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.     

Effect of 12 weeks continuous positive airway pressure on day and night arterial stiffness and blood pressure in patients with type 2 diabetes and obstructive sleep apnea: A randomized controlled trial

The objective of this study was to evaluate the effect of continuous positive airway pressure treatment on pulse wave velocity and blood pressure in patients with type 2 diabetes and obstructive sleep apnea. A randomized controlled study was performed, including 72 patients with type 2 diabetes and newly diagnosed obstructive sleep apnea recruited from outpatient clinics at three Danish hospitals. The patients were randomized to continuous positive airway pressure for 12 weeks or no continuous positive airway pressure. Office measurements were performed at baseline, 4 weeks and 12 weeks. At baseline and 12 weeks, a 24‐hr measurement of pulse wave velocity and blood pressure was performed. No significant change was observed in the primary outcome variable of carotid‐femoral pulse wave velocity measured with SphygmoCor. With the Mobil‐O‐Graph, changes in office pulse wave velocity between the groups were significant: 0.3 m/s; 95% confidence interval, 0.1–0.6; p = .02. The group receiving continuous positive airway pressure had a larger decrease in pulse wave velocity than controls but none of the changes within the groups were significant. No significant change in ambulatory blood pressure was observed in any of the two groups after 12 weeks. In conclusion, continuous positive airway pressure treatment for 12 weeks does not significantly reduce pulse wave velocity or blood pressure in patients with type 2 diabetes and obstructive sleep apnea.     

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。     

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。     

Dynamics of the Intrauterine Fluid–Wall Interface

Intrauterine fluid movements, which are responsible for embryo transport to a successful implantation site at the fundus, may be induced by myometrial contractions. Myometrial contractions in nonpregnant uteri were studied from in vivo measurements of intrauterine pressures with fluid-filled catheters and by visual observations of high-speed replaying of ultrasound images of the uterus. Transvaginal ultrasound (TVUS) images of sagittal cross sections of the nonpregnant uterus were scanned with an intravaginal ultrasound probe. Images at consecutive times (2 s apart) were digitized and processed by employing modern techniques of image processing. The sets of images were compared to evaluate time variation of the fluid–wall interface with respect to amplitude, frequencies, and wavelength of myometrial contractions. Analysis of TVUS images from 11 volunteers during the proliferative phase revealed that myometrial contractions are fairly symmetric and are propagated from the cervix towards the fundus at a frequency of about 0.01-0.09 Hz. The wavelength, amplitude, and velocity of the fluid–wall interface during a typical contractile wave were found to be 10-30 mm, 0.05-0.2 mm, and 0.5-1.9 mm/s, respectively. Additional data acquisition from a large number of normal subjects is needed to build a data base to predict normal characteristics of myometrial contractions in a nonpregnant uterus, in order to better understand their role in the preimplantation process. © 1999 Biomedical Engineering Society. PAC99: 8717Jj, 8719St, 4380Qf, 8763Df     

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。     

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.     

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.     

应用定量组织多普勒成像技术评价家族性高胆固醇血症患者的左室功能

目的探讨定量组织多普勒成像技术(quantitative tissue velocity imaging,QTVI)在评价家族性高胆固醇血症(familial hypercholesterolemia,FH)患者左心室功能方面的临床应用价值。方法运用QTVI对24例FH患者和25例健康人心肌各节段速度曲线进行分析,测量后室间隔、侧壁、前壁、下壁、前室间隔、后壁六个壁的瓣环、基底段和中间段三个位置的心肌收缩峰值速度(Vs),左室舒张早期的运动速度(Ve)和舒张晚期的运动速度(Va),计算Ve/Va值;常规超声心动图脉冲多普勒检测二尖瓣口E、A峰流速,计算E/A值;利用M型超声测量左室射血分数(EF);计算左室Tei指数。结果FH组与对照组常规超声心动图测值均在正常范围内,差别无统计学意义;QTVI方法测得的侧壁瓣环、侧壁基底段的Ve,侧壁瓣环、侧壁基底段、后间隔基底段、后壁基底段的Ve/Va,FH组均小于对照组,差别有统计学意义(P0.05)。结论QTVI为临床检测FH患者左室功能变化提供一种无创性方法。     

Longitudinal and transverse propagation of surface mechanomyographic waves generated by single motor unit activity

Multi-channel surface mechanomyographic (MMG) signals generated by individual motor units were analyzed to investigate whether the surface mechanical waves induced by fiber contraction propagate over the skin surface. The MMG signals were recorded from the tibialis anterior muscle of ten healthy subjects with 13 uniaxial accelerometers, located both along and transverse to the fiber direction. Intramuscular electromyographic signals served to identify individual motor units whose action potentials were used to trigger the averaging of the MMG signals. The spike-triggered averaged MMG had similar characteristics in locations along the longitudinal direction; however, its amplitude decreased along the transverse direction. Moreover, the time-to-positive peak increased along the transverse direction, indicating a transverse wave propagation with a velocity of 2.4 +/- 1.1 m/s in the linear direction. The results support the hypothesis that the MMG signal mainly originates from muscle fiber displacement underlining a bending mode due to contraction and provide the basis for interpreting the interference MMG in relation to motor unit activity.     

Fluid velocity greater than wavespeed and the transition from supercritical to subcritical flow in elastic tubes

The behaviour of the flow regime downstream of the choke point in a flow-limited water filled penrose tube was examined. The transmural pressure along the length of the tube was measured with a moveable side-tap catheter and tube area and stiffness were derived from the tube's static pressure/area curve. Stable supercritical flow, in which the local fluid velocity is greater than the local speed of wave propagation, was demonstrated to extend downstream from the choke point. Speed ratios (fluid velocity divided by tube wavespeed) as large as ten were measured in tube segments in which the area changed so gradually with length as to rule out significant longitudinal tension effects on the tube pressure/area curve. The predicted transition from supercritical to subcritical velocity, or elastic jump, was also studied. Sidewall friction along the jump and longitudinal tension effects due to longitudinal wall curvature were found to be significant factors governing the variation of pressure within the jump. Taking friction into account, the flow momentum equation was found to describe the overall size of the elastic jump adequately if its upstream and downstream limits were taken at points where wall curvature effects were negligible.