Method and apparatus for altering neural tissue function
A method and apparatus for altering a function of neural tissue in a patient. An electromagnetic signal is applied to the neural tissue through an electrode. The electromagnetic signal has a frequency component above the physiological stimulation frequency range and an intensity sufficient to product an alteration of the neural tissue, the alteration causing the patient to experience a reduction in pain, and a waveform that prevents lethal temperature elecation of the neural tissue during application of the electromagnetic signal to the neural tissue.
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This application is a continuation of application Ser. No. 08/671,927 filed on Jun. 27, 1996, now U.S. Pat. No. 5,983,141.
BACKGROUND OF THE INVENTIONThe use of radiofrequency (rf) generators and electrodes to be applied near or in neural tissue for pain relief or functional modification is well known. For instance, the RFG3C RF Lesion Generator of Radionics, Inc., Burlington, Mass., and its associated electrodes enable placement of the electrode near neural tissue and heating of that tissue by rf resistive power dissipation of the generator power in the tissue. Thermal monitoring by thermo sensor in the electrode has been used to control the process. Heat lesions with tissue temperatures of 60 to 95 degrees Celsius (° C.) are common. tissue dies by heating at about 45 to 50° C., so this process is a heat lesion generation and 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 local or general anesthetic is required during the heat procedure. Use of such anesthetics has 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, which is well known. 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; specifically see: (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): Neurosurgery. 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 criteria are used) are typical. A variety of waveforms and pulse trains in the “physiologic” frequency ranges of 0 to about 300 Hertz are 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, the 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 (viz. see the commercial systems by Medtronic, Inc., Minneapolis, Minn.), 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 (i.e., 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 high frequency technique. Chronically or permanently implanted stimulators often require battery changes or long-term maintenance and patient follow-up, which is expensive and inconvenient, often requiring repeated surgery.
Electrosurgical generators have been in common use for decades 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 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 which 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 anesthetic because of its violent and high-temperature effect on tissues.
SUMMARY OF THE INVENTIONThe present invention is directed to a modulated high frequency apparatus in conjunction with a signal applicator (for example an electrode or conductive plate or structure applied to the body) to modify neural function, the associated apparatus and method of use being functionally different from and having advantages over the rf heat lesioning systems, or the stimulation systems, and electrosurgical systems of the type described above. Pain relief or neural modification, for instance, can be achieved by the present invention 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 may not on average exceed approximately 45° C. This avoids the painful heat lesions associated with the typical rf 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 disfunction (such as for example motor disfunction, spasticity, Parkinsonism, tremors, modd 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. Some applications of this invention may include such examples as 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 intractible pain. This pain relief or control or elimination of motor or other neural disfunction can be comparable if not more effective than long-term stimulators with implanted electrodes, thus avoiding the need for permanent implants, expensive implanted devices and circuits, battery changes, involving repeated surgery and expense, and repeated application of stimulation energy over long periods (months and years). The pain relief or neural modification can be accomplished by the present invention in a non-violent, painless way, avoiding average tissue temperature elevations into the lethal range and violent macroscope tissue separations, and thus the present invention is opposite to the objectives, systems, and methods involved in electrosurgical systems.
Forms of the modulated frequency generator and output waveforms are disclosed herein in various embodiments. Specific embodiments with temperature monitors and thermal sensing electrodes are disclosed which are suited to control the modulated system and its use.
