Patent No. 3727616 Electronic system for the stimulation of biological systems

 

Patent No. 3727616  Electronic system for the stimulation of biological systems (Lenskes, Apr 17, 1973)

Abstract

A receiver totally implanted within a living body is inductively coupled by two associated receiving coils to a physically unattached external transmitter which transmits two signals of different frequencies to the receiver via two associated transmitting coils. One of the signals from the transmitter provides the implanted receiver with precise control or stimulating signals which are demodulated and processed in a signal processor network in the receiver and then used by the body for stimulation of a nerve, for example, while the other signal provides the receiver with a continuous wave power signal which is rectified in the receiver to provide a source of electrical operating power for the receiver circuitry without need for an implanted battery.

Notes:

BACKGROUND OF THE INVENTION

This invention is directed to means for providing a precisely controlled bipolar current pulse of given polarity, magnitude and duration to a living body for controlling pain, permitting movement of paralyzed extremities, controlling spasticity, stimulating paralyzed urinary bladders and preventing atrophy in clinical applications and for functional and behavioral changes in neurophysiological applications, for example. The system of the invention utilizes a pulse position modulation technique for electrically stimulating biological systems such as nerves, for example, in a manner which presently does not exist. The resulting stimulation output is a constant current biphasic or monophasic signal. Because of the digital nature of the inventive system, accurate and reliable current stimulating levels are achieved with fast rise and fall times. Safety features have been included in the system to prevent extraneous stimulation due to interfering signals. When the implanted receiver is not activated by the external transmitter, any extraneous signals are shunted by a low impedance path in the receiver.

The inventive system is essentially digital in nature, whereas known systems in the prior art employ analog techniques. In addition, the prior art systems employ pulse width modulation in which the resulting pulsed radio frequency signal is detected and filtered to obtain a stimulation waveform. This prior art method, while simple in nature, has many limitations. For example, it cannot provide a precisely controlled amplitude because of its dependency on the coupling coefficient between a primary tuned circuit and a secondary tuned circuit, it cannot provide a biphasic stimulation waveform nor can it generate a direct current stimulation. In addition, its unipolar pulses are not rectangular because an exponential discharge circuit is normally employed. Stimulators of the prior art are designed for specific applications and lack the parameter versatility and safety that can be achieved with the inventive system.

SUMMARY OF THE INVENTION

The system of the present invention includes a transmitter that is inductively coupled by two transmitting coils to a receiver located totally within a living body. The system of the present invention is sometimes called a "Biostimulator" and at other times a "Telestimulator". The transmitter, which is located outside the body, transmits two signals of different frequencies to the receiver via the two transmitting coils. The dual frequency link of the system provides the implanted receiver with control signals or operating information and also a signal from which the receiver can extract its electrical operating power. The receiver basically comprises two receiving coils, a signal processor and a power supply. The output of the receiver is coupled to two electrodes via very small electrical wires which may be attached to a nerve, for example, to stimulate the nerve or to block it. The desired stimulating pulse characteristics such as amplitudes, width, interpulse, periods, etc., are initially entered into the control panel of the transmitter via suitable switches such as rotary thumbwheel switches, for example. These data are converted to a digital format part of which is transmitted to the receiver as a 21-bit Amplitude Data Word. This information is received, decoded and stored by the signal processor portion of the receiver to provide the proper amplitude reference to stimulate the nerve. The remaining portion of the data which has been previously entered into the transmitter is sent to the receiver as a series of Stimulation Words. Each of the Stimulation Words comprises three 5-microsecond radio frequency (r-f) pulses at substantially 27.12 MHz. The time spacing between the pulses determines the time duration of the various parts of the stimulating waveform. Each word operates in real-time to alternately stimulate the nerve with a positive amplitude, a negative amplitude and a zero amplitude. The transmitter also provides a substantially 100 KHz continuous wave power signal which is inductively coupled into the power supply coil in the receiver and rectified to provide electrical power for the receiver circuitry. The power signal is always present whenever the sytem is in use.

Therefore, it is an object of this invention to provide an electronic system for the stimulation of biological systems in a living body in the form of an implantable receiver capable of providing proper stimulation when used in conjunction with an external transmitter.

Another object of this invention is to provide an electronic system for the stimulation of biological systems in a living body in which no internal batteries are utilized nor any direct wire connections into the body are made.

It is a further object of this invention to provide a stimulator system for a living body wherein a dual frequency external transmitter provides inductively coupled control and power signals to a compatible receiver located within the living body.