Bosnjak, Antonio

Escalona, OJ

Finn, Brommely

Karim, Mohammad

McEneaney, David

English

IntroductionLeft Ventricular Assist Devices (LVADs) are used as a bridge to cardiac transplantation, and for long-term support in patients with advanced Heart Failure. LVADs are relatively high-power demanding implanted devices (&gt;3W), provided via a percutaneous driveline (cable) from an external supply. However, incidence of driveline infection is a severe and frequent drawback. Wirelessly Pulsed Energy Transmission (WPET) transcutaneously is aimed to mitigate tissue-heating effects over conventional non-pulsed Transcutaneous Energy Transfer Systems (TETS). We comparatively assess the transient thermal profile of WPET in living and cadaver porcine models. MethodsDual-channel WPET pulsed and continuous TETS systems were investigate to characterise subcutaneous tissue transient thermal profiling for several ratings of RF-power losses between the primary and the implanted coils. Twelve Negative-Temperature-Coefficient thermistors were adhered at the surface of the implanted coils to monitor the thermal profiles for 3W, 5W, 6W, and 8W rated LVADs. The implanted coils (channel-1 and channel-2) are placed at about 6-10 mm underneath the skin surface. RF-transmission pulse duration ranged from 30ms to 480ms, and idle time (no-transmission) from 5s to 120s. Temperature change of the tissue were sensed by the 12-thermistor. ResultsThe average transient thermal profile of the living-model measurement, both in pulsed and continuous power transmission heating losses, are presented in Table1 below. The transient thermal profile of subcutaneous tissue shows an almost similar profile at low power levels (3W); however, 6 and 8 Watts pulsed transmission showed a significantly lower temperature profile. Table 2 presents the transient temperature profile of the cadaver model which indicated that in the cadaver model, the tissue heating is significantly higher in the absence of blood-perfusion. ConclusionWe developed and evaluated the transient thermal profile of both RF pulsed and continuous TETS systems. The pulsed system would suit high-power LVADs with minimised subcutaneous tissue heating effects via blood-perfusion.<br/

