Parametric model derivation of transfer function for noninvasiveestimation of aortic pressure by radial tonometry

Aortic pressure can be estimated noninvasively by applying a transfer function (TF) to radial tonometry signals. This study compares the performance of prior approaches, based on Fourier transform and inverted aortic-to-radial model, with direct radial-to-aortic autoregressive exogenous (ARX) model. Simultaneous invasive aortic pressure and radial tonometry pressure were recorded during rest in 39 patients in the supine position. Individual radial-aortic TF's were estimated from 20 patients, and the average TF was used to predict aortic pressures in the remaining 19 patients. The direct average TF yielded accurate aortic systolic pressure estimation (error 0.4 +/- 2.9 mmHg) and good reproduction of the aortic pressure waveform (root mean squared error 2.2 +/- 0.9 mmHg). The inverted reverse TF (aortic radial) yielded comparable results, while the Fourier-based TF had worse performance. Individual direct TF provided improved predictive accuracy only for indexes which are based on higher frequency components of the waveform (augmentation index, systolic time period). An ARX average TF can be used to accurately estimate central aortic pressure waveform parameters from noninvasive radial pulse tracings, and its performance is superior to previous techniques.     

基于示波法的血压测量新方法

血压是反映人体生理状况的最重要指标之一,血压测量的准确性对疾病诊断,临床医疗具有重要的意义。为了提高电子血压计血压测量的准确性,采用基于幅度系数法和波形特征法的综合改进方法．通过将二者结合起来应用,在比较宽松的幅值范围内寻找突变点,从而获得收缩压和舒张压。经过大量的测试,新方法能可靠作为收缩压和舒张压的判据,具有工程实现的可行性和面对不同个体的普遍适用性。     

A novel noninvasive measurement technique for analyzing the pressure pulse waveform of the radial artery

Previous noninvasive measurements of the pulse waveform of the radial artery have not employed standard positioning procedures. Here, we propose a new noninvasive measuring apparatus that has a two-axis mechanism and employs a standard positioning procedure for detecting the optimal site for accurately measuring the pressure pulse waveform (PPW). A modified sensor was designed to simultaneously measure the arterial diameter changed waveform (ADCW) and PPW. Considering the artery as a cylinder, the measured waveform would be distorted if the sensor were not at the middle of arterial width. Moreover, a blood vessel is elastic, and its compliance changes with the transmural pressure, being maximal when the transmural pressure is equal to zero. The sensor should detect the PPW with the lowest possible distortion and, hence, an analysis of the vascular geometry and an arterial model were used to design a standard positioning procedure based on the ADCW for the X and Z axes. In order to verify the resolution of the X axis scanning procedure, the echo method was used to measure the radial artery outer diameter in ten healthy subjects. The difference between the scanning width and the actual arterial diameter was 0.36 +/- 0.23 mm (mean +/- SD). Finally, the PPW as measured at the optimal position was used to diagnose myocardial ischemia symptoms in 60 elderly subjects whose chief complaint was chest pain, with the exercise electrocardiogram being used as a reference to compare between individuals with and without myocardial ischemia. The PPW analysis used the harmonic components in the frequency domain. We found that the fourth harmonic of the Fourier series differed significantly between the groups (p = 0.0039), which is consistent with previous studies. The results indicate that our noninvasive measurement apparatus is very suitable for analyzing the PPW of the radial artery.     

