Electrical power to run ventricular assist devices using the Free-range Resonant Electrical Energy Delivery system

Abstract

Background: Models of power delivery within an intact organism have been limited to ionizing radiation and, to some extent, sound and magnetic waves for diagnostic purposes. Traditional electrical power delivery within the intact human body relies on implanted batteries that limit the amount and duration of delivered power. The efficiency of current battery technology limits the substantial demands required, such as continuous operation of an implantable artificial heart pump within a human body.

Methods: The fully implantable, miniaturized, Free-range Resonant Electrical Energy Delivery (FREE-D) system, compatible with any type of ventricular assist device (VAD), has been tested in a swine model (HVAD) for up to 3 hours. Key features of the system, the use of high-quality factor (Q) resonators together with an automatic tuning scheme, were tested over an extended operating range. Temperature changes of implanted components were measured to address safety and regulatory concerns of the FREE-D system in terms of specific absorption rate (SAR).

Results: Dynamic power delivery using the adaptive tuning technique kept the system operating at maximum efficiency, dramatically increasing the wireless power transfer within a 1-meter diameter. Temperature rise in the FREE-D system never exceeded the maximum allowable temperature deviation of 2°C (but remained below body temperature) for an implanted device within the trunk of the body at 10 cm (25% efficiency) and 50 cm (20% efficiency), with no failure episodes.

Conclusions: The large operating range of FREE-D system extends the use of VAD for nearly all patients without being affected by the depth of the implanted pump. Our in-vivo results with the FREE-D system may offer a new perspective on quality of life for patients supported by implanted device.

Keywords: FREE-D; LVAD; TETS; driveline; wireless.

Figure 1.. Vision of FREE-D system for patients with LVAD.

(A) Conceptual schematic showing extendable range of wireless power transfer in three-dimensional space within a long-range configuration. (B) Artistic representation of FREE-D system transferring wireless power from the vest-worn transmit coil to the implanted receive coil for nearly any angular orientation. (C) Artistic representation of specific scenarios where the long-range FREE-D system can significantly improve VAD patients’ quality of life with transmit coils installed throughout the patient’s home and around the patient’s household items.

Figure 2.. Long-term continuous operation of the FREE-D system.

The system was continuously run in bench top preparation for 90 days without any interruptions or faults. Power consumption, system efficiency, and pump speed were all stably maintained.

Figure 3.. In-vivo FREE-D system configurations.

(A) Short-range configuration where the external transmit coil directly connected to the FREE-D transmitter stand 10 cm away from the implanted receive coil beneath the animal skin. (B) Long-range configuration where the large external transmit coil directly connected to the FREE-D transmitter stand 50 cm away from the implanted receive coil with an additional external coil placed between them as a relay coil, 10 cm away from the skin.

Figure 4.. Comparison of power efficiency between short- and long- range configuration.

The average system efficiency was significantly higher for short-range configuration compared to the long-range configuration (p<0.01). Dot and horizontal bar inside the box indicates mean and median value respectively.

Figure 5.. In-vivo FREE-D system performance measurements for short- and long-range configuration.

For both experiments, the adaptive tuning techniques allow for the system to maintain seamless wireless power delivery, without any backup battery assist. The VAD power and system efficiency fluctuations were attributed to systolic and diastolic cycles or expansions and contractions of the animals’ chest while they breathe. Measurements of wireless power delivered to the receiver, backup battery power, load power, pump speed, wireless power transfer efficiency, and temperature rise during (A) short- and (B) long- range configuration in-vivo experiment.

Figure 6.. Average temperature changes at four different locations between (A) short- and (B) long- range configuration.

Thermocouples were placed at four different locations, inside the skin above the receive coil, directly above the receive coil, directly below the receive coil, and core temperature. The greatest temperature rise occurred at directly above the receive coil. All temperature measurements never exceeded the maximum allowable temperature deviation of the body, 2 °C, for an implanted device inside the trunk.