Mark W. Kroll

A Minimal Model of the Single Capacitor Biphasic Defibrillation Waveform

A quantita tive model of the single capacitor biphasic defibrillation wave form is proposed. The primary hypothesis of this model is that the first phase leaves a residual charge on the membranes of the unsynchronized cells, which can then reinitiate fibrillation. The second phase diminishes this charge, reducing the potential for refibrillation. To suppress this potential refibrillation, a monophasic shock must be strong enoagh to synchronize a critical mass of nearly 100% of the myocytes. Since the biphasic waveform performs this protection function by removing the residual charge (with its second phase), its first phase may be of a lower strength than a monophasic shock of equivalent performance. A quantitative model was developed to calculate the residual membrane voltage, Vm, assuming a capacitive membrane being alternately charged and discharged by the first and second phases, respectively. It was further assumed that the amplitude of the first phase would be predicted by a minimum value plus a term proportional to Vm2. The model was evaluated on the pooled data of three relevant published studies comparing biphasic waveforms. The model explained 79% of the variance in the first phase amplitude and predicted optimal durations for various defibrillator capacitances and electrode resistances. Assuming a first phase of opti mal duration, the optimal second phase duration appears to be about 2.5 msec for all capacitances and resistances now seen clinically. Conclusion: The effectiveness of the single capacitor biphasic waveform may be explained by the second phase “burping” of the deleterious residual charge of the first phase that, in turn, reduces the synchronization requirement and the amplitude requirements of the first phase.

A Minimal Model of the Monophasic Defibrillation Pulse

A minimal model of the defibrillation capability of a monophasic capacitive discharge pulse is derived from the Weiss‐Lapicque strength duration model. The model suggests that present, empirically derived values of pulse durations and tilts are close to optimum for presently used values of capacitors and electrode resistances. The model suggests that neither the tilt nor fixed duration specification is universally superior to the other for dealing with electrode resistance changes. A tilt specification would appear to best handle resistance decreases while a fixed duration specification would best handle resistance increases. The model was used to study the effect of capacitance changes. It appears that the optimum tilt and pulse duration vary with the capacitance value. The model further suggests that decreasing the capacitance from presently used values may lower defibrillation thresholds.

Lung sound cancellation method and apparatus

A method and apparatus for deriving weak cardiac sounds by automatically cancelling lung sounds. The process is accomplished by providing a pair of acoustic sensors about the thorax of a patient, the first being disposed on the precordial region, adjacent to the sternum, and the second on the axillary region; obtaining sound signals from each sensor; amplifying the axillary signal by a predetermined factor; and subtracting the amplified signal from the precordial signal. An acoustic transmitter is placed on the axillary region opposite the axillary sensor. Sound waves of predetermined frequencies are emitted from the axillary transmitter to determine and compensate for phase shifts due to the electronic circuitry and the patient body. The apparatus of the present invention comprises a first acoustic sensor, a second acoustic sensor, an acoustic transmitter, a strap, transmitting cables, a processor, a cathode-ray tube, a printer, and headphones.

Application of Models of Defibrillation to Human Defibrillation Data Implications for Optimizing Implantable Defibrillator Capacitance

BACKGROUND Theoretical models predict that optimal capacitance for implantable cardioverter-defibrillators (ICDs) is proportional to the time-dependent parameter of the strength-duration relationship. The hyperbolic model gives this relationship for average current in terms of the chronaxie (t(c)). The exponential model gives the relationship for leading-edge current in terms of the membrane time constant (tau(m)). We hypothesized that these models predict results of clinical studies of ICD capacitance if human time constants are used. METHODS AND RESULTS We studied 12 patients with epicardial ICDs and 15 patients with transvenous ICDs. Defibrillation threshold (DFT) was determined for 120-microF monophasic capacitive-discharge pulses at pulse widths of 1.5, 3.0, 7.5, and 15 ms. To compare the predictions of the average-current versus leading-edge-current methods, we derived a new exponential average-current model. We then calculated individual patient time parameters for each model. Model predictions were validated by retrospective comparison with clinical crossover studies of small-capacitor and standard-capacitor waveforms. All three models provided a good fit to the data (r2=.88 to .97, P<.001). Time constants were lower for transvenous pathways (53+/-7 omega) than epicardial pathways (36+/-6 omega) (t(c), P<.001; average-current tau(m), P=.002; leading-edge-current tau(m), P<.06). For epicardial pathways, optimal capacitance was greater for either average-current model than for the leading-edge-current model (P<.001). For transvenous pathways, optimal capacitance differed for all three models (P<.001). All models provided a good correlation with the effect of capacitance on DFT in previous clinical studies: r2=.75 to .84, P<.003. For 90-microF, 120-microF, and 150-microF capacitors, predicted stored-energy DFTs were 3% to 8%, 8% to 16%, and 14% to 26% above that for the optimal capacitance. CONCLUSIONS Model predictions based on measured human cardiac-muscle time parameter have a good correlation with clinical studies of ICD capacitance. Most of the predicted reduction in DFT can be achieved with approximately 90-microF capacitors.

