Abstract
Direct power delivery to intracorporeal circulatory support devices risks infection. Electrical transformers spanning the integument (skin or mucosa) have long been attractive means of circumventing this risk. Yet all existing skin surface transformers leak substantial magnetic flux, with an intrinsic risk of battery draining cross-coupling by any nearby conductor, requiring strict control of surroundings. In a progression of designs, we have used the walls of a small pouch, surgically formed from ileum, rather than skin, as a barrier. Previously, we reported a torroidal design with complete magnetic circuits, having zero flux leakage and unmatched heat dissipation in a 2 week canine trial. This work was in three parts: (1) Devices were placed in eight dogs for 9-12 weeks to document performance of the existing design. (2) Based on these results, the device was further miniaturized. Iterative computational modeling was applied to material selection and design. Simultaneously, practical techniques for surgically constructing tiny accommodating ileal pouches were explored in cadavers, by using polymer "mock-ups" of potential designs. (3) The final design was tested by acute implantation in a live 52 kg goat and by in vitro testing of electrical transfer function. IN VIVO TRIALS: The earlier design demonstrated 97.2% AC/AC and 84.2% DC/DC efficiency with contiguous tissue warming of 0.1 degrees C. DESIGN AND PERFORMANCE: A transformer with a Square Permalloy torroidal core (6 cm3, 23 grams, both coils eight turns) was designed, by using human cadaver trials to optimize geometry. Input and output were 6 V, 12W at 9.2 kHz with AC-AC efficiency 96%. OPERATIVE PLACEMENT TRIAL: The primary coil easily fit into an isolated, vascularized, but otherwise disconnected "blind" ileal pouch < 2 cm long with a slender extension to a miniature stoma. With secondary turns, the pouch and transformer fit easily into the abdominal wall. This tiny system seems compatible with near "forgettable" power delivery allowing unprecedented freedom of environment and activity in circulatory support dependent people.
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