一种基于多参数融合的无袖带式连续血压测量方法的研究

针对现有基于脉搏波传输时间的无创连续性血压测量算法精度不高的问题,该文综合考虑心电信号和血氧容积波与血压变化的相关性,提出一种基于BP神经网络的无创连续性血压测量方法。该文首先利用改进的心电信号算法提取出心电信号的R点,利用差分、阈值的方法提取出血氧容积波的特征参数,再经过特征解析,提取出与血压相关的15维特征向量,构建基于BP神经网络的血压计算模型,计算出逐拍的血压值。该方法在天坛医院等单位进行了医学临床比对测试,并通过因子分析法分析了15个特征参数的权重比。实验证明:在预测血压上,脉搏波传输时间的权重,大于相邻特征点之间的时间信息权重,大于脉搏波面积信息权重,大于脉搏波幅值信息权重;该方法精度优于其它相近方法,单次测量的舒张压和收缩压误差的平均值标准差分别是-1.576.12 mmHg和-0.624.82 mmHg,重复测量误差的平均值标准差分别是-2.125.10 mmHg和-2.524.41 mmHg。收缩压和舒张压的测量精度均达到了BHS血压标准的Grade A类和AAMI标准。     

Effects of external pressure on arteries distal to the cuff during sphygmomanometry

The aim of this study was to examine the effect on distal arteries of external pressure, applied by upper arm sphygmomanometer cuff. Photoplethysmographic (PPG) signals were measured on the index fingers of 44 healthy male subjects, during the slow decrease of cuff air pressure. For each pulse the ratio of PPG amplitude to its baseline (AM/BL) and its time delay (deltaTD) relative to the contralateral hand were determined as a function of cuff pressure. At cuff pressures equal to systolic blood pressure, pulses reappeared with the pulse time delay in the cuffed arm significantly greater than in the noncuffed arm, with (deltaTD) (mean +/- SD) 150 +/- 31 ms (p < 0.001). At cuff pressures equal to diastolic blood pressure (81 +/- 12 mmHg), deltaTD was 42 +/- 19 ms (p < 0.001), and at 50 mmHg, which is below diastolic blood pressure, (deltaTD) was still significantly positive at 6 +/- 9 ms (p < 0.001). AM/BL relative to its initial value rose at cuff pressures between systolic and diastolic blood pressure, then deceased to 0.6 +/- 0.41 (p < 0.001) at diastolic blood pressure and 0.54 +/- 0.24 (p < 0.001) at 50 mmHg. The changes in (deltaTD) and AM/BL can be interpreted as originating from changes in the compliance of conduit arteries and small arteries with cuff inflation and deflation.     

Performance evaluation of the PC-2048: a new 15-slice encoded-crystal PET scanner for neurological studies

Initial experience is reported with the Scanditronix PC 2048-15B, a 15-slice positron emission tomography (PET) system using multicrystal/multiphoto-multiplier modules to obtain high spatial resolution. Random and scattered events are reduced using an orbiting (68)Ge rod source for transmission scans by only accepting coincidence lines which intersect the instantaneous position of the source. Scatter correction of the emission data is removed with a deconvolution kernel, random and dead-time correction by the use of observed singles rates. The peak count rates are 11.7/20.0 Kcps for the direct cross slices at concentrations of 4.5/5.1 muCi/cc. respectively. Over the radial range 0-9 cm from the ring center, radial transverse resolution is 4.6-6.4 mm, aid tangential transverse resolution is 4.6-5.1 mm using a Hanning filter. Over the same range, axial resolution varies from 6.1-6.2 mm in direct slices and from 5.4-7.1 mm in cross slices. This near-isotropic resolution allows collection of image volume data with no preferred direction for signal averaging errors.     

Systematic autoregulation counteracts the carotid baroreflex

The interaction between autoregulation and baroregulation and its effect on the gains of the short-term pressure regulatory system was studied by performing both open- and closed-loop experiments in the same five anesthetized, vagotomized dogs, and by analyzing the data making use of a new model. With carotid pressure constant (no baroregulation) the pressure-flow data were convex to the flow axis, thus indicating the presence of autoregulation. When baroregulation was present the data were convex to the pressure axis. Our model was able to fit the data as measured in both cases. From the fitting procedure the zero-flow pressure intercept Pzf, the autoregulation resistance gain Gra, and the baroregulation resistance gain Grb were estimated. Pzf was about 20 mmHg in three dogs and about zero in the other two. Average values of Gra and Grb were 13.0 +/- 3.5 mmHg min2/L2 and 0.83 +/- 0.25 min/L, respectively. The two curves which fitted the data points collected in the presence and in the absence of baroreflex intersected at a point (Qo, Po) generally different from the control point. We determined the open-loop gain, Goc = GrbQo, about the point (Qo, Po). The averaged value was 2.23 +/- 0.84. When autoregulation was neglected, the resistance gain Grb and the open-loop gain Goc obtained from the same closed-loop method were underestimated (0.32 +/- 0.15 min/L and 0.88 +/- 0.48, respectively). In the open-loop preparation the carotid sinuses were isolated and the aortic (P) versus carotid (Pca) pressure data were collected. A third-order polynomial was fitted to these data.(ABSTRACT TRUNCATED AT 250 WORDS)     

