Train Of Voltage Pulses Research Articles

How to test mode switching in pacemakers implanted in patients: the MOST study.

Optimal management of atrial arrhythmias with dual chamber pacemakers requires proper performance of automatic mode switching (AMS). The aim of this study was to develop a reliable technique to test the AMS function by using an external electronic device capable of mimicking the occurrence of supraventricular arrhythmias (Supraventricular Arrhythmia Simulator [SAS]). The SAS delivers low voltage pulse trains (200 mV, 20 ms) through two skin electrodes. Each pulse train lasts 15 seconds and starts synchronously with a pacing pulse of the implanted pacemaker to avoid interference from the operator. The pulse train rate is set at 350, 250, and 160 beats/min to simulate AF, atrial flutter, and atrial tachycardia (AT), respectively. Thirty-five patients implanted with Vitatron pacemakers, whose AMS system has been previously validated, were enrolled. Atrial and ventricular sensing were programmed in unipolar mode at 0.5 mV and in bipolar mode at > 2 mV, respectively. All pulses from the SAS were detected by the atrial channel at an amplitude ranging from 1 to 3 mV. The test proved to be safe and reliable at rest and during exercise. AMS occurred immediately at onset or at offset of atrial arrhythmias, and no adverse interference on pacemaker function was seen from the SAS. In conclusion, the described technique and the SAS are safe and reliable for patient and pacemaker function and can be proposed as a useful method to verify proper performance of AMS function irrespective of the type of implanted devices.

Protection of intrinsic nerves of guinea-pig detrusor strips against anoxia/glucopenia and reperfusion injury by taurine.

There is ample evidence that ischaemia is associated with partial denervation of the detrusor muscle and that this is responsible for much of its abnormal contractile behaviour, resulting in bladder dysfunction (instability). In guinea-pig nerves are very susceptible to the ischaemic damage as compared to the muscle cells. The purpose of this study was to assess the neuroprotection afforded by taurine on guinea-pig detrusor under ischaemic-like conditions. Guinea-pig detrusor strips were subjected for 60 min to ischaemic-like conditions, followed by 150 min reperfusion. Intrinsic nerves underwent every 30 min electrical field stimulation (EFS) by 5-s trains of square voltage pulses of 0.05 ms duration (15 Hz, 50 V). Detrusor strips were perfused with 0.1, 1, 3 or 10 mM taurine during the ischaemia-like exposure and the first 30 min of reperfusion. Taurine (1 and 3 mM) significantly improved the response of the strips to EFS both at the end of ischaemia and reperfusion. On the contrary, neither 0.1 nor 10 mM taurine had significant effects. It is concluded that taurine can partially counteract the ischaemia-reperfusion injury in the guinea-pig urinary bladder.

Termination of reentry by infra- and supra-threshold pulses

Two different experimental methods to terminate a reentrant activity were studied within the framework of nonlinear electronic circuits, which mimic the discrete nature of cardiac tissue at a microscopic scale. It was shown that trains of low voltage (with infra- and supra-threshold stimulating amplitude) and low frequency (period larger than that of reentry) pulses can be used efficiently to terminate a pinned reentry when applied near to the reentry.

Plasma-assisted deposition at atmospheric pressure

Most plasma-assisted deposition methods currently available use gas discharges at pressures below 1 hPa. In many cases, the process temperature can be kept low due to the fact that the energy necessary for the initiation of chemical reactions is transferred via charged particles. However, a low pressure requires a large amount of vacuum equipment. Processes at atmospheric pressure are more favourable if results similar to those of existing methods can be achieved. Barrier discharges provide the basis for a new plasma-assisted deposition method at atmospheric pressure. These discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated. Starting with some basic considerations on the properties of microdischarges, the deposition of thin polymeric films on glass surfaces is described using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained if trains of voltage pulses are used. The parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.

Plasma-Assisted Deposition at Atmospheric Pressure

In plasma-assisted deposition methods the activation energy necessary for the initiation of chemical reactions is transferred via charged particles. Due to this fact in many cases the process temperature can be kept small, if gas discharges at pressures below 1 hPa are used. On the other hand low pressure requires a great deal of vacuum equipment. Processes at atmospheric pressure are more favourable, if similar results compared to existing methods can be achieved. Basis for a new plasma-assisted deposition method at atmospheric pressure are barrier discharges. Those discharges consist of a large number of transient microdischarges in parallel which are distributed statistically on the surface to be coated. Starting with some basic considerations on the repetitive generation of microdischarges, the deposition of thin polymeric films on glass surfaces is described, using barrier discharges at atmospheric pressure and acetylene. Uniform polymeric films up to 1 μm are obtained, if trains of voltage pulses are used. Parameters influencing the deposition rate and the film quality are discussed. In addition, it is estimated whether further improvements of the deposition process are possible.

