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PubMed2003

Superluminal propagation of light pulses: A result of interference.

The propagation of pulses through dispersive media was investigated by solving Maxwell's equations without any approximation. We show that the superluminal propagation of pulses through anomalous dispersive media is a result of the interference of different frequency components composed of the pulse. The coherence of the pulse plays an important role for the superluminal propagation. With the decrease of the coherence of the pulse, the propagation changes from superluminal to subluminal. We have shown that the anomalous dispersion (the real part of the susceptibility) not the amplification (the imaginary part of the susceptibility) plays the essential role in the superluminal propagation. Although the superluminality always exists as long as the spectrum of the coherent pulse is within the anomalously dispersive region, both the energy propagation velocity and the frontal velocity never exceed the light speed in the vacuum. The output pulse through the medium is not the original pulse; instead it carries the information of the original pulse and the information of the prepared medium.

Journal Article↗
PubMed2004

Dynamics of laser-induced electroconvection pulses.

We first report that, for planar nematic 4-methoxy-benzilidene-4-butylaniline (MBBA), the electroconvection threshold voltage has a nonmonotonic temperature dependence, with a well-defined minimum, and a slope of about -0.12 V/degrees C near room temperature at 70 Hz. Motivated by this observation, we have designed an experiment in which a weak continuous-wave absorbed laser beam with a diameter comparable to the pattern wavelength generates a locally supercritical region, or pulse, in dye-doped MBBA. Working 10-20 % below the laser-free threshold voltage, we observe a steady-state pulse shaped as an ellipse with the semimajor axis oriented parallel to the nematic director, with a typical size of several wavelengths. The pulse is robust, persisting even when spatially extended rolls develop in the surrounding region, and displays rolls that counterpropagate along the director at frequencies of tenths of Hz, with the rolls on the left (right) side of the ellipse moving to the right (left). Systematic measurements of the sample-voltage dependence of the pulse amplitude, spatial extent, and frequency show a saturation or decrease when the control parameter (evaluated at the center of the pulse) approaches approximately 0.3. We propose that the model for these pulses should be based on the theory of control-parameter ramps, supplemented with new terms to account for the advection of heat away from the pulse when the surrounding state becomes linearly unstable. The advection creates a negative feedback between the pulse size and the efficiency of heat transport, which we argue is responsible for the attenuation of the pulse at larger control-parameter values.

Journal Article↗
PubMed2005

Attosecond and zeptosecond x-ray pulses via nonlinear Thomson backscattering.

Nonlinear Thomson backscattering of an intense circularly polarized laser by a counterpropagating energetic electron is investigated. The results show that in the scattering of a non-tightly-focused laser pulse with an intensity around 10(19) W/cm2 and a pulse duration of full width at half maximum by a counterpropagating electron with an initial energy of 10 MeV, a crescent-shaped pulse with a pulse duration of 469 s and the photon energy ranging from 230 eV to 2.5 keV is generated in the backward direction. It is shown that the radiated pulse shape and monochromaticity can be modified by changing the laser beam waist, while in the case of a tightly focused laser field, a single peak pulse with a shorter duration and better monochromaticity can be obtained. With increase of the electron initial energy, the peak power of the radiated pulse increases and the pulse duration decreases. An isolated powerful zeptosecond pulse with a peak power of about and photon energy up to several MeV can be obtained with a electron.

Journal Article↗
PubMed1991

The Effect of Ethylene and Propylene Pulses on Respiration, Ripening Advancement, Ethylene-Forming Enzyme, and 1-Aminocyclopropane-1-carboxylic Acid Synthase Activity in Avocado Fruit.

When early-season avocado fruit (Persea americana Mill. cv Hass) were treated with ethylene or propylene for 24 hours immediately on picking, the time to the onset of the respiratory climacteric, i.e. the lag period, remained unchanged compared with that in untreated fruit. When fruit were pulsed 24 hours after picking, on the other hand, the lag period was shortened. In both cases, however, a 24 hour ethylene or propylene pulse induced a transient increase in respiration, called the pulse-peak, unaccompanied by ethylene production (IL Eaks [1980] Am Soc Hortic Sci 105: 744-747). The pulse also caused a sharp rise in ethylene-forming enzyme activity in both cases, without any increase in the low level of 1-aminocyclopropane-1-carboxylic acid synthase activity. Thus, the shortening of the lag period by an ethylene pulse is not due to an effect of ethylene on either of the two key enzymes in ethylene biosynthesis. A comparison of two-dimensional polyacrylamide gel electrophoresis polypeptide profiles of in vitro translation products of poly(A(+)) mRNA from control and ethylene-pulsed fruit showed both up- and down-regulation in response to ethylene pulsing of a number of genes expressed during the ripening syndrome. It is proposed that the pulse-peak or its underlying events reflect an intrinsic element in the ripening process that in late-season or continuously ethylene-treated fruit may be subsumed in the overall climacteric response. A computerized system that allows continuous readout of multiple samples has established that the continued presentation of exogeneous ethylene or propylene to preclimacteric fruit elicits a dual respiration response comprising the merged pulse-peak and climacteric peak in series. The sequential removal of cores from a single fruit has proven an unsatisfactory sampling procedure inasmuch as coring induces wound ethylene, evokes a positive respiration response, and advances ripening.

