System Description

The second generation neuroprosthesis includes both implanted and external components, as shown in Figure 2.3. The implanted components are a ten-channel stimulator-telemeter (1ST), an IJAT, and ten electrodes. The external components are the external control unit, which provides the power and intelligence for the system, a transmit/receive coil that is placed on the user's chest over the 1ST device, and an on/off switch typically placed on the user's wheelchair. The entire system is portable and, once donned, can be operated independently by the user throughout the day.

FES Hand Grasp System with Implanted Joint Angle Transducer

Joint Angle Transducer

Joint Angle Transducer

FIGURE 2.3 Second generation neuroprosthesis for upper extremity control. This advanced system adds to the basic hand control of the first generation system additional stimulation channels to be used for control of both the digits and proximal limb muscles. It also provides an implanted sensor for ipsilateral control of the limb through a sensor placed in the wrist.

FIGURE 2.3 Second generation neuroprosthesis for upper extremity control. This advanced system adds to the basic hand control of the first generation system additional stimulation channels to be used for control of both the digits and proximal limb muscles. It also provides an implanted sensor for ipsilateral control of the limb through a sensor placed in the wrist.

The operation of the second generation neuroprosthesis is based on the operation of the first generation neuroprosthesis, in which the stimulus to the paralyzed muscles is controlled through user-initiated movements. Wrist motion is used to control grasp opening and closing. When the wrist is extended, the hand is closed, and when the wrist is flexed, the hand opens.

Communication and powering of the implanted components is accomplished by electromagnetic induction through radio frequency waves. To communicate with the implanted components, the external coil is placed over the implant and the system turned on. This transmits the radio frequency signal internally to power the 1ST and IJAT. Movements of the wrist are sensed and transmitted externally over the RF.23,47 The transducer signal is used by the external control unit to determine the appropriate stimulus levels for each electrode, and this information is transmitted back to the IST device. Figure 2.4 shows a user with this system.

FIGURE 2.4 User demonstrating reaching task with second generation neuroprosthesis. The control device is implanted in the ipsilateral wrist, and stimulated elbow extension is provided.

2.4.2 Enhanced Motor Function

The second generation neuroprosthesis provides two additional stimulus channels for added motor functions. The potential functional gains provided by adding stimulation of the finger intrinsic muscles, the triceps, and the pronator quadratus have been studied and are reviewed in the following paragraphs.

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