The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Burkhard Madea - One of the best experts on this subject based on the ideXlab platform.
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zum postmortalen verhalten der Rheobase
International Journal of Legal Medicine, 1990Co-Authors: Burkhard Madea, C HensgeAbstract:An einem Kollektiv von 20 Leichen wurde die Schwellenstromstarke (Rheobase) bestimmt, welche zu einer Kontraktionskraft von 2,5 mN fuhrt. Die Messung der Kontraktionskraft erfolgte mit in die Muskulatur (vorwiegend Thenar) eingestochenem Kraftaufnehmer. Es ergab sich ein weitgehend linearer Zusammenhang zwischen In der Schwellenstromstarke und der Todeszeit. Bei Verwendung des kollektiven Mittelwertes von Regressionskoeffizient und Intercept konnen am vorliegenden Material nach einmaliger Bestimmung der Rheobase Todeszeiten hoherer Prazision zuruckgerechnet werden als nach mehrmaliger Bestimmung der Rheobase mit dem von Joachim und Feldmann (1980) angegebenen Verfahren. Eine erste Anwendung an 8 Praxisfallen ergab damit ubereinstimmende Resultate.
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postmortem behavior of the Rheobase
International Journal of Legal Medicine, 1990Co-Authors: Burkhard Madea, C HenssgeAbstract:: Own investigations on the postmortem rise of muscular threshold were conducted on 20 bodies with exactly known time of death. Muscular contraction was objectified using a sensitive force transducer. The muscle was excitated using rectangular impulses of 1 second duration of a current intensity which produces a force of muscular contraction of 2.5 mN. These excitations were continued over the postmortem interval until a current intensity of 80 mN doesn't cause a contraction of 2.5 mN any more. Investigations were mainly performed at the thenar muscles. There is a linear relationship between ln of muscular threshold (current intensity) and the time since death (r = 0.965). For any case the linear regression line between ln of muscular threshold and time since death was calculated. With mean values for slope and intercept the time of death was calculated for each measured threshold. Extrapolation of the time since death with mean values also for the slope reveals a much more precise estimation of the time since death than an extrapolation with an individual slope as proposed by Joachim and Feldmann (1980). The method was proved on a random sample of 8 practical cases. The real time since death was always within the 95%-limits of confidence of the extrapolated time since death.
C Hensge - One of the best experts on this subject based on the ideXlab platform.
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zum postmortalen verhalten der Rheobase
International Journal of Legal Medicine, 1990Co-Authors: Burkhard Madea, C HensgeAbstract:An einem Kollektiv von 20 Leichen wurde die Schwellenstromstarke (Rheobase) bestimmt, welche zu einer Kontraktionskraft von 2,5 mN fuhrt. Die Messung der Kontraktionskraft erfolgte mit in die Muskulatur (vorwiegend Thenar) eingestochenem Kraftaufnehmer. Es ergab sich ein weitgehend linearer Zusammenhang zwischen In der Schwellenstromstarke und der Todeszeit. Bei Verwendung des kollektiven Mittelwertes von Regressionskoeffizient und Intercept konnen am vorliegenden Material nach einmaliger Bestimmung der Rheobase Todeszeiten hoherer Prazision zuruckgerechnet werden als nach mehrmaliger Bestimmung der Rheobase mit dem von Joachim und Feldmann (1980) angegebenen Verfahren. Eine erste Anwendung an 8 Praxisfallen ergab damit ubereinstimmende Resultate.
Werner Irnich - One of the best experts on this subject based on the ideXlab platform.
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Stimulation threshold comparison of time-varying magnetic pulses with different waveforms.
Journal of Magnetic Resonance Imaging, 2020Co-Authors: Werner Irnich, Franz HebrankAbstract:Purpose To clarify whether sinusoidal pulses possess lower thresholds than rectangular ones at perception threshold, a statement often made that contradicts the theory of stimulation. Materials and Methods The results of a nerve stimulation study with 65 volunteers and with trapezoidal and sinusoidal gradient pulses were used to apply the combination of the electric field, induced in the tissue of the human body, with the “Fundamental Law of Electrostimulation.” This law claims that the waveshape of a pulse is not essential as long as the amplitude of the pulse does not decrease below Rheobase (Rheobase condition). Results If the Rheobase condition is applied to sinusoidal waveforms and the pulse duration and amplitude is corrected accordingly, both trapezoidal and sinusoidal gradient pulses have identical threshold amplitudes as a function of pulse duration. Conclusion The “Fundamental Law of Electrostimulation,” including the “Rheobase condition,” proved to be a good basis for describing magnetic field stimulation (magnetostimulation) and that application of it to magnetostimulation is suitable as the basis for describing magnetic field stimulation with various waveforms. For nonrectangular pulses, pulse durations and pulse amplitudes must be corrected according to the “Rheobase condition.” The exponential Blair Equation is less suited to be applied in magnetostimulation. J. Magn. Reson. Imaging 2009;29:229–236. © 2008 Wiley-Liss, Inc.
