HK1072567B - Transcranial electrostimulation apparatus and method - Google Patents

Description

Transcranial electrical stimulation apparatus and method

Background

Bioelectric stimulation devices have been developed for applying current pulses to a patient via electrodes located on opposite sides of the patient's brain. Current pulses of a selected frequency are used to react with the central nervous system of the patient. Such devices, commonly referred to as transcranial electrostimulators (TCES) or Cranial Electrostimulators (CES), have been used in a number of non-invasive procedures, such as producing analgesia, reducing or controlling migraine headaches, and for some other treatment and electrical anesthesia.

The earliest prototype transcranial electrical stimulation devices originated in russia. These initial designs, although successfully used in several different forms of treatment, have the serious disadvantage of causing discomfort to the wearer or patient. In individual cases these earlier cranial stimulation devices can even cause pain to the patient. These earlier devices were found to be uncomfortable due to the use of direct current during a portion of the overall operation of the device. The direct current is used to destroy or reduce the electrical resistance of the skin so that therapeutic alternating current signals generated by electrodes placed on the patient's head penetrate the brain and nervous system to achieve the desired effect.

In these earlier types of apparatus, the wearer receives a combination of dc and ac wave packets using a series of electrodes attached to the head by straps. Typically, two electrodes, including a cathode or negative electrode based DC circuit, are placed approximately three inches around the center of the forehead. The other two electrodes, including the anode or positive electrode based DC circuit, were placed at the upper position behind and below the ears at the back of the skull. With this DC current based design, the wearer is required to add a thick pad between the skin and any electrodes. Typically, the pad is composed of several layers of raw, undyed cotton flannel or the like. For best results, the fabric pad is saturated with water to provide an electrically conductive path between the electrodes and the wearer's skin. Such devices can either burn the wearer's skin or cause considerable pain if the pad is not present (the pad being the only requirement due to the presence of direct current) before the therapeutic form of alternating frequency current can be achieved at a level that is available.

Although many types of treatment were used by such earlier transcranial electrostimulation devices, such devices generally required an average of 30 minutes per treatment cycle. The DC-based design cannot be used without the relatively cumbersome thick pads. With thick pads, such a DC design is tolerable to the wearer, but rarely brings a pleasant experience to the wearer.

Three russian patents that utilize such devices for different treatment methods include russian patents 1489719, 1507404 and 1522500. In all of these patents, a combination of direct current at a frequency of between 70 and 80 hertz and rectangular pulse current is used during each treatment at which the current intensity rises from a relatively small value to a high or highest level.

An additional potentially harmful drawback of DC-based designs is iontophoresis. A feature of this type of DC circuit application is that it can cause molecular-sized portions of metals, toxins or other undesirable impurities to move in the direction of current flow through the skin and into the bloodstream of such DC-based CES instrument wearers. Therefore, great care is taken to ensure that there is no material other than water which is used to make good electrical contact with the pad on the wearer's skin. Since virtually all forms of CES treatment require repeated treatments, the potential for iontophoresis as a detrimental factor is increasing.

Transcranial electrical stimulation (CES or TCES) was used initially to induce sleep in humans in the 60's of the 20 th century. These early devices typically used currents of less than 15 milliamps at a frequency of 100 hertz. U.S. patent No. 4627438 to Liss uses a higher frequency modulated by a low frequency square wave to generate a cyclic pulse burst. The modulation frequency determines the repetition rate of the Liss device, but the pulse bursts have uniform amplitude in each repetition period. The Liss patent device is particularly suited for use in conjunction with the treatment of migraine. The low frequency or modulated signal is asymmetrical using a 3: 1 duty cycle, i.e., three quarters of the time in a cycle period is "on" and the other quarter of the time is "off. This results in a burst of high frequency signal pulses separated by an off time when no signal is applied, followed by a burst of reapplied high frequency signal pulses. Some patient discomfort may occur in the operation of such "on/off" systems over the time period during which the pulses are applied during the treatment interval.

Some other us patents, which are directed to dual-frequency systems that use high frequency signals modulated by a low frequency modulated carrier, have the general nature of the device working in the existing Liss 4627438 patent. Typical of these patents are Limoge's 3835833 patent, Nawracaj's 4071033 patent, Kastrubin's 4140133 patent, Morawetz's 4922908 patent and Giordani's 5131389 patent. All of these patents employ a high frequency signal of uniform amplitude modulated at a low frequency that selectively modulates a carrier.