Journal Article↗
PubMed2004

Predicting the threshold of pulse-train electrical stimuli using a stochastic auditory nerve model: the effects of stimulus noise.

The incorporation of low levels of noise into an electrical stimulus has been shown to improve auditory thresholds in some human subjects (Zeng et al., 2000). In this paper, thresholds for noise-modulated pulse-train stimuli are predicted utilizing a stochastic neural-behavioral model of ensemble fiber responses to bi-phasic stimuli. The neural refractory effect is described using a Markov model for a noise-free pulse-train stimulus and a closed-form solution for the steady-state neural response is provided. For noise-modulated pulse-train stimuli, a recursive method using the conditional probability is utilized to track the neural responses to each successive pulse. A neural spike count rule has been presented for both threshold and intensity discrimination under the assumption that auditory perception occurs via integration over a relatively long time period (Bruce et al., 1999). An alternative approach originates from the hypothesis of the multilook model (Viemeister and Wakefield, 1991), which argues that auditory perception is based on several shorter time integrations and may suggest an NofM model for prediction of pulse-train threshold. This motivates analyzing the neural response to each individual pulse within a pulse train, which is considered to be the brief look. A logarithmic rule is hypothesized for pulse-train threshold. Predictions from the multilook model are shown to match trends in psychophysical data for noise-free stimuli that are not always matched by the long-time integration rule. Theoretical predictions indicate that threshold decreases as noise variance increases. Theoretical models of the neural response to pulse-train stimuli not only reduce calculational overhead but also facilitate utilization of signal detection theory and are easily extended to multichannel psychophysical tasks.

Algorithms↗
PubMed2006

Subharmonic emissions from microbubbles: effect of the driving pulse shape.

The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse.

Contrast Media↗
PubMed1992

Radiofrequency ablation of accessory pathways: characteristics of transiently and permanently effective pulses.

The purpose of this study was to characterize and compare the radiofrequency current applications that produced permanent or transient accessory pathway conduction block. One hundred fifty-two radiofrequency energy applications that induced permanent (permanently effective pulses, n = 48) or transient (transiently effective pulses, n = 104) accessory pathway block in 57 patients with 60 accessory pathways were analyzed. The time from the onset of current application to disappearance of preexcitation or termination of supraventricular tachycardia by permanently effective pulses was 1-15 seconds (mean 3.6 +/- 3.8 sec) compared to 2-29 seconds (mean 11.5 +/- 7.5 sec) by transiently effective pulses (P less than 0.01). After transiently effective pulses that induced block in accessory pathway, conduction resumed within 5 minutes while induced block by permanently effective pulses persisted in 44 of 48 patients (92%) during follow-up of 11 +/- 12 months. The accessory pathway conduction returned in the remaining four patients after ablation 2 weeks to 7 months. After transiently effective pulses, 41 impulses were delivered to the same site using a higher power output (n = 32) and/or longer energy delivery duration (n = 20) without new mapping of accessory pathway location. Thirty-six of these impulses again resulted in transient accessory pathway block, four had no effect, only one impulse induced a permanent block in the accessory pathway. Pulses with higher power outputs tended to induce transient effects more frequently than pulses with lower energy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

Thresholds of intradental A- and C-nerve fibres in the cat to electrical current pulses of different duration.