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Are Defibrillation Thresholds Ruled by a Hyperbolic Strength Duration Relationship
IFMBE Proceedings, 2020Co-Authors: Werner IrnichAbstract:Our defibrillation theory claims that mean voltage is a hyperbolic function of pulse duration if voltages below the Rheobase are avoided. To verify this theory, two animal experiments were carried out. The ‘Rheobase condition’ demands that pulses are truncated when the trailing edge voltage reaches the Rheobase. This creates a relationship between the time constant, pulse duration, and chronaxie. The integral over voltage pulse is a linear function of pulse duration from which the hyperbolic threshold function between mean voltage and pulse duration is derived. In this study, we determined defibrillation thresholds in swine. Parameters measured were: leading and trailing edge voltages and currents, pulse durations, and failure or success of shock. A step-up test was used; the lowest successful shock was defined as the ‘threshold’. Waveforms truncated according to theory yielded lower stored energy than either \(\raisebox{1mm}{\scriptsize 1}{\hspace*{-.5mm}\scriptsize /}\raisebox{-0.8mm}{\scriptsize 2}\) optimal duration or fixed 65% tilt pulses. Plots of voltage integral vs. pulse duration produced a strong linear correlation. Mean defibrillation voltage vs. pulse duration formed a hyperbola. Ranking of stored energy showed that lower capacitances reduce energy to the detriment of increased peak voltages. These are the first experiments in which defibrillation pulses were adjusted according to theory. Truncation above or below the Rheobase increased stored energy. The experimental results are consistent with theory. The algorithm for optimal truncation should be incorporated into ICD. If the energy required is lower at smaller output capacitances, a compromise between clinical and technical aspects can be attained. The current concept of ‘constant tilt’ in ICD should be abandoned in favour of ‘optimal truncation’. Additional studies are needed to determine the applicability of this theory to humans.
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A New Method of Measuring Stimulation Threshold
Current Directions in Biomedical Engineering, 2018Co-Authors: Werner IrnichAbstract:AbstractLouis Lapicque introduced the hyperbolic stimulation law with the key parameters “Rheobase” and “chronaxie” that were obtained with rectangular current pulses. With rectangular pulses Rheobase cannot be measured. It was found recently that hyperbolic stimulation rules are also valid for non-rectangular pulses and that their Rheobase or chronaxie values are identical with that of their rectangular counterparts. Threshold measuring with exponential pulses allow for determining Rheobase directly and chronaxie by calculation with only two measurements. The measuring procedure is described in detail.
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From defibrillation theory to clinical implications.
Pacing and Clinical Electrophysiology, 2009Co-Authors: Werner IrnichAbstract:Background: Our defibrillation theory claims that the mean voltage threshold is a hyperbolic function of pulse duration and that voltages below Rheobase should be avoided as being counterproductive. Truncation of the pulse just at Rheobase level yields minimal stored energy thresholds. To verify or falsify this theory, animal experiments were carried out. Material and Methods: In two animal experiments, 212 defibrillation thresholds in 22 swine were determined with different biphasic pulses of which 92 were optimally truncated in phase 1. Step-up test procedure was used with the first successful shock defined as “threshold.” Results: Experimental proof is gained that truncation according to “Rheobase condition” shows lowest stored energy. A ranking order of stored energy thresholds demonstrates that (1) lower output capacitances reduce needed energy, and (2) pulse durations shorter or longer than optimal increase needed energy. The voltage–pulse-content threshold is linearly correlated with pulse duration. Conclusions: Truncation above or below Rheobase increases the stored energy threshold. Voltage averaged during pulse duration is a hyperbolic function of pulse duration. The stored energy is reduced with decreasing output capacitance. The experimental results do not only fully verify our theory, they also suggest clinical implications: (1) the current usage of the “constant tilt concept” in implantable cardioverter defibrillator (ICD) should be abandoned in favor of “optimal truncation concept,” (2) an algorithm developed for calculating optimal truncation proved to be useful so that incorporation into ICD for automatic adjustment is recommended, and (3) the output capacitance should be reduced from about 100 μF to 60 to 70 μF. (PACE 2010; 33:814–825)
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Threshold measurements: ten rules for good measuring practice.