A bimorph-driven inertial micropositioner for scanning tunnelling microscopy

A bimorph-based inertial linear slider motor, suitable for the coarse approach of the scanning tunnelling microscope tip to the sample, is described. It is best suited for moving micropositioning structures of low height such as bimorph parallelograms, in the z direction, but also for sample stages carrying small samples. It is operated either by trains of voltage pulses of asymmetric shapes, produced by a digital-to-analogue converter, or, since it can also be moved by suitable combinations of binary ones and zeros, simply by switching between two voltage levels. The second case resulted in the most efficient horizontal movement, but it was less successful in moving against gravity.

A custom-chip-based functional electrical stimulation system.

The Functional Electrical Stimulation System consists of a host computer and up to 32 chips connected serially. Up to 256 different monophasic constant voltage (0 V-2.5 V), variable frequency (0 Hz-100 Hz in 2 Hz steps; 100 Hz-1700 Hz in 100 Hz steps), and adjustable duration (50 microseconds-200 ms in 50 microseconds steps) pulse trains can be continuously generated.

Somatic currents contribute to frequency-dependent spike-broadening in supraoptic neuroendocrine cells

Voltage-gated K and Ca currents were recorded in acutely dissociated neuroendocrine cells of the supraoptic nucleus. The effect of repeated activation of the currents by trains of (10) voltage pulses over a range of pulse-repetition frequencies were examined. There was a significant reduction of K-current amplitude and a significant increase of Ca-current amplitude during trains with high repetition frequencies. Frequency-dependent changes in K and Ca conductances may contribute to frequency-dependent spike-broadening which is exhibited during bursts of action potentials generated by these neurons.

Time-dependent transport through a mesoscopic structure.

We present a general formulation of the nonlinear, time-dependent current through a small interacting region, where electron energies are changed by time-dependent voltages. An exact solution is obtained for the non-interacting case when the elastic coupling to the leads is independent of energy. Temporal phase coherence in a double-barrier tunneling structure produces ``ringing" in the response of the current to a voltage pulse, which can be observed experimentally in the dc-current by varying the pulse length in a train of voltage pulses. The nonlinear current due to an ac-bias also shows complex time-dependence.

Characterization of K+ currents in rat malignant lymphocytes (Nb2 cells).

Membrane K+ currents of malignant lymphocytes (Nb2 cells) were studied with the whole-cell patch-clamp method. Upon depolarization, K+ currents activate with a delay and follow a sigmoid time course, resembling other delayed rectifier K+ currents present in nerve and muscle cells. The activation time constant of these currents is voltage dependent, increasing from 1 msec at +90 mV to approximately 37 msec at -30 mV. The fractional number of open channels has a sigmoid voltage dependence with a midpoint near -25 mV. Deactivation of K+ currents in Nb2 cells is voltage dependent and follows a simple exponential time course. Time constant of this process increases from 5 msec at -115 mV to almost 80 msec at -40 mV. The relative permeability of K+ channels to different monovalent cations follows the sequence: K+ (1) greater than Rb+ (0.75) greater than NH4+ (0.11) greater than Cs+ (0.07) greater than Na+ (0.05). Inactivation of K+ currents is a biexponential process with time constants of approximately 600 and 7,000 msec. Inactivation of K+ currents in Nb2 cells is not a voltage-dependent process. The steady-state inactivation curve of K+ currents has a midpoint near -40 mV. Following a 500-msec voltage pulse, inactivation of K+ currents recovers with a simple exponential process with a time constant of 9 sec. Short duration (approximately 50 msec) voltage-clamp pulses do not induce significant inactivation of these currents. K+ currents in malignant lymphocytes do not display the phenomenon of cumulative inactivation as described for other delayed rectifier-type K+ channels. Application of a train of voltage pulses to positive potentials at different frequencies induces a moderate decrease in peak outward currents. The use of substances (N-bromoacetamide, trypsin, chloramine-T, and papain) that remove the inactivation of Na+ and K+ currents in other cells are not effective in removing the inactivation of K+ currents present in this lymphoma cell line. Significant differences were found between the characteristics of K+ currents in this malignant cell line and those present in normal lymphocytes. Possible physiological implications for these differences and for the role of K+ currents in the proliferation of normal and malignant lymphocytes are discussed.

