“读心术”用计算机破解脑电图

有些中风患者或战场上脑部受伤的士兵在接受治疗时很难与医生进行言语交流，为了了解这类患者的心思，从而更加有针对性地施治，美国科学家正尝试用脑电图解读他们的心里话。加利福尼亚大学欧文分校一个研究小组的设计，给一些脑部有损伤、难以口头表达的患者戴上一种特制的帽子，帽子上的电极接触人的头皮并监测脑电波活动，所获得的监测信息传输到计算机中，供科学家解读。     

织物电极的皮肤-电极接触阻抗测量方法分析

随着可穿戴式健康监测技术的发展,新型心电传感器-织物电极成为人们关注的热点,本文对织物电极的皮肤-电极接触阻抗测量方法进行了综述。首先介绍了织物电极的概念,分析了织物电极的皮肤-电极电化学界面、皮肤-电极电化学界面的等效电路和简化电路模型,得出了皮肤-电极接触阻抗的计算公式;其次,将皮肤-电极接触阻抗的测量方法归纳为直接测量法、参比测量法和模拟皮肤测量法三类,讨论了它们的测量原理和优缺点。本文认为需将模拟皮肤测量法和真实皮肤测量法有机结合,才能有效评价织物电极的阻抗特性,为织物电极的性能评价和心电信号采集电路的设计提供重要依据。最后,本文对织物电极待解决的问题进行了分析讨论。     

测定人和动物心脏单相动作电位的新方法

用吸引电极记录人和动物在体心脏的单相动作电位(MAP),虽可获得心肌细胞群电活动的某些信息,但由于吸引电极对心肌细胞的损伤,因而限制了临床应用。本文介绍用接触电极导管代替吸引电极记录MAP的方法。对接触电极的制备、实验程序、MAP的形态、测量、特征以及应用价值均作了简要说明。     

人头皮微生物与相关头皮疾病的研究进展

近年来基于DNA测序和分子生物学技术的研究表明,头皮微生物特别是主要细菌和真菌与头皮生理指标、免疫状态、屏障功能等相关并且影响头皮健康。人头皮屑、脂溢性皮炎、斑秃、头皮型银屑病等头皮疾病常伴随微生物失衡。针对关键微生物及其相互平衡的干预可缓解或治疗疾病。本文总结了头皮微生物特别是细菌和真菌的研究概况、头皮微生物与头皮疾病,比较了目前的实验室研究方法,为头皮健康的维护、头皮产品开发和实验室研究方法提供参考。     

用单相动作电位研究触发性心律失常

触发性心律失常(triggered arrhythmia)以冲动起源异常机制为特征受到临床的普通重视。近年来,接触电极或接触电极导管记录人或动物心内、外膜单相动作电位新技术的出现,为在整体动物或人心脏上获得触发性活动提供了前提。目前,单相动作电位(mono-phasic action Potential,MAP)已用于冠状动脉搭桥术中的局部心肌缺血、心肌电生理     

细菌电极

美国最近研制成功一种分析精氨酸浓度的细菌电极,这是继发明酶电极以后又一种适用于分析体液或活组织中某些生化物质的有力工具。鉴于目前尚没有适于分析精氨酸的酶电极,研制者选用了一种可以分解精氨酸以释放氨的细菌,并把这种细菌的活细胞制成糊状。涂在一支对氨灵敏的标准玻璃电极上,外面裹着一层玻璃纸。当这种新电极与含精氨酸的液体接触时,即可以对在细菌作用下释放的氨作出响应。用其它化合物测试时,反应强度不到精氨酸的百分之一,表明这种电极对精氨酸是特异的。这种新电极的特点是制造时无需考虑酶的分离、鉴定和贮存以及如何把酶反应所需的辅因子与酶一起涂在电极头上的问题。     

期前收缩与代偿间歇教学实验的改进

期前收缩与代偿间歇实验,传统的方法是将普通电极接触在体蛙(或蟾蜍)心心室,在心舒张期给予单个刺激,通过描记装置观察心室的反应。由于电极与心室接触的紧密程度不易控制,一般均有接触不良或妨碍心搏影响描记等缺陷。我们参考了有关实验方法,改进了这一实验,收到了较好的效果。器材离体蛙心灌流实验装置一套,漆包线。实验方法和原理在离体蛙心灌流实验装置的基础上,用一直径约0.2毫米的漆包线(线端去掉漆膜)系在蛙心夹上。再取另一同规格的漆包线插入蛙心插管内任氏(Ringer)液中作为无关电极。将两漆     