In the drawings, which constitute a part of the specification, exemplary embodiments exhibiting various forms and features hereof are set forth, specifically:
Referring to
In operation, the voltage or current output from generator 4 and modulator 5 are impressed upon tissue NT, which may be neural tissue (viz. spinal nerves or roots, spinal cord, brain, etc.) or tissue near neural tissue. In accordance with the present invention, such electromagnetic output can cause energy deposition, electric field effects, and/or electromagnetic field effects on the nerve cells in the tissue NT so as to modify or destroy the function of such nerve cells. For example, such modification of neural function may include reduction or elimination of pain syndromes (such as spinal facet, mechanical back pain, facial pain) in some cases, alleviating motor disfunction, spasticity, Parkinsonism, etc., epilepsy or mood disorders. Because the rf output from 4 is modulated by element 5, its percent on-time is reduced so that sustained heating of tissue NT is reduced, yet the neural therapeutic effects of the impressed rf voltages and currents on the neural tissue NT are enough to produce the pain reducing result. The generator 5 can have a power, voltage, or current output control 5A (as on the Radionics Model RFG-3C rf generator) to increase or decrease the output power magnitude or modulated duty cycle to prevent excessive heating of tissue NT or to grade the level of pain interruption as needed clinically. Output control 5A may be a knob which can raise or lower the output in a smooth, venerated way, or it can be an automatic power control with feedback circuits. In this regard, temperature monitor 6 can provide the operator with the average temperature of tissue NT near electrode tip 1 to interactively prevent temperatures near tip 1 to exceed the range of approximately 45° C. (on average thermally lethal to tissue NT), and thus to avoid the higher temperature ranges for the usual heat lesioning procedures described above. For example, 6 may have feedback circuitry to change the modulation duty cycle (by, for example, longer or shorter on-times) to hold the temperature near tissue NT to below a set value (viz. 40 to 45° C.), illustrated by the feedback line 14 in FIG. 1. In addition, the high frequency waveform from the generator 5 can be free from substantial components in the 0 to about 300 to 400 Hertz range (which is much lower than radiofrequencies), and this will avoid the stimulation effects that are typical for stimulator system applications as described above.
As an example of a modulated rf waveform that accommodates the system of the present invention,
To give a representative example of values for parameters in an interrupted high frequency waveform as in
Variations of such waveforms are possible with the same intermittent high frequency effect for pain on neurological modification. For instance, a baseline V=0 may not pertain and a slowly varying baseline of non-zero value can be used. The time average of the signal need not be zero. The on and off switching of a high frequency signal such as in
Element 50 represents a signal generator which may create a high frequency signal of periodic or non-periodic frequency. This has input to element 31, which is a filter system which selectively filters out frequencies that could cause unpleasant, undesired, or damaging physiological signals. The signal is then fed into element 33, which is a waveform shaping circuit, and will shape the waveform input from element 32, which provides amplified modulation and/or frequency modulation and/or phase modulation control. Circuits of this type can be found, for instance in Radio Engineering by Terman (cited above). Additional waveform shaping can be done by element 40 and 41, which can control the amplitude of waveform and/or the duty cycle of the waveform, respectively. This resultant signal is then fed into a power amplifier represented of element 34. This is a wide band amplifier used to increase the signal to power levels appropriate for clinical use. This energy is then delivered to the patient via an electrode depicted as element 35.
A temperature sensor or plurality of temperature sensors, represented by element 36, can also be placed and connected in proximity to this electrode so as to insure that the temperature does not exceed desired limits. This temperature sensor signal is fed through element 37, which is a special filter module used to eliminate high frequency components, and thus not to contaminate the low-level temperature signals.
The temperature signal is fed to element 38, which is a standard temperature measuring unit that converts the temperature signal into a signal that can be used to display temperature and/or to control, in a feedback manner, either the amplitude and/or the duty cycle of the high frequency waveform. In this way, power delivery can be regulated to maintain a given set temperature. This flow is represented by element 39, which is simply a feedback control device. The dotted lines from element 39 to elements 40 and 41 represent a feedback connection that could either be electronic and/or mechanical. It could also simply be a person operating these controls manually, based on the visual display of temperature, as for example on a meter or graphic display readout 42.
As was explained with respect to the disclosed embodiments, many variations of circuit design, modulated high frequency waveforms, electrode applicators, electrode cannulas will be appreciated by those skilled in the art for example, electrodes or electrode applicators are practical, including tubular shapes, square shafts, flat electrodes, area electrodes, multiple electrodes, arrays of electrodes, electrodes with side outlets or side-issued tips, electrodes with broad or expandable or conformal tips, electrodes that can be implanted in various portions of the brain, spinal cord, interfecal space, interstitial or ventricular spaces, nerve ganglia can be considered within the system of the present invention.
The frequency range for the so-called high frequency waveforms, as shown for instance in
Mixtures of frequencies can be done as discussed above. These could be admixtures of “high frequencies” (above the physiologic stimulation range (say 0 to 300 Hertz) and lower frequencies (within that stimulation range of say 0 to 300 Hertz). Thus one skilled in the art could have both modulated high frequency and stimulation frequencies for various clinical effects, such as stimulation blockage of pain while neural modification is being applied according to the present invention.
