Electroporation safety factor of 300 nanosecond and 10 millisecond defibrillation in Langendorff-perfused rabbit hearts

AIMS: Recently, a new defibrillation modality using nanosecond pulses was shown to be effective at much lower energies than conventional 10 millisecond monophasic shocks in ex vivo experiments. Here we compare the safety factors of 300 nanosecond and 10 millisecond shocks to assess the safety of nanosecond defibrillation. METHODS AND RESULTS: The safety factor, i.e. the ratio of median effective doses (ED50) for electroporative damage and defibrillation, was assessed for nanosecond and conventional (millisecond) defibrillation shocks in Langendorff-perfused New Zealand white rabbit hearts. In order to allow for multiple shock applications in a single heart, a pair of needle electrodes was used to apply shocks of varying voltage. Propidium iodide (PI) staining at the surface of the heart showed that nanosecond shocks had a slightly lower safety factor (6.50) than millisecond shocks (8.69), p = 0.02; while PI staining cross-sections in the electrode plane showed no significant difference (5.38 for 300 ns shocks and 6.29 for 10 ms shocks, p = 0.22). CONCLUSIONS: In Langendorff-perfused rabbit hearts, nanosecond defibrillation has a similar safety factor as millisecond defibrillation, between 5 and 9, suggesting that nanosecond defibrillation can be performed safely

Nanosecond Stimulation and Defibrillation of Langendorff-Perfused Rabbit Hearts

The search for novel defibrillation methodologies focuses on minimizing deposition of energy to the heart, as this is an indicator for side effects including pain and tissue death. In this work, we investigate the effect of reducing the duration of the applied shocks from low milliseconds to the nanosecond range. 300 ns defibrillation was observed and confirmed to require lower energy than monophasic shocks by almost an order of magnitude with no tissue damage. Additionally, the safety factor, the ratio of median effective doses for electroporative damage and defibrillation, was similar for both durations. To predict how defibrillation shocks of any duration affect the heart, the stimulation strength-duration curve from 200 ns to 10 ms was determined. To investigate whether high frequency trains of nanosecond shocks (MHz compression) are capable of reducing the electric field and energy of defibrillation, they were compared with a single shock of the same duration. The average voltage for the pulse trains was slightly lower than for long shocks, but the energy almost doubled. Finally, to understand how shocks even shorter than 300 ns perform, we attempted to determine the defibrillation threshold of 60 ns shocks. Both the estimated electric field and energy were markedly higher than for 300 ns. We also investigated the stimulation threshold of 60 ns shocks followed by a negative phase of varying amplitude and showed that the negative phase reduces the ability of the shocks to stimulate. In conclusion, this work contributes to the understanding of how nanosecond shocks interact with cardiac tissues. It shows that 300 ns defibrillation is effective and similarly safe as 10 ms shocks, while requiring almost an order of magnitude less energy. The stimulation strength duration curve for cardiac tissue follows the same trend, with lower than expected thresholds for nanosecond shocks. However, low voltage MHz compressed nanosecond shocks are similarly effective as long shocks of the same duration, indicating that the greater efficacy of nanosecond defibrillation is linked to the effects of high voltage. Finally, investigations in 60 ns shocks show defibrillation and stimulation are possible, and that bipolar cancellation occurs in cardiac tissue

How to Alleviate Cardiac Injury From Electric Shocks at the Cellular Level

Electric shocks, the only effective therapy for ventricular fibrillation, also electroporate cardiac cells and contribute to the high-mortality post-cardiac arrest syndrome. Copolymers such as Poloxamer 188 (P188) are known to preserve the membrane integrity and viability of electroporated cells, but their utility against cardiac injury from cardiopulmonary resuscitation (CPR) remains to be established. We studied the time course of cell killing, mechanisms of cell death, and protection with P188 in AC16 human cardiomyocytes exposed to micro- or nanosecond pulsed electric field (μsPEF and nsPEF) shocks. A 3D printer was customized with an electrode holder to precisely position electrodes orthogonal to a cell monolayer in a nanofiber multiwell plate. Trains of nsPEF shocks (200, 300-ns pulses at 1.74 kV) or μsPEF shocks (20, 100-μs pulses at 300 V) produced a non-uniform electric field enabling efficient measurements of the lethal effect in a wide range of the electric field strength. Cell viability and caspase 3/7 expression were measured by fluorescent microscopy 2–24 h after the treatment. nsPEF shocks caused little or no caspase 3/7 activation; most of the lethally injured cells were permeable to propidium dye already at 2 h after the exposure. In contrast, μsPEF shocks caused strong activation of caspase 3/7 at 2 h and the number of dead cells grew up to 24 h, indicating the prevalence of the apoptotic death pathway. P188 at 0.2–1% reduced cell death, suggesting its potential utility in vivo to alleviate electric injury from defibrillation