电流耦合型人体通信的人体实验与衰减特性分析

目的:获取电流耦合型人体通信的人体信道衰减特性。方法:采用前期设计并验证的人体通信原理实验装置开展多名志愿者的人体实验。结果:对人体输入不同大小安全电流,产生的电位衰减近似相同;理疗电极较心电电极具有更小的信号衰减;发送电极面积越大信号衰减越小;接收电极的差异对信号检测效果影响较小;直径较粗的人体部位具有较小的信号衰减;信号衰减率随收发电极距离的增大而减小。结论:人体是安全电流激励的线性响应系统;发送电极与人体的接触阻抗越小越利于信号传输;肌肉是体内电流传输的主要路径;输入电流产生的耦合电位在发送电极附近急速衰减,约20cm后以近似稳定的电位传遍全身。     

母女共患犬小孢子菌感染2例

报道2例少见的女童单次接触宠物猫致头皮脓癣,女童再传染给妊娠母亲致体癣的病例。女童因枕部头皮多发脓肿12d就诊,妊娠母亲因右腰部孤立性红斑伴瘙痒2d就诊。皮损经真菌镜检、培养及分子生物学测序均鉴定为犬小孢子菌。女童经内服特比萘芬和强的松联合外用酮康唑洗剂6周后治愈,母亲经外用酮康唑洗剂和联苯卞唑乳膏3周后治愈。     

基于脑电信号识别采集的假肢控制系统

本文介绍了脑电信号（EEG）的模式识别和步骤,分析了EEG采集领域的发展和医学原理。通过研究脑电信号和假肢运动的联系,总结脑电控制假肢的可行性结论。设计出从头皮电极到模／数转换器的基于脑电信号识别采集的假肢控制系统,能够满足脑电假肢的各种要求。     

Optimal combination of electrodes and conductive gels for brain electrical impedance tomography

Background

Electrical impedance tomography (EIT) is an emerging imaging technology that has been used to monitor brain injury and detect acute stroke. The time and frequency properties of electrode–skin contact impedance are important for brain EIT because brain EIT measurement is performed over a long period when used to monitor brain injury, and is carried out across a wide range of frequencies when used to detect stroke. To our knowledge, no study has simultaneously investigated the time and frequency properties of both electrode and conductive gel for brain EIT.

Methods

In this study, the contact impedance of 16 combinations consisting of 4 kinds of clinical electrode and five types of commonly used conductive gel was measured on ten volunteers’ scalp for a period of 1 h at frequencies from 100 Hz to 1 MHz using the two-electrode method. And then the performance of each combination was systematically evaluated in terms of the magnitude of contact impedance, and changes in contact impedance with time and frequency.

Results

Results showed that combination of Ag⁺/Ag⁺Cl^? powder electrode and low viscosity conductive gel performed best overall (Ten 20^® in this study); it had a relatively low magnitude of contact impedance and superior performance regarding contact impedance with time (p?<?0.05) and frequency (p?<?0.05).

Conclusions

Experimental results indicates that the combination of Ag⁺/Ag⁺Cl^? powder electrode and low viscosity conductive gel may be the best choice for brain EIT.

     

Effects of different electrodes on bioelectrical impedance values

Effects of different electrodes on bioelectrical impedance values measured by the Selco bioelectrical impedance plethysmograph (SIF-881, Japan) were investigated using 8 adult females (age: 35.3 +/- 7.6 yr, Ht: 156.9 +/- 3.8 cm, Wt: 57.1 +/- 9.9 kg, and hydrodensitometrically determined body fat: 29.4 +/- 6.0%). The Lectec MP3000 electrode (Liberty Carton, USA) and the Bipolar electrode (Sanwa, Japan) produced significantly higher impedance values when compared to the Disposable electrode (Adovance, Japan) and the ECG electrode (Nihon Kohden, Japan). The coefficient of variation was significantly lower for the Disposable electrode (0.8%) and the ECG electrode (0.2%) than that for the Lectec MP3000 electrode (2.3%) and the Bipolar electrode (4.9%). In conclusion, the ECG electrode provides higher bioelectrical impedance values with the highest reproducibility in the assessment of human body composition by the bioelectrical impedance plethysmography.     

