Noninvasive automatic monitoring of instantaneous arterial blood pressure using the vascular unloading technique

For the noninvasive monitoring of the beat-to-beat systolic and diastolic pressure and pressure waveform in the human finger, a new automated instrument was designed. This measurement is based on a principle called the vascular unloading technique. Using a hydraulic servocontrol system, the vascular volume change caused by intra-arterial pressure change can be compensated by applying counter pressure to maintain a constant vascular volume in the unloaded state. In this state the controlled counterpressure instantaneously follows the intra-arterial pressure. In this instrument all the necessary procedures, such as the setting of the reference value for the servocontrol, control of the servogain, processing and displaying of the data on a recorder, were carried out automatically. The simultaneous comparison of data with direct measurements and a few examples of the indirect pressure recordings by this instrument are shown and the principles, operation and evaluation of this method are described. This instrument was shown to permit the nonivasive and accurate tracking of instantaneous arterial pressure and to perform acceptably over a wide range of arterial pressure.     

Continuous Non-Invasive Arterial Pressure Technique Improves Patient Monitoring during Interventional Endoscopy

Introduction: Close monitoring of arterial blood pressure (BP) is a central part of cardiovascular surveillance of patients at risk for hypotension. Therefore, patients undergoing diagnostic and therapeutic procedures with the use of sedating agents are monitored by discontinuous non-invasive BP measurement (NIBP). Continuous non-invasive BP monitoring based on vascular unloading technique (CNAP®, CN Systems, Graz) may improve patient safety in those settings. We investigated if this new technique improved monitoring of patients undergoing interventional endoscopy.     

Long-term ambulatory monitoring of indirect arterial blood pressure using a volume-oscillometric method

A new portable instrument equipped with a microprocessor was designed for the long-term ambulatory monitoring of indirect arterial pressure in the human finger at desired intervals using a volume-oscillometric technique. All the necessary procedures such as (1) programmed control of cuff pressure, (2) detection of the systolic end-point and the point of maximum amplitude of arterial volume pulsations, (3) reading of the cuff pressures corresponding to these two points, (4) its processing and (5) recording of the systolic and mean pressure together with heart rate on a digital memory integrated circuit were performed automatically. After the monitoring, the data were reproduced and analysed by a conventional personal computer. Simultaneous comparison of the data with direct measurement, operation and evaluation of this instrument, and ambulatory monitoring were carried out. With this instrument noninvasive and accurate monitoring of arterial pressure could be made in unrestricted subjects during daily activities.     

利用脉搏波特征参数连续测量血压的方法研究

通过研究血压与脉搏波特征参数的关系，提出了一个选择多个与血压相关的脉搏波特征参数,通过回归分析建立适合不同人的特征方程，进行血压的连续测量的新方法，为了验证测量结果的准确性；研制了张力计。实验结果表明：该方法具有较高的测量精度，可以应用于临床危重病人的血压监护和一般医学研究中，经过进一步地改进和完善后可应用于载人航天和日常动态环境。     

A correlation analysis between pulse transit time and instantaneous blood pressure measured indirectly by the vascular unloading method

Linear correlation coefficients (r) between pulse transit time (PTT) and blood pressure (BP) were evaluated on within-subject by within-condition level. Beat-to-beat systolic and diastolic BP was measured noninvasively using the vascular unloading technique (Yamakoshi, Shimazu and Togawa, 1980). PTT was determined from the time interval between the R-wave of ECG and the peak of the finger pulse wave. Five male subjects underwent a 2 min resting (RE), a 1 min cold pressor test (CP), eight 15 sec anagram tests (AN), and another 1 min CP. Significant r values were most frequently obtained for systolic BP and PTT in the RE condition. Under the CP or AN conditions, no consistent tendencies were observed. It was suggested that none of the r values are sufficiently high to warrant the use of PTT as an alternative index of BP. Some factors lowering the r values were discussed.     

