Noninvasive measurement of local arterial pulse wave velocity in humans by ultrasound

An improved method for noninvasive measurement of the local velocity of arterial pulse wave propagation by an echo-tracking-based ultrasound system is described. A data acquisition image interface was programmed in the ultrasound machine simultaneously to record M-mode ultrasound signals at two locations of a given distance apart along an artery. The selections of measurement sites, separation, and time resolution were performed on the control interface. The temporal sampling frequency could be as high as 10?kHz. The displacements of the blood vessel wall along the time axis were calculated from the M-mode signals by cross-correlation of the radio-frequency data and the distension waveforms were obtained. The temporal separation of the feet of the distension curves from the two measurement locations was derived to give the travel time of the pulse wave. Measurements were made in vivo on human carotid arteries. The pulse wave velocities measured from four volunteers were from 4.1 to 7.2 m/s with coefficients of variation from 5.9 to 29.5%. Some of the factors contributing to the variation in measured values of the velocity are discussed. The method is simple to implement and should be suitable for clinical research into local pulse wave velocity.     

Estimation of aortic compliance using magnetic resonance pulse wave velocity measurement

A method for compliance estimation employing magnetic resonance pulse wave velocity measurement is presented. Time-resolved flow waves are recorded at several positions along the vessel using a phase contrast sequence, and pulse wave velocity is calculated from the delay of the wave onsets. Using retrospective cardiac gating in combination with an optically decoupled electrocardiogram acquisition, a high temporal resolution of 3 ms can be achieved. A phantom set-up for the simulation of pulsatile flow in a compliant vessel is described. In the phantom, relative errors of pulse wave velocity estimation were found to be about 15%, whereas in a volunteer, larger errors were found that might be caused by vessel branches. Results of pulse wave velocity estimation agree with direct aortic distension measurements which rely on a peripheral estimate of aortic pressure and are therefore less accurate. Studies in 12 volunteers show values of pulse wave velocity consistent with the literature; in particular the well-known increase in pulse wave velocity with age was observed. Preliminary results show that the method can be applied to aortic aneurysms.     

基于超声回波信号的指端脉搏波提取

脉搏波可作为检测人体心血管系统生理病理状态的重要依据。为了验证用超声波测量脉搏波的可能、解决脉搏波的测量部位受限的问题,本研究提出一种从超声回波信号中提取脉搏波的方法。设计一种跟随式超声传感器,用数据采集系统采集指端超声回波信号,经过滤波、选点及小波去噪等处理后得到较为纯净的脉搏波信号;同时采集心电信号以及光电容积脉搏波信号作为参考信号。结果表明,可以从提取的指端脉搏波中准确地获取心率;与同步测得的光电容积脉搏波数据相关系数大部分在0.8以上;波形中的重搏前波、重搏波等细节部分也能明显地表现出来。本研究提出的方法实现了从指端超声回波信号中获取完整可靠的脉搏波信号,为日后获取不同部位的脉搏信号提供了基础。     

Potential and limitations of wave intensity analysis in coronary arteries

Wave intensity analysis (WIA) is beginning to be applied to the coronary circulation both to better understand coronary physiology and as a diagnostic tool. Separation of wave intensity (WI) into forward and backward traveling components requires knowledge of pulse wave velocity at the point of measurement, which at present cannot accurately be determined in human coronary vessels. This prompted us to study the sensitivity of wave separation to variations in wave speed. An estimate of wave speed (SPc) was calculated based on measured distal intracoronary pressure and Doppler velocity in normal and diseased coronary vessels of patients during hyperemia. Changes of the area under separated WI waveforms were determined for a range of wave speeds from 25 to 200% of the calculated value. Variations in wave speed between half to twice the calculated value did not substantially alter separated WI. In conclusion, although SPc lacks accuracy in determining local coronary wave speed it is within limits still applicable for wave separation in coronary WIA.     

Pulse onset detection using neighbor pulse-based signal enhancement

Detecting onsets of cardiovascular pulse wave signals is an important prerequisite for successfully conducting various analysis tasks involving the concept of pulse wave velocity. However, pulse onsets are frequently influenced by inherent noise and artifacts in signals continuously acquired in a clinical environment. The present work proposed and validated a neighbor pulse-based signal enhancement algorithm for reducing error in the detected pulse onset locations from noise-contaminated pulsatile signals. Pulse onset was proposed to be detected using the first principal component extracted from three adjacent pulses. This algorithm was evaluated using test signals constructed by mixing arterial blood pressure, cerebral blood flow velocity and intracranial pressure pulses recorded from neurosurgical patients with white noise of various levels. The results showed that the proposed pulse enhancement algorithm improved (p<0.05) pulse onset detection according to all three different onset definitions and for all three types of pulsatile signals as compared to results without using the pulse enhancement. These results suggested that the proposed algorithm could help achieve robustness in pulse onset detection and facilitate pulse wave analysis using clinical recordings.     

