Translation of Vibration From a Vibrational Plate to the Human Body

This study was done to validate the results of our previous study [1] as well as analyze how the Soloflex Whole Body Vibration Platform translates vibration to the human body. The purpose of causing vibration within the human body is to increase bone density, possibly by activating osteoblasts within the bone. When the body is subjected to stress, it adapts as quickly as possible to counteract this stress. There is evidence that vibration caused by low magnitude mechanical signals (LMMS) increases bone in children with disabling conditions [2] and young women (15-20 years) with low bone mineral density [3]. Our results show that Soloflex dial settings of 0.8g or greater produce frequencies as expected by the manufacturer. Lower dial settings produce frequencies that are higher than expected values. The results obtained showed that vibration at the foot had no linear association with increased acceleration (R = 0.56, p = 0.20), but vibration frequencies increased with increased acceleration at the hip (R = 0.86. p = 0.01). The mean frequencies measured over the range of accelerations (0.3-1.1g) were not different between the foot and the hip (56 ± 5 vs. 52 ± 12 Hz, p = 0.45; mean ± SD; respectively). Mean frequencies measured at the four different locations on the plate over the range of accelerations (0.3 – 1.1g) were not different when tested by Tukey’s HSD test

Effect of Contact Force on Pulsed Field Ablation Lesions in Porcine Cardiac Tissue.

BACKGROUND Contact force has been used to titrate lesion formation for radiofrequency ablation. Pulsed Field Ablation (PFA) is a field-based ablation technology for which limited evidence on the impact of contact force on lesion size is available. METHODS Porcine hearts (n=6) were perfused using a modified Langendorff set-up. A prototype focal PFA catheter attached to a force gauge was held perpendicular to the epicardium and lowered until contact was made. Contact force was recorded during each PFA delivery. Matured lesions were cross-sectioned, stained, and the lesion dimensions measured. RESULTS A total of 82 lesions were evaluated with contact forces between 1.3 g and 48.6 g. Mean lesion depth was 4.8 ± 0.9 mm (standard deviation), mean lesion width was 9.1 ± 1.3 mm and mean lesion volume was 217.0. ± 96.6 mm3 . Linear regression curves showed an increase of only 0.01 mm in depth (Depth = 0.01*Contact Force + 4.41, R2 = 0.05), 0.03 mm in width (Width = 0.03*Contact Force + 8.26, R2 = 0.13) for each additional gram of contact force, and 2.20 mm3 in volume (Volume = 2.20*Contact Force + 162, R2 = 0.10). CONCLUSIONS Increasing contact force using a bipolar, biphasic focal PFA system has minimal effects on acute lesion dimensions in an isolated porcine heart model and achieving tissue contact is more important than the force with which that contact is made. This article is protected by copyright. All rights reserved

Determination of lethal electric field threshold for pulsed field ablation in ex vivo perfused porcine and human hearts

IntroductionPulsed field ablation is an emerging modality for catheter-based cardiac ablation. The main mechanism of action is irreversible electroporation (IRE), a threshold-based phenomenon in which cells die after exposure to intense pulsed electric fields. Lethal electric field threshold for IRE is a tissue property that determines treatment feasibility and enables the development of new devices and therapeutic applications, but it is greatly dependent on the number of pulses and their duration.MethodsIn the study, lesions were generated by applying IRE in porcine and human left ventricles using a pair of parallel needle electrodes at different voltages (500–1500 V) and two different pulse waveforms: a proprietary biphasic waveform (Medtronic) and monophasic 48 × 100 μs pulses. The lethal electric field threshold, anisotropy ratio, and conductivity increase by electroporation were determined by numerical modeling, comparing the model outputs with segmented lesion images.ResultsThe median threshold was 535 V/cm in porcine ((N = 51 lesions in n = 6 hearts) and 416 V/cm in the human donor hearts ((N = 21 lesions in n = 3 hearts) for the biphasic waveform. The median threshold value was 368 V/cm in porcine hearts ((N = 35 lesions in n = 9 hearts) cm for 48 × 100 μs pulses.DiscussionThe values obtained are compared with an extensive literature review of published lethal electric field thresholds in other tissues and were found to be lower than most other tissues, except for skeletal muscle. These findings, albeit preliminary, from a limited number of hearts suggest that treatments in humans with parameters optimized in pigs should result in equal or greater lesions