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                      Subcutaneous Tissue Transient Thermal Profiling Under RF-energy Pulsed WirelessSupply to 3W-8W Rated LVAD in the Living and Cadaver Models.Escalona, OJ., Finn, B., Karim, M., Bosnjak, A., & McEneaney, D. (in press). Subcutaneous Tissue TransientThermal Profiling Under RF-energy Pulsed Wireless Supply to 3W-8W Rated LVAD in the Living and CadaverModels.. Abstract from Computing in Cardiology 2023, Atlanta, USA, Atlanta, Georgia, United States.Link to publication record in Ulster University Research PortalPublication Status:Accepted/In press: 25/06/2023General rightsCopyright for the publications made accessible via Ulster University's Research Portal is retained by the author(s) and / or other copyrightowners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with theserights.Take down policyThe Research Portal is Ulster University's institutional repository that provides access to Ulster's research outputs. Every effort has beenmade to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content inthe Research Portal that you believe breaches copyright or violates any law, please contact pure-support@ulster.ac.uk.Download date: 04/11/2023Subcutaneous Tissue Transient Thermal Profiling Under RF-energy Pulsed Wireless Supply to 3W-8W Rated LVAD in the Living and Cadaver Models Omar J. Escalona1, Brommely Finn1, Mohammad L. Karim1, Antonio Bosnjak1, David McEneaney2 1 Nanotechnology & Integrated BioEngineering Centre (NIBEC), Ulster University, UK  2 Cardiovascular Research Unit, Craigavon Area Hospital, Portadown, UK  Abstract Left Ventricular Assist Devices (LVADs) are used as a bridge to cardiac transplantation, and for long-term support in patients with advanced Heart Failure. LVADs are relatively high-power demanding implanted devices (>3W), provided via a percutaneous driveline (cable) from an external supply. However, incidence of driveline infection is a severe and frequent drawback.  Wireless Pulsed Energy Transmission (WPET) transcutaneous system is aimed to mitigate tissue-heating effects over conventional non-pulsed Transcutaneous Energy Transfer Systems (TETS). We comparatively assess the transient thermal profile of WPET in living and cadaver porcine models. This study focuses on the transient thermal analysis of the subcutaneous tissue heating effects, in a dual-channel WPET (pulsed transmission mode) and conventional continuous mode TETS systems.  1 . Introduction     Heart failure (HF) is a clinical syndrome, and patients with advanced heart failure have a reduced ability of the heart to pump and impaired blood circulation through the body. Heart Failure (HF) can be considered a global pandemic, affecting more than 64 million people worldwide in 2017 [1]. The prevalence of symptomatic HF in the adult population is 1%-3 %, increasing to 20% over 75 years of age. In end-stage HF, one-year mortality is 30% [2]. In HF refractory to drug therapy, cardiac transplantation is an option, although strictly limited by donor availability.       Left Ventricular Assist Devices (LVADs) are small electrically powered implanted blood pumps connected to the heart and aorta. Initially used to 'bridge' to transplantation, LVADs are increasingly used as long-term 'destination' therapy. LVADs significantly improve quality-of-life and survival rates in patients with end-stage HF patients [3].      The power demand of LVADs is high (5W-40W) and necessitates a percutaneous driveline to an external power supply. However, driveline site infection is a serious issue, requiring hospitalization and prolonged antibiotic therapy. Driveline related complications also lead to premature LVAD failure and increased patient mortality [4-6].      A wireless power transmission (WPT) in implantable medical devices is becoming increasingly relevant in the medical device industry [7]. A wireless power solution would eliminate the driveline, improve the quality of life for the patient, reduce hospitalisation and increase patient survival. However, the main limitation to WPT use is the related tissue heating effect from the radiofrequency coils leading to local tissue damage. Even at relatively low power transmission levels (4W), the heating effect in the implanted receiver element (coil) would exceed 2°C above baseline body temperature, leading to tissue injury.       We have addressed this issue and developed a novel Wireless Pulsed Energy Transmission (WPET) system for LVADs, using high-energy pulses transmitted in a relatively short time interval, followed by an idle time to reduce the temperature of the tissue by capillary blood thermal perfusion action around the implanted coil. Thus, WPET transdermal energy supply systems are aimed to mitigate tissue-heating effects over conventional non-pulsed Transcutaneous Energy Transfer Systems (TETS). In this study, we assess the transient thermal profile of WPET in living and cadaver porcine models against the conventional continuous transmission TETS. Thus, this study complements our previously reported work for further characterisation of WPT solution for LVADs [8,9].  