Electro-medical stimulator system

Abstract

A body stimulation system including a remote low frequency transmitter, a low frequency receiver, a power transmitter controlled by the low frequency receiver, and an implantable stimulator device with means for receiving signals from the power transmitter. The power signal is synchronized to the low frequency transmitter, and interference protection circuitry is included in the system. Special circuitry is also provided to decrease the effect of the spacial relationships between the power antenna and the implanted receiver.

Description

BACKGROUND OF THE INVENTION

Implantable body stimulators exist in the prior art and are of many types and for many purposes. A particular function of the system of this invention is as an orthotic system, such as for stimulating the peroneal nerve to aid paraplegic patients. The prior art includes such orthotic systems including one described in "Development of Orthotic Systems Using Functional Electrical Stimulation and Myoelectric Control," UNIVERSITY OF LJUBLJANA, Faculty for Electrical Engineering, Project No. SRS-YUGO 23-68, Progress Report No. 2, Apr., 1970. The system described in that article has a remote transmitter which gives a high frequency signal burst. The signal is picked up by a high frequency receiver which then causes a power transmitter to emit a predetermined number of pulses, which are in turn picked up by an implanted stimulator.

The apparatus of this invention has advantages over the prior art, some of which derive from the use of the low frequency transmitter, including the ability to synchronize the stimulation signal with the remote transmitter signal, a decreased use of power, and an increased ability to block interference signals. The apparatus of this invention has further advantages over the prior art including structure for loading the power antenna to flatten the curve of the antenna field to avoid rapid changes due to minor spacial displacements between the power antenna and the implanted receiver.

SUMMARY OF THE INVENTION

Briefly described, the apparatus of this invention in its preferred embodiment comprises a low frequency electromagnetic transmitter which can be remotely located with respect to the portion of the body to be stimulated. The low frequency transmissions are picked up by an electromagnetic receiver which includes interference detection circuitry for removing unwanted noise signals. The receiver controls the output of a power transmitter which is connected to a power antenna adapted to be placed in spaced relation to an implanted power receiver which receives the power signals and in turn provides stimulation pulses to implanted electrodes connected to the portion of the body to be stimulated.

In the preferred embodiment, the system is in modular form and the low frequency receiver can be unplugged from the power transmitter which carries the power supply for the receiver-transmitter system. When the receiver is unplugged from the power transmitter, the transmitter will provide continuous stimulation signals. A cycler module is provided which may be plugged into the power transmitter in place of the low frequency receiver. The cycler module will provide control of the power transmitter such that the stimulation signals are turned on and off for adjustable periods of time.

Also provided in the power transmitter is a control comprised of three adjustable members whereby an attending physician can set the limits of maximum and minimum power for the stimulation signal, to assure that the patient is receiving benefit from the stimulation without undue discomfort; the patient is free to adjust a third control which will vary the power output between the maximum and minimum controls to the patient's feeling of greatest comfort.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the system of this invention;

FIG. 2 is a schematic diagram of the low frequency transmitter of the apparatus of this invention;

FIG. 3 is a combined block and schematic diagram of the low frequency receiver and interference signal detector portion of the apparatus of this invention;

FIG. 4 is a combined block and schematic diagram of the power transmitter apparatus of this invention;

FIG. 5a is a graph of a prior art antenna field plot;

FIG. 5b is a graph of the power antenna field plot of the system of this invention; and

FIG. 6 is a schematic diagram of the cycler module of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1 there is shown a low frequency transmitter 10 which carries its own power supply and includes a switch by means of which a patient may cause operation of the transmitter from a remote portion of his body, for example by placing his weight on one foot or the other.

There is also shown a low frequency receiver 11 which is constructed to receive the low frequency signals from transmitter 10. Preferrably, the low frequency range will be from about 2 kilohertz to approximately 10 kilohertz. Low frequency receiver 11 provides the received signals to interference protection circuitry 12 which will reject all signals which are not of the proper frequency, which do not have the proper pulse height and which do not have the proper pulse width. The output signal of circuitry 12 is provided to power transmitter 13 which is connected to power supply 14. Supply 14 is connected to circuitry 12 and receiver 11 through transmitter 13.