Excitation and Injury of Adult Ventricular Cardiomyocytes by Nano- to Millisecond Electric Shocks

Intense electric shocks of nanosecond (ns) duration can become a new modality for more efficient but safer defibrillation. We extended strength-duration curves for excitation of cardiomyocytes down to 200 ns, and compared electroporative damage by proportionally more intense shocks of different duration. Enzymatically isolated murine, rabbit, and swine adult ventricular cardiomyocytes (VCM) were loaded with a Ca2+ indicator Fluo-4 or Fluo-5N and subjected to shocks of increasing amplitude until a Ca2+ transient was optically detected. Then, the voltage was increased 5-fold, and the electric cell injury was quantified by the uptake of a membrane permeability marker dye, propidium iodide. We established that: (1) Stimuli down to 200-ns duration can elicit Ca2+ transients, although repeated ns shocks often evoke abnormal responses, (2) Stimulation thresholds expectedly increase as the shock duration decreases, similarly for VCMs from different species, (3) Stimulation threshold energy is minimal for the shortest shocks, (4) VCM orientation with respect to the electric field does not affect the threshold for ns shocks, and (5) The shortest shocks cause the least electroporation injury. These findings support further exploration of ns defibrillation, although abnormal response patterns to repetitive ns stimuli are of a concern and require mechanistic analysis

ORCHESTRATING FEAR RESPONSES IN LARVAL ZEBRAFISH: A ROLE FOR THE HABENULA

Master'sMASTER OF SOCIAL SCIENCE

Top-Down and Bottom-Up Fear Regulation: Experimental Combinations to Reduce the Return of Fear and an Examination of its Neural Correlates

The regulation of fear can be considered as driven from stimulus properties, considered bottom-up, and cognitive constructions, considered top-down. This dissertation contains three papers that investigated how these approaches may complement one another for the purposes of clinical translation to optimize long-term fear amelioration in treatments for fear-related disorders.In Study 1, a fear-conditioning experiment was conducted manipulating the use of a low-cost, re-evaluative, and contingency-directed cognitive reappraisal against passive and active control conditions (i.e., react-as-normal and expressive suppression). The experiment examined how this strategy changed responses during extinction training and during a test of rapid reacquisition one-week later. In Study 2, the experiment was replicated twice. The first replaced the test of rapid reacquisition with an induction of fear reinstatement. The second replaced the test of rapid reacquisition with an induction of context renewal. Results indicated that reappraisal led to faster reductions in threat expectancy to the CS- during extinction training relative to suppression. This was not observed when extinction training featured CSs overlaid atop visual contexts. Results also indicated that in one of three experiments, reappraisal, relative to reacting as normal, led to increases in CS+ valence after extinction training and reductions in the spontaneous recovery of skin conductance responses. Reappraisal, relative to suppression, also led to faster recovery of CS+ US expectancy after fear reinstatement. Suppression led to greater skin conductance responding to the CS- relative to reappraisal and reacting as normal during rapid reacquisition and greater skin conductance responding to the CS+ during context renewal relative to reacting as normal.Study 3 examined how individuals who express above average spontaneous recovery in skin conductance responses differentially recruit neural activity in structures that putatively implement fear (amygdala, BNST, anterior insula), top-down regulation (dlPFC and vlPFC) and bottom-up regulation (vmPFC and sgACC) during a test of spontaneous recovery 24-48 hours after fear extinction training. Results suggested sparse evidence for fear over-generation in fear regions, and more evidence for misregulation, underregulation/disconnection, and competitive co-regulation in regions that implement fear regulation. Results are discussed in terms of the granular mechanisms underlying extinction and cognitive reappraisal, and implications for clinical application

Understanding new regimes for light-matter interactions

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 179-194).This thesis focuses on achieving new understanding of the principles and phenomena involved in the interaction of light with a variety of complicated material systems, including biomaterials and nanostructured materials. We will show that bone piezoelectricity may be a source of intense blast-induced electric fields in the brain, with magnitudes and timescales comparable to fields with known neurological effects, and may play a role in blast-induced traumatic brain injury. We will also shed new light on the localization of photons in a variety of complex microstructured waveguides. We will reveal the principles behind the design of single-polarization waveguides, including design strategies that did not seem to have been considered previously. Finally, we designed a 3D photonic crystal slab structure to exhibit negative-index behavior at visible wavelengths, which was fabricated and experimentally demonstrated by our collaborators to show negative refraction with, to our knowledge, the lowest loss at visible wavelengths to date.by Ka Yan Karen Lee.Ph.D