In view of these considerations, as will be appreciated by persons skilled in the art, implementations and systems should be considered broadly and with reference to the claims set forth below.
Claims
1. A method for sustained neural function modification in a patient comprising:
- generating an amplitude modulated signal having at least one frequency component above a physiologic stimulation frequency range; and
- applying the amplitude modulated signal to selected neural tissue in the patient for altering a function of the tissue without heating the tissue to temperatures lethal to the tissue, wherein said amplitude modulated signal has a peak voltage, said peak voltage being sufficient to alter the function of the tissue in the patient, wherein the function remains altered for a given period of time after application of the signal to the tissue is ceased.
2. The method of claim 1 wherein altering the function of the tissue reduces pain experienced by the patient.
3. The method of claim 1 wherein altering the function of the tissue reduces pain by tremor experienced by the patient.
4. The method of claim 1 wherein altering the function of the tissue reduces symptoms of Parkinson's disease experienced by the patient.
5. The method of claim 1 wherein altering the function of the tissue reduces symptoms of spasticity experienced by the patient.
6. The method of claim 1 wherein altering the function of the tissue reduces symptoms of mood disorder experienced by the patient.
7. The method of claim 1 wherein altering the function of the tissue reduces symptoms of epilepsy experienced by the patient.
8. The method of claim 1 wherein altering the function of the tissue alleviates motor disfunction.
9. The method of claim 1 wherein the at least the frequency component of the amplitude modulated signal alters the function of the tissue.
10. The method of claim 1 wherein applying the amplitude modulated signal to the tissue comprises engaging the tissue with an electrode coupled with a signal generator generating the amplitude modulated signal.
11. The method of claim 1 wherein temperatures lethal to the tissue are greater than 45° C.
12. The method of claim 1 wherein the at least one frequency component has a frequency greater than 300 Hz.
13. An apparatus for sustained alteration of a function of selected neural tissue in a patient comprising
- a signal generator and an electrode coupled to the signal generator, said signal generator being adapted to generate an amplitude modulated signal having at least one frequency component above a physiologic stimulation frequency range, said electrode being adapted to apply the signal to the tissue, wherein application of the amplitude modulated signal to the tissue alters a function of the tissue while inhibiting heating of the tissue to temperatures lethal to the tissue, wherein said amplitude modulated signal has a peak voltage, said peak voltage being sufficient to alter the function of the tissue in the patient, and wherein alteration of the function of the tissue persists even after application of the signal to the tissue ceases.
14. The apparatus of claim 13 wherein altering the function of the tissue reduces pain experienced by the patient.
15. The apparatus of claim 13 wherein altering the function of the tissue causes the patient to experience a reduction in pain by tremor.
16. The apparatus of claim 13 wherein altering the function of the tissue causes the patient to experience reduced symptoms of Parkinson's disease.
17. The apparatus of claim 13 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of spasticity.
18. The apparatus of claim 13 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of mood disorder.
19. The apparatus of claim 13 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of epilepsy.
20. The apparatus of claim 13 wherein altering the function of the tissue alleviates motor disfunction.
21. The apparatus of claim 13 wherein the at least one frequency component of the amplitude modulated signal alters the function of the tissue.
22. A method for lasting modification of neural tissue function in a patient comprising:
- placing an electrode in or near selected neural tissue of the patient;
- generating an amplitude modulated signal and transmitting the signal to the electrode, said signal having at least one frequency component above a physiologic stimulating frequency range for alteration of a function of the tissue without heating the tissue to temperatures lethal to the tissue, wherein said amplitude modulated signal has a peak voltage being sufficient to alter the function of the tissue in the patient, said alteration being sustained even after transmission of the signal to the electrode ceases.
23. The method of claim 22 wherein altering the function of the tissue reduces pain experienced by the patient.
24. The method of claim 22 wherein altering the function of the tissue causes the patient to experience a reduction in pain by tremor.
25. The method of claim 22 wherein altering the function of the tissue causes the patient to experience reduced symptoms of Parkinson's disease.
26. The method of claim 22 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of spasticity.
27. The method of claim 22 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of mood disorder.
28. The method of claim 22 wherein altering the function of the tissue causes the patient to experience a reduced symptoms of epilepsy.