Power transmitter 13 provides radio frequency signals to power antenna 15 which is placed in space relation to an implanted receiver such as implantable receiver 16. Receiver 16 is adapted to be connected to electrodes connected to the portion of the body to be stimulated, and receiver 16 will accept the RF signals from power antenna 15 and provide stimulation pulses to the electrodes.

Referring now to FIG. 2 there is shown a schematic of low frequency transmitter 10. A power supply 20 has one terminal connected to a conductor 21, and another terminal connected to a conductor 22. Conductor 21 is connected to one terminal of a normally open switch 23. The other terminal of normally open switch 23 is connected to a conductor 24. A resistor 25 and a capacitor 26 are serially connected between conductors 24 and 22. A programable unijunction transistor 27 has its anode 28 connected to a junction between resistor 25 and capacitor 26. The cathode 29 of transistor 27 is connected through a resistor 31 to conductor 22. A pair of resistors 32 and 33 are serially connected between conductors 24 and 22, and the gate 34 of transistor 27 is connected to a junction between resistors 32 and 33. The cathode 29 of transistor 27 is also connected to the base of a transistor 35. The emitter of transistor 35 is connected to conductor 22. A collector of transistor 35 is connected through a coil 36 to conductor 24. A capacitor 37 is connected in parallel with coil 36.

In operation, the circuitry operates in the manner of a relaxation oscillator utilizing the properties of the programable unijunction transistor. When switch 23 is closed, capacitor 26 will begin to charge through resistor 25. When capacitor 26 has charged to a predetermined level dependent on the biasing at the gate 34, transistor 27 will turn on causing a current flow through resistor 31 and a resultant turn on of transistor 35. When transistor 35 turns on there will be a current flow through the tank circuit comprising coil 36 and capacitor 37, thus transmitting the desired signals to be received by low frequency receiver 11. The selected circuitry is designed to use a minimum of power and to provide a low frequency output, preferably in the range of 2 to 10 kilohertz.

Referring now to FIG. 3 there is shown a combined block diagram and schematic of low frequency receiver 11 and interference detection circuitry 12. A receiving coil 38 is connected in parallel across a capacitor 39 which is connected to the input of a tuned amplifier 40. Tuned amplifier 40 has internal bandpass circuitry 43. Amplifier 40 is connected to a Schmitt trigger 41. Schmitt trigger 41 is connected to a differentiater 42. Blocks 40-43 represent circuitry well-known to those skilled in the art, and have been shown here in block diagram to facilitate understanding of the operation of the apparatus of this invention and avoid unnecessary description and extensive drawings.

Also shown in FIG. 3 are a positive power input terminal 44 and a negative power input terminal 45. Terminal 44 is connected to a conductor 46 which is connected through a diode 47 to a conductor 48. Conductor 48 is connected to each of blocks 40, 41 and 42. Terminal 45 is connected to a conductor 50 which is connected to each of blocks 40, 41, 42 and 43.

The output of differentiater 42 is connected to the base of a transistor 51. The emitter of transistor 51 is connected to conductor 48. The collector of transistor 51 is connected through a serial combination of diodes 53, 54 and 55 to the base of a transistor 56. The collector of transistor 51 is also connected to a parallel combination of a resistor 57 and a capacitor 58 to conductor 50. The base of transistor 56 is connected through a parallel combination of a resistor 61 and a capacitor 62 to conductor 50.

