Patent No. 3835833 Method for obtaining neurophysiological effects

 

Patent No. 3835833  Method for obtaining neurophysiological effects (Limoge, Sep 17, 1974)

Abstract

A method and apparatus for obtaining neurophysiological effects on the central and/or peripheral systems of a patient. Electrodes are suitably positioned on the body of the patient and a composite electric signal is applied at the electrodes. The composite signal is formed by the superpositioning of two signals: a first signal which is a rectified high-frequency carrier modulated in amplitude to about 100 percent by substantially square-shaped pulses whose duration, amplitude and frequency are chosen according to the neurophysiological effects desidered, and a second signal which has a relatively white noise spectrum. The mean value of the first electric signal has a predetermined sign which is opposite the sign of the mean value of the second electric signal.

Notes:

BACKGROUND OF THE INVENTION

The present invention concerns a method and apparatus for obtaining neurophysiological effects by the application of electric currents to the central and/or peripheral nervous systems of the human body.

It is known that the application of electrical signals at electrodes placed at suitably chosen points on the body of a patient is capable of causing various effects such as general or local anaesthesia, sleep or relaxion of the subject depending on the location of the electrodes and the parameters defining the signal.

Among the various types of signals for obtaining such results, it has been established that the use of square-shaped pulses of suitable amplitude, frequency and period is particularly effective.

Such signals, may, however, cause bothersome secondary phenomena such as contractures, polarization or electrolysis effects which could be redhibitory in numerous cases.

With regard to these drawbacks, it has been proposed to use for similar applications a complex signal consisting of a rectified high-frequency signal which is about 100 percent amplitude modulated by low frequency square-shaped pulses which in the majority of cases enables the total elimination of the contractures remaining when the low frequency pulses shapes a direct current signal instead of the envelope of a rectified high frequency signal.

The effects so obtained are clearly superior to those of the former technique. Nevertheless, the rectified high-frequency signals modulated by low-frequency square-shaped pulses is not entirely satisfactory in all applications, because they do not enable the complete elimination of undesirable phenomena such as local electrolysis, disagreeable tingling or other unacceptable reactions necessitating the reduction of the current of the applied signals or the shortening of the length of application thereof.

SUMMARY OF THE INVENTION

The present invention enables the reduction or even the complete elimination of undesirable secondary effects by reducing the mean value of the currents applied on which the said secondary effects directly depend, without substantially reducing the desired principal neurophysiological effects.

To this effect, the present invention provides a method for obtaining neurophysiological effects on the central and/or peripheral nervous systems of a patient, comprising positioning electrodes on the body of the patient, applying a composite electric signal at the electrodes formed by the superpositioning of a first and second electric signal, said first electric signal being a rectified high-frequency carrier modulated in amplitude to about 100 percent by substantially square-shaped pulses whose duration, amplitude and frequency are chosen according to the desired neurophysiological effects, the mean value of said first electric signal being of a predetermined signal said second signal having a relatively white noise spectrum, the sign of the mean value of said second electric signal being opposite that of the mean value of said first electric signal.

The white noise constituting the said second signal may have a substantially continuous spectrum ranging from 1 KHz to 60 KHz and preferably between 20 and 60 KHz. Such a noise signal could be easily obtained by means of a gas discharge tube, a semi-conductor or other appropriate means.

As previously indicated, it has been observed throughout that the undesirable secondary effects of electrophysiological treatment are all the more accentuated when the average current passing through the electrodes applied to the body of the patient is increased.

In the method according to the invention, this average current intensity, whose value is the algebraic sum of the respective mean values of said first and second signals, is the difference between these mean values.

I was surprised to find that the presence of white noise which enables the reduction of the overall mean current strength, the electrolysis effects and the intolerance of the body, remains without any detriment to the effectiveness of the treatment. It is thought that this very advantageous property comes from the fact that the relatively continuous spectrum of the white noise signal avoids the generation of undesired possibly detrimental discrete beat frequencies from the pulse modulated carrier and the white noise signal, while being capable of bringing about by an appropriate choice of the limits of this continuous spectrum complementary neurophysiological effects resulting in a renforcement of the principal desired effect.

According to the intended application, the relative proportion of the noise component and the modulated high-frequency component may be advantageous between one-fourth and one-half in the majority of cases, this proportion designating the ratio of the mean current strength of these components.

The method according to the invention is particularly applicable to obtaining neurophysiological effects such as relaxation, sleep, general analgesia, local-regional anaesthesia, and general anaesthesia.

Its use is particularly advantageous when the current strength of the pulse modulated high-frequency signal whose average value is the product of the r.m.s. value of the high-frequency carrier by the mark-to-space ratio of the square-shaped low-frequency pulses must be rather large, as for example in the case of electro-analgesia or electro-anaesthesia treatments.

Also disclosed is a device for carrying out the method described above comprising a high-frequency signal generator, a low-frequency pulse generator, means for modulating the amplitude of the said high-frequency signals by the low-frequency pulses, a noise generator adapted to generate electric signals having a relatively continuous frequency spectrum and mixing means adapted to superimpose the modulated high-frequency signal generated by said modulation means and the signals from the noise generator for providing a composite signal with a mean amplitude proportional to the difference between the respective mean amplitudes of the modulated high-frequency signal and said noise signal.

Preferably, the apparatus comprises control means selectively adjusting certain or all parameters defining the composite output signal, i.e., the peak amplitude of the modulated high-frequency signal, the amplitude of the noise signal, the frequency of the high-frequency signal, the length and the spacing of the low frequency modulation pukes, as well as the spectrum of the signal delivered by the noise generator.

Suitable switching means may be advantageously provided to make available one or more elementary signals utilised to generate the above-defined composite signal at one of the outputs of the device. Indeed, it could be advantageous in certain electro-neurophysiological treatments to combine the application of composite signals according to the invention with signals of different characteristics simultaneously or sequentially with the composite signals, and it is therefore advantageous to provide a single device to generate these different signals.