An implantable electrical interface for in vivo studies of the neuromuscular system

Abstract

The purposes of this study were to develop and test an implantable interface that could be used for repeated temporary electrical connections between implanted stimulating and recording devices and external equipment. The implantable multi-use interface (TIMI) consists of an implanted set of connectors and temporary percutaneous leads. The connector(s) and attached devices are implanted during a sterile surgery. For each experimental session, a percutaneous lead is introduced into each connector with a hypodermic needle. The external ends of the percutaneous leads are then connected to the desired equipment. After the session is finished, the percutaneous leads are removed. TIMIs have been used successfully with nerve cuff stimulating electrodes, a tendon force transducer and an electromyography electrode, and have been implanted with nerve cuffs for up to 14 weeks without failure. The advantages of the TIMI over the standard backpack connector include: (1) the internal location of the connector reduces the risk that the animal will damage the connector and (2) the temporary and relatively controlled nature of the percutaneous connection reduces the risk of infection associated with permanent percutaneous leads. The TIMI provides an inexpensive, simple and reliable electrical connection between implanted devices and external equipment.

Introduction

Many studies focused on the in vivo behavior of the neuromuscular system utilize implanted devices to characterize electrical and mechanical signals associated with neuromuscular function (e.g. Prochazka et al., 1976; Hoffer et al., 1987; Gregor et al., 1988; Herzog et al., 1993a,b). These implanted devices include nerve cuff stimulating and recording electrodes, electromyography (EMG) electrodes, tendon force transducers, distensible tube length transducers and a variety of other transducers and electrodes. These devices typically require an electrical interface with external equipment such as power supplies, amplifiers, telemetry, and other signal conditioning and recording equipment.

The interface between implanted devices and external equipment is usually located external to the animal. Such connectors include backpacks and skull pedestals (Loeb and Gans, 1986). Leads from implanted transducers are routed to the back or head of the animal and exit through a small incision in the skin. The leads are then soldered to a connector which is sutured or glued to bone or fascia at the desired location. These connectors have been used successfully in a variety of studies (Prochazka et al., 1976; Hoffer et al., 1987; Gregor et al., 1988; Herzog et al., 1993a,b). However, the external location of the connector involves risk of (1) the animal accidentally or intentionally damaging the connector and (2) bacteria tracking down leads or sutures causing infection. The need for eliminating the external interface arose in our laboratory when many rabbits chewed on their own backpacks and holding sutures. The rabbits destroyed their backpacks despite antichew creams, sprays, and backpack covers.

One method for sending signals between implanted devices and external equipment without external connectors or percutaneous leads is radio-frequency telemetry. For example, telemetry has been used to monitor blood pressure (Truett and West, 1995) and spinal loads (Rohlmann et al., 1994) in vivo. However, a simpler and cheaper alternative to telemetry may be desirable in many situations.

The purposes of this study were to develop and test a simple, inexpensive, implantable interface that could be used for repeated temporary electrical connections between implanted devices and external equipment. A review of the literature revealed no mention of such an interface. Use of this interface could reduce the risk of damage by the animal and reduce the risk of infection associated with permanent percutaneous leads and sutures.