The system variation of the above patent is disclosed by U.S. patent number 5540736 to Haimovich. The device of this patent uses two different current generators to provide current delivered to two electrode pairs operating at different locations in the patient's brain. This allows independent control of the current generators to manage the independent adjustment of the current through each electrode pair to adjust for different impedances, quality of the conductive medium, and other factors due to the physiological and anatomical properties of different parts of the brain in the patient. In all other respects, the system disclosed in this patent operates similarly to the system disclosed in the above-mentioned Liss patent.

Russian patent publication No. 2139111 is directed to a method for treating mania, which can also be used in other CES patents as described above for the treatment of drowning in alcohol and anesthesia. In this patent, transcranial electrical stimulation is accomplished with a current packet lasting 4 milliseconds at a modulation frequency of 100 hertz. Within each packet, the high frequency signal has the same frequency and current amplitude.

It would be desirable to provide a transcranial electrical stimulation apparatus and method which overcomes the disadvantages of the prior art and which provides improved therapeutic results and increased patient comfort.

Disclosure of Invention

It is an object of the present invention to provide an improved transcranial electrical stimulation apparatus and method.

It is another object of the present invention to provide improved transcranial electrical stimulation apparatus and methods that do not use a direct current component.

It is a further object of the present invention to provide improved transcranial electrical stimulation apparatus and methods employing only alternating current components.

It is a still further object of the present invention to provide improved transcranial electrical stimulation apparatus and methods which utilize packets or bursts of high frequency pulses, the amplitude of which varies in the same manner within each packet and wherein the packets are repeated at a lower modulation frequency, applied to electrodes used to generate transcranial electrical stimulation.

In accordance with a preferred embodiment of the present invention, a transcranial electrical stimulation apparatus includes a first generator of bipolar pulses at a first predetermined frequency. A source of modulation control signals at a second frequency lower than the first predetermined frequency is used in conjunction with an amplitude control circuit receiving pulses at the first predetermined frequency to produce bipolar pulses at the first predetermined frequency which vary in amplitude in an asymmetric fashion at the frequency of the modulation control signals.

Drawings

Fig. 1 is a block diagram of the general principle of operation of a system according to a preferred embodiment of the present invention.

Fig. 2 is a waveform of a typical signal pattern of a preferred embodiment of the present invention.

Fig. 3 is a block diagram of a system for generating the signals shown in fig. 2.

Detailed Description

The preferred embodiments of the present invention and their operation will now be described with reference to the accompanying drawings. Figure 1 is a block schematic diagram of salient operational features of an implementation circuit capable of producing unique asymmetric triple waveforms useful for a variety of transcranial electrical stimulation applications. The unique waveform detailed in connection with fig. 2 may create little to no discomfort to the user of the instrument.

As depicted in fig. 1, a basic high frequency current signal is generated by a high frequency generator 10 that may use a frequency control 12 and a pulse duration control 14 to establish the fundamental frequency and provide the required asymmetry between the positive and negative portions of each pulse generated by the generator 10. Typically, the generator 10 may comprise a crystal oscillator operating at between 1000 and 1200 kilohertz, which is then divided down to the desired operating frequency of the alternating current pulses for the transcranial electrical stimulation electrodes. Typically, the division ratio may be 1: 4 to produce a signal which is then modulated by the low frequency signal generator 16.

As illustrated in the block diagram of fig. 1, the output of the low frequency signal generator 16 may be established using a conventional frequency control 18, pulse duration control 20 and modulation depth control 22 to produce a composite modulated output signal at 24 that includes pulses output from the high frequency generator 10 that are modulated by the low frequency generator 16. The output 24 is then provided to an amplitude control 26 to establish the amplitude of the pulse train supplied by the system to a power amplifier 28. The current of the power amplifier 28 may vary depending on the therapy mode to which the system is applied, and its current is measured by the ammeter 34. The power amplifier 28 then provides suitable transcranial alternating current pulses to one or more electrode pairs, such as the pair of electrodes 30 and 32 shown in fig. 1.