Electrical current pulses of quite variable duration have been used in activation of intradental nerves both in human subjects and experimental animals. It seems, however, that little information is available about the effect of pulse duration on the responses of single pulp nerve units. The aim of the present study was to investigate the effect of pulse duration on excitation thresholds of intradental A- and C-fibres in the cat. In 12 anesthetized cats 61 C- and 53 A-nerve units were identified and recorded. Electrical thresholds were determined with current pulses of different duration from 0.2 to 50.0 ms. The maximal stimulus intensity was 200 microA. Conduction velocities of all recorded units and absolute refractory periods of 20 A- and 20 C-units were determined. Intradental A- and C-fibres had different strength-duration properties. with all pulse durations A-fibres had the lowest thresholds. Part of the C-fibres did not respond to the shortest current pulses even with the maximum stimulus intensity (200 microA). with 0.2 ms pulses only 31.1% of the recorded C-fibres could be activated. In some A-fibres a single current pulse of long duration was capable of inducing several action potentials, when the stimulus intensity was increased suprathreshold. Refractory periods of A-units were less than 2.0 ms and those of C-units 5.0-9.0 ms. It is concluded that in electrical stimulation of teeth duration of current pulses strongly affects responses of single intradental fibre units.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2006

Effect of frequency and pulse duration on human muscle fatigue during repetitive electrical stimulation.

Different combinations of stimulation frequency and intensity can generate a targeted force during functional electrical stimulation (FES). This study compared isometric performance and muscle fatigue during repetitive stimulation with three different combinations of frequency and pulse duration that produced the same initial peak forces: protocol 1 used long pulse duration (fixed at 600 micros) and 11.5 +/- 1.2 Hz (low frequency); protocol 2 used 30 Hz (medium frequency) and medium pulse duration (150 +/- 21 micros); and protocol 3 used 60 Hz (high frequency) and short pulse duration (131 +/- 24 micros). Twenty and 60 Hz pre- and postfatigue testing trains were delivered at the pulse duration used by the fatiguing trains and at 600 micros pulse duration. The percentage decline in peak force between the first and last fatiguing train of each protocol was the measure of muscle performance. The declines in peak force of the 60 Hz testing trains were used to measure muscle fatigue. The 20 Hz:60 Hz peak force ratio was used as a measure of low-frequency fatigue. The results showed that protocol 1 produced the least decline in peak force in response to the fatiguing trains, as well as the least muscle fatigue and low-frequency fatigue when the pulse duration was maintained at the level used by the fatiguing trains. Interestingly, protocol 2 produced the least muscle fatigue, and there were no differences in the levels of low-frequency fatigue across protocols when a comparable motor unit population was tested using 600 micros pulse duration. The results suggest that if the frequency and intensity are kept constant during FES, using the lowest frequency and longest pulse duration may maximize performance.

Adult↗
PubMed1978

Responses of olfactory receptor cells to step pulses of odour at different concentrations in the salamander.

1. The response properties of single olfactory receptor cells in the salamander have been analysed in unitary recordings obtained with platinum-black metal-filled micro-electrodes. 2. Stimulation has been carried out using an apparatus which delivers odour pulses of abrupt onset, steady plateau and abrupt termination. The pulses have been monitored near the site of stimulation on the olfactory epithelium during the experiments. 3. The main type of response was a discharge of impulses that was time locked to the stimulus pulse. The pattern of the responses consisted of a relatively brief latency of onset, a rapid rise in impulse frequency, a continuation of impulse firing during the plateau of the pulse, and an abrupt termination of the discharge correlated with the termination of the pulse. 4. There was a clear relationship between the receptor responses and odour concentration. In general, impulse firing frequency increased with increasing odour concentration. The firing frequency ranged from approximately 1--3 impulses/sec at threshold, up to 20 impulses/sec at the highest concentration. 5. Two types of reduced impulse activity were observed. One occurred after the termination of the pulse and lasted 1--3 sec; this was a common occurrence. The other type was seen during a pulse as a reduction of impulse activity compared to the background level; this type was rarely observed. 6. The receptor responses resembled those of mitral cells in the olfactory bulb to odour pulses in their sensitivity to odour concentration. They differed in that mitral cells show primary response categories consisting of brief excitation followed by suppression, and pure suppression, that are rarely seen at the receptor level. These differences may be ascribed to synaptic interactions in the olfactory bulb. 7. It is concluded that the majority of receptor cells have a stereotyped discharge response pattern and a systematic relation to odour concentration. These properties appear to reflect the simple time course of the odour pulses used in these experiments. This represents an initial step toward analysing olfactory coding at the receptor level using stimuli controlled in a manner similar to that used in other sensory systems.

Action Potentials↗
PubMedDate not supplied

Recombination correction factors for an ionization chamber exposed to discrete patterned pulsed swept beams.