A mathematical study of some biomechanical factors affecting theoscillometric blood pressure measurement

A mathematical lumped parameter model of the oscillometric technique for indirect blood pressure measurement is presented. The model includes cuff compliance, pressure transmission from the cuff to the brachial artery through the soft tissue of the arm, and the biomechanics of the brachial artery both at positive and negative transmural pressure values. The main aspects of oscillometry are simulated i.e., the increase in cuff pressure pulsatility during cuff deflation manoeuvres, the existence of a point of maximum pulsations (about 1.5 mmHg) at a cuff pressure close to mean arterial pressure, and the characteristic ratios for cuff pressure pulsatility at systole and diastole (0.52 and 0.70, respectively, with this model, using basal parameters and an individual set of data for the arterial pressure waveform). Subsequently, the model is used to examine how alterations in some biomechanical factors may prejudice the accuracy of pressure measurement. Numerical simulations indicate that alterations in wall viscoelastic properties and in arterial pressure pulse amplitude may significantly affect the accuracy of pressure estimates, leading to errors as great as 15-20% in the computation of diastolic and systolic arterial pressure. By contrast, changes in arterial pressure mean value and cuff compliance do not seem to have significant influence on the measurement. Evaluation of mean arterial pressure through a characteristic ratio is not robust and may lead to misleading results. Mean arterial pressure may be better evaluated as the lowest pressure at which cuff pulse amplitude reaches a plateau. The obtained results may help to explain the nature of errors which usually limit the reliability of arterial pressure measurement (for instance in the elderly)     

基于脉搏波速法的动态血压测量系统设计

提出一种利用脉搏波传导速度法的血压测量方案。采用新型可穿戴式光电传感器分别采集人体左侧桡动脉和指端的脉搏波,摆脱传统袖带式的测量方式。通过分析脉搏波的波形,计算脉搏波传导速度,建立数学模型方程,对非侵入式的动态血压测量进行研究,并采用听诊法进行校准和误差分析,实现连续血压测量。实验结果表明,该系统测量方便,精度较高,与听诊法具有良好的一致性。     

Nonlinear transient chirp signal modeling of the aortic and pulmonary components of the second heart sound

This paper describes a new approach based on the time-frequency representation of transient nonlinear chirp signals for modeling the aortic (A2) and the pulmonary (P2) components of the second heart sound (S2). It is demonstrated that each component is a narrow-band signal with decreasing instantaneous frequency defined by its instantaneous amplitude and its instantaneous phase. Each component is also a polynomial phase signal, the instantaneous phase of which can be accurately represented by a polynomial having an order of thirty. A dechirping approach is used to obtain the instantaneous amplitude of each component while reducing the effect of the background noise. The analysis-synthesis procedure is applied to 32 isolated A2 and 32 isolated P2 components recorded in four pigs with pulmonary hypertension. The mean +/- standard deviation of the normalized root-mean-squared error (NRMSE) and the correlation coefficient (rho) between the original and the synthesized signal components were: NRMSE = 2.1 +/- 0.3% and rho = 0.97 +/- 0.02 for A2 and NRMSE = 2.52 +/- 0.5% and rho = 0.96 +/- 0.02 for P2. These results confirm that each component can be modeled as mono-component nonlinear chirp signals of short duration with energy distributions concentrated along its decreasing instantaneous frequency.     

