血液复阻抗频率特性的测量

本研究构造了用于测量血液复电阻抗频率特性的测量系统，测量了不同压积的血液复电阻抗频率特性，并根据频率响应分析方法对测量结果进行的血液复电阻抗讨论。本研究为生物复阻抗测量提供一种方法。     

单极和双极起搏模式起搏阻抗的临床观察及相应起搏电路分析

目的分析双极起搏导线双极模式测量起搏阻抗大于单极模式测量起搏阻抗的原因。方法先前研究中双极测量起搏阻抗始终高于单极测量起搏阻抗,推测这种现象源自电子在双极环路和单极环路有着不同的运动途径。通过对比双极模式和单极模式的等效电路图,显见双极阻抗要高于单极阻抗。结果双极测量起搏阻抗与单极测量起搏阻抗的不同主要在导线阳极环及附近组织的阻抗。结论单双极电极起搏阻抗不同的原因源于电子在双极环路与单极环路运动的不同。     

生物组织复电阻抗频谱测量及电阻抗断层成像系统的研究

作者在离体时间对复阻抗频谱的影响、在体组织复阻抗频谱测量以及血细胞压积对血液复阻抗频谱的影响、静态电阻抗断层成像 （EIT）重构算法、实时 EIT系统及其成像等方面进行了探索性研究 ,通过以上研究进一步证实了阻抗方法在医学研究中的重要性 ,并得到了如下提示性结论 :1在体动物组织缺血后短期内复阻抗频谱发生的变化主要原因可能在于缺血引起的细胞外液成分的变化 ;2离体动物组织复阻抗频谱随离体时间发生的变化主要可能是由于细胞膜活性的改变引起 ,其机制有待进一步深入研究 ;3血液中血细胞含量是血液复阻抗频谱特性变化的主要原因 ,血细胞含量越高 ,复阻抗实部越大 ,虚部最大值也越大 ;血液的特征频率与血细胞含量基本无关 ,从而提示这一特性与血细胞自身活性及状态有关 ;4EIT方法为一种观察微小阻抗分布扰动的敏感方法 ,初步的成像实验提示这一成像方法可以被用来诊断血流异常的病变 ,并能被用于长时间图像监护。     

互联智能体质量秤测量主动脉脉搏波速度

正测量动脉僵硬度的方式应该更容易获得。本研究旨在显示只需单脚站立在带有心脏冲击扫描图和阻抗血流图功能的体质量秤上就能有效地测量主动脉脉搏波传导速度(aortic pulse wave velocity,aPWV)。方法:通过106名普通自愿者对体质量秤进行校准。在仰卧位时用SphygmoCor测量颈股动脉脉搏波传导     

硝苯吡啶对充血性心衰的血液动力学效应

本研究的目的是探讨硝苯吡啶对心衰的血液动力学效果。 8例正常窦性心律的慢性心衰患者,年龄为31～64岁,男女各4人。血液动力学测量:采用常规心导管术或Swam-Gang导管连续测量肺动脉与压心输出量。体动脉和肺动脉压及心室内压力用Hewlett-Packard 1280c压力传感器进行测量。测量用药前(对照)和舌下含化20mg硝苯吡啶后10～30分钟的     

食管粘膜阻抗在诊断胃食管反流病的意义

胃食管反流病（GERD）是一种复杂的疾病,具有异质的症状特征和多方面的致病基础。食管粘膜阻抗是反流的标志。受损的食管粘膜完整性在引起GERD症状中起作用。测量了沿食道的粘膜阻抗的变化程度,可用于诊断GERD患者反流对食管粘膜造成的影响。使用食管多通道腔内阻抗pH实验测量食管基线阻抗被认为是检查食管粘膜完整性研究的替代技术,有助于鉴别GERD与非GERD。内镜引导下粘膜阻抗试验是一项新技术,它利用一根直视导管接触食管内壁,以确定慢性胃十二指肠内容物引起的上皮细胞变化。这个测试本质上是测量食管上皮细胞对电流的传导能力。慢性GERD患者的食管上皮细胞改变,细胞间的间隙扩大和长期处于湿润状态,导致高导电性和低粘膜阻抗。内窥镜检查指导下的粘膜阻抗和粘膜导纳的实时测量可能有助于估计粘膜完整性,并可能以类似于24 h食管多通道腔内阻抗pH监测的方式成为GERD患者的有用诊断工具。     