An equation for a recombination correction factor for a pulsed swept beam of electrons was derived by Boag. This equation is based on an integration technique, which assumes that a large number of spot beams cover the radiation field, that the field size is much larger than the spot beam size, and that the spot beam size is much larger than the chamber size. However, for computer-controlled pulsed swept beams of electrons, the spot beam pattern can be altered, may not cover all of the field area, and the locations are reproducible. In this report, a summation method is proposed for this type of beam. Calculations for two such beams are demonstrated with the chamber located in the center of the field, and with the chamber half-way to and at the edge of the field for a linear accelerator. The results lie between the integration pulsed swept and pulsed beam curves. Moving the ionization chamber from the center toward the edge of the field produces curves closer to the pulsed swept beam curve. Increasing spot beam size produces curves closer to the pulsed beam curves. It is therefore concluded that the pulsed swept beam cannot be characterized by a single recombination correction factor curve. The actual curve will be bounded by the integration pulsed swept and pulsed beam curves.

Electrons↗
PubMed1996

Pulsed fluoroscopy detectability from interspersed adaptive forced-choice measurements.

Using a new reference/test, adaptive forced-choice method, we investigated detectability of low contrast disks in simulated x-ray fluoroscopy image sequences. The method minimized effects of undesirable variables, such as changes in subject attention level by alternating conventional fluoroscopy (reference) and low acquisition rate fluoroscopy (test) presentations. To compare absolute target detectability and x-ray dose requirements of reference and test presentations, the contrast of the test presentation was set equal to that of the reference presentation, and the dose of the test presentation was adapted to give equivalent detectability of disk targets. Comparing pulsed fluoroscopy at 15 acq/s (pulsed-15) and 7.5 acq/s (pulsed-7.5) with conventional fluoroscopy at 30 acq/s (pulsed-30), dose savings were found in 22 of 24 experiments. When averaged over 3 disk sizes and 4 subjects, savings were 22% and 26% for pulsed-15 and pulsed-7.5, respectively. In most experiments, the subject was given an unlimited time to view presentations. With unlimited display times, subjects took slightly longer to respond for pulsed-15 or pulsed-7.5 than for pulsed-30. In other experiments, display times were limited. As the restricted display time increased, absolute target detectability increased while the x-ray dose for equivalent detectability was unchanged. The number of frames, N, in a repeating loop was also varied. Absolute detectability increased as N increased from 1 to 30 but changed little as more frames were added up to 150. The new experimental paradigm gives efficient, robust comparisons of image data and is applicable to a wide variety of medical image perception problems.

Adult↗
PubMed1998

Comparison of the efficacies of three fluoroquinolone antimicrobial agents, given as continuous or pulsed-water medication, against Escherichia coli infection in chickens.

This study compared the efficacy of continuous or pulsed-water medication with enrofloxacin, danofloxacin, and sarafloxacin in eight groups of 90 chicks each by using an infectious bronchitis virus-Escherichia coli model of colisepticemia. The model produced lesions of typical those occurring in birds with severe colisepticemia; for the infected, nonmedicated birds the mortality was 43.5% and the morbidity was 89%, 17.8% of birds had severe lesions, and the birds had a mean air sac lesion score of 2.58. This experiment showed that continuous dosing and pulsed dosing are clinically equivalent. However, for all fluoroquinolones studied, there was a trend for the continuously mediated birds to have lower mortality and less severe disease than birds receiving pulsed doses. Compared with infected, nonmedicated controls, only birds continuously medicated with enrofloxacin had a significantly lower morbidity (32%), and only birds medicated with enrofloxacin and danofloxacin (continuous and pulsed treatments) had significantly lower mortality (6.7 and 11.0% and 16.8 and 19.2% for continuous and pulsed treatments with enrofloxacin and danofloxacin, respectively). A significantly lower proportion of birds only in the groups medicated with enrofloxacin had severe lesions (for birds receiving continuous and pulsed treatments, 2.2 and 6.7%, respectively). Birds medicated with any of the three fluoroquinolones (continuous and pulsed treatments) except pulsed-water treatment with sarafloxacin had significantly reduced mean air sac lesion scores compared with the scores for nonmedicated birds (air sac lesion scores, 0.60 and 0.83, 1.38 and 1.63, and 1.80 and 2.05 for birds receiving continuous and pulsed treatments with enrofloxacin, danofloxacin, and sarafloxacin, respectively). The performance of the birds that survived the challenge or that recovered after receiving medication was not compromised compared to the performance of noninfected birds. Enrofloxacin was more efficacious than either danofloxacin or sarafloxacin for the treatment of colisepticemia in chickens by medication in drinking water. Similarly, danofloxacin appeared to be more effective than sarafloxacin in treating colisepticemia.

