Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Patent
1995-09-18
1998-07-07
Getzow, Scott M.
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
A61N 136
Patent
active
057761701
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the field of electrotherapy, and provides apparatus for a particular application of such therapy.
BACKGROUND OF RELATED ART
The nervous system is able to respond to an interrupted DC or alternating current, provided the repetition rates or frequencies do not exceed values that vary according to the particular properties of each class of nerve. Severe dull or aching pain is associated with the firing of unmyelinated or C fibres (Class IV). These fibres cannot follow a maintained frequency higher than about 2 Hz. In addition they have a high threshold and normally only respond to excessive mechanical or thermal stimulation that injures cells. Sharp pain is associated with the firing of A.delta. (Class III) fibres. They cannot follow electrical stimulation rates higher than about 50-80 Hz. There is also a class of nerve fibres that may faithfully follow electrical stimulation at rates up to approximately 800 Hz; these are called A.beta. or Class II fibres. The Class II receptors have a low threshold to any form of stimulation and respond to such innocuous events as movement or light touch.
Melzack and Wall (1965) and Wall (1986) describe how analgesia can be produced when the Class II or A.beta. fibres are stimulated electrically at 100 Hz, a frequency that none of the other nerves can follow.
Wall (1986) produced these effects by applying the current through needles inserted into the patient's nerves. To avoid the inconvenience and possible complications of inserting needles into nerves, surface electrodes were later employed, leading to the term Transcutaneous (Electrical) Nerve Stimulation (TNS or TENS).
Woolf (1989) has reviewed the use of these devices, and described their electrical parameters. The usual TENS machine develops a pulse, whose width can be varied from 50-500 .mu.s, employing a current whose amplitude can be increased from 0-50 mA, and whose frequency is generally 80 or 100 Hz.
The TENS pulse width (50-500 .mu.s) is intended to be sufficiently long in duration to excite A.beta. nerves to cause a painless tingling at low voltage.
In known TENS devices, the maximum current density and sensation tends to occur in tissues immediately underlying the electrodes, and only a proportion of the applied current reaches the deep tissues. Thus, when choosing a comfortable level of stimulation, the patient is first guided by sensations arising from peripheral nerve stimulation in tissues immediately below the electrodes. If the amplitude is increased to try and produce more current in the deep tissues, pain may be produced when there is sufficient voltage to recruit A.delta. fibres. This tends to limit the amplitude of TENS that can be tolerated by a patient.
Although tingling produced by the TENS method is usually painless and reasonably well accepted by patients, it tends to produce a rather short-lived, localised region of analgesia, as each electrode probably stimulates a few hundred A.beta. fibres in the immediate vicinity of the electrodes. Accordingly, in patients where there may be several large areas of the body in pain, there is a need to improve the method to produce a more long-lasting and generalised form of analgesia.
In an attempt to fire more A.beta. fibres, wire electrodes have been implanted in the spinal canal to stimulate the central nervous system itself, in particular the dorsal columns (tracts through which the A.beta. fibres pass up and down the spinal chord). This is called Dorsal Column Stimulation, and is reviewed by Krainick et al (1989). The present technique employs small bare tips of otherwise insulated wires, probably stimulating a few thousand A.beta. fibres. However, the implantation of the wires involves surgery and the risk of infection along the track of the wires.
SUMMARY OF THE INVENTION
In order to avoid the risks of implanting electrodes in direct contact with the central nervous system, U.S. Pat. No. 3,835,833 (Limoge) describes application to a patient's head of intermittent 4 ms blocks of high frequency cu
REFERENCES:
patent: 4554923 (1985-11-01), Batters
Coates Timothy William
MacDonald Alexander John Ranald
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