Simplified electrode array for impedance cardiography

Impedance cardiography has enjoyed widespread interest owing to the promise of noninvasive monitoring of cardiac function. In clinical practice, one factor limiting its use has been the need to use circumferential electrodes. These electrodes can be inconvenient to apply, may interfere with chest tubes or intravenous lines, and can cause additional apprehension in critically ill patients. The paper describes a more convenient electrode array. It uses four disposable electrocardiographic electrodes, two on the base of the neck and two on the lower left, anterolateral surface of the thorax. Simultaneous impedance derivative recordings were made with this ‘spot’ electrode array and with the conventional ‘band’ electrode array, at rest and after exercise on ten normal volunteers. On a given individual, the two signals had shapes which were remarkably similar and relative heights which correlated well, exhibiting correlation coefficients (r′) between 0·77 and 0·98. This new array should facilitate impedance cardiographic measurements in the clinical setting.     

An analysis of the relationship between transthoracic impedance variations and thoracic diameter changes

The relationship between transthoracic impedance variations and thoracic diameter changes (distance changes between the impedance-measuring electrodes) associated with both respiration and circulation was studied in 15 anaesthetised dogs. Respiratory records obtained by both impedance and inductance methods during respiration were very similar. After replacing oxygen within the lung and trachea with physiological saline, an injection of saline into the airway produced a decrease of impedance and an increase of thoracic diameter. The withdrawal of saline produced directly opposite effects. When a highly conducting solution of saline was injected into the inferior vena cava, the thoracic diameter increased simultaneously with a decrease of the impedance. Even though the thoracic-diameter response was constant and simultaneous with injections into the inferior vena cava, the orifice of the right atrium or right ventricle, the decrease of the impedance lagged behind the diameter change as the injection site was shifted distally to the lung. The impedance increased with a decrease of the thoracic diameter following reduced venous return to the right ventricle by an occlusion of the inferior vena cava. This experimental evidence suggests that the variations of the impedance on the surface of the thorax originate from conductivity changes within the lung irrespective of airway and pulmonary vascular spaces, and not from distance changes between electrodes.     

Impedance plethysmography: the origin of electrical impedance changes measured in the human calf

Electrical impedance plethysmography of the lower leg is now a widely used test for detection of deep vein thrombosis. The origin of the impedance signal is difficult to evaluate in the living subject, and experimental animals have important anatomic differences. A controlled study on human cadavers was therefore undertaken. Conductive and nonconductive fluids were injected into the lower legs of cadavers, while electrical impedance changes were recorded utilising a 4-electrode technique. X-ray studies confirmed the localisation of the injections. Results from ten cadavers showed that significant impedance changes occurred only in response to injections of saline in the region between the electrodes. Injections of nonconductive silicone oil caused a small increase in the measured impedance. It is concluded that electrical impedance plethysmography reflects changes in conductivity confined to the region between the electrodes; and that the ratio of deep to superficial impedance sensitivity is a function of the electrode spacing.     

利用生物电阻抗法分析西藏藏族青少年脂肪分布特点

目的 利用生物电阻抗分析法测量西藏藏族青少年身体各部脂肪含量的数值,提出适合西藏藏族青少年的脂肪含量基准值,探讨西藏藏族青少年的脂肪分布特点与规律。方法 在知情同意的前提下,随机抽取1427例(男为710例,女为717例)父母均为藏族的西藏藏族健康青少年作为研究对象,应用体成分分析仪对所有受试者进行检测,得出脂肪总量、左上肢（左下肢、右上肢、右下肢、躯干）脂肪量等与脂肪相关的数值,进而推算出体脂肪率、左上肢（左下肢、右上肢、右下肢、躯干）脂肪率。所有结果输入SPSS 19.0统计学软件,进行独立样本t检验和方差分析统计学处理。结果 西藏藏族青少年各年龄段的脂肪总量、四肢脂肪量、躯干脂肪量,男性均低于女性（P <0.05）。总体西藏藏族青少年的脂肪含量随年龄增长而增加,女性的增加趋势更加显著。结论 西藏藏族青少年的脂肪含量随年龄变化特点与体内激素分泌水平有关,体现了不同发育时期的生理特点。     

An implantable impedance pneumograph monitor for detection of diaphragm contraction and airway obstruction during diaphragm pacing