Ultrasonic transit-time system for arterial diameter measurement

An ultrasonic transit-time micrometer has been developed to measure pulsatile changes in arterial diameter with sufficient accuracy to verify haemodynamic theories. The instrument samples up to four distances at repetition frequencies above 1 kHz and is calibrated by a separate determination of the velocity of ultrasound in blood. New methods of transmitter pulse triggering and received pulse amplification and detection, and construction and testing of small arterial transducers, are described. The system will resolve distance changes smaller than 1 μm and will run continuously for long periods without temperature drift. Trials by measurement of the dynamic distension of a long water-filled rubber tube and comparison with the manometrically measured phase velocity showed that the technique yields results within the range of predicted values from pulsatile flow theory.     

基于指端脉搏波视频信号的心率稳定检测算法

目的:研究一种基于脉搏波的稳定检测心率的算法。 方法:提出一种基于快速独立成分分析（FastICA）算法处理指端脉搏波视频信号。首先通过手机摄像头采集手指视频,在每帧图片中提取感兴趣区域（ROI）,根据每个区域中像素灰度值的变化得到血液容积变化的时序曲线;然后通过对ROI进行RGB通道分离和FastICA后,分别选取红、绿色分量与盲源分离后的估计信号进行相关性分析,筛选出相关性最大的作为后续提取心率的信号,并与波峰法测得的心率进行对比,得到一种稳定的心率检测算法,并利用SPSS软件做相关性分析。 结果:选取R、G通道信号的一致性在95%以上,基于FastICA的算法与统计波峰法获取心率的一致性在95%以上。 结论:FastICA算法能够有效地提高心率测量的稳定性,实验结果验证了该方法的可行性和有效性,对于基于脉搏波的人体生理参数获取具有重要意义。     

Non-linear separation of pressure, velocity and wave intensity into forward and backward components

Separating pressure, flow/velocity and wave intensity signals into forward and backward components provide insights about arterial wave propagation and reflection. A linear wave separation is normally used, but ignores the pressure-dependence of wave speed. While a non-linear separation could incorporate this pressure-dependence, no such method exists for wave intensity decomposition. Moreover, although linear separation errors for pressure (5-10?%) have been quantified previously, errors for velocity and wave intensity have not. Accordingly, we describe a non-linear wave separation technique based on the method of characteristics. Data from a computer model suggest that the percentage linear separation errors for velocity and wave intensity are approximately one-half and twice that for pressure, respectively. Although comparable to measurement uncertainty in many instances, linear separation errors may become more significant: (1) if wave speed varies substantially over the cardiac cycle, e.g. if pulse pressure or vessel compliance is high, (2) if the degree of wave reflection in the arterial system is large, or (3) if the constant wave speed used for the linear separation is closer to the minimum or maximum pressure-dependent value rather than the mean. Consideration of linear separation errors may therefore be important in some physiological settings.     

Self-mixing in a diode laser as a method for cardiovascular diagnostics

Our aim is the development of a simple optical method for pulse wave profile, pulse wave delay time, and blood flow measurement. The method is based on recording the Doppler frequency shift related to a moving target--blood vessel walls or small particles. The Doppler signal is detected using the self-mixing that occurs in the diode laser cavity when radiation scatters back from the moving target into the laser and interferes with the field inside. Two different ways can be simultaneously used for the self-mixing signal extraction: a photodiode accommodated in the rear facet of the diode laser package and a resistor from the laser pump current. An experimental device with a pigtail laser diode is developed that is able to detect the pulsation of major arteries with potentially useful information, including the pulse wave profile and the pulse wave delay time. The pulse wave delay time in different regions of the human body is measured relative to the electrocardiogram (ECG) signal. Also the flow velocity of a liquid suspension containing particles the size of erythrocytes (equivalent to blood flow) is measured. Registered signals are stored after digitalization and preprocessed using LabView for a Windows environment. The described device has the application of the self-mixing method and highlights significant advantages of simplicity, compactness, and robustness as well as the self-aligning and self-detecting abilities of such method, compared with the use of conventional interferometric method.     