Animals↗
PubMed1997

Evaluation of variable-angle uniform signal excitation, tilted optimized nonsaturating excitation, and flat radio-frequency pulses in free-breathing non-contrast-enhanced pulmonary MR angiography.

PURPOSE: To improve the visualization of distal pulmonary vessels at magnetic resonance (MR) angiography so effects of pathologic lung conditions (eg, emboli) on circulation may be more easily observed. MATERIALS AND METHODS: Radio-frequency pulses with flip angles that were uniform (flat), linearly increasing (tilted optimized nonsaturating excitation [TONE]), or nonlinearly increasing (variable-angle uniform signal excitation [VUSE]) were used at pulmonary MR angiography in 15 healthy volunteers. Three-dimensional fast imaging with steady-state precession was performed with free breathing. Statistical analysis of signal-to-noise ratios (S/Ns) was performed. RESULTS: At examinations in both lungs, a higher S/N was achieved with VUSE pulses than with TONE pulses, and with both VUSE pulses and TONE pulses than with flat pulses. Relative dispersion was best with VUSE pulses in all lobes of both lungs. Results were statistically significant (P < .01) in 19 of 27 comparisons in the right lung. CONCLUSION: Higher S/N and better signal uniformity were achieved with VUSE pulses than with TONE or flat pulses at pulmonary MR angiography.

Humans↗
PubMed1982

Dark pulses affect the circadian rhythm of activity in hamsters kept in constant light.

We compared the effects of light pulses in constant darkness (DD) and dark pulses in constant light (LL) on the free-running rhythm of locomotor activity in male golden hamsters. Light pulses yielded advances, delays, or no change in the rhythm of activity. These data conform to a typical phase-response curve; this curve was unaffected by pinealectomy. Dark pulses occurring either late in the subjective night or early in the subjective day had little effect. In contrast, dark pulses occurring either late in the subjective day or early in the subjective night altered the rhythm in one of three ways: advance of the rhythm; splitting into two components; or induction of a new component, in phase with the pulse. Because dark pulses in LL perturb the circadian system in a different manner than do light pulses in DD, they may have value in identifying heretofore unknown aspects of circadian systems. As such, the use of dark pulses to perturb circadian rhythmicity will be a useful tool in examining the formal properties of circadian systems.

Animals↗
PubMed2001

Cerebral blood-flow changes induced by paired-pulse transcranial magnetic stimulation of the primary motor cortex.

Positron emission tomography (PET) was used to assess changes in regional cerebral blood flow (CBF) induced by paired-pulse transcranial magnetic stimulation (TMS) of primary motor cortex (M1). The study was performed in eight normal volunteers using two Magstim-200 stimulators linked with a Bistim module. A circular TMS coil was held in the scanner by a mechanical arm and located over the left M1. Surface electrodes were used to record motor evoked potentials (MEPs) from the contralateral first dorsal interosseous muscle (FDI). Cortical excitability was evaluated in the relaxed FDI using a paired conditioning-test stimulus paradigm with two interstimulus intervals (ISIs): 3 and 12 ms. The subjects were scanned three times during each of the following four conditions: 1) baseline with no TMS (BASE); 2) single-pulse TMS (TMSsing); 3) 3-ms paired-pulse TMS (TMS3); and 4) 12-ms paired-pulse TMS (TMS12). CBF and peak-to-peak MEP amplitudes were measured over each 60-s scanning period. To assess TMS-induced changes in CBF, a t-statistic map was generated by first subtracting the single-pulse TMS condition from the 3- and 12-ms paired-pulse TMS conditions and then correlating the CBF differences, respectively, with the amount of suppression and facilitation of the EMG responses. A significant positive correlation was observed between the CBF difference (TMS3-TMSsing) and the amount of suppression of EMG response, as well as between the CBF difference (TMS12-TMSsing) and the amount of facilitation of EMG response. This positive correlation was observed in the left M1, left lateral premotor cortex, and right M1 in the case of 3-ms paired-pulse TMS, but only in the left M1 in the case of 12-ms paired-pulse TMS. The above pattern of CBF response to paired-pulse TMS supports the possibility that suppression and facilitation of the EMG response are mediated by different populations of cortical interneurons.