Impedance pneumography signals were characterised during diaphragm pacing using stimulating and recording electrodes placed on the abdominal surface of the diaphragm. These measurements were useful for the detection of muscle contraction without confounding effects from stimulus artifacts. Impedance pneumography signals were measured using 23 epimysial electrodes implanted in seven dogs with 1-5 experiments on each electrode. The polarity of the change in impedance associated with diaphragm pacing differed for each recording electrode and its configuration. Thirty-four of 57 cases produced increased impedance, 11 produced decreased impedance and the remaining 12 depended on the level of diaphragm activation. Impedance pneumography signals were useful for detecting complete airway obstruction. The mean difference between the impedance measured during open and obstructed airway conditions was 80% of the open airway impedance signal. The difference between open and obstructed airway impedance measurements was a mean of 2.3 times larger with a recording electrode on the same hemidiaphragm as the stimulating electrode, compared to an electrode placed on the opposite hemidiaphragm (p < 0.05, paired t test, four dogs). In addition, the differences between open and completely obstructed airways were a mean of 2.8 times larger when the second recording electrode was placed on the thorax at the fifth intercostal space, compared to the ninth intercostal space (p < 0.05, two-factor ANOVA, one dog, two replicates). It was concluded that impedance pneumograph circuitry could be incorporated into an existing diaphragm pacer using electrodes placed on the diaphragm to provide valuable measurements of the function of the device.     

Memory-related EEG power and coherence reductions in mild Alzheimer's disease.

OBJECTIVES: To examine memory-related EEG power and coherence over temporal and central recording sites in patients with early Alzheimer's disease (AD) and normal controls. METHOD: EEG was recorded from central (Fz, Cz and Pz) and temporal (T3 and T4) electrodes while ten very mild AD patients and ten controls performed a Sternberg-type memory scanning task with three levels of working memory load. Spectral power in delta (0-3 Hz), theta (3-5 Hz), lower alpha1 (5-7 Hz), lower alpha2 (7-9 Hz), upper alpha (9-11 Hz) and beta (15-30 Hz) was averaged for temporal and central electrodes. Coherence was averaged between central electrodes, between central and right temporal electrodes and between central and left temporal electrodes. RESULTS: While behavioral performance of very mild AD patients did not differ significantly from that of normal controls, findings suggest that normal controls but not AD patients respond to memory demands by increasing upper alpha power over temporal cortex. When compared with normal controls, AD patients had reduced upper alpha coherence between central and right temporal cortex. DISCUSSION: Results are consistent with previous research on the role of upper alpha in semantic memory and suggest that very mild AD may inhibit selective synchronization of upper alpha in temporal lobes. Reduced coherence between central and temporal cortex is discussed in light of a neurological model of AD that hypothesizes reduced electrocortical efficiency and a breakdown of neural network communication to temporal lobes possibly resulting from temporal lobe atrophy.     

The impedance of a spherical monopolar electrode

The impedance of a monopolar electrode immersed in an environmental volume conductor consists of two parts; the impedance of the active electrode-electrolyte interface, and the resistance of the environmental conductor. Two studies were carried out to quantitate these components. First, impedance-frequency data were collected for five spherical stainless-steel electrodes (ranging from 0.473 to 1.11 cm in diameter) immersed in 0.9% saline (ρ=70 Ω-cm). Impedance measurements were made from 100 Hz to 100 kHz and two sets of data were obtained; one before and one after each electrode was polished with fine emery paper. At low frequency, the measured impedances were high and varied with electrode surface preparation. However, above a transition frequency, the impedances were resistive, independent of the electrode surface preparation, and equal to ρ/2πd as predicted from the theory. This study indicates that the low frequency impedance of a monopolar electrode is dominated by the impedance of the electrode-electrolyte interface. Above a transition frequency, the resistance of the environmental conductor dominates, the value of this resistance depending on the electrode geometry and the resistivity (ρ) of the environmental conductor. A second study was conducted, to examine the effect of the distance to the indifferent electrode. A frequency (100 kHz) above the transition frequency was used and impedance data were collected for various distances between the monopolar and indifferent electrodes. The measured resistance increased asymptotically as the distance between the electrodes was increased. When the indifferent electrode diameter was at least 10 times the diameter of the spherical monopolar electrode, the measured resistance was within 5% of the value predicted for an indifferent electrode at infinity.     

