the steering control algorithm sends two output signals: the control signal to the steering EH circuit valve and the control signal to the steering wheel force feedback device (i.e. a brake or a motor) to give operator feedback about the steering conditions.Finite state machine (FSM) concept is used to design the fault handling algorithms for both the component level and the system level failure. The probability of the system being at normal steering state or at any other steering failure state is determined. Failure mode probabilities of steering system components are also determined.     

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。