The collector of transistor 56 is connected through a serial combination of resistors 63 and 64 to conductor 46. The emitter of transistor 56 is connected through a resistor 65 to conductor 50. A transistor 66 has its base connected to a junction between resistors 63 and 64, its emitter connected to conductor 46 and its base connected to the base of a transistor 67. The collector of transistor 67 is connected to conductor 46, and the emitter of transistor 67 is connected through a resistor 68 to conductor 50. The emitter of transistor 67 is also connected through a diode 69 to the base of a transistor 70. The emitter of transistor 70 is connected to conductor 46, and the collector of transistor 70 is connected through a capacitor 71 to conductor 50. The collector of transistor 70 is also connected to an output signal terminal 72. A negative power output terminal 73 is connected to conductor 50.

In operation, the apparatus of FIG. 3 will receive signals from low frequency transmitter 10 at the tank comprising coil 38 and capacitor 39. These signals are provided to tuned amplifier 40 where they will not only be amplified but where frequency detection will take place to prevent the passage of noise signals outside the tuned range of amplifier 40. The signals will then be presented from amplifier 40 to Schmitt trigger 41. Here pulse height detection takes place, for if the input pulses are not of sufficient magnitude they will not be able to turn on Schmitt trigger 41. The output of Schmitt trigger 41 is a well-known pulse shape dependent on the length of time between the turn on of the Schmitt trigger and its turn off by the input pulses. These Schmitt trigger output pulses are differentiated by circuitry 42 which has the effect of pulse width detection to further eliminate noise signals. The output of differentiater 42 is presented to the base of transistor 51 which is connected as a current source. Diodes 53, 54 and 55 act as a threshold detector and will cause the turn on of transistor 56 when the charge on capacitor 58 has reached the threshold level of transistor 56. Transistors 66 and 67 act as a complementary current driver, well-known to those familiar with the art, and transistor 67 will turn on when transistor 56 turns on. This in turn will cause transistor 70 to turn off thus providing an output signal at terminal 72.

When the signal from low frequency transmitter 10 ceases, and no further input is provided to amplifier 40, the lack of output at differentiater 42 will cause the turn off of transistor 67 to turn on transistor 70. The signal to enable power transmitter 13 can be taken off terminal 72 or from the emitter of transistor 67. If the signal is taken from terminal 72, the transmitter 13 will be off during the time the low frequency transmitter 10 is transmitting. If the signal is taken from the emitter of transistor 67, the transmitter 13 will be on during the time the low frequency transmitter 10 is transmitting. Thus, the output signal is synchronized to the input signal from low frequency transmitter 10. It is important to recognize that the advantage of synchronization is offered in the apparatus of this invention with comparatively low power drain because of the use of the low frequency system. Prior art systems used high frequency and did not synchronize but merely used a burst from the remote transmitter to turn on the signal for a predetermined period of time. This was because of the significant power drain required to provide continuous high frequency signals from the remote transmitter. The synchronous signal has many advantages; for example, when the device is being used to help a paraplegic patient to walk, he can control his own gait through the synchronous method.

In the preferred embodiment of FIG. 3, it has been found to be of great value to pot the circuitry in a substance resistant to vibration for minimizing magneto-strictive reaction due to mechanical shocks.

Referring now to FIG. 4, there is shown a block diagram and schematic diagram of power transmitter 13 and power supply 14 of FIG. 1.

A rate and pulse width generator 75 is connected between a positive power conductor 76 and a negative power conductor 77. The output of generator 75 is connected to the input of a Colpitts oscillator 78 which is also connected to conductor 77. A stabilizing amplifier 79 is connected between conductor 76 and oscillator 78. Blocks 75, 78 and 79 are well-known to those familiar with the art and have been shown in block diagram form to avoid excessive description and drawings.