放射性同位素扫描和上腹部阻抗测定胃排空率

交流电的阻抗相当于直流电电阻.阻抗可在呼吸描记法中用以监护气容量,也是测定血容量的敏感而又精确的方法.阻抗也用于测定胃容量;低电导的液体进入胃时,上腹部的阻抗增加,随后下降,这种下降逻辑上代表了胃的排空.闪烁图是测定胃排空的一个准确方法.本研究对阻抗法与闪烁图在监护液餐胃排空中的应用作了比较.     

舒张早期时的异常阻抗波形:心脏病人预后不良的预示

Kubicek、Patterson等研究的阻抗测定方法,可通过测量心动周期时发生的阻抗变化来估计心排出量。由于心脏收缩喷血的结果,在胸腔范围内可测量到一个很小的电阻抗下降。胸部阻抗变化的一阶导数(dz/dt)与主动脉流量计测得的收缩射血成正比,其高度与射血成线性关系。以阻抗法测定的心排出量与Fick方法作比较,计算所得的心搏出量指数的相关系数为0.91。本文对冠心     

双通道阻抗/导纳检测仪（阻抗检测仪器的革命——从一维到二维）

<正> 阻抗容积图（impedance plethysmography）是企图通过人体电阻抗变化的测量来检测人体局部血液容积变化的一种技术。这种技术已在肢体血流检测等应用中获得成功,加之该技术具有简便、安全、可重复等特点,因而近些年来受到越来越多的重视。但是有关技术的理论基础与应用不断暴露出许多问题。尤其在用于胸部检测、企图反映心脏泵血活动时褒贬不一,结果也颇有争议。针对这些问题,第四军医大学生理学教研室臧益民教授指导其博士生     

心脏阻抗图对缺血性心脏病左室功能 的研究

心脏阻抗图是一种无损伤性方法,且可重复测量,因而此法对评定缺血性心脏病病人的左室功能是有价值的。本研究用此法对35例具有或不具有心房颈动脉旁路的缺血性心脏病病人和用微型球形乳剂闭塞多条冠状动脉的5支狗进行观察。其结果如下:心脏指数从运动开始即较休息时     

Investigation of the parallel conductor model of impedance cardiography by means of exchange transfusion with stroma free haemoglobin solution in the dog

To test one of the assumptions underlying the calculation of stroke volume--namely, that the transthoracic impedance consists of a parallel connection of a tissue impedance and a blood resistance--experiments were carried out on four dogs in which blood was gradually replaced by a stroma free haemoglobin solution, with the purpose of changing the blood resistance while leaving the tissue impedance unchanged. This was accomplished by exchange transfusion in such a way that the volume of the circulating fluid remained constant and the distribution of fluid volume between the fluid compartments was not altered. During the exchange transfusions the mean decrease in resistivity of the circulating fluid was 54%. The packed cell volume and resistivity of every volume of removed circulating fluid were measured. Just before each exchange the real and imaginary parts of the transthoracic impedance were measured. The packed cell volume decreased exponentially with the number of exchanges. This indicates that the circulating fluid volume remained constant during the exchange transfusion. From the packed cell volumes an estimate of the circulating fluid volume was made. Because of the parallel connection all calculations were based on the use of admittance, which is the reciprocal value of impedance. The real and imaginary parts of the transthoracic admittance were calculated from the measured values of the real and imaginary parts of the transthoracic impedance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased impedance to inspiration ameliorates hemodynamic changes associated with movement to upright posture in orthostatic hypotension: a randomized blinded pilot study.