An implantable impedance pneumograph monitor for detection of diaphragm contraction and airway obstruction during diaphragm pacing

Impedance pneumography signals were characterised during diaphragm pacing using stimulating and recording electrodes placed on the abdominal surface of the diaphragm. These measurements were useful for the detection of muscle contraction without confounding effects from stimulus artifacts. Impedance pneumography signals were measured using 23 epimysial electrodes implanted in seven dogs with 1–5 experiments on each electrode. The polarity of the change in impedance associated with diaphragm pacing differed for each recording electrode and its configuration. Thirty-four of 57 cases produced increased impedance, 11 produced decreased impedance and the remaining 12 depended on the level of diaphragm activation. Impedance pneumography signals were useful for detecting complete airway obstruction. The mean difference between the impedance measured during open and obstructed airway conditions was 80% of the open airway impedance signal. The difference between open and obstructed airway impedance measurements was a mean of 2.3 times larger with a recording electrode on the same hemidiaphragm as the stimulating electrode, compared to an electrode placed on the opposite hemidiaphragm (p<0.05, paired t test, four dogs). In addition, the differences between open and completely obstructed airways were a mean of 2.8 times larger when the second recording electrode was placed on the thorax at the fifth intercostal space, compared to the ninth intercostal space (p<0.05, two-factor ANOVA, one dog, two replicates). It was concluded that impedance pneumograph circuitry could be incorporated into an existing diaphragm pacer using electrodes placed on the diaphragm to provide valuable measurements of the function of the device.     

利用生物电阻抗法分析辽宁汉族成人脂肪分布特点

目的 运用生物电阻抗分析法,测量辽宁汉族成人身体各部份脂肪含量,提出适合于辽宁汉族群体的脂肪含量基准值,进而探讨辽宁汉族成人的脂肪分布特点与规律。 方法 在知情同意的前提下,随机抽取父母均为汉族的辽宁汉族健康成人作为研究对象,共选取1034人(男性379例,女性655例)。应用体成分分析仪,对所有受试者进行检测,得出脂肪总量、去脂体重、内脏脂肪等级、左上肢（左下肢、右上肢、右下肢、躯干）脂肪量等与脂肪相关的各项数值,进而推算出体脂肪率、左上肢（左下肢、右上肢、右下肢、躯干）脂肪率。结果采用SPSS统计学软件,进行独立样本t检验和方差分析处理。 结果 多数年龄段,男性的脂肪总量、四肢脂肪量、躯干脂肪量均低于女性（ EM>P /EM><0.01）,     

A field-theory model of blood-pulse measurement by impedance plethysmography

A field-theory model of blood-pulse measurement by four-electrode impedance plethysmography was developed and tested empirically. The model relates current distribution in the upper arm to the configuration of the drive electrodes. It predicts observed impedance change as a function of sense-electrode configuration and the increase in segmental volume associated with each blood pulse. The model was simulated on a digital computer for a number of critical cases. Corresponding measurements were taken on human subjects with an improved instrumentation system, which virtually eliminated the artifact caused by the skin-electrode interface. These measurements substantiated the major predictions of the model. It was concluded that precise impedance measurements were closely related to changes in segmental volume, and that any change in conductivity caused by the incoming arterial blood probably played a minor role. Insight was gained into the optimum placement of drive and sense electrodes at this measurement location.     

Impedance measurements on metal needle electrodes

The paper brings the results of measurements of the impedance characteristics of metal needle electrodes made from a variety of metals. It is shown that the magnitude and frequency dependence of the impedance of highly polarisable electrode systems are, in general, similar. Of the metals examined, silver and mainly indium show a markedly different behaviour. Hope is expressed that further work could produce an indium-based electrode system which might, for certain applications, be superior to presently used electrodes.     

A Simulation Study on the Effect of Thoracic Conductivity Inhomogeneities on Sensitivity Distributions

A high-resolution 3D finite difference model of the electrical conductivity distribution in a human thorax based on a 43-slice MRI data set along with lead field theory was used to examine the effect of thoracic conductivity inhomogeneities on sensitivity distributions. The electrode configurations used in the present study were based on an eight-electrode array positioned evenly around the thoracic model at a level close the nipple line. Sensitivity distributions of each possible adjacent pair current excitation pattern for both the homogeneous thoracic model and the heterogeneous thoracic model were evaluated. The results show that thoracic inhomogeneities significantly perturb sensitivity distribution patterns. Although for a given thoracic geometry the electrode configuration gives the overall sensitivity distribution features, sharp large local changes occur near the boundaries between different tissues in the heterogeneous model. The results of sensitivity distributions of the heterogeneous thoracic model demonstrate the feasibility of impedance source localization. Selectivity can be used to as a guide to finding favorable electrode configuration for regional impedance monitoring.     