The output of oscillator 78 is connected through a potentiometer 80 through a junction 81. Junction 81 is connected through a serial combination of diodes 82, 83 and 84 to conductor 77. The wiper arm of potentiometer 80 is connected through a potentiometer 85 to junction 81. The wiper arm of potentiometer 80 is also connected through a potentiometer 86 to the wiper arm of potentiometer 85. The wiper arm of potentiometer 86 is connected to the base of a transistor 87. The collector of transistor 87 is connected through a resistor 88 to a positive power conductor 90. The emitter of transistor 87 is connected through a resistor 91 to conductor 77. A transistor 92 has its base connected through a resistor 93 to conductor 90, its collector connected to conductor 90 and its emitter connected to conductor 76. A transistor 94 has its base connected to the collector of transistor 87, its collector connected to conductor 77 and its emitter connected to the base of a transistor 95. The collector of transistor 95 is connected to conductor 77. The emitter of transistor 95 is connected through a coil 96 to an output terminal 97. The emitter of transistor 95 is also connected through a portion of coil 96 to conductor 90. The emitter of transistor 95 is further connected through a capacitor 98 to an output terminal 99. Terminals 97 and 99 are adapted to be connected to power antenna 15 as shown in FIG. 1.

A power switch 100 has one terminal connected to conductor 90, and the other terminal connected to the positive terminal of a power supply 101. The negative terminal of supply 101 is connected to conductor 77. A capacitor 102 is connected in parallel across supply 101. A positive power output terminal 103 is connected to conductor 90, and a negative power output terminal 104 is connected to conductor 77. A negative power input terminal 105 is connected to the base of transistor 92. An input signal terminal 106 is connected to conductor 76.

To best understand the operation of the apparatus of FIG. 4, it should be understood that the apparatus of this invention is intended in its preferred embodiment to be in modular form. Preferably, blocks 11 and 12 of FIG. 1 would be in a single module which would be plugged through standard connectors into a second module which would comprise blocks 13 and 14. Therefore, power output terminal 103 of FIG. 4 would connect to power input terminal 44 of FIG. 3. Power output terminal 104 of FIG. 4 would connect to terminal 45 of FIG. 3. Power output terminal 73 of FIG. 3 would connect to power input terminal 105 of FIG. 4, and signal output terminal 72, or the emitter junction of transistor 67, of FIG. 3 would connect to input signal terminal 106 of FIG. 4.

Referring now to the operation of FIG. 4, assume first that the two modules have not been plugged together. When switch 100 is closed, which can be manually done by the patient, power will be applied between conductor 90 and conductor 77. Transistor 92 will be biased on and positive power will appear on conductor 76. This will cause rate and pulse width generator 75 to operate, in the preferred embodiment at a rate of from 20 to 50 pulses per second. The output of rate generator 75 will be felt on Colpitts oscillator 78 to provide a current flow through potentiometer 80. Stabilizing amplifier 79 serves to stabilize the amplitude of the system as supply 101 ages. The current flow through potentiometer 80 will be felt on potentiometers 85 and 86. These three potentiometers comprise a unique circuit for setting an adjustable range for an individual patient using the system of this invention. Potentiometer 80 can be adjusted by an attending physician to set a maximum level for the power of the output signal. Potentiometer 85 can be used by the physician to set a minimum setting for the power of the output signal. Thereafter, the patient may have available to him the control of potentiometer 86 which will allow him to adjust the power of the output signal between the maximum and minimum settings. Therefore, he has full control over the entire range of potentiometer 86 to find the most comfortable setting for his own reactions to the stimulation signal but cannot adjust the signal to be above maximum, thus avoiding unpleasant sensations, or below minimum to a point where the signals would not cause the desired function.

The wiper arm of potentiometer 86 is connected to transistor 87 to provide the signal on the wiper arm of potentiometer 86 to the power amplifier combination of transistors 94 and 95. The output of the power amplifiers will be felt across coil 96 and through capacitor 98 on the power antenna output terminals 97 and 99. The function of coil 96 in the apparatus of this invention will be more fully described below in a discussion of FIGS. 5a and 5b.

It is apparent from the above description that the apparatus of FIG. 4 will continually provide stimulation signals when the module containing receiver 11 and circuitry 12 is not plugged into it. When the module is plugged in, not only is power from supply 14 provided to receiver 11 and enter interference protection circuitry 12 through the above described terminals, but the base of transistor 92 is connected to the negative power line through the connection of terminal 105 to terminal 73. Thus, transistor 92 will be turned off and no positive power from conductor 90 will reach conductor 76. The apparatus of FIG. 4 therefore stops providing stimulation signals until a signal appears at input terminal 106 in the manner described in the operation of FIG. 3 above.