Ambulatory instrument for monitoring indirect beat-to-beat blood pressure in superficial temporal artery using volume-compensation method

A portable instrument, based on a volume-compensation technique, is designed for ambulatory monitoring of indirect beat-to-beat blood pressure (BP) in the superficial temporal artery. The instrument consists of a small disc-type cuff and a portable unit carried by the subject. Several components are integrated in the cuff for applying counter-pressure to the artery, i.e. a reflectance-type photo-plethysmographic sensor for arterial volume detection, a pressure sensor for cuff pressure P_c measurement and a nozzle flapper-type electro-pneumatic convertor for controlling P_c. The portable unit includes volume servo control circuitry and a microprocessor-based signal-processing and recording unit. This automatically performs all the necessary measurement procedures and stores into a memory IC element the processed systolic, mean and diastolic blood pressure data, together with pulse intervals on a beat-to-beat basis from the servo-controlled P_c (indirectly measured BP waveform). With this instrument, momentary changes in BP during ambulatory situations such as bicycle ergometer exercise and daily activities including motorway driving are successfully recorded. From the results of simultaneous measurement of the subject's posture changes, the effect of posture change on blood pressure, e.g. baroreceptor-cardiac reflex, is also clearly demonstrated.     

Electrical admittance cuff for non-invasive and simultaneous measurement of haematocrit, arterial pressure and elasticity using volume-oscillometric method

An improved technique based on the electrical admittance cuff was designed for the non-invasive measurement of haematocrit (Hct), together with blood pressure (BP) and arterial elasticity represented as volume elastic modulus (E_v), in human fingers. This device is made of a rigid annular chamber installed with a surrounding thin-walled tube (cuff), which is filled with electrolyte solution. A tetrapolar method is used to detect the admittance signals, both in the solution and in a finger segment placed through the cuff. With this device, it is theoretically shown that the resistivity of blood flowing into the segment is equal to that of the solution multiplied by the ratio of the admittance variation in the solution to that in the segment. Thus, the blood resistivity and therefore Hct can be non-invasively determined from the electrolyte resistivity and these two admittance variations. On the other hand, BP and E_v are also simultaneously measured from the admittance signals following the gradual change of the chamber pressure based on the volume-oscillometric method. Experiments were successfully made in 14 subjects, showing that the indirect Hct values agreed well with the direct values obtained from sampled blood and that this simle technique was significant for the non-invasive ad simultaneous measurement of these physiological variables.     

Noninvasive measurement of beat-to-beat vascular viscoelastic properties in human fingers and forearms

Static and dynamic (beat-to-beat) arterial viscoelastic properties were measured noninvasively in human fingers and forearms. The volume change and pressure change were detected simultaneously by admittance plethysmography and by sphygmomanometry using the vascular unloading technique in the index and middle finger, or vice versa. These simultaneous measurements were also made on the forearms of one side and the fingers of the other side. The arterial viscoelastic properties in these segments could be successfully determined at different transmural pressure levels from 0 mm Hg to around the mean arterial pressure.     

基于脉搏波的新型血压与血管硬度测量仪的研制

目的：根据脉搏波理论研制出一种新型血压与血管硬度测量仪。方法：利用示波法原理在波形特征法和幅度系数法的基础上提出一种系数差分比值法来间接测量血压的新方法，通过采集肱动脉和桡动脉两处波形，获得了脉搏波传播速度（PWv）、动脉顺应性（C1、C2）和动脉硬化指数（ASI）三个反映受试者动脉弹性的参数指标。结果：通过大量病例分析和临床测试证实了算法的有效性和可靠性，而且此算法已经应用LabVIEW开发成软件并在医院进行临床应用。结论：血压与血管硬度检测仪能判断心血管病患者与正常人的差异性，对我国心血管病方面流行病学的调查、疾病预防、疾病早期发现都具有很大的意义。     

Vascular Unloading Method for Noninvasive Measurement of Instantaneous Arterial Pressure: Applicability in Psychophysiological Research