Surface mapping of thoracic impedance cardiograms

A method is desbribed for mapping the electrical impedance cardiac signal on the anterior thoracic surface in man. A sinusoidal current was injected through electrodes placed around the neck and lower abdomen and voltage differences were measured with a single exploratory electrode at 30 well defined position on the thorax and upper abdomen. The expected interbeat variability was minimised by digital processing. Different pattern of dZ/dt, the first derivative of the cardiac impedance change were obtained at different points on the thoracic showing the additional information and discrimination provided by impedance surface mapping. The results of this work suggest that classical impedance cardiography detects mainly blood flow changes in the large upper thoracic vessels of the clavicular region. With the present method it is possible to visualise the effect of changes in heart volume and shape on the local impedance distribution and the spreading of blood flow related impedance changes across the thoracic and upper abdominal surfaces.     

Field calculations in the head of a newborn infant and their application to the interpretation of transcephalic impedance measurements

A spherical model, of five regions, has been applied to the head of a typical premature baby for the purpose of computing the potential and current density fields, with a constant total current applied via small electrodes at opposite poles. The results have been compared within vivo transcephalic impedance measurements, and the model has been used to determine the magnitudes of the impedance effects to be expected in various clinical situations. The model predictions are found to agree well with impedance measurements as a function of the distance between the potential and current electrodes. It is calculated that a large intracranial haemorrhage would produce an increase in the transcephalic impedance of the order of 1 Ω. The model predicts a decrease of up to 20% in the impedance for a change in head circumference of 2 cm due to increased cerebrospinal fluid content. This confirms the conclusion ofReigel et al. (1977) that transcephalic impedance is a sensitive indicator of developing hydrocephalus.     

Event-Related Potential Indices of Selective Attention and Cortical Lateralization in Schizophrenia

Auditory event-related potentials (ERPs) from a multidimensional selective attention task were recorded from 10 unmedicated schizophrenic patients and 10 age- and sex-matched healthy controls. Tone pip stimuli varying on the dimensions of pitch (high or low) and location (left or right ear) formed four 'channels' of stimuli: left low, left high, right low, and right high. The pitch difference was considerably more difficult to discriminate than the location difference. Subjects were instructed to pay attention to a designated channel and press a button whenever they detected a long-duration, rare target tone that occurred amongst frequent short-duration standard tones. There were a number of differences between unmedicated schizophrenics and controls in processing negativity elicited by standard tones. There was no evidence of hierarchical processing of stimulus dimensions in the early processing negativity component, and the late frontal component was virtually absent in schizophrenics. Furthermore, there was evidence that in schizophrenics the processing of the location dimension was delayed for standard tones having the same pitch as the target. The P300 component to attended target tones was substantially reduced in schizophrenics over parietal sites but there was no difference between the two groups over frontal sites. The results are interpreted in terms of multiple attentional deficits in schizophrenics that are indicative of a failure in the planning and execution of selective listening strategies. Such a failure may result from a dysfunction in the prefrontal regions of the brain.     

Sonic phase delay from trachea to chest wall: spatial and inhaled gas dependency

A parametric phase delay estimation technique is used to determine the spatial and inhaled gas composition dependencies of sound propagation time through an intact human lung at frequencies of 150–1200 Hz. Noise transmission measurements from the mouth to the extrathoracic trachea and six sites on the posterior chest wall are performed in 11 healthy adult subjects at resting lung volume after equilibration with air, an 80% helium-20% oxygen mixture, and an 80% sulfurhexafluoride-20% oxygen mixture. The phase delay, τ(f), exhibits a bilateral asymmetry with relatively decreased delays to the left posterior chest as compared with the right. The phase delay to lower lung sites is greater than to upper sites at frequencies below 300 Hz; yet the opposite is found at higher frequencies, indicating changing propagation pathways with frequency. There is no measurable effect of inhaled gas composition on τ(f) below 300 Hz. At higher frequencies, changes in τ(f) that reflect the relative sound speed of the particular inhaled gas are observed. These findings support and extend previous measurements and hypotheses concerning the strong frequency dependence of the acoustical properties of the intact respiratory system.     

利用生物电阻抗法分析西藏藏族青少年肌肉发育特点

目的 利用生物电阻抗分析法,通过测量得出西藏藏族青少年身体各部肌肉质量的数值,提出适合于西藏藏族青少年的肌肉质量基准值,进而探讨西藏藏族青少年的肌肉发育特点与规律。方法 在知情同意的情况下,整体随机抽取西藏藏族的健康青少年作为研究对象,其父母均为藏族,共选取1427人(男性710、女性717),应用体成分分析仪对所有受试者进行检测,得出全身肌肉量、躯干肌肉量、左上肢、右上肢、左下肢、右下肢肌肉量。所有结果输入SPSS19.0统计软件包,进行独立样本t 检验和方差分析统计学处理。 结果 西藏藏族青少年各年龄段的全身肌肉量、躯干肌肉量、左上肢、右上肢、左下肢、右下肢肌肉量,在12岁之前有性别差异,
但不明显;12岁之后,以上各项数据均出现性别间差异的显著性,均表现为男性大于女性（P <0.05或P <0.01）,而且随着年龄增长,这种差异越趋明显。12岁之后,女性的增长幅度出现显著下降,而男性在15岁之后,增长趋势才开始下降,而女性此时几乎进入肌肉生长发育的平台期。结论 西藏藏族青少年的肌肉含量随年龄变化特点与体内激素分泌水平有关,体现了不同发育时期的生理特点。     