Flexible Piezoresistive Sensor Patch Enabling Ultralow Power Cuffless Blood Pressure Measurement

Noninvasive and real‐time cuffless blood pressure (BP) measurement realizes the idea of unobtrusive and continuous BP monitoring which is essential for diagnosis and prevention of cardiovascular diseases associated with hypertension. In this paper, a wearable sensor patch system that integrates flexible piezoresistive sensor (FPS) and epidermal electrocardiogram (ECG) sensors for cuffless BP measurement is presented. By developing parametric models on the FPS sensing mechanism and optimizing operational conditions, a highly stable epidermal pulse monitoring method is established and beat‐to‐beat BP measurement from the ECG and epidermal pulse signals is demonstrated. In particular, this study highlights the compromise between sensor sensitivity and signal stability. As compared with the current optical‐based cuffless BP measurement devices, the sensing patch requires much lower power consumption (3 nW) and is capable of detecting subtle physiological signal variations, e.g., pre and postexercises, thus providing a promising solution for low‐power, real‐time, and home‐based BP monitoring.     

基于注入锁定技术的非接触式免校准脉搏检测传感器

为了实现手腕脉搏检测系统的免校准脉冲检测,提出了一种基于注入锁定原理的邻近耦合射频传感器。该传感器由两个主要部分组成,包括谐波振荡器和具有压控振荡器的锁相回路（PLL）合成器。谐波振荡器由具有两个端口的微带谐振器（叉指电极机构）制成的,该微带谐振器可将桡动脉的膨胀或收缩转换为阻抗变化。然后,PLL合成器通过锁相振荡器将频率变化转换为直流电压内的变化。测量结果表明,由于桡动脉的变化,谐振器的阻抗变化会导致谐波振荡器产生高达0.68 MHz的频率变化。在脉搏的一个周期内,测得的电压峰间值为10-15mV。证明了提出传感器可用于有效的非接触式手腕脉搏检测系统。     

Ambulatory assessment of ankle and foot dynamics

Ground reaction force (GRF) measurement is important in the analysis of human body movements. The main drawback of the existing measurement systems is the restriction to a laboratory environment. This paper proposes an ambulatory system for assessing the dynamics of ankle and foot, which integrates the measurement of the GRF with the measurement of human body movement. The GRF and the center of pressure (CoP) are measured using two six-degrees-of-freedom force sensors mounted beneath the shoe. The movement of foot and lower leg is measured using three miniature inertial sensors, two rigidly attached to the shoe and one on the lower leg. The proposed system is validated using a force plate and an optical position measurement system as a reference. The results show good correspondence between both measurement systems, except for the ankle power estimation. The root mean square (RMS) difference of the magnitude of the GRF over 10 evaluated trials was (0.012 +/- 0.001) N/N (mean +/- standard deviation), being (1.1 +/- 0.1)% of the maximal GRF magnitude. It should be noted that the forces, moments, and powers are normalized with respect to body weight. The CoP estimation using both methods shows good correspondence, as indicated by the RMS difference of (5.1 +/- 0.7) mm, corresponding to (1.7 +/- 0.3)% of the length of the shoe. The RMS difference between the magnitudes of the heel position estimates was calculated as (18 +/- 6) mm, being (1.4 +/- 0.5)% of the maximal magnitude. The ankle moment RMS difference was (0.004 +/- 0.001) Nm/N, being (2.3 +/- 0.5)% of the maximal magnitude. Finally, the RMS difference of the estimated power at the ankle was (0.02 +/- 0.005) W/N, being (14 +/- 5)% of the maximal power. This power difference is caused by an inaccurate estimation of the angular velocities using the optical reference measurement system, which is due to considering the foot as a single segment. The ambulatory system considers separate heel and forefoot segments, thus allowing an additional foot moment and power to be estimated. Based on the results of this research, it is concluded that the combination of the instrumented shoe and inertial sensing is a promising tool for the assessment of the dynamics of foot and ankle in an ambulatory setting.     