A new method proposed previously by us (1980) was described to evaluate its applicability in psychophysiological research. In this method, beat-to-beat systolic and diastolic pressure as well as the pressure waveform can be measured noninvasively in the human finger. By use of a hydraulicservosystem, the photoplethysmographically detected vascular volume changes associated with intraarterial pressure in the finger are compensated by an applied counterpressure (cuff pressure) to maintain a proper value corresponding to the unloaded vascular volume. At this state the controlled cuff pressure follows instantaneously the intraarterial pressure. Comparison data were obtained by direct measurement of blood pressure in the brachial artery in 3 normotensive and 3 hypertensive subjects. High correlations between the two measures were obtained in each subject under various conditions. By maintaining circulation in the finger, this method enables the noninvasive and continuous measurement of instantaneous arterial pressure for more than one hour without much discomfort. This indirect method should be useful in many areas of psychophysiological research.     

Baroreceptors and the long-term control of blood pressure

The current consensus is that arterial baroreceptors are vitally important in the short term (seconds to minutes) control of mean arterial pressure (MAP) but are unimportant in determining the long-term level of MAP. The latter statement is based primarily on two observations: first, that baroreceptors rapidly reset to the prevailing level of MAP and second, that total baroreceptor denervation has no lasting effect on the average daily MAP, although the variability of MAP is increased dramatically. However, recent studies in intact experimental animals have produced results that suggest baroreceptor resetting may not be as rapid or complete as previously thought. Furthermore, reconsideration of the responses to baroreceptor denervation suggest that the condition may accurately represent responses to short-term baroreceptor unloading but not long-term unloading. Results obtained using a new model of chronic baroreceptor unloading indicate that the condition results in a sustained increase in MAP. These results strongly suggest that the role of baroreceptors in the long term control of MAP needs to be revisited.     

示波法血压测量技术仿真研究

示波法血压测量技术是目前在血压自动测量仪器中被广泛采用的一种测量方法，这一方法的判据是通过大量的人群实验由统计学方法给出，因此这种测量方法必将造成个体测量之间的误差，有时误差是较大的，但是目前这一方法仍被广泛用于临床血压的监测。本文利用可塌陷管理论，根据示波法血压的测量过程和测量原理，建立了示波法动脉血压测量过程的物理模型，根据这种模型，在引用前人获取的模型参数的基础上对示波法血压测量技术进行了仿真。从仿真结果可以看出，示波法可以被用来监测同一人体血压随时间的变化，但在对不同个体进行测量时会导致测量误差。     

基于PPG收缩期上升波形特征参数的无创血压检测模型

旨在提出一种基于光电容积脉搏波（PPG）收缩期上升波形（SUW）特征提取的血压计算模型。首先，采集130例成年志愿者的II导心电图、手指PPG信号以及袖带血压值。数据被随机分为训练集（共80例，其中46例血压正常）和测试集（共50例，其中35例血压正常）。然后从PPG信号的SUW中提取时间、面积、斜率最大点与波谷点连线与时间轴夹角的正切值、上升期占脉宽的比例等特征，采用偏最小二乘回归法分别建立收缩压和舒张压的检测模型。最后与基于脉冲到达时间（PAT）的模型以及PAT联合PPG的模型进行对比。结果显示，本模型计算的收缩压和舒张压与参考值的相关系数分别为0.80和0.62，判断血压异常的准确率为90%。这些指标均显著高于基于PAT和PAT联合PPG参数的血压模型（P<0.05）。研究表明，基于PPG收缩上升波形特征参数的无创血压检测模型具有较好的鲁棒性和较强的异常血压检测能力。     

Noninvasive measurement of arterial blood pressure and elastic properties using photoelectric plethysmography technique