Ag-AgCl electrode noise in high-resolution ECG measurements

The authors measured the noise and impedance from face-to-face Ag-AgCl electrode pairs, as well as the noise from Ag-AgCl electrodes placed on the human body surface, in the frequency band from 0.5 Hz to 500 Hz, which corresponds to high-resolution ECG measurements. Electrode noise and electrode impedance were measured simultaneously to compare electrode noise with the thermal noise from the real part of electrode impedance. The results show that electrode noise depends on electrode area, electrolytic gel, the patient, and the placement site. In the frequency band from 0.5 Hz to 500 Hz, root-mean-square electrode noise is typically less than 1 microV for electrodes placed face-to-face and ranges from 1 microV to 15 microV for electrodes on the body surface. The noise spectral density increases at low frequencies as 1/fa and it is always higher than the thermal noise from the real part of the electrode impedance. There is a high correlation between electrode dc offset voltage and electrode noise. Thus, offset voltage measurements allow identification of noise from low-noise electrodes.     

Impedance analysis of bio-fuel cell electrodes

To determine the criteria for the selection of an electrode suitable for a bio-fuel cell (BFC), five electrodes, i.e. silver, aluminum, nickel, stainless steel and carbon fiber cloth were investigated. The performance of the BFC according to the electrode material, including the generated voltage, current density and power density was observed. These results show that the materials used for constructing the electrodes affect the performance of the BFC. An impedance analysis was used to describe the characteristics of the electrodes in the solution. Equivalent circuits of each component such as solution, electrodes-solution interface and electrode were determined from the impedance data. The constant-phase element (CPE) model was applied for data analyzing. It was found that stainless steel, nickel and aluminum behaved like a polarized electrode which has a high electrode-solution interfacial impedance, while carbon fiber cloth and silver had a low impedance like a non-polarized electrode. The impedance data indicated that a higher interfacial impedance will result in a higher loading effect. The results can be summarized that the carbon fiber cloth electrode offers a good electron transfer in the system and thus supplies higher power to the external load.     

Visual evoked potentials in the vicinity of the optic tract during stereotactic pallidotomy

We recorded visual evoked responses in eight patients with Parkinson's disease, using a depth electrode either at or below the stereotactic target in the ventral part of the globus pallidus internus (GPi), which is located immediately dorsal to the optic tract. Simultaneously, scalp visual evoked potentials (VEPs) were also recorded from a mid-occipital electrode with a mid-frontal reference electrode. A black-and-white checkerboard pattern was phase reversed at 1 Hz; check size was 50 min of arc. Pallidal VEPs to full field stimulation showed an initial positive deflection, with a latency of about 50 ms (P50), followed by a negativity with a mean latency of 80 ms (N80). The mean onset latency of P50 was about 30 ms. P50 and N80 were limited to the ventralmost of the GPi and the ansa lenticularis. Left half field stimulation evoked responses in the right ansa lenticularis region while right half field stimulation did not, and vice versa. These potentials thus seemed to originate posterior to the optic chiasm. The scalp VEPs showed typical triphasic wave forms consisting of N75, P100 and N145. The location of the recording electrode in the ansa lenticularis region did not modify the scalp VEP. These results suggest that P50 and N80 are near-field potentials reflecting the compound action potentials from the optic tract. Therefore, N75 of the scalp VEPs may represent an initial response of the striate cortex but not of the lateral geniculate nucleus.     

Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans

Flash and pattern reversal visual evoked potentials were recorded in awake patients undergoing stereotactic procedures for severe dyskinetic disorders resistant to medical treatment. The nucleus ventralis lateralis thalami was reached via an occipital approach. VEPs were recorded on the scalp at the entracce of the intracerebral electrode, and serially from sites at different depths. A polarity reversal of the surface recorded wave form took place as the intracerebral electrode was advanced beneath the surface cortical layers. As concerns F-VEPs, most of the scalp activity mirrored the potentials recorded down to the depth of 70-65 mm from the thalamus. The largest amplitude of intracerebral F-VEPs was obtained from recording sites at 50–70 mm from the thalamus, i.e., in the depth of the calcarine fissure. A negative wave, peaking around 47–50 msec, became evident in recording sites at 30–40 mm from the thalamus but vanished as the electrode was advanced farther. In only one patient could we record a small negative wave, peaking at 33 msec, in the vicinity of the corpus geniculatum externum. Furthermore, the oscillatory activity recorded from the scalp appeared to be generated in the cortical layers. PR-VEPs also underwent polarity reversal as the electrode traversed the cortex. PR-VEPs disappeared more superficially than F-VEPs. No PR-evoked activity could be recorded in the vicinity of the corpus geniculatum externum.We conclude that slow and fast components of VEPs recorded from the scalp are entirely generated in cortical layers.     