BACKGROUND: Movement to upright posture may result in marked drop of blood pressure with susceptibility to injury from syncope and falls in patients with orthostatic hypotension. OBJECTIVE: The purpose of this study was to determine if increasing negative intrathoracic pressure by using an inspiratory impedance threshold device before change of posture diminishes blood pressure fall by enhancing venous return. METHODS: Eighteen healthy subjects and 22 orthostatic hypotension patients were randomized to either an active (impedance 7 cmH2O) or sham (no inspiratory impedance) impedance threshold device. Arterial blood pressure, heart rate, and estimated stroke volume and total peripheral resistance were recorded in the supine and upright postures using a noninvasive finger arterial blood pressure monitor. After a rest period, the alternate impedance threshold device (sham or active) was tested in each individual. RESULTS: Compared with the sham impedance threshold device test, the active impedance threshold device resulted in significant reduction in the magnitude of upright posture-induced fall in blood pressure and a greater increase of total peripheral resistance after standing in both healthy subjects and orthostatic hypotension patients. Stroke volume was not measurably altered. Among all subjects who exhibited a postural blood pressure drop >10 mmHg on the day of study, active impedance threshold device treatment consistently blunted blood pressure fall during the initial 100 seconds after standing (<0.04). Induced orthostatic symptoms were less severe with the active impedance threshold device both at onset of upright posture and during 30 seconds of standing. CONCLUSION: Enhancing impedance to inspiration may prove useful as adjunctive therapy for diminishing symptoms associated with movement to upright posture in individuals with orthostatic hypotension.     

Investigation of the origin of the impedance cardiogram by means of exchange transfusion with stroma free haemoglobin solution in the dog

PURPOSE OF INVESTIGATION - To determine the contribution of variations in orientation of erythrocytes (orientation effect) to the heart synchronous variations in thoracic impedance in impedance cardiography. DESIGN - The blood of four dogs was gradually replaced by stroma free haemoglobin solution, causing a decrease in resistivity and orientation effect. The decrease in orientation effect was used to determine the contribution of the orientation effect using an extended form of the "parallel conductor" model of the thorax (parallel connection of a tissue admittance Yt and a blood conductance Gb). SUBJECTS - Four adult splenectomised mongrel dogs. MEASUREMENTS and RESULTS - Packed cell volume and resistivity at body temperature of every volume of circulating fluid removed was measured. Real and imaginary parts of the transthoracic impedance and the modulus of the heart synchronous impedance variations were measured just before each exchange. The parallel conductor model was extended to account for the influence on Gb of packed cell volume and orientation of erythrocytes. Applying this extended model, the average variations in Gb at a packed cell volume of 40% were estimated to be 7.46%:3.03% due to volume variations, 4.43% due to orientation effect. After further extending the model to account for the influence of small changes in blood pressure and heart rate, the average volume variations were estimated to range from 2.8% to 3.3% and the average orientation effect from 4.1% to 4.7% at a packed cell volume of 40%. CONCLUSION - Resistivity of the blood is far from constant and the contributions of variations in blood conductivity and volume to the heart synchronous thoracic impedance are of comparable magnitude. The contribution of the volume variations is the sum of the volume variations in the contributing intrathoracic vessels. The effects of variations in orientation are added up in proportion to the relative volumes of the contributing vessels. The extensions of the parallel conductor model brought out all physiological factors determining the heart synchronous thoracic impedance variations: pulse pressures and flows, mean pressures and flows, compliances of all contributing blood vessels, packed cell volume and heart rate, as well as the relevant properties of blood: the relations between volume, flow and orientation effect and the change in orientation effect during decelerating flow.     

Blood-flow indices in amputee and control limbs by mutual electrical impedance plethysmography

Arterial insufficiency is recognized in amputee segments of thighs by bioelectrical impedance indices of blood flow. The radiofrequency method of volume detection is painless, noninvasive, and reproducible for diagnostic or therapeutic management of circulatory impairments. It interprets complex changes in electrical conductances in real volumetric terms which are easily understood by physicians.Blood flow indices based on bioelectric impedance in the present study indicate a statistically significant circulatory deficit is present in the amputated thigh of traumatic and nontraumatic amputees. Vascular and degenerative diseases are almost invariably present in the nontraumatic amputee group.     