Optimizing defibrillation waveforms for ICDs

While no simple electrical descriptor provides a good measure of defibrillation efficacy, the waveform parameters that most directly influence defibrillation are voltage and duration. Voltage is a critical parameter for defibrillation because its spatial derivative defines the electrical field that interacts with the heart. Similarly, waveform duration is a critical parameter because the shock interacts with the heart for the duration of the waveform. Shock energy is the most often cited metric of shock strength and an ICD’s capacity to defibrillate, but it is not a direct measure of shock effectiveness. Despite the physiological complexities of defibrillation, a simple approach in which the heart is modeled as passive resistor–capacitor (RC) network has proved useful for predicting efficient defibrillation waveforms. The model makes two assumptions: (1) The goal of both a monophasic shock and the first phase of a biphasic shock is to maximize the voltage change in the membrane at the end of the shock for a given stored energy. (2) The goal of the second phase of a biphasic shock is to discharge the membrane back to the zero potential, removing the charge deposited by the first phase. This model predicts that the optimal waveform rises in an exponential upward curve, but such an ascending waveform is difficult to generate efficiently. ICDs use electronically efficient capacitive-discharge waveforms, which require truncation for effective defibrillation. Even with optimal truncation, capacitive-discharge waveforms require more voltage and energy to achieve the same membrane voltage than do square waves and ascending waveforms. In ICDs, the value of the shock output capacitance is a key intermediary in establishing the relationship between stored energy—the key determinant of ICD size—and waveform voltage as a function of time, the key determinant of defibrillation efficacy. The RC model predicts that, for capacitive-discharge waveforms, stored energy is minimized when the ICD’s system time constant τs equals the cell membrane time constant τm, where τs is the product of the output capacitance and the resistance of the defibrillation pathway. Since the goal of phase two is to reverse the membrane charging effect of phase one, there is no advantage to additional waveform phases. The voltages and capacitances used in commercial ICDs vary widely, resulting in substantial disparities in waveform parameters. The development of present biphasic waveforms in the 1990s resulted in marked improvements in defibrillation efficacy. It is unlikely that substantial improvement in defibrillation efficacy will be achieved without radical changes in waveform design.

Implantable cardioverter defibrillator therapy : the engineering-clinical interface

Preface. 1. Sudden Cardiac Death M. Akhtar, et al. 2. History of the ICD W.S. Staewen, M.M. Mower. 3. The Electrophysiological Effects of Defibrillation Shocks S.M. Dillon. 4. Defining the Defibrillation Dosage M.W. Kroll, et al. 5. The Defibrillation Threshold I. Singer, D. Lang. 6. Pathways for Defibrillation Current M.J. Kallok. 7. The Defibrillation Waveform S.M. Blanchard, et al. 8. The System C.G.J. Supino. 9. Leads for the ICD R.S. Nelson, et al. 10. The Battery C.F. Holmes. 11. The High Voltage Capacitor J.B. Ennis, M.W. Kroll. 12. The Pulse Generator R.S. Nelson. 13. High Power Circuitry S.M. Bach, P. Monroe. 14. The Amplifier: Sensing the Depolarization D.A. Brumwell, et al. 15. Tachyarrhythmia Detection S.M. Bach, et al. 16. Anti-Tachycardia Pacing and Cardioversion M.L. Hardage, M.B. Sweeney. 17. Implantation: Pre-Operative Evaluation to Discharge W. Grimm, F.E. Marchlinski. 18. ICD Infection Avoidance: Science, Art, Discipline R.B. Shepard, A.E. Epstein. 19. Safety Margins for Sensing and Detection: Programming Tradeoffs W. Olson. 20. Patient Followup Systems T.P. Adams. 21. Troubleshooting Suspected ICD Malfunction M.E. Rosenthal, et al. 22. Clinical Results R.N. Fogoros. 23. Sudden Death Despite ICD Therapy M.H. Lehmann, et al. 24. Future Clinical Challenges M.H. Lehmann, M.W. Kroll. Glossary. Index.