The operation of a preferred embodiment of the present invention for generating asymmetric triple waveforms for generating effective transcranial electrical stimulation will now be studied in conjunction with the waveforms of fig. 2 and the system block diagram of fig. 3. The block diagram of the system shown in fig. 3 is one way of typically implementing the various circuit functions required to generate the waveforms of fig. 2, but other designs for generating such signal waveforms may be utilized.

In fig. 3, a crystal oscillator 50 is used to provide the basic ac operating signal for the high frequency pulses and modulated pulses generated by the high frequency generator 10 and the low frequency generator 16 as shown in fig. 1. Typically, oscillator 50 may have an operating frequency on the order of 1000 kilohertz to 1200 kilohertz (although other frequencies may be used). The output of oscillator 50 is provided to a frequency divider 52, which comprises a plurality of frequency dividing stages, to generate a lower modulation frequency (as generated by low frequency generator 16, shown in fig. 1). The output signal of the oscillator 50 also produces an operating signal waveform, such as the square wave signal waveform shown in fig. 2, through the frequency divider 54, which after being shaped by the pulse shaper 56, results in the general square wave waveform of fig. 2. In the example given, the pulses occur at an ac level of 100 khz, but may be higher or lower depending on the particular application of the system.

The pulses output by divider 54 are also provided to a counter 60, which may be of any suitable type such as a cascade counter or a ring counter, for generating output signals on conductors 64 and 66 used to control the amplitude of the pulses of pulse shaping 56. Counter 60 is reset by the output of divider 52, resetting the counter at each cycle of operation of divider 52 via conductor 62. In this example, the output of frequency divider 52 (containing the low frequency modulated control signal) was selected to be 77.5 hertz, since this repetition frequency proved to be highly effective when connected to a transcranial electrical stimulation instrument. A repetition rate in the range of 70 hz to 85 hz has proven effective, but a frequency of 77.5 hz has been experimentally identified as the ideal frequency for maximum efficiency of the system.

The modulation or reset frequency applied through line 62 may also be provided by a second separate crystal oscillator, which may operate at a lower initial frequency than oscillator 50 if desired. If two different signal sources are used, synchronization between the two signals should be effected such that the various pulse transitions of the signals are correlated with one another to produce the signal waveforms of FIG. 2. The system shown in figure 3 is however an effective way of achieving this.

In the present example, it is assumed that counter 60 is reset to its initial or "0" count state. The system begins operation by providing a high frequency output pulse of the divided down signal of divider 54 to the counter input, which counts one step earlier than each applied pulse. In the waveform of fig. 2, the initial pulses (the first four of fig. 2) cause the counter outputs at 64 and 66 to be such that: these outputs, when applied to the amplitude controller 68, produce a maximum amplitude (which may be adjusted if desired). This is illustrated in the left portion of the waveform signal as in fig. 2. When the fourth pulse in a group or packet is applied, a signal is available from one or both of the outputs 64 and 66 of the counter 60 and applied to an amplitude control circuit 68 to convert it to a lower amplitude, as shown in the right-hand portion of the signal in fig. 2.

This causes the output of the amplitude control circuit 68 to be applied to the adjustable amplifier 58 to produce an asymmetric signal waveform as shown in fig. 2, in which the left quarter (42) of each signal pulse is of high amplitude and the right portion (44) containing the remainder of the pulse is of low amplitude. The ratio is such that one quarter (initial amplitude) is in the high amplitude range and the remaining three quarters are in the low amplitude range. This is the first level of signal asymmetry used.

The conditioning amplifier 58 also operates on the square wave shaped pulses obtained from the pulse shaper 56 to produce a second asymmetry in the positive and negative directions of the signal. As shown in fig. 2, the negative going amplitude is one-quarter of the total amplitude of the signal and the positive going portion is three-quarters of the total amplitude. This is true both in the maximum amplitude pulse 42 at the beginning of the pulse of each burst or packet and in the lower amplitude portion 44 at the end of each burst or packet.

Finally, a third asymmetry is produced within the 13 millisecond square wave pulse packet illustrated at 40 in FIG. 2. This is a result of the operation of the divider signal on conductor 62 including the reset operation of counter 60.

The composite asymmetric signal shown in fig. 2 is then provided by the output of the conditioning amplifier 58 to the power amplifier 70. This amplification may be adjusted to vary the amount of current the system operates (while maintaining the relevant waveform shape and pattern shown in fig. 2) depending on the treatment modality utilized by the system user. The ammeter 74 is used to measure the amount of current provided by the system. It may be a simple analog ammeter or a digital ammeter which provides readings of the maximum and minimum amplitude portions of the signal shown in figure 2, respectively.