An Injection-Locked Frequency-Tracking Σ∆ Direct Digital Frequency Synthesizer

A bandpass (BP) sigma-delta modulator (SigmaDeltaM)-based direct digital frequency synthesizer (DDS) architecture is presented. The DDS output is passed through a single-bit, second-order BPSigmaDeltaM, shaping quantization noise out of the signal band. The single-bit BPSigmaDeltaM is then injection locked to an LC-tank oscillator, which provides a tracking BP filter response within its locking range, suppressing the BPSigmaDeltaM out of band quantization noise. The instantaneous digital frequency control word input of the DDS is used to tune the noise shaper center frequency, achieving up to 20% tuning range around the fundamental. The BPSigmaDeltaM-based synthesizer is fabricated in a 0.25-mum digital CMOS process with four layers of metal. With a second-order BP noise shaper and a 44-MHz LC tank oscillator, an SFDR of 73 dB at a 2-MHz bandwidth and phase noise lower than -105 dBc/Hz at a 10-kHz offset is achieved     

A closed-loop mechanical ventilation controller with explicit objective functions

A closed-loop lung ventilation controller was designed, aiming to: 1) track a desired end-tidal CO2 pressure (Pet CO2), 2) find the positive end-expiratory pressure (PEEP) of minimum estimated respiratory system elastance (Ers,e), and 3) follow objective functions conjectured to reduce lung injury. After numerical simulations, tests were performed in six paralyzed piglets. Respiratory mechanics parameters were estimated by the recursive least squares (RLS) method. The controller incorporated a modified PI controller for Pet CO2 and a gradient descent method for PEEP. In each animal, three automated PEEP control runs were performed, as well as a manual PEEP titration of Ers,e and a multiple PetCO2 step change trial. Overall performance indexes were obtained from PEEP control, such as minimum Ers,e (37.0 +/- 4.5 cmH2O x L(-1)), time to reach the minimum Ers,e (235 +/- 182 s) and associated PEEP (6.5 +/- 1.0 cmH2O), and from Pet CO2 control, such as rise time (53 +/- 22 s), absolute overshoot/undershoot of PetCO2 (3 +/- 1 mmHg), and settling time (145 +/- 72 s). The resulting CO2 controller dynamics approximate physiological responses, and results from PEEP control were similar to those obtained by manual titration. Multiple dependencies linking the involved variables are discussed. The present controller can help to implement and evaluate objective functions that meet clinical goals.     

Flexible Weaving Constructed Self‐Powered Pressure Sensor Enabling Continuous Diagnosis of Cardiovascular Disease and Measurement of Cuffless Blood Pressure

Pulse wave carries comprehensive information regarding the human cardiovascular system (CS), which is essential for directly capturing CS parameters. More importantly, cuffless blood pressure (BP) is one of the most critical markers in CS. Accurately measuring BP via the pulse wave for continuous and noninvasive diagnosis of a disease associated with hypertension remains a challenge and highly desirable. Here, a flexible weaving constructed self‐powered pressure sensor (WCSPS) is reported for measurement of the pulse wave and BP in a noninvasive manner. The WCSPS holds an ultrasensitivity of 45.7 mV Pa^?1 with an ultrafast response time of less than 5 ms, and no performance degradation is observed after up to 40 000 motion cycles. Furthermore, a low power consumption sensor system is developed for precisely monitoring pulse wave from the fingertip, wrist, ear, and ankles. A practical measurement is performed with 100 people with ages spanning from 24 to 82 years and different health statuses. The discrepancy between the measured BP results using the WCSPS and that provided by the commercial cuff‐based device is about 0.87–3.65%. This work demonstrates an efficient and cost‐effective way for human health monitoring, which would be a competitive alternative to current complex cardiovascular monitoring systems.     

