Impedance electrodes positioned on proximal portions of limbs quantify fluid compartments in dogs

Body resistance and reactance to the conduction of an alternating electrical current were measured using electrodes attached to distal and proximal portions of limbs in anesthetized dogs. Body impedance was calculated from these measurements obtained at 30-min time intervals during a control period and after intravenous administration of 0.9% saline. Extracellular (ECW) and total body water (TBW) were determined by bromide and heavy water dilution techniques, respectively. Baseline impedance obtained from proximal electrodes was related to ECW (r = 0.95, P less than 0.001) and TBW (r = 0.80, P less than 0.02). After saline infusion, proximal electrodes detected a significant fall in impedance (P less than 0.001), whereas distal electrodes did not (P = 0.06). Furthermore, ECW and TBW could be estimated from the drop of proximal impedance after this bolus infusion (r = 0.82, P less than 0.02, and r = 0.86, P less than 0.01, respectively), but not from distal impedance measurements. Proximally placed impedance electrodes are superior to traditionally used distal electrodes for assessment of body fluid changes in the dog.     

Some Relations between Changes in the Linear Electrical Properties of Striated Muscle Fibers and Changes in Ultrastructure

Some of the linear electrical properties of frog sartorius muscle have been investigated in Ringer's fluid and in a Ringer fluid made hypertonic by the addition of sucrose or NaCl. Electrical constants were determined from measurements of the phase angle of the admittance of a fiber for an applied alternating current, from measurements of the voltage induced by an inward pulse of current, and from measurements of the conduction velocity of the action potential and the time constant of its foot. The dilation of the transverse tubular system induced by the sucrose hypertonic Ringer fluid was correlated with the change in the electrical constants. From this it is concluded that a two time constant equivalent circuit for the membrane, as proposed by Falk and Fatt, is in good agreement with our results. Both the area of the membrane of the transverse tubular system, and the capacity (c_e) attributed to it, increased in the sucrose hypertonic Ringer fluid. The resistance r_e, which is in series with c_e, did not fall when the transverse tubular system was dilated and probably is not located in that system.     

Chronic instrumentation and longterm investigation in the fetal and maternal baboon: tether system, conditioning procedures and surgical techniques

A tether system, conditioning procedures and surgical techniques were designed to maintain chronic catheters and electrodes in the pregnant baboon and her fetus. The tether system was comprised of a lightweight metal backpack containing catheters and electrodes, couplers, pressure transducers and electrical cabling. The backpack was held snugly in place by shoulder and body straps. A flexible metal tether connected the pack to a ball bearing assembly mounted on the top of the animal's home cage. Attached to the assembly were two infusion pumps, fluid reservoir and slip ring electrical connector. The entire system rotated freely with the movements of the animal; thus, the instrumentation and connectors were secure while access was maintained for continuous physiologic recording and intravascular infusion or intermittent blood sampling with minimal physical restraint. Animals were conditioned to accept the system prior to pregnancy and animals who demonstrated tolerance were bred. An initial group of 10 pregnant animals were sham tethered during pregnancy at 102 +/- 7 days with term gestation estimated at 180 days. Surgical procedures were done at 136 +/- 4 days with placement of catheters in the maternal femoral artery and vein, fetal carotid artery jugular vein and trachea, amniotic fluid cavity, and electrodes for fetal electrocardiogram and electroencephalogram. The mean fetal survival time was 9.3 (range 0 to 29) days. The major complications which led to early delivery were placental abruption and rupture of amniotic membranes. With ultrasonic localization of the placenta and determination of fetal position before surgery, these complications may be avoided.(ABSTRACT TRUNCATED AT 250 WORDS)     