The objective of this paper is to review our developed method for measuring noninvasively the arterial blood pressure as well as the mechanical properties of the vascular system in a thin portion of the biological segment such as human fingers or small animal extremities like rat tails and rabbit forelegs. This measurement is based on a principle called the 'volume-oscillometric method'. During the gradual change in cuff pressure, the amplitude of consecutive arterial volume pulsations associated with pulse pressure shows change characteristically due to the nonlinearity of arterial pressure-volume(P-V) relation. Arterial pressure can be accurately determined by detecting this characteristic change in the amplitude, while the arterial elastic properties such as P-V relationship and volume elastic modulus can be noninvasively obtained as a function of arterial transmural pressure, provided that the arterial volume changes are quantitatively determined during this pressure measurement. The validity and accuracy of this pressure and elasticity measurement with photoelectric plethysmography technique for detecting arterial volume changes are clearly demonstrated on the in vitro and in vivo experiments. Considering the simplicity and practicability of this measurement using the photoelectric plethysmography, we present a new portable instrument for the long-term ambulatory monitoring of indirect arterial pressure and a handy fully-automatic instrument for the noninvasive measurement of arterial elastic properties, and a few examples obtained by each instrument are also described.     

Assessment of Baroreceptor Reflex Function During Mental Stress and Relaxation

This paper describes a method of measuring baroreceptor cardiac reflex sensitivity noninvasively from spontaneous patterns of blood pressure and interbeat interval, and the application of this technique in psychophysiology. Baroreflex function was assessed in 24 female volunteers during relaxation and performance of the cold pressor test and a non-verbal mental arithmetic task. Blood pressure and interbeat interval were monitored continuously from the finger using the vascular unloading technique. Sequences of three or more cardiac cycles were identified over which systolic blood pressure increased progressively in conjunction with lengthening interbeat interval, or systolic blood pressure decreased as interbeat interval was reduced. The regression between systolic blood pressure and interbeat interval was computed as an index of baroreflex sensitivity. Relaxation was associated with a small prolongation of interbeat interval, whereas baroreflex sensitivity increased from 17.1 to 19.8 ms/mmHg. Baroreflex sensitivity was reduced significantly during mental arithmetic (mean 14.2 ms/mmHg) but not during the cold pressor test (mean 17.4 ms/mmHg). The difference between mental arithmetic and the cold pressor test may be related to the relative intensity of cardiac and vascular responses in the two situations. The implications of these results for the understanding of behavioural influences on haemodynamic function are discussed and the advantages of noninvasive methods are considered.     

抢救危重病人的心血管循环反馈治疗仪及动物实验

目的：国内外医疗仪器的发展正朝着自动化、智能化、模块化方向发展，但主要集中于诊断方面，用于治疗仪器极少，本仪器目的是为危重病人的抢救。材料与方法：本仪器是综合临床成功经验设计研制，程序结合实验中数学模型汇编，通过在线闭环自动检测，直接、快速、连续、高密度地采集血压，肺毛细血管契压（PCW）、心率等重要生理参数，经压力传感器、A／D转换卡实时连续地输入计算机，通过用户界面人机对话，由医生选择药物，经数学模型及程序的运算，D／A转换器输出指令经输液器控制给药量，药物在机体反应及时、迅速地反馈回计算机，计算机不断更新计算结果，以此调节给药速率及剂最。此外该系统还有监控、报警、故障自诊断、智能化运行等特点。结果：通过八只犬的实验表明。计算机取样及时、准确、快速。给药结果证明能按照预期设计要求达到治疗目的。结论：传统的临床治疗方法从收集病人数据到决定准确的给药节反馈过程太长，还有不少人为及计算的干扰和误差，因此抢救成功率极低。该系统从获取血压变化到多次反馈调整给药整个周期短、计算准确，疗效可靠。是一个很有发展前景的抢救危重病人的仪器，目前该仪器仍待进入临床评价。     

Anticipatory adjustments of multi-finger synergies in preparation for self-triggered perturbations

