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     

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.     

Observation of faults in convertor bridges

A method of simultaneously monitoring the seven valves in a 3-phase Graetz bridge circuit is described. The d.c. smoothing-inductor voltage is observed for this purpose. It is shown that the point of failure on the voltage wave of the malfunctioning valve can be found.     

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.     

Computer model for simulation of first transit cardiac radionuclidecurves. I

A discrete-time, lumped-parameter mathematical model of the human cardiopulmonary circulation as it appears during a first-transit radionuclide study is developed. Eleven compartments, four delays, and 26 transfer paths are modeled, including the entire circulation from an input compartment before the vena cava to an output compartment after the aorta. The 26 transfer paths include forward and reverse flow through the heart valves, backflow from the atria into the veins, and five types of shunts. A method of modeling continuously-variable delay segments with only discrete-time sample points is devised to allow more versatility in specifying delays. The model simulates discrete time-activity curves for the various compartments of the cardiopulmonary system. The curves are obtained for end-systole and end-diastole. Simulation of curves indicative of a normal heart and several heart defects is presented. The use of this model for computer analysis of first-transit cardio-radionuclide curves is discussed.     

Spectral distortion properties of the integral pulse frequencymodulation model

The integral pulse frequency modulation (IPFM) model has been used for the following two purposes. First, it has been utilized to verify the correspondence between the spectral structure of autonomic input and the estimated spectrum of heart rate variability (HRV), relying mainly on the theoretical work of Bayly (1968). Second, the IPFM model provides a framework for evaluating how precisely the proposed method of HRV analysis could estimate the input spectral structure. However, the appropriateness of the IPFM model for both purposes has not been examined sufficiently in realistic situations. Here, the spectral structure of the pulse train generated by the IPFM model is theoretically derived for an input signal containing multiple frequency components. This is a more general condition than the single sinusoidal input signal used earlier. In accordance with the theoretical results, the magnitude of the spectral distortion is computed for a pair of varied frequencies, considering the corresponding coefficient of variation of interpulse intervals. Results show that the distortion could be nonnegligible under practical values of the coefficient of variation. Such distortion may well affect the spectral structure in the wide frequency range. This study suggests that the spectral structure of HRV should be interpreted carefully, taking the above distortion properties into account, even though the IPFM model appears to be established as a mechanism mediating between autonomic input and heart rate variability     

一种新型压电陶瓷固液一体化作动器

提出了一种基于压电陶瓷的新型固液一体化作动器。该作动器通过两个压电陶瓷泵协调工作,由压电陶瓷提供动力,液压油为介质,用泵体代替普通一体化作动器中的单向阀,克服了单向阀的响应频率瓶颈,从而有效地利用了压电陶的高频响应特性,同时集成的一体化结构设计,避免了普通液压作动器的分布管路。对设计的一体化作动器进行了建模仿真,得到仿真曲线,结果表明该作动器相对体积小,输出位移大,响应频率高,承载能力强,动态特性好,并且实现了全电工作。     

Packet reordering is not pathological network behavior

It is a widely held belief that packet reordering in the Internet is a pathological behavior, or more precisely, that it is an uncommon behavior caused by incorrect or malfunctioning network components. Some studies of Internet traffic have reported seeing occasional packet reordering events and ascribed these events to “route fluttering”, router “pauses” or simply to broken equipment. We have found, however, that parallelism in Internet components and links is causing packet reordering under normal operation and that the incidence of packet reordering appears to be substantially higher than previously reported. More importantly, we observe that in the presence of massive packet reordering transmission control protocol (TCP) performance can be profoundly effected. Perhaps the most disturbing observation about TCP's behavior is that large scale and largely random reordering on the part of the network can lead to self-reinforcingly poor performance from TCP     

Localizing heart sounds in respiratory signals using singular spectrum analysis

Respiratory sounds are always contaminated by heart sound interference. An essential preprocessing step in some of the heart sound cancellation methods is localizing primary heart sound components. Singular spectrum analysis (SSA), a powerful time series analysis technique, is used in this paper. Despite the frequency overlap of the heart and lung sound components, two different trends in the eigenvalue spectra are recognizable, which leads to find a subspace that contains more information about the underlying heart sound. Artificially mixed and real respiratory signals are used for evaluating the performance of the method. Selecting the appropriate length for the SSA window results in good decomposition quality and low computational cost for the algorithm. The results of the proposed method are compared with those of well-established methods, which use the wavelet transform and entropy of the signal to detect the heart sound components. The proposed method outperforms the wavelet-based method in terms of false detection and also correlation with the underlying heart sounds. Performance of the proposed method is slightly better than that of the entropy-based method. Moreover, the execution time of the former is significantly lower than that of the latter.     

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)     

Islanding detection technique using wavelet energy in grid-connected PV system

This paper proposes a new islanding detection method using wavelet energy in a grid-connected photovoltaic system. The method detects spectral changes in the higher-frequency components of the point of common coupling voltage and obtains wavelet coefficients by multilevel wavelet analysis. The autocorrelation of the wavelet coefficients can clearly identify islanding detection, even in the variations of the grid voltage harmonics during normal operating conditions. The advantage of the proposed method is that it can detect islanding condition the conventional under voltage/over voltage/under frequency/over frequency methods fail to detect. The theoretical method to obtain wavelet energies is evolved and verified by the experimental result.     