The central effects of morphine on fetal breathing movements in the fetal sheep

The fetal respiratory and electrocortical effects of 0.6 microgram to 600 micrograms of morphine, administered into the lateral cerebral ventricle, have been studied in chronically catheterised, unanaesthetized fetal sheep at 115-135 days gestation. Morphine at 0.6 microgram had no effect on breathing movements or electrocorticographic activity, and at 6 micrograms induced a period of apnoea (43-122 min) but had no effect on electrocortical activity. Intravenous naloxone (2 mg bolus and infusion of 2 mg/kg/h for 2 h) to the fetus had no effect on this apnoea. Morphine at 60 micrograms induced an initial period of apnoea (30-65 min) followed by episodic but significantly deep breathing movements with no effect on electrocortical activity and at 600 micrograms induced an initial period of apnoea (22-95 min) which was followed by deep, irregular and continuous (126-302 min) breathing movements. During the apnoea electrocortical activity initially remained cyclic, but as apnoea progressed there was a gradual reduction in the voltage of the electrocorticogram to a low voltage state. Intravenous naloxone (2 mg bolus and infusion of 2 mg/kg/h for 2 h) reversed both the respiratory and electrocortical effects. The hyperventilation was also inhibited by hypoxia. Naloxone alone had no effect on fetal breathing activity.     

Dielectrophoretic separation of cells: Continuous separation

Dielectrophoresis is the movement of particles in non-uniform alternating and direct current (AC, DC) electric fields. When nonuniform electric fields are created between microelectrodes, cells will redistribute themselves around the electrodes, the force holding the cells in place dependig on the local electric field and on the electrical properties of the cells themselves and the suspending medium. Steric drag forces produced by a gentle fluid flow in the chamber can be used to separate cells by selectively lifting cells from potential energy wells produced by the electric field. The technique is demonstrated in the batch separation of bacteria, yeast cells, and plant cells. Continuous separation and extraction of two cell types can be achieved by repeated reversing of the fluid flow direction in phase with the switching on and off of the applied voltage, and the efficacy of the technique is demonstrated for viable and nonviable (heat-treated) yeast cells. (c) 1995 John Wiley & Sons, Inc.     

弥猴单侧软腭肌肉对针式电极刺激的反应

目的建立针电极口内刺激猴软腭肌肉诱发腭咽闭合运动的模式,取得软腭肌肉运动的有效刺激数值,为软腭肌肉功能重建奠定基础。方法通过解剖成年猕猴软腭的五组肌肉,确定其体表位置;利用实验动物用腭部肌肉电极定位刺激器及针式电极对软腭肌肉进行有效刺激;结合鼻咽纤维镜、头颅侧位X片及软腭造影技术观察、记录肌肉收缩及腭咽闭合动作。结果在猕猴口内定位目标肌肉进行针电极刺激可诱发肌肉收缩。刺激电压为3 V、刺激频率为20 Hz时均能诱发单侧软腭肌肉的有效收缩;单侧腭帆提肌在刺激电压为5 V、20 Hz时可发生腭咽闭合动作。咽腭肌、舌腭肌在刺激电压5 V、刺激频率100 Hz时发生软腭下降动作。腭帆张肌仅发生收缩,而未发生腭咽闭合。应用鼻咽纤维镜和X线成像技术配合能记录腭咽闭合动作。结论弥猴可作为研究软腭肌肉运动模式的实验动物。应用电极刺激软腭肌肉,可初步建立腭咽闭合的动作模式。     

A microprocessor-regulated constant voltage, current, wattage, and temperature electrophoresis power supply

The analog control circuitry typically found in commercial electrophoresis power supplies was replaced by a digital microcomputer. Analog to digital converters were used to monitor the voltage applied to and current passed through an electrophoresis cell. Microcomputer programming was employed to compare converter input values with preselected operating parameters and then calculate a required output voltage. Timing sequences were generated through programming utilizing clocks located on the interface boards. A digital to analog converter was employed to apply a control voltage to a constant voltage power supply. This process was completed at least 20 times each second. BASIC programming subroutines were written to maintain constant voltage, current, power (wattage), and temperature. To these operating procedures, other techniques such as automated endpoint detection of isoelectric focusing and pulsed waveform outputs were easily added. This power supply containing a microcomputer system as the feedback element was shown to have a greater stability and versatility than conventional supplies.     