We studied changes in multi-finger synergies associated with predictable and unpredictable force perturbations applied to a finger during a multi-finger constant total force production task. The main hypothesis was that indices of multi-finger synergies can show anticipatory changes in preparation for a predictable perturbation. Subjects sat in a chair and pressed on force sensors with the four fingers of the right hand. The task was to produce a constant level of total force. The fingers acted against loads that produced upward directed forces. The loads (applied either to the index or to the ring finger) could be disengaged either by the subject or by the experimenter. An index of finger co-variation, ΔV was computed across sets of 12 trials at each time sample and for all tasks separately. During steady-state force production, all subjects showed positive ΔV values corresponding to strong negative covariation among finger forces interpreted as a force-stabilizing synergy. Prior to self-triggered unloading, subjects showed an anticipatory drop in ΔV that started 100–125 ms prior to the unloading time. Such early changes were absent in trials with experimenter-triggered unloading. After an unloading, subjects changed forces of both perturbed and unperturbed fingers and reached a new sharing pattern of the total force. In experimenter-triggered conditions, changes in the forces of unperturbed fingers could be seen as early as 120 ms following an unloading. The index ΔV dropped following a perturbation and then recovered; the recovery occurred faster in self-triggered conditions. We conclude that humans can use feed-forward changes in multi-finger synergies (anticipatory synergy adjustments) in anticipation of a predictable perturbation. These changes may help avoid prolonged weakening of a multi-digit force-stabilizing synergy. We discuss a possibility that anticipatory postural adjustments may represent a particular case of the phenomenon of anticipatory synergy adjustments and suggest a hierarchical control scheme that incorporates a possibility of independent control over the output of a multi-element system and covariation patterns among outputs of its elements.     

Effect of room temperature on percentage finger systolic blood pressure response to finger cooling

Percentage finger systolic blood pressure (%FSBP) in response to finger cooling is used to assess vascular components of the hand-arm vibration syndrome and the measurement method is under discussion for standardization. It has been suggested that measurement circumstances including room temperature may affect %FSBP. We investigated the effect of room temperature on %FSBP response to finger cooling in healthy subjects. Six healthy male subjects who were medical students volunteered for the study. Multi-channel plethysmograph was used for simultaneous multi-finger FSBP measurements. The examination room was kept at 21±1°C and 25±1°C, and the subjects were randomly assigned. Percentage finger systolic blood pressures for the index, middle, ring and little fingers at 15°C and 10°C cuff-water temperatures were calculated. Four-way analysis of variance was performed to determine the independent effect of subject, room temperature, finger and cuff-water temperature factors on %FSBP. The room temperature as an independent factor affecting %FSBP was statistically significant (P<0.01). From the results, it can be concluded that %FSBP response to finger cooling in healthy subjects may be affected by room temperature. Therefore, room temperature is expected to be controlled when assessing peripheral vascular components of the upper extremities using %FSBP response to finger cooling.     

Clinical applications of pulse transit time in paediatric critical care

A simple and non-invasive technique, termed pulse transit time (PTT), has shown its potential in long-term investigations such as respiratory sleep studies and cardiovascular studies. Based on these findings, the PTT technique shows relevance for continuous haemodynamic monitoring in critical care. The objective of this review is to understand the potential, applications and limitations of PTT in this clinical setting. Present non-invasive haemodynamic monitoring methods such as automated oscillometric blood pressure (BP) and auscultatory techniques have their known limitations. They tend to underestimate systolic BP while overestimating diastolic BP. Due to the periodic increase in cuff pressure cycles during data acquisition, these techniques may cause much discomfort in elderly geriatric patients, or lessen the cooperation of younger paediatric patients. Thus, there can be adverse effects on therapeutic decisions and possibly clinical outcomes. Documented evidences have indicated that changes observed in PTT are inversely correlated to the corresponding BP changes. In critical care, a simple and accommodating technique like PTT may be useful in providing better comfort for patients during extended monitoring. Being a semi-quantitative measure, blanket recommendations for its utility can then become possible. The basic instrumentations needed are often part of standard critical care monitoring system. Furthermore, PTT also has the potential to monitor the often tachypnoeic respiratory dependent BP changes seen in small infants during critical care.