The Measurement of Heart Rate Variability Spectra with the Help of a Personal Computer

The analysis of fluctuations in heart rate or heart rate variability (HRV) has found applications in, among others, the study of the neural cardiovascular system and ergonomic psychology. In particular, the study of the frequency components of HRV is becoming increasingly important. A method for the computation of HRV spectra directly from the heart beat event series as derived from the electrocardiogram has been developed. Because of the computational efficiency achieved, this method is implemented on a personal computer. Apart from an external QRS detector, a completely stand-alone system is realized. User interaction takes place on a menu card display basis. The system can operate at both real time and up to eightfold increased speed. The resultant spectra are displayed as histograms. Different ways of smoothing and segment averaging are possible.     

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.     

Rogue Commercial Geosynchronous Communications Satellites

The growth in numbers of commercial communications satellites in geosynchronous orbit raises the possibilities for radio frequency interference into space-earth transmission systems due to a malfunctioning satellite and of physical damage to an operating satellite due to collision with co-orbiting objects. These possibilities are addressed and recommendations are presented to minimize such occurrences.     

Locating the faulty component in a malfunctioning repetitiveoperation

When the output of a repetitive operation is nonconforming, it is desirable to use a method that can locate the particular component that caused the nonconforming output. To minimize the probability of a wrong decision, a Bayes decision approach is used to develop a criterion for locating the source. The criterion is the ratio of the posterior and prior probability values of the parameters associated with each component when parameters assume values within their tolerance ranges. This criterion provides an ordering of inspection of the components of the process and locates the most likely malfunctioning component. It can be applied to an existing faulty model whose parameters can have been determined in an arbitrary way (physical principles, brainstorming, etc.). The criterion can be used in conjunction with expert opinion to improve decision accuracy. It is particularly suitable when there is little information about the performance of the components of an operating process. Supporting examples are provided     

Improved heart rate variability signal analysis from the beat occurrence times according to the IPFM model

The heart rate variability (HRV) is an extended tool to analyze the mechanisms controlling the cardiovascular system. In this paper, the integral pulse frequency modulation model (IPFM) is assumed. It generates the beat occurrence times from a modulating signal. This signal is thought to represent the autonomic nervous system action, mostly studied in its frequency components. Different spectral estimation methods try to infer the modulating signal characteristics from the available beat timing on the electrocardiogram signal. These methods estimate the spectrum through the heart period (HP) or the heart rate (HR) signal. We introduce a new time domain HRV signal, the Heart Timing (HT) signal. We demonstrate that this HT signal, in contrast with the HR or HP, makes it possible to recover an unbiased estimation of the modulating signal spectra. In this estimation we avoid the spurious components and the low-pass filtering effect generated when analyzing HR or HP.     

High-Frequency Carrier-Signal Voltage Selection for Stator Winding Fault Diagnosis in Inverter-Fed AC Machines

The diagnosis of stator winding faults in inverter-fed ac machines using an injected high-frequency carrier-signal voltage is analyzed in this paper. Measurement of the resulting carrier signals (either the negative-sequence carrier-signal current or the zero-sequence components) is used to detect turn faults at an incipient stage. The carrier frequency and magnitude are shown to have significant impact on the performance of the method, with the criteria for their selection being presented. The proposed technique shows low sensitivity to the working condition of the machine, i.e., torque level, flux levels, and fundamental excitation frequency.      

Bias and variability of diagnostic spectral parameters extractedfrom closing sounds produced by bioprosthetic valves implanted in themitral position

A method is proposed to estimate the bias and variability of eight diagnostic spectral parameters extracted from mitral closing sounds produced by bioprosthetic heart valves. These spectral parameters are: the frequency of the dominant (F1) and second dominant (F2) spectral peaks, the highest frequency of the spectrum found at -3 dB (F-3), -10 dB (F-10) and -20 dB (F-20) below the highest peak, the relative integrated area above -20 dB of the dominant peak (RIA20), the bandwidth at -3 dB of the dominant spectral peak (BW3), and the ratio of F1 divided by BW3 (Q1). The bias and variability of four spectral techniques were obtained by comparing parameters extracted from each technique with the parameters of a spectral "standard." This "standard" consisted of 19 normal mitral sound spectra computed analytically by evaluating the Z transform of a sum of decaying sinusoids on the unit circle. Truncation of the synthesized mitral signals and addition of random noise were used to simulate the physiological characteristics of the closing sounds. Results show that the fast Fourier transform method with rectangular window provides the best estimates of F1 and Q1, that the Steiglitz-McBride method with maximum entropy (pole-zero modeling with four poles and four zeros) can best evaluate F2, F-20, RIA20 and BW3, and that the all-pole modeling with covariance method (16 poles) is best suited to compute F-3. It was also shown that both the all-pole modeling and the Steiglitz-McBride methods can be used to estimate F-10. It is concluded that a single algorithm would not provide the best estimates of all spectral parameters.     

Unconditionally stable D-H FDTD formulation with anisotropic PMLboundary conditions

An unconditionally stable finite difference time domain (FDTD) method based on a D-H formulation and the recently proposed alternating-direction-implicit (ADI) marching scheme is presented. The advantage of the D-H algorithm over the conventional E-H is the possibility to easily implement an unsplit field components formulation of the PML absorbing boundary condition that is independent from the background material used in the FDTD grid. The method allows therefore immersing any dielectric in the PML layers without any special consideration, and is amenable for models truncation often used in biomedical simulations. Furthermore, the proposed scheme can be extended to account for frequency dispersive dielectrics