Mechanically induced electrical potentials of articular cartilage

While there is increasing evidence that chondrocytes are affected by mechanically induced stimuli, endogenous force-related electrical potentials within articular cartilage have been so far observed only in-vitro. Using a porcine ex-vivo model (German Land Race), 8 knee joints were explanted and exposed to mechanical force (up to 800 N) using a special device. Electrodes were inserted into the cartilage matrix. With an amplifier and an A/D transducer the changes of electrical voltage between the electrodes as well as those of the force were recorded online and simultaneously on a computer. Additionally, we located one pair of electrodes on the surface of the cartilage tissue to detect electrical fields outside the cartilage tissue. In relation to the applied force we observed that electrical potentials derived from inside and outside the articular cartilage showed a correspondence. When an alternating force with an amplitude of 360 N and a frequency of about 0.2 Hz was periodically applied, we measured peak amplitudes ranging from 2.1 to 5.5 mV within the cartilage tissue with electrical negativity within the weight bearing area of the cartilage tissue. The measured voltages depended on the applied force, the location of the electrodes, and on anatomical variations. We found an almost linear relation between the magnitude of the applied force and the recorded voltage. With the help of the electrodes located outside and within the cartilage tissue, we were able to show that force dependent fields are generated inside the cartilage. There are several theories explaining the origin of these electrical phenomena, many of them focusing on the negative charges of the proteoglycans in relation to the flow of interstitial fluid and ions under compression. However, the consequences of these phenomena are yet not clear.     

Automatic Fall Detection System Based on the Combined Use of a Smartphone and a Smartwatch

Due to their widespread popularity, decreasing costs, built-in sensors, computing power and communication capabilities, Android-based personal devices are being seen as an appealing technology for the deployment of wearable fall detection systems. In contrast with previous solutions in the existing literature, which are based on the performance of a single element (a smartphone), this paper proposes and evaluates a fall detection system that benefits from the detection performed by two popular personal devices: a smartphone and a smartwatch (both provided with an embedded accelerometer and a gyroscope). In the proposed architecture, a specific application in each component permanently tracks and analyses the patient’s movements. Diverse fall detection algorithms (commonly employed in the literature) were implemented in the developed Android apps to discriminate falls from the conventional activities of daily living of the patient. As a novelty, a fall is only assumed to have occurred if it is simultaneously and independently detected by the two Android devices (which can interact via Bluetooth communication). The system was systematically evaluated in an experimental testbed with actual test subjects simulating a set of falls and conventional movements associated with activities of daily living. The tests were repeated by varying the detection algorithm as well as the pre-defined mobility patterns executed by the subjects (i.e., the typology of the falls and non-fall movements). The proposed system was compared with the cases where only one device (the smartphone or the smartwatch) is considered to recognize and discriminate the falls. The obtained results show that the joint use of the two detection devices clearly increases the system’s capability to avoid false alarms or ‘false positives’ (those conventional movements misidentified as falls) while maintaining the effectiveness of the detection decisions (that is to say, without increasing the ratio of ‘false negatives’ or actual falls that remain undetected).     

A multichannel microcomputer-based system for continuously measuring and recording ion activities of uptake solutions during ion absorption by roots of intact plants

Abstract. A microcomputer-based system for the measurement of changes of ion activity (H⁺, NO₃⁻, K⁺) in the uptake solutions during ion absorption by roots of intact plants is described. Ion activities are measured by means of ion-specific electrodes in a multichannel programmable voltmeter (data acquisition/control unit) which is activated by means of a microcomputer. Incoming data are stored digitally on tape cassettes or floppy discs via the microcomputer. The speed of sampling and large numbers of samples which can be simultaneously measured and recorded make this an extremely versatile system which might be employed for measuring and recording any number of analogue voltage signals.     

Modulation of a gated ion channel admittance in lipid bilayer membranes.

A future class of amperometric biosensors may utilize gated ion channels such as acetylcholine and glutamate receptors as chemical detection components. In this study, bilayer lipid membranes containing voltage-dependent anion channels (VDAC) were used to model an ion-channel-based biosensor which could continuously monitor AC amperometric changes resulting from induced changes in channel conductance. The in-phase and quadrature components of the induced alternating membrane current were monitored as a function of the applied DC offset voltage which was superimposed on the sinusoidal test voltage. The accuracy and sensitivity of the AC-measured VDAC response was dependent on the magnitude of the AC test voltage relative to the DC offset necessary for channel closure. The VDAC channel appears to be a suitable model protein for AC impedance-based biosensor fabrication.     