From the above description of the operation of the circuitry shown in the drawings, it becomes apparent that when transmitter 10 is on, its signal turns off the stimulation signal, and when there is no signal from transmitter 10, the stimulation signal is operable. This on-off relationship could be reversed, but has been chosen as described in the preferred embodiment to perform in the situation where the stimulator is implanted and connected to the peroneal nerve of a paraplegic patient and where switch 23 is located in the shoe of the patient. Thus, when the patient's foot is down the low frequency transmitter will be on and no stimulation will occur. However, when the patient raises his foot to step, switch 23 will open and transmitter 10 will turn off thus allowing stimulation. In the specific case described the stimulation will result from the lifting of the patient's foot to enable walking without dragging the foot.

One of the major problems in a patient used stimulation system, such as the apparatus of this invention, is that of spacial relationship between power antenna 15 and the receiving coil of receiver 16. Two of the factors involved are the depth of the implant and the lateral displacement between the power antenna and the implanted receiver. As can be seen in the graph of the prior art antenna field of FIG. 5a, the voltage peaks sharply when there is no lateral displacement between the power antenna and the implanted receiver, however, when lateral displacement occurs, the voltage drops off sharply. This causes a problem as it is difficult for the patient to place and keep the external power antenna in the most desirable spaced relation to the implanted receiver.

To avoid this problem the apparatus of this invention includes circuitry which results in the antenna field shown in the graph of FIG. 5b. Here it is seen that the curve has been deliberately flattened and that lateral displacement of the power antenna from the implanted receiver has much less effect until the displacement becomes great.

The flattening of the curves as shown in FIG. 5b is accomplished through detuning. As can be seen in FIG. 4, the apparatus of this invention does not use an output power oscillator which would result in the curves of FIG. 5a, but uses a power amplifier which is loaded with the receiver. The output tank is driven by a voltage source, which is preferable over a current source because with a current source the available voltage will not enable the output tank to have a lower impedance as desired. By loading the output power amplifier with the mutual conductance of the receiver, the desired result is achieved.

Reference is now made to FIG. 6, which comprises a schematic diagram of a cycler module to be used with the apparatus of this invention. As described above, in this preferred embodiment the system is comprised of modules, and the cycler can be plugged into power transmitter 13 in place of receiver 11 and circuitry 12. The purpose of the cycler of FIG. 6 is to enable a patient to exercise his muscles, for example, when he is bedridden. The effect of the cycler is to cause the stimulation signal from transmitter 13 to alternately turn on and off. Provision is made for varying the proportions between the on and off parts of the cycle.

Referring now to FIG. 6 there is shown a positive power input terminal 110 and a negative power input terminal 111. When the cycler is plugged into transmitter 13, terminal 110 will be connected to terminal 103, and terminal 111 will be connected to terminal 104. Terminal 110 is connected to a conductor 112 and terminal 111 is connected to a conductor 113.

A capacitor 114 is connected between the conductors 112 and 113. A transistor 115 has its emitter connected to conductor 113, its collector connected through a resistor 116 to conductor 112, and its base connected through a serial combination of a resistor 117 and a variable resistor 118 to conductor 112. The collector of transistor 115 is also connected through a capacitor 119 to the base of a transistor 120. The base of transistor 120 is also connected through a resistor 121 to conductor 112. The base of transistor 115 is connected through a capacitor 122 to the collector of transistor 120. The collector of transistor 120 is connected through a serial combination of resistors 123 and 124 to conductor 112, and is directly connected to the collector of a transistor 125. The emitters of transistors 120 and 125 are connected to conductor 113. The base of transistor 125 is connected through a serial combination of a resistor 126 and a resistor 127 to conductor 113. A capacitor 128 is connected from a junction between resistors 126 and 127 to conductor 112. A resistor 129 is connected from a junction between resistors 123 and 124 to the base of a transistor 130. Transistor 130 has its emitter connected to conductor 112, and its collector connected to the base of a transistor 131. The collector of transistor 131 is connected to conductor 112, and the emitter of transistor 131 is connected to an output terminal 132 which connects to input signal terminal 106 of FIG. 4. A negative power output terminal 133 is connected to conductor 113, and when the cycler is plugged into transmitter 13, power output terminal 133 will be connected to power input terminal 105 as shown in FIG. 4.