Adult↗
PubMed1984

Effects on plasma luteinizing hormone and follicle-stimulating hormone of varying the frequency and amplitude of gonadotropin-releasing hormone pulses in ovariectomized ewes with hypothalamo-pituitary disconnection.

The effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion of various regimens of pulsatile gonadotropin-releasing hormone (GnRH) replacement were examined in ovariectomized (OVX) ewes after hypothalamo-pituitary disconnection (HPD). Hourly pulses of 500 ng GnRH restored gonadotropin secretion in OVX-HPD sheep. Replacement beginning 2 days after HPD gave consistent responses of LH and FSH within a week. Replacement beginning 61-96 days after HPD caused more gradual re-establishment of LH and FSH secretion with LH responses appearing immediately and FSH responses appearing 2 weeks later. When hourly GnRH pulses were increased in amplitudes from 250 to 500 ng the plasma LH baseline, peak values and pulse amplitudes were increased. There was no significant change in plasma FSH levels over 10 pulses at the higher dose. Decreases in GnRH pulse frequency led to increases in LH pulse amplitude and decreases in plasma LH baseline. In contrast, immediately after a change from a 2-hourly to an hourly mode, an increase in LH baseline occurred without an immediate reduction in LH pulse amplitude. Mean plasma FSH concentrations increased when the frequency was reduced from hourly to 2-hourly or 4-hourly. However, a change from 4-hourly to hourly pulses did not reduce FSH values within 7 days. It is concluded that changes in the pattern of LH secretion observed during the ovine estrous cycle could be accounted for, in part, by changes in GnRH pulse frequency.

Animals↗
PubMed1995

A prospective randomized comparison in humans of biphasic waveform 60-microF and 120-microF capacitance pulses using a unipolar defibrillation system.

BACKGROUND: Improving unipolar implantable cardioverter-defibrillator (ICD) effectiveness has favorable implications for ICD safety, efficacy, and size. Advances in defibrillation efficacy would accelerate ICD ease of use by decreasing device size and by minimizing morbidity and mortality related to an improved defibrillation safety margin. The specific purpose of the present study was to determine whether unipolar defibrillation efficacy could be improved further in humans by lowering biphasic waveform capacitance. METHODS AND RESULTS: We prospectively and randomly compared the defibrillation efficacy of a 60-microF and a 120-microF capacitance asymmetrical 65% tilt biphasic waveform using a unipolar defibrillation system in 38 consecutive cardiac arrest survivors before implantation of a presently available standard transvenous defibrillation system. The right ventricular defibrillation electrode had a 5-cm coil located on a 10.5F lead and was used as the anode. The system cathode was the electrically active 108-cm2 surface area shell (or "can") of a prototype titanium alloy pulse generator placed in a left infraclavicular pocket. The defibrillation pulse was derived from either a 60-microF or a 120-microF capacitance and was delivered from RV-->CAN. Defibrillation threshold (DFT) stored energy, delivered energy, leading-edge voltage and current, pulse resistance, and pulse width were measured for both capacitances examined. The 60-microF capacitance biphasic pulse resulted in a stored-energy DFT of 8.5 +/- 4.1 J and a delivered-energy DFT of 8.4 +/- 4.0 J. In 34 of 38 patients (89%), the stored-energy DFT was < 15 J. Leading-edge voltage at the DFT was 517 +/- 128 V. Mean pulse impedance for the 60-microF waveform was 60.6 +/- 7.1 omega. The 120-microF capacitance biphasic pulse resulted in a stored-energy DFT of 10.1 +/- 7.4 J and a delivered-energy DFT of 10.0 +/- 7.2 J (P = .13 and .13, respectively). In 28 of 38 patients (74%), the stored-energy DFT was < 15 J (P = .052). Leading-edge voltage at the DFT with the 120-microF capacitance pulse was 386 +/- 142 (P < .00001). Mean pulse impedance for the 120-microF waveform was 60.7 +/- 7.0 omega (P = .80). CONCLUSIONS: The results of the present study suggest that a relatively small capacitance, 60 microF, can be used for unipolar defibrillation systems without compromising defibrillation energy requirements compared with more typical ICD capacitance values, but this will require a higher circuit voltage. The use of lower capacitance also provides a modest increase in the percent of patients who have very low energy defibrillation requirements, an important issue should maximum ICD energy be decreased from the present level of 34 J. Such a move to smaller output devices could allow significant decreases in device size, a necessary feature of making cardioverter-defibrillator implantation comparable to that of standard pacemaker surgery.

Adult↗