Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Thermal applicators
Reexamination Certificate
1999-07-19
2001-06-12
Sykes, Angela D. (Department: 3736)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Thermal applicators
Reexamination Certificate
active
06246912
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to medical systems and procedures for prolonging or improving human life. More particularly, this invention relates to an improved method and apparatus for modifying the function or characteristics of neural and other tissue by applying pulsed or modulated high frequency electromagnetic fields to the tissue.
BACKGROUND OF THE INVENTION
The use of radiofrequency (RF) generators with electrodes applied near or in neural tissue for pain relief or functional modification is well known. For instance, the RFG-3C RF Lesion Generator available from Radionics, Inc., Burlington, Mass. can be used with electrodes placed near neural tissue to heat the tissue by RF resistive power dissipation of the generator power in the tissue. Thermal monitoring by a thermo sensor in the electrode is used to control the process. Heat lesions produced at tissue temperatures of 60 to 95 degrees Celsius (° C.) are common. Tissue dies by heating at about 45 to 50° C., so heat lesion generation is designed to elevate the neural tissue above this lethal temperature threshold. Often, the procedure of heating above 45 to 50° C. causes severe pain to the patient, which is so unpleasant (and frequently unbearable) that a local or general anesthetic is required during the heat procedure. Use of anesthesia poses a degree of undesired risk to the patient, and the destructive nature of and unpleasant side effects of the RF heat lesion are limitations of this technique.
Heat lesion generators typically use continuous wave RF generators with radiofrequencies of between 100 KiloHertz to several MegaHertz (viz. the RF generators of Radionics, Fischer, OWL, Elekta, Medtronic, Osypka, EPT companies). The theory and use of RF lesion generators and electrodes for pain and functional disorders is described in various papers (see, e.g., (1) Cosman, et al. “Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone,”
Neurosurg
15:945-950, 1984; and (2) Cosman E R and Cosman B J. “Methods of Making Nervous System Lesions,” in Wilkins R H, Rengachary S S (eds):
Neurosurgeny
. New York, McGraw-Hill, Vol. III, 2490-2498, 1984).
Neural stimulation is also now a common method of pain therapy. Stimulus generators with outputs of 0 to 10 volts (or zero to several milliamperes of current are used) are typical. A variety of waveforms and pulse trains in the “physiologic” frequency ranges of 0 to about 300 Hertz is also typical. This output is delivered to electrodes placed near or in neural tissue on a temporary basis (acute electrode placement) or permanent basis (chronic electrode implants). Such stimulation can relieve pain, modify neural function, and treat movement disorders. Typically, the stimulation is sustained to have a long-term effect, i.e., usually when the stimulus is turned off, pain will return or the therapeutic neural modification will cease after a short time (hours or days). Thus permanent implant electrodes and stimulators (battery or induction driven) is standard practice (e.g., the commercial systems by Medtronic, Inc., Minneapolis, Minnesota), and the stimulus is usually sustained or repeated on an essentially continuous basis for years to suppress pain or to treat movement disorders (viz. Parkinsonism, bladder control, spasticity, etc.). Stimulators deliver regular pulse trains or repetitive bursts of pulses in the range of 0 to 200 Hertz (a physiologic range similar to the body's neural frequency pulse rates), so this method simulates or inhibits neural function at relatively low frequency. It does not seek to heat the neural tissue for destructive purposes as in the high frequency technique. Chronically or permanently implanted stimulators often require battery changes, long-term maintenance and patient follow-up, which are expensive and inconvenient, often requiring repeated surgery.
Electrosurgical generators have been commonly used for decades for cutting and coagulating tissue in surgery. They typically have a high frequency, high power generator connected to an electrode that delivers a high power output to explode tissue for tissue cutting and to cook, sear, and coagulate tissue to stop bleeding. Examples of such generators are the generators of Codman, Inc., Randolph Mass., Valley Labs, Inc., Boulder, Colo., and EMC Industries, Montrouge, France. Such generators have high frequency output waveforms that are either continuous waves or interrupted or modulated waves with power controls and duty cycles at high levels so that tissue at the electrode is shattered and macroscopically separated (in cutting mode) or heated to very high temperatures, often above cell boiling (100° C) and charring levels (in coagulation or cauterizing mode). The purpose of electrosurgery generators is surgical, not therapeutic, and accordingly their output controls, power range, duty cycle, waveforms, and monitoring is not designed for gentle, therapeutic, neuro-modulating, sub-lethal temperature application. Use of an electrosurgical unit requires local or general anesthesia because of its violent and high-temperature effect on tissues.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus (a modulated high frequency signal generation apparatus in conjunction with a signal applicator, e.g., an electrode or conductive plate or other structure applied to the body) for modifying neural function of a patient's tissue. The inventive apparatus and method are functionally different from and have advantages over the RF heat lesioning systems, the stimulation systems, and electrosurgical systems previously described. Pain relief or neural modification, for instance, can be achieved by the inventive system without average heating of tissue above 45 to 50° C., without stimulating at frequencies in the range of 0 to about 300 Hertz and without burning or cauterizing tissue. Thus, as one advantage of the present invention, painful RF lesioning episodes at high lesion temperatures can be avoided and the need for chronic stimulation can be circumvented.
For example, by using an RF waveform output connected to an electrode inserted into the body near or in neural tissue, and by interrupting the RF waveform with bursts of RF power with interposed periods of off-time, a pain relieving effect or other neural modulating effect is accomplished, but the tissue temperature does not on average exceed approximately 45° C. This avoids painful heat lesions and potential side effects associated with the typical RF heat lesions, which involve tissue temperatures at a region near the electrode of substantially greater than 45° C. The modulated RF system can be used painlessly and easily, avoiding usual discomforts of standard RF heating procedures, yet relief of the pain or the neural dysfunction (such as, e.g., motor dysfunction, epilepsy spasticity, Parkinsonism, tremors, mood disorders, incontinence, etc.) can be long lasting using the novel system of the present invention, giving results in many cases that are comparable to those of RF heat lesions done at much higher temperatures. Another advantage of the modulated high frequency procedure is that it avoids the unwanted and sometimes harmful side effects of heat lesions, such as sensory or motor loss and can be performed on neural structures such as the dorsal root ganglion, in which making a heat lesion would not be recommended because of the delicate nature of that structure. Some applications of this invention include relief of back, head, and facial pain by procedures such as dorsal root ganglion or trigeminal ganglion treatments, spinal cord application for relief of intractable pain, spasticity, or motor control, treatment of the basal ganglia in the brain for relief of Parkinsonism, loss of motor control, tremors, or intractable pain. This pain relief or control or elimination of motor or other neural dysfunction can be comparable if not more effective than long-term stimulators with implanted electrodes, thus providing an alternative to avoiding the need for permanent stim
Cosman Eric R.
Rittman, III William J.
Sluijter Menno E.
Carter Ryan
Sherwood Services AG
Sykes Angela D.
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