Pulsed Transmission Waveform to Mitigate Tissue Thermal Effects in Transcutaneous Wireless Energy Supply Systems for High-Power Rated Medical Implants

Escalona, OJ; Waterman, N.; McLaughlin, James; McEneaney, David

doi:10.1007/978-981-10-9038-7_175

Cited by 3 publications

(28 citation statements)

References 6 publications

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“…We thus developed a Power Loss Emulating (PLE) system for WPT associated inefficiencies heating effects when driving LVADs at different power rate levels. The study presented here complements previous work [ 28 ] and provides reliable experimental (in vivo) and numerical (in silico) methods for the development of advanced WPT systems.…”

Section: Introductionsupporting

confidence: 69%

“…The overall results for various experimental settings are presented in Figure 11 . Regarding the estimated maximum average temperature change (ΔT) at the implanted element, it was consistently revealed throughout the study that pulsed transmission [ 28 ] yields about 30% lower temperature effects than conventional continuous transmission [ 21 ]. Hence, blood perfusion factors, along with the idle time of the pulse transmission, can be harnessed to help reduce the skin heating effect using suitable WPT technology, as suggested by pulsed RF transmission waveforms proposed by the TWESMI system concept [ 28 ].…”

Section: Discussionmentioning

confidence: 99%

“…This section describes the prototype Power Loss Emulation (PLE) system, used for both the novel pulsed (TWESMI) transmission waveforms [ 28 ] and the conventional continuous transmission modes [ 21 ], the experimental setup, and the protocol design for studying the thermal effects on in vivo measurements (porcine model skin tissue), both on the alive and cadaver (no blood circulation) model states, within the same pig case. For the supporting in silico model, the geometry, multiphysics and solver setup to simulate the temperature inside the subcutaneous tissue due to RF power transfer between the primary and implanted coil are described.…”

Section: Methodsmentioning

confidence: 99%

“…In addition to thermal injury existing WPT systems generate electromagnetic (EM) fields interacting with the living tissue, characterised by the specific absorption rate (SAR) metric, and which may cause cellular damage [ 24 , 25 , 26 , 27 ]. In our previous studies, a Transcutaneous Wireless Energy System for Medical Implants (TWESMI) concept, with a novel high-energy pulsed RF transmission waveform for mitigating tissue thermal effects, has been presented as a multichannel WPT proprietary system [ 28 ] (see Patents section in this article), and proposed as a solution for driving high-power rated LVADs [ 28 , 29 ]. A multichannel system approach offers several advantages: (a) to reduce the overall coupling energy density (a 4-channel system would present less skin heat for a fixed load power level), (b) to offer higher operational reliability by redundancy (in case a transfer channel fails), and (c) to enable capacitive coupling (using plates; not coils) [ 17 ], which is only possible with an even number of channels (minimum of two channels).…”

Section: Introductionmentioning

confidence: 99%

“…A multichannel system approach offers several advantages: (a) to reduce the overall coupling energy density (a 4-channel system would present less skin heat for a fixed load power level), (b) to offer higher operational reliability by redundancy (in case a transfer channel fails), and (c) to enable capacitive coupling (using plates; not coils) [ 17 ], which is only possible with an even number of channels (minimum of two channels). The proprietary TWESMI concept includes the use of thin, compact, flexible, biocompatible flat spiral coil elements [ 28 , 29 ].…”

Section: Introductionmentioning

confidence: 99%

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Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results

Karim

Bosnjak

McLaughlin

et al. 2022

Sensors

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This article presents the development of a power loss emulation (PLE) system device to study and find ways of mitigating skin tissue heating effects in transcutaneous energy transmission systems (TETS) for existing and next generation left ventricular assist devices (LVADs). Skin thermal profile measurements were made using the PLE system prototype and also separately with a TETS in a porcine model. Subsequent data analysis and separate computer modelling studies permit understanding of the contribution of tissue blood perfusion towards cooling of the subcutaneous tissue around the electromagnetic coupling area. A 2-channel PLE system prototype and a 2-channel TETS prototype were implemented for this study. The heating effects resulting from power transmission inefficiency were investigated under varying conditions of power delivery levels for an implanted device. In the part of the study using the PLE setup, the implanted heating element was placed subcutaneously 6–8 mm below the body surface of in vivo porcine model skin. Two operating modes of transmission coupling power losses were emulated: (a) conventional continuous transmission, and (b) using our proposed pulsed transmission waveform protocols. Experimental skin tissue thermal profiles were studied for various levels of LVAD power. The heating coefficient was estimated from the porcine model measurements (an in vivo living model and a euthanised cadaver model without blood circulation at the end of the experiment). An in silico model to support data interpretation provided reliable experimental and numerical methods for effective wireless transdermal LVAD energization advanced solutions. In the separate second part of the study conducted with a separate set of pigs, a two-channel inductively coupled RF driving system implemented wireless power transfer (WPT) to a resistive LVAD model (50 Ω) to explore continuous versus pulsed RF transmission modes. The RF-transmission pulse duration ranged from 30 ms to 480 ms, and the idle time (no-transmission) from 5 s to 120 s. The results revealed that blood perfusion plays an important cooling role in reducing thermal tissue damage from TETS applications. In addition, the results analysis of the in vivo, cadaver (R1Sp2) model, and in silico studies confirmed that the tissue heating effect was significantly lower in the living model versus the cadaver model due to the presence of blood perfusion cooling effects.