2. Methods   This section describes the prototype WPET system, the experimental setup, and the protocol design for studying the porcine model's thermal effects on in vivo and cadaver measurements under the same experimental condition. Dual-channel WPET pulsed and continuous TETS systems were developed to investigate the subcutaneous tissue transient heating profiling for several ratings of RF-power losses between the primary and the implanted coils. Twelve Negative-Temperature-Coefficient thermistors were adhered at the surface of the implanted coils to monitor the thermal profiles for 3W, 6W, and 8W rated LVADs. The implanted coils (channel-1 and channel-2) are placed at about 6-10 mm underneath the skin surface [9]. RF-transmission pulse duration ranged from 30ms to 480ms, and idle time (no-transmission) from 5s to 120s. Temperature change of the tissue were sensed by the 12-thermistor.  2.1. Radiofrequency power loss effects       To investigate the heating effect both in pulsed and continuous transmission system resulting from inefficiency in electromagnetic power loss between transmitter and receiver coils in 2-channel WPET systems is developed. Figure 1 showed a schematic diagram of a 2-channel system. Each channel has a pair of coils: an external coil and an implanted coil.    Figure 1. Schematic block diagram of the 2-channel WPET system and porcine model setup [9].        Each WPET coupling coil element is attached with 12 adhered negative temperature coefficient (NTC) thermistors [8, 9]. Thermistors had hair-thin wires (80 µm) connected to very-high input impedance instrumentation amplifiers at the operating RF (200 kHz).  2.2. In-vivo and cadaver model studies        The in-vivo measurements were carried out in 18 pig cases (average weight 50 kg; average body temperature 37°C, male and female) under the same measurement conditions with various power levels, pulse width and idle time (No transmission). Note that the results in Section 3 are based on the received power level for the LVAD application. The porcine study was endorsed by the Agri-Food and Bioscience Institute (AFBI) and the Animal Welfare & Ethical Review Board, and a project licence (PPL 2900) was obtained, under the Animals (Scientific Procedures) Act, from the Department of Health, UK.       2.3. Transient heating effect profiles (ΔT)          The transient heating profile of the subcutaneous tissue was evaluated from the implanted coil. The recorded 12-NTC thermistor signals used to calculate average temperature of the tissue. Note that recorded thermistor signals are subtracted from the body’s baseline temperature, to estimate the transient thermal profile (ΔT) of the tissue with 3, 6 and 8W of LVADs.  3. Results and Discussions  3.1       Thermal profile vs LVAD power level        Here the thermal profile data analysis obtained from the implanted (approx. 6-8 mm beneath skin surface) coils; channel 1 & channel. 2 (see Figure 1), in both in-vivo (alive) and cadaver experimental stages of the pig model under same experimental condition.        The average transient thermal profile of the in-vivo model at 3, 6, and 8 watts power levels, for both in pulsed and continuous transmission heating effects, ΔT (°C), are presented in Table1. There, it can be observed that the pulsed transmission protocol showed a lower thermal profile than the continuous transmission protocols. This tendency is stronger as the level of operating power increases (from 3 W to 8 W). Table 2 presents the comparative thermal profile for the cadaver model stage (no blood circulation) study, for both in pulsed and continuous transmission protocols, and for the particular operating LVAD power rate of 8 W. There, the mean temperature increase (ΔT) in 12 minutes, is at least twice larger than mean ΔT values in Table 1, for the 8W power level.       Table 1. Transient thermal profile of pulsed and continuous transmission (Ch.1 and Ch.2), in the in-vivo, model stage, for 3, 6 and 8 watts power rates LVADs.  Power (W) Pulsed ±SD (ΔT) In-vivo Continuous ±SD (ΔT) In-vivo  Ch.1(°C)  Ch.2 (°C)  Ch.1 (°C)  Ch.2 (°C)   3 0.85±1.75x 10-2 1.19±1.78x 10-2 0.99±3.05x 10-5 1.19±3.08x 10-5 6 1.58±1.60x 10-2 1.86±2.01x 10-2 1.92±2.86x 10-5 2.22±4.49x 10-5 8 0.40±1.93x 10-1 0.49±2.41x 10-1 0.64±3.52x 10-1 0.73±3.55x 10-1       Table 2. Transient thermal profile of pulsed and continuous transmission (Ch.1 & Ch.2) in cadaver model.  Watts Pulsed. ±SD (ΔT) Cont. ±SD (ΔT)  Ch.1(°C) Ch.2 (°C)  Ch.1 (°C)  Ch.2 (°C)   8 0.88±4.46x 10-1 1.15±5.63x 10-1 1.56±7.68x 10-1 2.00±9.77x 10-1  3.2. Thermal profiles analysis for 8W case       In-vivo and cadaver temperature measurements from channels 1 and 2, were recorded for both modes of pulsed transmission protocols and their respective continuous transmission protocols. Figures 2 and 3 depict the transient  Figure 2.  In-vivo transient thermal profile (ΔT)  for 8W.   Figure 3.  Cadaver transient thermal profile (ΔT) for 8W.  Figure 4.  Scatter plot and linear regression model for in-vivo model Ch.1: Pulsed vs. Continuous.  thermal profile of channel 1 and channel 2, in pulsed and continuous transmission protocols. In both cases, the channel 1 shows a lower temperature than channel 2. The average temperature increase (ΔT) rises to 0.8°C and 0.9°C for channel 1 and channel 2 but in continuous transmission the temperature increase is considerably higher: 1.1°C, and 1.2°C respectively.       The cadaver ΔT trend shows a higher profile than the in-vivo  model. Thus, it reveals that blood perfusion plays a significant role in reducing thermal damage due to tissue heating effect, both with pulsed and conventional continuous transmission protocol. In the in-vivo model, the continuous protocol presented a higher temperature change (ΔT) profile than the pulsed transmission. Thus, the idle (no transmission) time of the pulsed system allowed to reduce the temperature of the tissue.       