It will be recognized by those skilled in the art that the circuitry shown in FIG. 6 comprises an astable multivibrator connected to amplifiers which provide the output signal. The astable multivibrator has a period which is controlled by adjustment of variable resistor 118, which will vary the charging time of capacitor 122, thus apportioning the on/off cycle of the astable multivibrator, and thus controlling the amount of time that a stimulation signal will be provided to the patient.

When the module of FIG. 6 is plugged into the apparatus of FIG. 4, the connection of terminal 133 to terminal 105 will cause transistor 92 to turn off, and the input signal from terminal 132 will appear at terminal 106 to control the on off time of transistor 95 in the same manner as for the above description of the operation of the circuitry when the module including the apparatus of FIG. 3 was plugged into the apparatus of FIG. 4. Therefore utilizing much of the same circuitry, the patient can be provided with the cycler module of FIG. 6 to provide him a capability for controlling the exercise of his muscles.

It will be apparent that what has been described specifically above is the preferred embodiment of the apparatus of this invention and that variations can be made therefrom without departing from the scope of the invention.

Claims

What is claimed is:

1. A body stimulation system comprising: first means adapted to be implanted in a body and including receiver means for receiving externally transmitted signals of radio frequency energy and means adapted to connect the receiver means to a portion of the body; second means adapted to be mounted external to the body for establishing an electromagnetic connection with said receiver means and including controlled radio frequency energy transmitter means for transmitting signals of radio frequency energy to the receiver means; third means for controlling the transmission of radio frequency energy from the second means, and including low frequency electromagnetic receiver means; fourth means including remote low frequency electromagnetic energy transmitter means for transmitting energy waves at a frequency in the range of approximately 2 kilohertz to 10 kilohertz, and including switch means connected to the low frequency transmitter means for controlling the operation thereof; and synchronizer means connected to the third means for turning the controlled radio frequency energy transmitter means on and off substantially coincident with a switching of the low frequency transmitter means between on and off states.

2. The apparatus of claim 1 in which the third means includes: protection circuit means connected between the low frequency receiver means and the second means and including frequency detection means, pulse height detection means and pulse width detection means, for blocking interference energy signals from effecting the second means.

3. The apparatus of claim 1 in which: the third means is potted in a substance resistant to vibration for minimizing magneto-strictive reaction in the third means due to mechanical forces striking the third means.

4. The apparatus of claim 1 including: cycler means for providing selectable series of control pulses to the second means for actuating the controlled transmitter means, said apparatus further including means for selectively connecting one of said cycler means and said third means to said second means.

5. The apparatus of claim 1 in which the switch means includes: means for selectively providing a signal to actuate the low frequency transmitter means; and electrical time constant means connected to the switch means and the low frequency transmitter means for deactuating the low frequency transmitter means after the switch means signal has ended for a predetermined period of time.

6. The apparatus of claim 1 in which the second means includes: output voltage control means connected to the controlled transmitter means, and including means manually adjustable for setting a maximum voltage output level, means manually adjustable for setting a minimum voltage output level and means manually adjustable for selecting an output voltage between the maximum and minimum set levels.

7. The apparatus of claim 1 in which the second means includes means for detuning the electromagnetic connection between the controlled energy transmitter means and the receiver means, to allow for less critical placement of the controlled energy transmitter means with respect to the receiver means.