Comparison of Spot and Band Impedance Cardiogram Electrodes across Different Tasks

Impedance cardiography has become of widespread interest as a noninvasive cardiovascular monitoring technique. This study compared the use of spot electrodes and two different types of band electrodes in the determination of systolic time intervals and stroke volume. EKG, impedance cardiogram, and phonocardiogram were recorded on 12 volunteers during rest, during a reaction time task, and after a short exercise task. Systolic time intervals (pre-ejection period and left ventricular ejection time) were computed on a beat-to-beat basis and on the ensemble-averaged signals. The only differences between spot and band electrodes were for impedance base level and electrode conductance. For stroke volume and the systolic time interval measures there were no differences between electrode arrays, nor were there any interactions with tasks. Correlations for stroke volume and systolic time interval measures as determined under different electrode conditions were around .8.     

Comparison of Impedance Cardiographic Measurements using Band and Spot Electrodes

The comprehensive assessment of cardiac function using impedance cardiography has led to increasingly widespread use of the technique in psychophysiology. Disposable adhesive band electrodes have been the most widely used electrode type, but spot electrode configurations present attractive alternatives in terms of convenience and subject comfort. The present study was designed to evaluate whether one such spot electrode configuration yielded the same information as the more standard band electrodes for cardiac output and systolic time interval measurement. Male and female healthy adult subjects (N = 20) were tested. Comparisons between spot and band electrodes were made for the absolute magnitude of cardiac output and systolic time intervals, as well as for responses to the highly reproducible effects of bicycle exercise. Consistent with previous findings, systolic time interval measurements were unaffected by electrode type. However, for cardiac output measurements, differences between spot and band electrode measurements were found. Under resting conditions, the absolute magnitudes of cardiac output values measured using spot electrodes were smaller than for band electrodes. Subtle, yet significant differences were also found for cardiac output responses to exercise, with spot electrodes indicating greater increases in cardiac output than band electrodes. At the same time, anticipated gender differences found for cardiac output at rest and in response to exercise were unaffected by electrode type. Overall, these findings suggest that when comparing the results of studies that have utilized different impedance electrode types, it would be prudent to remain alert to the possibility of confounding influences.     

Body fluid distribution in man in space and effect of lower body negative pressure treatment

Summary The lack of hydrostatic forces in space eventually produces a fluid deficit within the circulatory system. This deficit may alter the circulatory regulation patterns. The aim of the present study was to determine how much of this fluid deficit is attributable to interstitial fluid losses and to determine the effects of lower body negative pressure (LBNP) treatment on fluid distribution. The body fluid distribution of one subject was assessed before, during, and after weightlessness using two electrical impedance methods: (a) standard quadripole impedance for the segments of upper torso, lower torso, thigh, and calf and (b) an electrical impedance tomography technique (applied potential tomography) for a thigh cross-section. To assess the content of interstitial free fluid a thigh cuff overlying the electrodes for applied potential tomography was inflated to suprasystolic values to ascertain how much fluid can be squeezed out of blood vessels and tissue of skin and muscle. After the first thigh cuff maneuver (CUFF I) the subject performed a cardiovascular stress test with LBNP to mimic the gravity-induced blood shift to the lower part of the body. Then the compression maneuver was repeated (CUFF II). (a) This experimental sequence demonstrated a reduction in interstitial fluid in weightlessness of roughly 40% at the thigh. (b) The CUFF I and LBNP experiment demonstrated a reduced ability to cope with blood pooling in microgravity. (c) The CUFF II experiment suggests that LBNP in microgravity can refill the interstitial spaces and counteract the associated cardiovascular deterioration. The impedance measurements provided estimates of the contribution of different body sections to the observed body weight loss of more than 6 kg. The chest contributed nothing of significance, the lower torso more than 0.5 1, and both calves roughly 1.5 1. The thigh segments of both legs contributed between 1.51 and 2.01 with an interstitial free fluid reduction in muscle and skin by 40%.Abbreviations APT applied potential tomography - AU arbitrary units - LBNP lower-body negative pressure