The output of the amplifier 70 may be applied, if desired, by a polarity switch 72 which causes the polarity of the signal applied to the space electrode to be changed. The polarity switch 72 provides signals on a pair of spatial output electrodes 76 and 78, which may be in the form of separate anode and separate cathode pairs or a single "anode" and "cathode" pair. Because no dc component is present, the electrode paths connected to the outputs 76 and 78 are not true anodes and cathodes; but depending on the treatment modality being effected, it may be necessary to provide one or the other of these electrodes with a positive part of the pulse and the other with a negative part in order to achieve a particular effect.

It is noted that there is no dc component in the above-described system shown. It should also be noted that although the system is illustrated with the 70 khz to 120 khz tone pulses per pulse packet 40 as shown in fig. 2, other frequencies may be used. As noted, a 77.5 hz waveform from a timing cycle is used to complete each pulse packet in accordance with the signal pattern of fig. 2 including a first pulse of relatively high amplitude followed by a series of pulses of relatively low amplitude.

In the disclosed system, a single square wave pulse of 0.01 milliseconds is used with a negative pulse value of 0.0075 milliseconds and a positive pulse value of 0.0025 milliseconds in each pulse. The general asymmetric waveform described above in connection with fig. 2 has proven effective when overall system operation is near a ratio centered at 3: 1. These ratios may of course be varied in accordance with corresponding variations in other ratios of the system. It has been found that this disclosed asymmetric relationship can replace the DC portion of the earlier system operating protocol that was previously ordered and uncomfortable.

The DC current used in some prior art devices is designed to provide a path through the natural capacitive impedance of human skin. The DC current reduces the impedance to about 300 to 400 ohms. But at the expense of a high degree of discomfort for the user of the apparatus. It has been found in practice that the use of the unique asymmetric signal generated by the system shown in figure 3 and shown by the waveform of figure 2 effectively reduces the skin layer capacitive impedance to the order of about 100 ohms. Because the impedance is lower at the combined 77.5 hz modulation frequency, the lower magnitude current can receive the same desired effect that previously required a higher current magnitude. For patients using the present apparatus, lower levels of current translate to higher levels of comfort.

The foregoing description of the preferred embodiments of the invention is by way of example and not of limitation. Those skilled in the art will envision many variations and modifications that perform substantially the same function in substantially the same way to achieve substantially the same result without departing from the true scope of the invention as defined by the appended claims.

Claims (7)

1. A transcranial electrical stimulation apparatus characterized by comprising:

a bipolar pulse source (50) of a first preset frequency;

a modulation control signal source (52, 60) generating a second frequency lower than said first preset frequency;

an amplitude control device (68) is coupled to the bipolar pulse source at a first predetermined frequency (via 58) in response to the modulation control signal to vary the amplitude of the bipolar pulses in successive groups of bipolar pulses in a predetermined asymmetrical pattern at a second frequency, the amplitude control device having a greater amplitude in a first portion (42) of each group of pulses and a lesser amplitude in a second portion (44) of each group of pulses.

2. The transcranial electrical stimulation apparatus according to claim 1, further comprising: a pulse shaper (56) coupled to the bipolar pulse source (50) at the first predetermined frequency to vary the delay time of the bipolar pulses at the first predetermined frequency.

3. The transcranial electrical stimulation apparatus according to claim 1, wherein the pulse amplitude of the first portion (42) of each pulse burst is about three times greater than the pulse amplitude of the second portion (44).

4. The transcranial electrical stimulation apparatus according to claim 3, further comprising: output electrodes (76, 78) are coupled (via 58, 70) to the amplitude control device (68).

5. The transcranial electrical stimulation apparatus according to claim 3, wherein the modulation control signal source is a frequency divider (52) coupled to the first preset frequency bipolar pulse source (50).

6. The transcranial electrical stimulation apparatus according to claim 1, further comprising: output electrodes (76, 78) coupled to the amplitude control device (68) via (58, 70).

7. The transcranial electrical stimulation apparatus according to claim 1, wherein the modulation control signal source is a frequency divider (52) coupled to the first preset frequency bipolar pulse source (50).