PBF在1550nm传输波段受径向压力的影响研究

为了研究光子带隙光纤在1550nm波长下受径向压力的影响,采用有限元法做仿真计算进行了定量研究,并通过搭建实验系统对比分析了实测与仿真计算结果的差异。结果表明,限制损耗随径向压力变化的灵敏度为0.00067（dB/km）/（N/m）,归一化分界面场强F参量随径向压力的变化率为0.6810-6/（N/m）,折射率随径向压力的变化率为1.010-8/（N/m）。该研究为光子带隙光纤在光纤传感领域的应用提供了一种实验分析途径。     

Electrocardiogram-assisted blood pressure estimation

Accurate automatic noninvasive assessment of blood pressure (BP) presents a challenge due to conditions like arrhythmias, obesity, and postural changes that tend to obfuscate arterial amplitude pulsations sensed by the cuff. Researchers tried to overcome this challenge by analyzing oscillometric pulses with the aid of a higher fidelity signal-the electrocardiogram (ECG). Moreover, pulse transit time (PTT) was employed to provide an additional method for BP estimation. However, these methods were not fully developed, suitably integrated, or tested. To address these issues, we present a novel method whereby ECG-assisted oscillometric and PTT (measured between ECG R-peaks and maximum slope of arterial pulse peaks) analyses are seamlessly integrated into the oscillometric BP measurement paradigm. The method bolsters oscillometric analysis (amplitude modulation) with more reliable ECG R-peaks provides a complementary measure with PTT analysis (temporal modulation) and fuses this information for robust BP estimation. We have integrated this technology into a prototype that comprises a BP cuff with an embedded conductive fabric ECG electrode, associated hardware, and algorithms. A pilot study has been undertaken on ten healthy subjects (150 recordings) to validate the performance of our prototype against United States Food and Drug Administration approved Omron oscillometric monitor (HEM-790IT). Our prototype achieves mean absolute difference of less than 5 mmHg and grade A as per the British Hypertension Society protocol for estimating BP, with the reference Omron monitor.     

Analysis and Simulation of an Adaptive System for Forced Ventilation of the Lungs

A design technique, based on the model reference adaptive control approach for the long term ventilation of the lungs is presented. The design objective is to minimize the harmful effects (e.g., interference in the circulatory system, mechanical damage, etc.) due to possible change in the patient's respiratory parameters (i.e., the airway resistance and the lung and chest wall compliance) during the long term ventilation of the lungs. A model, consisting of a fixed resistance capacitance, RC, analog network is used to generate a ``desire' alveolar pressure profile. The instantaneous difference in the alveolar pressures, obtained from the comparison of the actual patient and his ``desired' behavior, is fed to an ``adaptive controller.' The controller, in turn, will adjust the respirator's output pressure (to the patient) in such a way, that the instantaneous difference in alveolar pressure is reduced to zero. The stability of this newly designed adaptive system is ensured by using Lyapunov's direct method in obtaining the updating laws for the adaptive controller. Using a similar design approach, a respiratory parameters identification scheme is introduced. This identification process is able to generate, indirectly, a continuous estimation of the patient's alveolar pressure (which normally is not monitorable in the actual patient) for the purpose of comparison, in this newly designed adaptive system. Digital simulations of the respirator's pressure control and the identification process, as well as the simulation of the combined system, were performed. The result has indeed demonstrated the ability of a speedy performance of this adaptive system.     

全光型激光微片高灵敏度压强传感器

提出并实现了一种新型全光型压强传感器。用LD输出光经光纤抽运圆片状Nd∶YAG微片 ,被测压强通过传递膜片加到晶体径向上。由于应力双折射效应 ,此微片激光器输出光的频率发生分裂。输出的频率分裂激光经光纤传输至光电接收器 ,其拍频经光电转化成正弦频率电信号 ,探测该频差即可得到被测压强。对此激光器的出光模式对测量的影响进行了研究。实验获得了 1.31MHz/kPa的测量灵敏度。证明此压强传感器适于高灵敏度测量 ,有广泛的应用前景