Accuracy of electrical impedance cardiography for measuring cardiac output in children with congenital heart defects

This study determined whether noninvasive electrical impedance cardiography accurately measures systemic blood flow (cardiac output) in children with congenital heart defects. A total of 37 patients ranging in age from 2 to 171 months underwent complete right- and left-sided heart catheterizations that included simultaneous Fick and impedance measurement of cardiac output. Based on the diagnosis, 4 groups were formed consisting of a control group (n = 11) with no shunts, a group with intracardiac left-to-right shunting and an atrial septal defect (n = 7), another with a ventricular septal defect (n = 12) and an extracardiac left-to-right shunting with patent ductus arteriosus group (n = 7). Impedance values for systemic blood flow were compared with systemic and pulmonary blood flow obtained by the direct Fick method with measured oxygen consumption. The difference between impedance and Fick systemic blood flow was less than or equal to 5% in each of the 4 groups. The highest correlation between impedance and Fick systemic blood flow was with the atrial septal defect group (r = 0.89) and lowest with the ventricular septal defect and control (r = 0.69) groups. Fick pulmonary blood flow was significantly greater than impedance or Fick systemic flow in all 3 shunt groups. Impedance cardiography accurately measured systemic blood flow in children without shunts or valvular insufficiency. Likewise, systemic blood flow was accurately measured by impedance in the presence of intracardiac left-to-right shunts (atrial and ventricular septal defects) and extracardiac left-to-right shunts (patent ductus arteriosus).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of vasoactive drugs upon haemodynamic power and input impedance in normal rats.

STUDY OBJECTIVE--The objectives were (a) to describe the effects of vasoactive drugs in normal rats upon cardiovascular function assessed by computing aortic haemodynamic power and input impedance, each separated into their component parts, and (b) to study the relationship between left ventricular pulsatile power output and the vascular impedance. DESIGN--Haemodynamic power and input impedance were computed from measurements of aortic blood pressure and flow in normal rats. The rats were then given an infusion of a vasoconstrictor drug (methoxamine) followed by a vasodilator drug (hydralazine) in order to study the effects of changes in vascular impedance upon haemodynamic power. EXPERIMENTAL MATERIAL--The measurements were made on pentobarbitone anaesthetised male Wistar rats of approximately 400 g body weight (10 infused with Hartmann's solution as controls and 10 infused with the drugs). MEASUREMENTS AND MAIN RESULTS--Aortic total haemodynamic power was between 9.96 mW and 10.37 mW during the control period and reached a maximum of 11.36 mW during the methoxamine infusion, but this difference was not statistically significant. It then decreased significantly to 4.32 mW by the end of the hydralazine infusion. Pulsatile power was only 0.32(SEM 0.08) mW (2.8% of the total power) in the control state and decreased to 0.12(0.1) mW (1.7%) during the methoxamine infusion, but increased to 0.59(0.15) mW (12.5%) by the end of the hydralazine infusion. The vascular effects were complex and involved all four of the input impedance parameters--peripheral resistance, characteristic resistance, arterial compliance, and inertance. Reflex responses of the vascular wall were apparent as temporal changes in characteristic resistance and arterial compliance. CONCLUSIONS--Changes in cardiovascular function can be described by computing haemodynamic power and input impedance and then separating these into their component parts. Administration of the vasoactive drugs affected left ventricular mean and pulsatile power output and all four components of the input impedance. The frequency distribution of left ventricular pulsatile power output may be matched to the vascular impedance in order to optimise tissue perfusion.     