Electroporation of Cardiac Cell Membranes with Monophasic or Biphasic Rectangular Pulses

During defibrillation, cardioversion, and electrocution trauma, heart cells are exposed to potential gradients that increase the transmembrane potential (Vm). At sufficiently high Vm, pathological increases in cell permeability can occur. With enzymatically isolated frog heart cells (n = 29) we investigated the voltage and time sufficient for electroporation or cardiac cell membranes with rectangular voltage pulses, particularly with 5-msec monophasic, and 5- or 10-msec biphasic pulses. The rectangular voltage pulse (monophasic 0.1-1.5 V, 0.1-100 msec or symmetric biphasic 0.1-1 V, 0.4-10 msec [total duration]) was applied to the cell membrane using the cell-attached patch clamp technique, and a low voltage pulse train was added so that membrane conductance could be monitored continuously. Step increases in membrane conductance (breakdown) were observed, indicative of electroporation, and occurred with different combinations of pulse amplitude and duration; for example, for monophasic square pulses: (1 V, 0.2 msec) or (0.5 V, 0.5 msec), and for biphasic pulses: (1 V, 0.4 msec total duration) or (0.5 V, 0.8 msec). Using 5- or 10-msec rectangular pulses, breakdown occurred at a voltage around 0.4 V independent of polarity or waveform. The recovery of the permeabilized cell membrane after the voltage pulse was highly variable, in some cases not recovering at all while in other cases recovering after a lapse of seconds to minutes. These results suggest that monophasic and biphasic pulses of approximately 1 V, 0.2-0.4 msec and approximately 0.4 V, 5 msec can permeabilize the heart cell membrane even for minutes, time enough to cause an alteration in the cellular ionic composition leading to depressed or unexcitable tissue, a precursor for cardiac arrhythmia.

Calcium entry increases the sensitivity of cerebellar Purkinje cells to applied GABA and decreases inhibitory synaptic currents

The sensitivity to GABA of Purkinje cells in thin cerebellar slices was examined by recording either spontaneous inhibitory synaptic currents or ionic currents elicited by local GABA applications. The effects of Ca 2+ entry induced by depolarizing voltage pulses were opposite for the two types of currents. Currents due to exogenous GABA applications were increased by a train of voltage pulses. This potentiation was transient with an average half recovery period of 3.7 min. Spontaneous synaptic currents were reduced by depolarizing voltage pulses, with a half recovery time of about 20 s. The inhibition was largely explained by a decrease of the frequency of synaptic events, suggesting that the primary location of the effect was presynaptic. Thus, a Cal' rise increases the sensitivity of Purkinje cells to GABA and induces a retrograde inhibition of presynaptic terminals. The latter effect may be due to a diffusible Ca 2+-dependent messenger.

A method to apply current source inverter to single-phase UPS.

At present, most of all inverters used in UPS are voltage-source types. In this case, a series reactor is an essential component of the output filter of the inverter because the waveforms of the output voltages consist of trains of voltage pulses. One of major issues of this type of system is magnetic noises, which are produced by the output voltage and appear at the series reactor and the output transformer.The use of the current-source inverter has merits not only reducing noises when compared to the case of voltage-source type but also getting a quasi-sinusoidal output voltage without any series reactors. However, there are few cases of applying the current-source inverters to the UPSs because built-in batteries of constant voltage are utilized as a voltage supply in the system.The feasibility of applying the current-source inverter to the UPSs is attempted in this paper, and a new circuit topology suitable for the UPSs is proposed. At the output terminal of the inverter only a capacitor is connected in parallel with a load, and the output voltage of the inverter is controlled so as to make it coincide with reference sinusoidal voltage. In order to realize this strategy, two choppers have to be connected between the DC input voltage source and the inverter.After showing the circuit configuration, the validity of the proposed method is confirmed by means of both simulation and measurement. When this type of the inverter is applied to an UPS, the waveforms of the inverter output voltage and the switching frequency depend strongly on the circuit constants and output voltage error. Then, these are discussed in quantity to get a design guide. A comparison with conventional current-source inverters shows that the new inverter system has a plenty of merits.

Apical Na+ permeability of frog skin during serosal Cl− replacement

Gluconate substitution for serosal Cl- reduces the transepithelial short-circuit current (Isc) and depolarizes short-circuited frog skins. These effects could result either from inhibition of basolateral K+ conductance, or from two actions to inhibit both apical Na+ permeability (PapNa) and basolateral pump activity. We have addressed this question by studying whole-and split-thickness frog skins. Intracellular Na+ concentration (CcNa) and PapNa have been monitored by measuring the current-voltage relationship for apical Na+ entry. This analysis was conducted by applying trains of voltage pulses, with pulse durations of 16 to 32 msec. Estimates of PapNa and CcNa were not detectably dependent on pulse duration over the range 16 to 80 msec. Serosal Cl- replacement uniformly depolarized short-circuited tissues. The depolarization was associated with inhibition of Isc across each split skin, but only occasionally across the whole-thickness preparations. This difference may reflect the better ionic exchange between the bulk medium and the extracellular fluid in contact with the basolateral membranes, following removal of the underlying dermis in the split-skin preparations. PapNa was either unchanged or increased, and CcNa either unchanged or reduced after the anionic replacement. These data are incompatible with the concept that serosal Cl- replacement inhibits PapNa and Na,K-pump activity. Gluconate substitution likely reduces cell volume, triggering inhibition of the basolateral K+ channels, consistent with the data and conclusions of S.A. Lewis, A.G. Butt, M.J. Bowler, J.P. Leader and A.D.C. Macknight (J. Membrane Biol. 83:119-137, 1985) for toad bladder. The resulting depolarization reduces the electrical force favoring apical Na+ entry. The volume-conductance coupling serves to conserve volume by reducing K+ solute loss. Its molecular basis remains to be identified.