Four-point electrode measurement of impedance in the vicinity of bovine aorta for quasi-static frequencies

Results are presented here of experimental measurements using a four-point electrode technique to measure the complex impedance of bovine aorta submerged in Ringer's solution. Impedance measurements were taken at 250 microm intervals, ranging from 0 (the electrode directly on the surface of the tissue) to 10 mm. Frequencies ranged from 1 kHz to 10 MHz. Throughout this range, the measured impedance changed by an average of 400% when the electrode was 10 mm from the tissue as compared to when the electrode was in direct contact with the tissue. The change in impedance made it possible to determine when the electrode made contact with the arterial wall.     

Effects of cavities on EEG dipole localization and their relations with surface electrode positions

Effects of cavities in the human head on EEG dipole localization have been investigated by computer simulation. The human head is represented by a homogeneous spherical conductor including an eccentric spherical cavity which approximates effects of actual cavities inside the head. The homogeneous sphere model is used for assessing the effects caused by neglecting the cavity in the volume conductor model in the inverse dipole fitting procedure. Four electrode configurations have been examined to investigate their relation to the EEG inverse dipole solution. After examination of 2520 dipoles in the brain, the effects of cavities in the human head are found to be negligible when the dipole is located in the cortex or in the subcortex. When the dipole is located in the brain stem, the EEG inverse dipole solution is strongly affected by the cavity and is sensitive to the electrode configuration on the scalp. The EEG inverse dipole solution in the deep brain is sensitive to inhomogeneity in the lower part of the head when a single positive or negative potential pole is observed by the electrodes on the scalp, and at the same time is sensitive to the extent of the scalp covered by the electrodes. In conclusion, the electrodes should cover as much of the upper scalp as possible for deep source localization.     

Linear and Nonlinear Measures and Seizure Anticipation in Temporal Lobe Epilepsy

In a recent paper, we showed that the value of a nonlinear quantity computed from scalp electrode data was correlated with the time to a seizure in patients with temporal lobe epilepsy. In this paper we study the relationship between the linear and nonlinear content and analyses of the scalp data. We do this in two ways. First, using surrogate data methods, we show that there is important nonlinear structure in the scalp electrode data to which our methods are sensitive. Second, we study the behavior of some simple linear metrics on the same set of scalp data to see whether the nonlinear metrics contain additional information not carried by the linear measures. We find that, while the nonlinear measures are correlated with time to seizure, the linear measures are not, over the time scales we have defined. The linear and nonlinear measures are themselves apparently linearly correlated, but that correlation can be ascribed to the influence of a small set of outliers, associated with muscle artifact. A remaining, more subtle relation between the variance of the values of a nonlinear measure and the expectation value of a linear measure persists. Implications of our observations are discussed.     

Detection of viable Salmonella typhimurium by impedance measurement of electrode capacitance and medium resistance

Three-electrode electrochemical impedance technique was investigated for detection of Salmonella typhimurium by monitoring the growth of bacteria in selenite cystine (SC) broth supplemented with trimethylamine oxide hydrochloride (TMAO.HCl) and mannitol (M). The change in the system impedance during the growth of bacteria was studied using frequency spectral scanning. It was found that the impedance at low frequencies (<10 kHz) mainly came from the double-charged layer capacitance, reflecting the changes at the electrode interface and the adsorption on the electrode surface. While at high frequencies (>10 kHz), the system impedance mainly depended on the medium resistance. The adsorption of bacteria on the electrode surface was detected by measuring low frequency impedance, and verified with Faradic impedance spectroscopy. Enumeration of S. typhimurium using a low frequency (1 Hz) capacitance measurement and a high frequency (1 MHz) resistance measurement were compared. The detection times were determined for quantitative analysis based on the growth curves of bacteria referring to either the medium resistance or electrode capacitance. The regression equations for the detection times (t(d), h) and the initial cell number (N, cells.ml(-1)) were t(d)=-1.24logN+13.4 with R(2)=0.98 and t(d)=-1.40logN+14.46 with R(2)=0.97 for the medium resistance and electrode capacitance methods, respectively.