Virtual electrode effects in defibrillation

This modeling study demonstrates that a re-entrant activity in a sheet of myocardium can be extinguished by a defibrillation shock delivered via extracellular point-source electrodes which establish spatially non-uniform applied field. The tissue is represented as a homogeneous bidomain with unequal anisotropy ratios in the cardiac conductivities. Spiral wave re-entry is initiated in the bidomain sheet following an S1-S2 stimulation protocol. The results indicate that the point-source defibrillation shock establishes large-scale changes in transmembrane potential in the tissue (virtual electrodes) that are ‘superimposed’ over regions of various degrees of membrane refractoriness in the myocardium. The close proximity of large-scale shock-induced regions of alternating membrane polarity is central to the ability of the shock to terminate the spiral wave. The new wavefronts generated following anode/cathode break phenomena restrict the spiral wave and render the tissue too refractory to further maintain the re-entry. In contrast, shocks delivered via line electrodes establish, in close proximity to the electrode, changes in transmembrane potential that are of same-sign polarity. These shocks are incapable of terminating the re-entrant activation.     

Mechanical and electrical anisotropy in Mimosa pudica pulvini

Thigmonastic or seismonastic movements in Mimosa pudica, such as the response to touch, appear to be regulated by electrical, hydrodynamical and chemical signal transduction. The pulvinus of Mimosa pudica shows elastic properties, and we found that electrically or mechanically induced movements of the petiole were accompanied by a change of the pulvinus shape. As the petiole falls, the volume of the lower part of the pulvinus decreases and the volume of the upper part increases due to the redistribution of water between the upper and lower parts of the pulvinus. This hydroelastic process is reversible. During the relaxation of the petiole, the volume of the lower part of the pulvinus increases and the volume of the upper part decreases. Redistribution of ions between the upper and lower parts of a pulvinus causes fast transport of water through aquaporins and causes a fast change in the volume of the motor cells. Here, the biologically closed electrochemical circuits in electrically and mechanically anisotropic pulvini of Mimosa pudica are analyzed using the charged capacitor method for electrostimulation at different voltages. Changing the polarity of electrodes leads to a strong rectification effect in a pulvinus and to different kinetics of a capacitor discharge if the applied initial voltage is 0.5 V or higher. The electrical properties of Mimosa pudica''s pulvini were investigated and the equivalent electrical circuit within the pulvinus was proposed to explain the experimental data. The detailed mechanism of seismonastic movements in Mimosa pudica is discussed.Key words: electrophysiology, plant electrostimulation, pulvinus, Mimosa pudica, charged capacitor method, electrical circuits, ion channels     

Modulation of renal type IIa Na+/Pi cotransporter kinetics by the arginine modifier phenylglyoxal

The effects of the arginine-modifying reagent phenylglyoxal on the kinetics of the type IIa Na + /Pi cotransporter expressed in Xenopus, oocytes were studied by means of 32Pi uptake and electrophysiology. Phenylglyoxal incubation induced up to 60% loss of cotransport function but only marginally altered the Na+-leak. Substrate activation and pH dependency remained essentially unaltered, whereas the voltage dependency of Pi-induced change in electrogenic response was significantly reduced. Presteady-state charge movements were suppressed and the equilibrium charge distribution was shifted slightly towards hyperpolarizing potentials. Charge movements in the absence of external Na+ were also suppressed, which indicated that the empty-carrier kinetics were modified. These effects were incorporated into an ordered alternating access model for NaPi-IIa, whereby the arginine modification by phenylglyoxal was modeled as altered apparent electrical distances moved by mobile charges, together with a slower rate of translocation of the electroneutral, fully loaded carrier.     

Evidence for a central role for electro-osmosis in fluid transport by corneal endothelium

The mechanism of transepithelial fluid transport remains unclear. The prevailing explanation is that transport of electrolytes across cell membranes results in local concentration gradients and transcellular osmosis. However, when transporting fluid, the corneal endothelium spontaneously generates a locally circulating current of approximately 25 microA cm(-2), and we report here that electrical currents (0 to +/-15 microA cm(-2)) imposed across this layer induce fluid movements linear with the currents. As the imposed currents must be approximately 98% paracellular, the direction of induced fluid movements and the rapidity with which they follow current imposition (rise time < or =3 sec) is consistent with electro-osmosis driven by sodium movement across the paracellular pathway. The value of the coupling coefficient between current and fluid movements found here (2.37 +/- 0.11 microm cm(2) hr(-1) microA (-1), suggests that: 1) the local endothelial current accounts for spontaneous transendothelial fluid transport; 2) the fluid transported becomes isotonically equilibrated. Ca(++)-free solutions or endothelial damage eliminate the coupling, pointing to the cells and particularly their intercellular junctions as a main site of electro-osmosis. The polycation polylysine, which is expected to affect surface charges, reverses the direction of current-induced fluid movements. Fluid transport is proportional to the electrical resistance of the ambient medium. Taken together, the results suggest that electro-osmosis through the intercellular junctions is the primary process in a sequence of events that results in fluid transport across this preparation.     