In order to find a linear regression model of pulsed versus continuous in a scatter plot of  pairs of continuous and corresponding pulsed ΔT, for both Ch1 and Ch2, the pulsed thermal time series (see orange and blue raw waveforms in Fig. 2 and Fig. 3)  were first smoothed using a 2nd order, 80 ms window size Savitzky–Golay FIR filter, before inputting it to the y-axis of a scatter plot versus respective continuous ΔT series (x-axis), of same channel and porcine model type (in-vivo/cadaver); see Figure 4 to Figure 7. Thus, linear model slopes and their coefficient of determination (R2) values computed. Figure 5.  Scatter plot and linear regression model for in-vivo model Ch.2: Pulsed vs. Continuous.    Figure 6.  Scatter plot and linear regression model for cadaver model Ch.1: Pulsed vs. Continuous.   Figure 7. Scatter plot and linear regression model for cadaver model Ch.1: Pulsed vs. Continuous.  3.3. Thermal correlation matrix pattern      Correlations between pairs of “channel #” mode-protocol (total of 8 channel modes), were assessed by Pearson correlation coefficients to construct a correlation matrix [10].  Figure 8 presents the correlation coefficient between the 8 protocols for in vivo and cadaver models, for both continuous and pulsed power (8 W) transmission modes, and thermal profile of the subcutaneous coil/tissue. The correlation matrix is used to visualise the distribution pattern of correlation between pairs of mode-protocol within the 8 sets of data obtained, with the darker shades indicating stronger positive correlations, thus, depicting the strength of the correlation between each channel-mode paired temperature profiles; as a WPT system fingerprint.    Figure 8. Thermal correlation matrix for 8W power rate.   4. Conclusions      In this study, the thermal profile differences due to the type of transmission has been characterised quantitatively; evidencing a lower rise in temperature (ΔT) for pulsed transmission versus continuous transmission, regardless of WPT skin-coupling channel or living/cadaver model mode, as revealed by all four linear regression models: slopes < 0.66, with good coefficient of determinations values (R2 > 0.92). The latter analysis perspective corroborates the 30% lower heating effect of pulsed transmission (WPET) advantage over conventional continuous transmission TETS, as previously reported [9].  Acknowledgments  This study was funded by Heart Research UK (HRUK), UK, grant reference number RG2678.   References  [1] Benjamin EJ, et al. (2017). “Heart Disease and Stroke Statistics - 2017 Update: A Report from the American Heart Association (7/Mar/2017)”, Circulation, 135:00–00, e390, 2017. [2] Savarese, G., Becher, P.M., Lund, L.H., Seferovic, P., Rosano, G.M. and Coats, A.J., 2022. Global burden of heart failure: a comprehensive and updated review of epidemiology. Cardiovascular research, 118(17), pp.3272-3287. [3] Jefferson, H.L., Kent, W.D., MacQueen, et al. (2021). Left ventricular assist devices: A comprehensive review of major clinical trials, devices, and future directions. Journal of Cardiac Surgery, 36(4), pp.1480-1491. [4] Pienta, M., Shore, S., Pagani, F.D., et al. (2021). Rates and types of infections in left ventricular assist device recipients: a scoping review. JTCVS open, 8, pp.405-411. [5] Campi, T., Cruciani, S., Maradei, F., et al. (2022). Thermal Analysis of a Transcutaneous Energy Transfer System for a Left Ventricular Assist Device. IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, 6(2), pp.189-195. [6] McEneaney, D., Escalona, O., Bosnjak, A., Karim, M., Crawford, P. and McLaughlin, J. (2023). A Novel Wireless Power Transmission System for Left Ventricular Assist Devices. The Journal of Heart and Lung Transplantation, 42(4), p.S183. [7] Khan, S.R., Pavuluri, S.K., Cummins, G. and Desmulliez, M.P. (2020). Wireless power transfer techniques for implantable medical devices: A review. Sensors, 20(12), p.3487. [8] Karim, M.L., Bosnjak, A., McLaughlin, J., Crawford, P., McEneaney, D. and Escalona, O.J. (2022). Harnessing Dermal Blood Flow to Mitigate Skin Heating Effects in Wireless Transdermal Energy Systems for Driving Heart Pumps. In 2022 Computing in Cardiology, Vol. 49, pp. 1-4.  [9] Karim, M.L., Bosnjak, A.M., McLaughlin, J., Crawford, P., McEneaney, D. and Escalona, O.J. (2022). Transcutaneous Pulsed RF Energy Transfer Mitigates Tissue Heating in High Power Demand Implanted Device Applications: In Vivo and In Silico Models Results. Sensors, 22(20), p.7775. [10] Mukaka M. M. (2012). Statistics corner: A guide to appropriate use of correlation coefficient in medical research. Malawi medical journal: the journal of Medical Association of Malawi, 24(3), 69–71  Correspondence:   Name: Prof Omar J Escalona.  Address: Ulster University, York St, Belfast, BT15 1ED, UK.  E-mail address:  oj.escalona@ulster.ac.uk 

Subcutaneous Tissue Transient Thermal Profiling Under RF-energy Pulsed Wireless Supply to 3W-8W Rated LVAD in the Living and Cadaver Models.

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Subcutaneous Tissue Transient Thermal Profiling Under RF-energy Pulsed Wireless Supply to 3W-8W Rated LVAD in the Living and Cadaver Models.

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