Reproducibility of the measurement of thoracic electric impedance

Recordings of thoracic electrical impedance were consecutively taken in 10 normal subjects (age 18-48 years, mean 38.6) two times during the same day, during the following day and after 1 month. The following parameters were evaluated: heart rate, systolic blood pressure, diastolic blood pressure, left ventricular ejection time, pre-ejection time, baseline electrical impedance, DZ positive peak, Q-dZ/dt interval and Heather Index. Data were processed in order to quantify the different source of variability: subjects or biological variability, days, beats. Total variability was expressed in absolute units as coefficient of variation. Results were as follows: Q-dZ/dt interval had the lowest coefficient of variation (7.7%). Inter subject was the largest source of variability for all the indices showed, ranging from 70.5% to 89.3%. On the contrary intraindividual variability was moderate racing from 1% to 2.6% for various impedance measurements. In conclusion, thoracic electrical impedance measurements showed good reproducibility, especially when successive measurements were compared in a same subject.     

Biophysical aspects of high frequency catheter ablation. Studies of the significance of sudden changes in impedance]

To determine the effects and the underlying mechanisms of sudden rise of impedance during radiofrequency (RF) catheter ablation, 60 RF applications were delivered to isolated preparations of ventricular myocardium at three different power levels (mean: 3.7, 11.3, 19.3 watts). Pulse duration was 30 s, current voltage and catheter tip temperature were continuously monitored. Impedance rise occurred during 34 of 60 applications; the incidence of impedance rise increased at higher power levels. Impedance rise was significantly more often observed when the preparations were superfused with heparinized blood compared to saline solution (p less than 0.05). Catheter-tip temperature during radiofrequency application without impedance rise was significantly lower compared to applications with impedance rise (mean = 108 degrees C vs. 121 degrees C, p less than 0.01). The increase of catheter-tip temperature and maximal-tip temperature following impedance rise was significantly higher in blood when compared to saline solution (mean = +48 degrees C vs. +13 degrees C (p less than 0.001), Tmax: 121 degrees C vs. 245 degrees C). Following impedance rise, insulation defects of the electrode catheter and vaporized crater formation of the myocardium was often observed. Conclusions: During radiofrequency catheter ablation impedance rise occurs following overheating of the catheter electrode (greater than 110 degrees C). After impedance rise, catheter-tip temperature markedly increases. Insulation defects of the catheter and vaporized craters in the myocardium frequently occur after impedance rise. The results have important implications for the clinical use of RF-currents for catheter ablation; energy application should be immediately stopped after the occurrence of impedance rise.     

Detection of pulmonary embolisms by recording of the variations of thoracic impedance at each lung]

It is possible to record changes of volume caused by variations of the blood supply to each lung by measuring the transthoracic electrical impedance. A theoretical study was performed beforehand to define the variations of the impedance of the deep-lying structures. The form, number and distribution of the electrodes were determined by experiments on a model so that only variations of the impedance of the pulmonary parenchyma, and not of the mediastinum, were recorded. In this way the origins of the signals recorded were known. The validity of the method was tested on patients having undergone pneumonectomy and on patients with defects of pulmonary perfusion. Using the data obtained during the preceding experimental studies it was possible to defect perfusion defects caused by pulmonary embolism. Five cases of pulmonary embolism, confirmed by angiography and lung scan, of varying severity and chronicity, are reported. The amplitude of the impedance curve was reduced on the affected side, the difference of amplitude between the two being related to the degree of vascular amputation.     

Body impedance recording in the assessment of stroke volume

The first derivative of the integral tetrapolar rheogram of the body, body impedance recording, was found to show changes in blood flow in the arterial compression chamber. Evidence was given for a close relation of the distance between the electrodes while recording an integral rheogram of the body and the examinees' height. The relation of the distance to the examinees' height was equal in males and females and proved to be lower than that previously applied. For calculation of the stroke blood volume from the body impedance recording, the Kubicek equation was proposed to be used by introducing the height of an examinee instead of the distance between measuring electrodes. There was a good coincidence of results while calculating the stroke volume by impedance recording and Doppler echocardiography.