An investigation of the power output and gap voltage during electrical discharge machining using microcomputer-based instrumentation

An analogue wattmeter has been developed for direct measurement of electrical power dissipation at the discharge gap during electrical discharge machining (EDM). A microcomputer samples power and corresponding gap voltage at regular intervals. Digitally encoded waveforms, which represent blocks of continuous power and voltage pulse trains, are stored on floppy disks for subsequent display and analysis. The advantage of using this microcomputer-based integrated measurement system is the ability to capture both typical and random events or phenomena in EDM and also to extract and process information from the digitized waveforms which represent characteristics of these events.In this investigation, samples of power and voltage pulse characteristics during four EDM tests have been recorded, analysed for unit and time-averaged variations and meticulously studied with the aid of the microcomputer-based system. Power and voltage waveforms have been reconstructed from the digital data and are suitably displayed. Random and systematic or cyclic variations as shown by the analysed data, together with the corresponding reconstructed waveforms, are presented. Reasons for the variations are discussed in the light of similar observations verified by other researchers.This paper reports part of a continuing programme involving the use of microcomputer-based measurement systems for both on-line monitoring and off-line analysis of the EDM process.

Interfacial effects related to backgating in ion-implanted GaAs MESFET's

Deep trap levels in Si-implanted GaAs FET's have been observed, using backgating and optical excitation. Transconductance decays, as deduced from drain-current transients, were generated either by applying a voltage pulse train to the semi-insulating substrate, or with an infrared photon pulse to the FET. These decays were analyzed for their trap emission rate parameters, and a "signature" obtained for the deep levels so activated. Additionally, the spectral dependence of the (photo-FET) transconductance was measured, as a cross check on the trap energies. A 0.81-eV electron trap prominent in backgating experiments was readily shown to match the EL2 native donor signature. Also found from the backgating work were the EB3 and EB4 electron traps, related to lattice damage. These and other effects detected could result from part of the so-called "U-band" of implantation defects that resists thermal annealing. It is likely that these defects congregate near the FET channel-substrate interface, and the measurements are most sensitive to traps in that interfacial region.

High Speed Colour Switching Element Utilizing Ferroelectric Liquid Crystal

Characteristics of ferroelctric liquid crystals mixed with dichroic dyes are studied by the application of a dc voltage and voltage pulse trains to understand the fundamental processes as a high speed colour switching element. The guesthost effect and its combined effect with the transient light scattering are observed in ferroelectric liquid crystals. The response speed does not change by the introduction of dichroic dyes. The contrast as the optical switching element of the transient scattering mode has been found to increase by the introduction of dichroic dyes.

An electrochemical reactivation method for solid electrodes used in electrochemical detectors for high-performance liquid chromatography and flow injection analysis

An electrochemical reactivation method for solid electrodes used in electrochemical detectors is optimized for glassy carbon electrodes. Application of a voltage pulse train for 5 min is effective in restoring the response of the electrode after deactivation by organic compounds. Potassium hexacyanoferrate(II) and dl-synephrine were used to test the reactivation of electrodes; 2,6-dihydroxybenzoic acid and urine served to deactivate them. The effects of the amplitude, d.c. level, and frequency of the applied voltage pulse train, as well as the mode of termination, are discussed.

Humidity-sensitive electrical properties and switching characteristics of BN films

This paper reports on the electrical properties of polycrystalline boron nitride (BN) films deposited on silicon substrates in a B 2H 6NH 3H 2 system. Virgin (unformed) samples exhibit humidity-sensitive electrical resistances. A current obeying Ohm's law at low humidities and low fields becomes space-charge-limited at high humidities and high fields. Some of the properties fundamental to their use as humidity sensors are also examined. After electroforming, BN films in the form of Ag/BN/Si/Al sandwiches begin to exhibit threshold switching only in atmospheres containing moisture. This switching behavior depends not only on the humidity but also on the sweep speed, the frequency of oscillation and the polarity of the applied sawtooth voltage pulse trains. A revised form Dearnaley's filamentary model is proposed.

Waveguide CO2laser with a pulsed high-frequency discharge

A description is given of a waveguide-resonator CO2 laser operating at working-mixture pressures up to 3 atm. A cavity discharge is maintained by a train of electrodeless voltage pulses with a high carrier frequency (about 30 MHz) and a repetition frequency up to 250 Hz. Feasibility of cw operation is considered.