Bio-electric noise cancellation system

A device and method are provided for bio-electric monitoring apparatus to cancel bio-electric noise on the body of a patient. The device comprises a plurality of monitoring electrodes for reception of bio-electric signals from the body, each monitoring electrode having a conductive lead and a surrounding shield. The device further has a driving electrode for transmission of a correction voltage to the body. The driving electrode has a conductive lead and a surrounding shield. The device has a signal averager with an input and an output. The monitoring electrode leads are connected to the input of the signal averager. An amplifier is connected to the output of the signal averager which has its output connected to the driving electrode lead to provide the correction voltage. The shield around the driving electrode lead is conductively connected to the output of the amplifier. The method comprises the steps of obtaining bio-electric signals from a plurality of locations on the body and transmitting the signals via shielded leads. The signals are averaged to provide a signal that is amplified by a predetermined large, negative factor to provide a correction signal, which is then driven to the body via a shielded lead. A conductive link is established between the driving lead shield and the correction signal.

Physiology and pathology of TASER electronic control devices

TASER ECDs (electronic control device) are small, battery powered, handheld devices. They deliver short duration, low energy pulses to stimulate motor neurons, causing transient paralysis. While the experience is painful, proper use of the device is rarely associated with significant side effects in spite of 1070 human worldwide exposures daily. In fact, there have been more than 780,000 training exposures and 630,000 field uses (total of over 1.4 million human uses) without any credible evidence of a resulting cardiac arrhythmia. In this article we describe the mechanisms by which the device operates, and review possible morbidities.

Large Change in Voltage at Phase Reversal Improves Biphasic Defibrillation Thresholds Parallel-Series Mode Switching

BACKGROUND Multiple factors contribute to an improved defibrillation threshold of biphasic shocks. The leading-edge voltage of the second phase may be an important factor in reducing the defibrillation threshold. METHODS AND RESULTS We tested two experimental biphasic waveforms with large voltage changes at phase reversal. The phase 2 leading-edge voltage was twice the phase 1 trailing-edge voltage. This large voltage change was achieved by switching two capacitors from parallel to series mode at phase reversal. Two capacitors were tested (60/15 microfarads [microF] and 90/22.5 microF) and compared with two control biphasic waveforms for which the phase 1 trailing-edge voltage equaled the phase 2 leading-edge voltage. The control waveforms were incorporated into clinical (135/135 microF) or investigational devices (90/90 microF). Defibrillation threshold parameters were evaluated in eight anesthetized pigs by use of a nonthoracotomy transvenous lead to a can electrode system. The stored energy at the defibrillation threshold (ion joules) was 8.2 +/- 1.5 for 60/15 microF (P < .01 versus 135/135 microF and 90/90 microF), 8.8 +/- 2.4 for 90/22.5 microF (P < .01 versus 135/135 microF and 90/90 microF), 12.5 +/- 3.4 for 135/135 microF, and 12.6 +/- 2.6 for 90/90 microF. CONCLUSIONS The biphasic waveform with large voltage changes at phase reversal caused by parallel-series mode switching appeared to improve the ventricular defibrillation threshold in a pig model compared with a currently available biphasic waveform. The 60/15-microF capacitor performed as well as the 90/ 22.5-microF capacitor in the experimental waveform. Thus, smaller capacitors may allow reduction in device size without sacrificing defibrillation threshold energy requirements.

TASER® Conducted Electrical Weapons: Physiology, Pathology, and Law

Make more knowledge even in less time every day. You may not always spend your time and money to go abroad and get the experience and knowledge by yourself. Reading is a good alternative to do in getting this desirable knowledge and experience. You may gain many things from experiencing directly, but of course it will spend much money. So here, by reading taser conducted electrical weapons physiology pathology and law, you can take more advantages with limited budget.