基于脉搏波信号和血管弹性腔模型的动脉血压连续测量方法

目的为满足健康监护中的连续测量血压的要求,研究并实现一种基于脉搏波信号和血管弹性腔模型的动脉血压拟合计算方法。方法利用自制的穿戴式人体生理参数监测系统收集测试对象的脉搏波信号、心电信号以及血压数据。根据心电信号与脉搏波信号的时间关系,推导出收缩压和脉搏波传导时间的回归分析方程,而舒张压的测量,则是通过脉搏波的波形系数分析以及血管单弹性腔模型的参数计算完成。结果试验结果表明,该方法血压测量结果的平均偏差和标准偏差为(0.51±0.74)kPa([384±5.54)mmHg],达到了美国医疗仪器促进协会建议的(0.665±1.064)kPa([5±8)mmHg]标准。结论结合脉搏波信号和弹性腔模型可以估算人体血压值,为连续血压测量提供了新的实现方法。     

双通道脉搏波速度测量系统的研制

本文是脉搏波速度的测量及研究课题的系列论文之一，介绍了双通道光电传感器脉搏波测量系统的设计，对光电传感器的制作及测最位置的选择、脉搏波传递时间的计算方法以及脉搏波干扰的处理等关键技术给出了详细的解决方案，为脉搏波及其速度的研究提供一个精确稳定、操作方便、体积小功耗低且成本低廉的工具。     

人体脉搏波传播时差检测系统

脉搏波的波形和传播速度与血管的几何和物理性质有密切关系,可通过检测脉搏波形和传播速度的变异判别动脉血管的弹性功能。作者采用固体压阻式脉压传感器,脉搏信号预处理装置,TP—801单板机组成检测脉搏波及其传播时差的系统,可对脉搏信号进行无创提取,贮存及处理,以供临床分析应用。     

一种无创脉搏波检测分析系统的研制

研制了一套无创脉搏信号检测分析系统，系统采用生理压力传感器同时采集两路脉搏波信号，实现了脉搏波信号的实时采集、存储、动态显示、波形波速度分析和诊断报告的打印，能够较全面的评价心血管系统的功能。该系统采用单片机与计算机结合的设计方式，同时具有单片机小型化、便携的特点和计算机强大的数据存储、分析、处理的能力。初步临床实验表明，该系统操作方便，稳定性好，检测的可重复性较好。     

组织声学特性对高强度聚焦超声温度场的影响

目的 数值仿真组织声学特性对高强度聚焦超声（HIFU）焦域处温度场的影响,为HIFU治疗安全性和可靠性提供理论依据.方法 以实测新鲜离体猪肝组织不同温度下的声速和衰减系数为依据,利用时域有限差分（FDTD）法数值仿真研究HIFU治疗过程中组织内声速、衰减系数的变化和温度场的分布,分析讨论声速和衰减系数变化对60 ℃以上可治疗区域大小、位置的影响.结果 随着照射时间的延长,焦域处肝组织温升增大,声速下降,声衰减系数增大.随着声速的变化,形成的可治疗区域变大,焦点位置向远离换能器方向移动;随着声衰减系数的变化,焦域大小和焦点位置几乎不变.结论 猪肝组织内声速的变化对可治疗焦域的位置和大小影响较大;声衰减系数的变化对焦域的影响较小.     

一种可监测人体脉搏波的汽车方向盘辅助装置

目的脉搏波的波形特征与心血管疾病密切相关。本文拟设计一种安装在汽车方向盘上的能独立实时监测脉搏波信号的辅助装置,在驾驶员无意识下获取其血流动力学的相关信息,为监测健康状况提供数据支持。方法该装置利用置于方向盘套表面的反射式脉搏波光电传感器采集脉搏波信号。经过滤波、放大和A／D转换,利用嵌于方向盘助力器内的配套装置对脉搏波信号进行数字处理,实现对脉搏波信号周期的确定、心率和平均动脉压数据的计算,以及信号和数据的存储。最后将处理后的脉搏波波形、心率数据及平均动脉压显示在配套装置的液晶显示屏上,还可通过配套装置中的SD卡接口进行数据传输及存储。结果经受试者实际测试,传感器能够准确测出手指脉搏波并输出,使得方向盘套和助力器具有测量脉搏波、心率及平均动脉压的功能。结论该汽车方向盘辅助器可为用户实时监测脉搏波、心率和平均动脉压,帮助使用者实时监测自己的健康状况。     

Jet formation and shock wave emission during collapse of ultrasound-induced cavitation bubbles and their role in the therapeutic applications of high-intensity focused ultrasound

The dynamics of inertial cavitation bubbles produced by short pulses of high-intensity focused ultrasound near a rigid boundary are studied to get a better understanding of the role of jet formation and shock wave emission during bubble collapse in the therapeutic applications of ultrasound. The bubble dynamics are investigated by high-speed photography with up to 2 million frames/s and acoustic measurements, as well as by numerical calculations. The significant parameter of this study is the dimensionless stand-off, gamma, which is defined as the distance of the bubble centre at its maximum expansion scaled by the maximum bubble radius. High-speed photography is applied to observe the bubble motion and the velocity of the liquid jet formed during bubble collapse. Hydrophone measurements are used to determine the pressure and the duration of the shock wave emitted during bubble rebound. Calculations yield the variation with time of the bubble wall, the maximum velocity and the kinetic energy of the re-entrant jet. The comparisons between experimental and numerical data are favourable with regard to both shape history and translational motion of the bubble. The acoustic energy constitutes the largest individual amount in the energy balance of bubble collapse. The ratio of the shock wave energy, measured at 10 mm from the emission centre, to the cavitation bubble energy was 1:2.4 at gamma = 1.55 and 1:3.5 at gamma = 1. At this distance, the shock wave pressure ranges from 0.122 MPa, at gamma = 1, to 0.162 MPa, at gamma = 1.55, and the temporal duration at the half maximum level is 87 ns. The maximum jet velocity ranges from 27 m s(-1), at gamma = 1, to 36 m s(-1), at gamma = 1.55. For gamma < 1.2, the re-entrant jet can generate an impact pressure on the nearby boundary larger than 50 MPa. We discuss the implications of the results for the therapeutic applications of high-intensity focused ultrasound.     