Pacing and Clinical Electrophysiology, 2003Co-Authors: Werner IrnichAbstract:: The following rules for professionally measuring thresholds are derived and discussed: RULE 1: Thresholds should be expressed as voltage averaged over pulse duration to get reproducible and comparable results! RULE 2: Pacing threshold measurements with exponentially decaying pulses should not be extended beyond 1.4 ms as that portion of the pulse below Rheobase does not contribute to the stimulation effect! RULE 3: Threshold measurements are best carried out with fixed pulse duration and variable voltage! RULE 4: If threshold measurements are carried out in discrete steps, the steps should be chosen such that the relative step size is as equal as possible! RULE 5: Accuracy of threshold measurements is highly increased if the arithmetically averaged value of the last effective and the first ineffective pulse is defined as threshold! RULE 6: To determine strength-duration-curves, a linear regression of the quantity versus pulse duration should be calculated which yields simply the numerical values of the chronaxie and Rheobase! RULE 7: To reach representative strength-duration-curves, measurements with at least four pairs of values must be carried out! RULE 8: Measuring defibrillation thresholds, the relative voltage step size should be chosen equally to have equal accuracy for all steps. RULE 9: If the result of a defibrillation threshold investigation does not reach significance, a too large voltage step size could be an explanation! RULE 10: Comparing intraindividually the threshold of two different defibrillation systems or parameter settings, the threshold ratios should be formed and averaged! Obeying these rules guaranties professional threshold measurements expressed as "Rheobase" and "chronaxie" even with devices with discrete steps in parameter programming.
Hesham Aldhalaan - One of the best experts on this subject based on the ideXlab platform.
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intraoperative direct cortical stimulation motor evoked potentials stimulus parameter recommendations based on Rheobase and chronaxie
Clinical Neurophysiology, 2017Co-Authors: Tariq Abalkhail, David B Macdonald, Ibrahim Althubaiti, Faisal Alotaibi, B Stigsby, Amal Mokeem, Iftetah A Alhamoud, Maher I Hassounah, Abdulaziz Alsemari, Hesham AldhalaanAbstract:Abstract Objective To determine optimal interstimulus interval (ISI) and pulse duration (D) for direct cortical stimulation (DCS) motor evoked potentials (MEPs) based on Rheobase and chronaxie derived with two techniques. Methods In 20 patients under propofol/remifentanil anesthesia, 5-pulse DCS thenar MEP Rheobase and chronaxie with 2, 3, 4 and 5 ms ISI were measured by linear regression of five charge thresholds at 0.05, 0.1, 0.2, 0.5 and 1 ms D, and estimated from two charge thresholds at 0.1 and 1 ms D using simple arithmetic. Optimal parameters were defined by minimum threshold energy: the ISI with lowest Rheobase 2 × chronaxie , and D at its chronaxie. Near-optimal was defined as threshold energy Results The optimal ISI was 3 or 4 (n = 7 each), 2 (n = 4), or 5 ms (n = 2), but only 4 ms was always either optimal or near-optimal. The optimal D was ∼0.2 (n = 12), ∼0.1 (n = 7) or ∼0.3 ms (n = 1). Two-point estimates closely approximated five-point measurements. Conclusions Optimal ISI/D varies, with 4 ms/0.2 ms being most consistently optimal or near-optimal. Two-point estimation is sufficiently accurate. Significance The results endorse 4 ms ISI and 0.2 ms D for general use. Two-point estimation could enable quick individual optimization.
Ban C H Tsui - One of the best experts on this subject based on the ideXlab platform.
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the effects of general anaesthesia on nerve motor response characteristics Rheobase and chronaxie to peripheral nerve stimulation
Anaesthesia, 2014Co-Authors: Ban C H TsuiAbstract:Summary Using a simple surface nerve stimulation system, I examined the effects of general anaesthesia on Rheobase (the minimum current required to stimulate nerve activity) and chronaxie (the minimum time for a stimulus twice the Rheobase to elicit nerve activity). Nerve stimulation was used to elicit a motor response from the ulnar nerve at varying pulse widths before and after induction of general anaesthesia. Mean (SD) Rheobase before and after general anaesthesia was 0.91 (0.37) mA (95% CI 0.77–1.04 mA) and 1.11 (0.53) mA (95% CI 0.92–1.30 mA), respectively. Mean (SD) chronaxie measured before and after general anaesthesia was 0.32 (0.17) ms (95% CI 0.26–0.38 ms) and 0.29 (0.13) ms (95% CI 0.24–0.33 ms), respectively. Under anaesthesia, Rheobase values increased by an average of 20% (p = 0.05), but chronaxie values did not change significantly (p = 0.39). These results suggest that threshold currents used for motor response from nerve stimulation under general anaesthesia might be higher than those used in awake patients.