組込型計算機を用いたFES麻痺手把持補助システムの開発

抄録

A programmable hybrid FES system for restoration of pinch motion disabled C5 quadriplegics has been developed. Because of the paralysis of wrist motion as well as hand motion in persons who have spinal cord injury at the cervical fifth level, pinch orthosis can not be applied for these persons. In the developed hybrid system, the FES system was utilized for restoration of wrist motion. The FES-generated wrist motion was converted to thumb and index finger motion by using a pinch orthosis. The system consists of magnetic distance sensors for the detection of stimulation control motion, a two-channel electrical stimulator, and a PIC16F877 microprocessor for system control and stimulation pulse generation. The processor manages the magnetic sensor monitoring through a 10-bit analog-to-digital converter, generation of stimulating pulses, modulation of the stimulation pulse width for stimulus strength control, the state of the “stimulation mode,” and monitoring of the switches for mode control at 50-millisecond intervals. Use of a microprocessor offers system flexibility which enables modification of the system function after implementation, and storage of settings such as sensor threshold.
The developed system was evaluated in able-bodied volunteers. The maximal pinch force was measured under voluntary, voluntary with extended fingers, voluntary with pinch orthosis, and hybrid FES conditions. The average pinch force with hybrid FES system was 1.5 kgf, which is about twenty percent of the voluntary pinch with finger extension in nine volunteers. It appears sufficient for light activity for daily living, such as writing and eating. The working efficiency was also evaluated in an object moving task. Six volunteers were required to move pens on a desk from right to left, and each task time was recorded. The stimulus increment/decrement rate was varied and the working efficiency was compared. The best performance was obtained at the rate of 100 percent per second. Under that condition, the average task time for pinch and move was 4.0 seconds and the release and move time was 2.7 seconds. Clinical evaluation and further development for extension of the applicable subject remain to be done.