A mathematical model to investigate the effects of intravenous fluid administration and fluid loss

The optimal fluid administration protocol for critically ill perioperative patients is hard to estimate due to the lack of tools to directly measure the patient fluid status. This results in the suboptimal clinical outcome of interventions. Previously developed predictive mathematical models focus on describing the fluid exchange over time but they lack clinical applicability, since they do not allow prediction of clinically measurable indices. The aim of this study is to make a first step towards a model predictive clinical decision support system for fluid administration, by extending the current fluid exchange models with a regulated cardiovascular circulation, to allow prediction of these indices. The parameters of the model were tuned to correctly reproduce experimentally measured changes in arterial pressure and heart rate, observed during infusion of normal saline in healthy volunteers. With the resulting tuned model, a different experiment including blood loss and infusion could be reproduced as well. These results show the potential of using this model as a basis for a decision support tool in a clinical setting.     

Behavior and viability of tobacco protoplasts in response to electrofusion parameters

This investigation examines responses of protoplasts in a systematic and quantitative way to the various electrical treatments used to achieve electrofusion and their individual and cumulative effect on protoplast viability. Mesophyll and cell suspension protoplasts from two species of the same genera, Nicotiana tabacum and N. rustica var brasilia were used in these experiments. Optimal frequencies for alignment of tobacco protoplasts were between 500 kilohertz and 2 megahertz at 100 volts per centimeter. Variations in frequency and voltage of the alternating current (AC) field caused predictable movements of protoplasts within an electrofusion chamber. AC frequencies below 10 hertz or above 5 megahertz significantly decreased the viability of protoplasts in the fusion chamber as estimated by fluorescein diacetate staining 1 hour after treatment. Although the direct current (DC) pulse appeared to have a slight detrimental effect on protoplast viability, this effect was not significantly different from untreated control preparations.

Protoplasts from both leaf mesophyll cells and suspension cells were induced to fuse with one or more 10 to 30 microseconds DC square wave pulses of approximately 1 kilovolt per centimeter after the protoplasts had been closely appressed with an AC field.

     

Action of combined magnetic fields on aqueous solution of glutamic acid: the further development of investigations

In the present work the results of the known investigation of the influence of combined static (40 μT) and alternating (amplitude of 40 nT) parallel magnetic fields on the current through the aqueous solution of glutamic acid, were successfully replicated. Fourteen experiments were carried out by the application of the combined magnetic fields to the solution placed into a Plexiglas reaction vessel at application of static voltage to golden electrodes placed into the solution. Six experiments were carried out by the application of the combined magnetic fields to the solution placed in a Plexiglas reaction vessel, without electrodes, within an electric field, generated by means of a capacitor at the voltage of 27 mV. The frequency of the alternating field was scanned within the bounds of 1.0 Hz including the cyclotron frequency corresponding to a glutamic acid ion and to the applied static magnetic field. In this study the prominent peaks with half-width of ~0.5 Hz and with different heights (till 80 nA) were registered at the alternating magnetic field frequency equal to the cyclotron frequency (4.2 Hz). The general reproducibility of the investigated effects was 70% among the all solutions studied by us and they arose usually after 40–60 min. after preparation of the solution. In some made-up solutions the appearance of instability in the registered current was noted in 30–45 min after the solution preparation. This instability endured for 20–40 min. At the end of such instability period the effects of combined fields action appeared practically every time. The possible mechanisms of revealed effects were discussed on the basis of modern quantum electrodynamics.     

Investigation of Electrode Erosion Parameters in Direct and Alternating Current Plasma Torches

Plasma Physics Reports - This paper deals with the study of the wear resistance (erosion) of the material of electrodes in direct and alternating current plasma torches. The life time of electrodes...