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Section: Introductionsupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results

Karim

Bosnjak

McLaughlin

et al. 2022

Sensors

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Harnessing Dermal Blood Flow to Mitigate Skin Heating Effects in Wireless Transdermal Energy Systems for Driving Heart Pumps

Karim¹,

Bosnjak²,

McLaughlin³

et al. 2022

Computing in Cardiology Conference (CinC)

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This work focuses on the thermal analysis of a transdermal wireless radiofrequency (RF) energy transfer system, to power artificial heart pumps, particularly leftventricular assist devices (LVADs). We aim to understand the blood perfusion factors to mitigate the skin heating effects and thermal injury to subcutaneous tissue under the RF coupling area. A 2-channel RF power loss emulator (RFPLE) system was developed to conduct a study independent of the wireless RF supply coupling method. The heating coils were implanted subcutaneously 6-8 mm beneath the porcine model skin. Heating effects due to RF coupling inefficiency power losses for conventional and our novel pulsed transmission waveform protocol were emulated. The thermal profiles were studied for varying levels of LVAD power requirement. An in-silico model was developed in parallel with the in-vivo experiments to aid the interpretation of results.

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Robust Arm Impedocardiography Signal Quality Enhancement Using Recursive Signal Averaging and Multi-Stage Wavelet Denoising Methods for Long-Term Cardiac Contractility Monitoring Armbands

Escalona,

Cullen,

Weli

et al. 2023

Sensors

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Impedance cardiography (ICG) is a low-cost, non-invasive technique that enables the clinical assessment of haemodynamic parameters, such as cardiac output and stroke volume (SV). Conventional ICG recordings are taken from the patient’s thorax. However, access to ICG vital signs from the upper-arm brachial artery (as an associated surrogate) can enable user-convenient wearable armband sensor devices to provide an attractive option for gathering ICG trend-based indicators of general health, which offers particular advantages in ambulatory long-term monitoring settings. This study considered the upper arm ICG and control Thorax-ICG recordings data from 15 healthy subject cases. A prefiltering stage included a third-order Savitzky–Golay finite impulse response (FIR) filter, which was applied to the raw ICG signals. Then, a multi-stage wavelet-based denoising strategy on a beat-by-beat (BbyB) basis, which was supported by a recursive signal-averaging optimal thresholding adaptation algorithm for Arm-ICG signals, was investigated for robust signal quality enhancement. The performance of the BbyB ICG denoising was evaluated for each case using a 700 ms frame centred on the heartbeat ICG pulse. This frame was extracted from a 600-beat ensemble signal-averaged ICG and was used as the noiseless signal reference vector (gold standard frame). Furthermore, in each subject case, enhanced Arm-ICG and Thorax-ICG above a threshold of correlation of 0.95 with the noiseless vector enabled the analysis of beat inclusion rate (BIR%), yielding an average of 80.9% for Arm-ICG and 100% for Thorax-ICG, and BbyB values of the ICG waveform feature metrics A, B, C and VET accuracy and precision, yielding respective error rates (ER%) of 0.83%, 11.1%, 3.99% and 5.2% for Arm-IG, and 0.41%, 3.82%, 1.66% and 1.25% for Thorax-ICG, respectively. Hence, the functional relationship between ICG metrics within and between the arm and thorax recording modes could be characterised and the linear regression (Arm-ICG vs. Thorax-ICG) trends could be analysed. Overall, it was found in this study that recursive averaging, set with a 36 ICG beats buffer size, was the best Arm-ICG BbyB denoising process, with an average of less than 3.3% in the Arm-ICG time metrics error rate. It was also found that the arm SV versus thorax SV had a linear regression coefficient of determination (R2) of 0.84.

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Pulsed Transmission Waveform to Mitigate Tissue Thermal Effects in Transcutaneous Wireless Energy Supply Systems for High-Power Rated Medical Implants

Cited by 3 publications

References 6 publications

Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results

Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results

Harnessing Dermal Blood Flow to Mitigate Skin Heating Effects in Wireless Transdermal Energy Systems for Driving Heart Pumps

Robust Arm Impedocardiography Signal Quality Enhancement Using Recursive Signal Averaging and Multi-Stage Wavelet Denoising Methods for Long-Term Cardiac Contractility Monitoring Armbands

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