An Examination of the Cardiothoracic Tissue Biophysical Response to Electroporation Therapies

University of Minnesota Ph.D. dissertation. February 2019. Major: Biomedical Engineering. Advisor: Paul Iaizzo. 1 computer file (PDF); xi, 178 pages.Atrial fibrillation (AF) is a disease that affects an estimated 2.7 to 6.1 million people in the United States alone. Currently there are two primary ways to treat the disease: drug or ablation therapy. Ablation therapy is used to kill or isolate the cardiac tissue that is causing abnormal cardiac conduction. The two primary ablation technologies used are radiofrequency ablation (RF) and cryoablation (Cryo). While both technologies have shown clinical efficacy, they are not without their drawbacks. Both RF and Cryo are thermal ablation modalities that cause cell death by either heating or cooling the tissue. Due to variations in anatomy, blood flow, and how the energy is applied, complications can occur when the thermal energy propagates beyond the intended target zone. This may result in collateral damage, such as phrenic nerve injury or atria-esophageal fistula. Electroporation is a new technology that is being investigated as a novel way to treat cardiac arrhythmias. It uses short, high voltage, DC electrical pulses to disrupt the cell membrane that can lead to cell death. The work presented here quantifies the biophysical responses of electroporation on different cardiothoracic tissue types. The functional response of skeletal, smooth, and cardiac muscle was evaluated using isolated muscle baths. Following this, a uniaxial pull test was performed to evaluate any effects on tissue integrity. Phrenic nerve functional response to electroporation was evaluated with elicited compound action potential recordings. The complete dataset provides an understanding of how to target different tissue types which can be useful when developing therapeutic protocols or medical device design.Mattison, Lars. (2019). An Examination of the Cardiothoracic Tissue Biophysical Response to Electroporation Therapies. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/213129

Elucidating the mechanisms of microbubble formation in intracardiac pulsed field ablation

Delivery of electrical energy for sensing or therapeutic purposes often involves electrochemical phenomena at the electrode-electrolyte solution interface. Release of gaseous bubbles that accompanies delivery of pulsed electric fields to tissues in applications such as electrochemotherapy of tumours and irreversible electroporation or pulsed field ablation in cardiac electrophysiology needs to be understood and characterized. We present an in vitro study using pulsed field delivery into saline, employing multiple different treatment protocols, two electrode geometries (pair of needles and a modified RF catheter), and two imaging systems to elucidate the complex relationship between the electrical treatment protocol, temperature changes at and around the electrodes, and gas release due to pulse delivery. Our primary objective was to identify the key parameters responsible for bubble formation and to highlight the importance of the treatment parameters and their interplay – ranging from the temperature to appropriate choice of electrode geometry, and, most importantly, to the choice of the treatment protocol. We found that bubbles originating from electrochemical reactions are more prevalent in monophasic pulsing protocols, whereas in high frequency biphasic pulsing protocols the bubbles are mainly caused by boiling of the medium. Degassing of liquid due to lower solubility of gasses at elevated temperatures does seems to play a role, though a minor one. We also observed that bubbles caused by boiling collapse very rapidly, whereas electrochemically produced bubbles or those produced through degassing appear to have longer lifetimes. Therefore, the treatment protocols most suited to minimizing gas release are biphasic trains of short ($mu$s) pulses with a significant inter-pulse delay (i.e. low duty cycle) to prevent excessive heating. Moreover, electrodes must be designed to avoid high local current densities. Our findings have broad implications extending from lab-on-a-chip cell electroporation devices to intracorporeal pulsed field applications in the cardiovascular system, particularly pulsed field ablation procedures