颈动脉不同径向位置的流速波形比较

本文分析颈动脉中血液流动的速度波形随径向位置的变化规律，详细讨论径向位置对流速波形中的最大值Ｖｍａｘ和最小值Ｖｍｉｎ的影响情况。以评估临床上超声流速探头偏离颈动脉管轴位置对所检测的流速可能产生的影响。结果表明当探头偏离血管轴的位置为ｙ＝ｒ／Ｒ≤０．２时，流速测量的相对误差能控制在１０％左右，这对指导无创伤检测血流速度的操作和分析有重要价值。     

Pulse propagation in muscle.

A technique is described for measuring the propagation velocity of a mechanical pulse along a muscle. The pulse is generated and detected by piezoelectric crystals (bimorph benders). Measurement of the time delay for a known crystal separation gives the propagation velocity v (of the order of 100 m s-1) from which the Young's modulus is calculated. Primary results for elastic moduli of frog and toad muscles at 5 degrees C are: 2.6 X 10(6) N m-2 at rest, 3.1 X 10(7) N m-2 in tetanus and 2.1 X 10(7) N m-2 in rigor. Exploratory experiments are also described showing the application of the technique to (i) the development of tetanus, (ii) variation with sarcomere length and (iii) the mechanics of rigor. The pulse technique gives an almost instantaneous measurement of the purely elastic response of a muscle and is thereby of value in basic studies of the mechanism of contraction. It is also a useful non-destructive probe in following the effects of such variables as temperature, fatigue or chemical treatments.     

Ballistocardiogaphic studies with acceleration and electromechanical film sensors

The purpose of this research is to demonstrate and compare the utilization of electromechanical film (EMFi) and two acceleration sensors, ADXL202 and MXA2500U, for ballistocardiographic (BCG) and pulse transit time (PTT) studies. We have constructed a mobile physiological measurement station including amplifiers and a data collection system to record the previously mentioned signals and an electrocardiogram signal. Various versions of the measuring systems used in BCG studies in the past are also presented and evaluated. We have showed the ability of the EMFi sensor to define the elastic properties of the cardiovascular system and to ensure the functionality of the proposed instrumentation in different physiological loading conditions, before and after exercise and sauna bath.The EMFi sensor provided a BCG signal of good quality in the study of the human heart and function of the cardiovascular system with different measurement configurations. EMFi BCG measurements provided accurate and repeatable results for the different components of the heart cycle. In multiple-channel EMFi measurements, the carotid and limb pulse signals acquired were detailed and distinctive, allowing accurate PTT measurements. Changes in blood pressure were clearly observed and easily determined with EMFi sensor strips in pulse wave velocity (PWV) measurements.In conclusion, the configuration of the constructed device provided reliable measurements of the electrocardiogram, BCG, heart sound, and carotid and ankle pulse wave signals. Attached EMFi sensor strips on the neck and limbs yield completely new applications of the EMFi sensors aside from the conventional seat and supine recordings. Higher sensitivity, ease of utilization, and minimum discomfort of the EMFi sensor compared with acceleration sensors strengthen the status of the EMFi sensor for accurate and reliable BCG and PWV measurements, providing novel evaluation of the elastic properties of the cardiovascular system.     

Application of air-borne ultrasound to biomedical measurements

Remote measurement of distance, direction, size, form and volume are common but intricate measurement problems. We have applied the ultrasound pulse echo method, well-known from diagnostic ultrasound, for remote measurement in air. Short ultrasound pulses are emitted in air by electric excitation of an ultrasound transducer. When the ultrasonic wave is incident on a boundary between media of different acoustic impedance, part is reflected back as an echo. The time delay between transmission of the ultrasound pulse and the reception of an echo is a measure of the distance between the transducer and the echo-generating structure. The information obtained can be processed in different ways to produce the three main types of display: A-mode, B-mode and TM-mode. As a consequence most methods from diagnostic ultrasound can be applied also for ultrasound in air. Examples are given of biomedical applications, including a real-time ultrasound scanner for use in air.