29. The method of claim 22 wherein altering the function of the tissue alleviates motor disfunction.
30. The method of claim 22 wherein the at least one frequency component of the amplitude modulated signal alters the function of the tissue.
31. The method of claim 22 wherein temperatures lethal to the tissue are greater than 45° C.
32. The method of claim 22 wherein the at least one frequency component has a frequency greater than 300 Hz.
33. A method for sustained neural function modification in a patient comprising:
- generating interrupted radiofrequency waveforms having predetermined time periods of on-time bursts of radiofrequency output of a first predetermined duration followed by relatively substantial off-time periods of very low output at a second predetermined duration; and
- applying the interrupted radiofrequency waveforms to selected neural tissue in the patient for a predetermined treatment time sufficient to result in alteration of a function of the tissue without heating the tissue to temperatures lethal to the tissue, wherein the interrupted radiofrequency waveforms have a peak voltage sufficient to result in said alteration, wherein the function remains altered for a given period of time after application of the signal to the tissue is ceased.
34. The method of claim 33, wherein altering the function of the tissue reduces symptoms experienced by the patient selected from the group consisting of pain, tremor, Parkinson's disease, spasticity, mood disorder, epilepsy, and motor dysfunction.
35. The method of claim 33, wherein the step of applying the interrupted radiofrequency waveforms to the tissue includes engaging the tissue with an electrode coupled with a signal generator.
36. The method of claim 33, wherein the generating step includes having a ratio of on-time bursts of radiofrequency output to off-time bursts of approximately two percent.
37. An apparatus for sustained alteration of a function of selected neural tissue in a patient comprising:
- a signal generator which generates interrupted radiofrequency waveforms having predetermined time periods of on-time bursts of radiofrequency output of a first predetermined duration followed by relatively substantial off-time periods of very low output at a second predetermined duration,
- an electrode coupled to the generator and being adapted to apply the interrupted radiofrequency waveforms to the tissue, wherein application of the interrupted radiofrequency waveforms to the tissue alters a function of the tissue while inhibiting heating of the tissue to temperatures lethal to the tissue, wherein the interrupted radiofrequency waveforms have a peak voltage, said peak voltage being sufficient to result in said alteration, and wherein alteration of the function of the tissue persists even after application of the signal to the tissue ceases.
38. The apparatus of claim 37, wherein altering the function of the tissue reduces symptoms experienced by the patient selected from the group consisting of pain, tremor, Parkinson's disease, spasticity, mood disorder, epilepsy, and motor dysfunction.
39. The apparatus of claim 37, wherein the generator is adapted to apply the interrupted radiofrequency waveforms to the tissue in a ratio of on-time bursts of radiofrequency output to off-time bursts of approximately two percent.
40. An apparatus for sustained alteration of a function of selected neural tissue in a patient comprising:
- a signal generator which generates interrupted radiofrequency waveforms having predetermined time periods of on-time bursts of radiofrequency output of a first predetermined duration followed by relatively substantial off-time periods of very low output at a second predetermined duration;
- an electrode coupled to the generator and being adapted to apply the interrupted radiofrequency waveforms to the tissue by being surgically inserted in or on the patient, wherein application of the interrupted radiofrequency waveforms to the tissue alters a function of the tissue while inhibiting heating of the tissue to temperatures lethal to the tissue, and wherein alteration of the function of the tissue persists even after application of the signal to the tissue ceases, and wherein the interrupted radiofrequency waveforms have a peak voltage sufficient to alter the neural tissue, and wherein said peak voltage is in a range that includes tens of volts.
919139 | April 1909 | Duke |
3127895 | April 1964 | Kendall et al. |
3791373 | February 1974 | Winkler et al. |
3817254 | June 1974 | Maurer |
3888261 | June 1975 | Maurer |
3894532 | July 1975 | Morey |
3897789 | August 1975 | Blanchard |
3911930 | October 1975 | Hagfors et al. |
3946745 | March 30, 1976 | Hsiang-Lai et al. |
4014347 | March 29, 1977 | Halleck et al. |
4055190 | October 25, 1977 | Tany |
4177819 | December 11, 1979 | Kofsky et al. |
4210151 | July 1, 1980 | Keller, Jr. |
4237899 | December 9, 1980 | Hagfors et al. |
4324253 | April 13, 1982 | Greene et al. |
4338945 | July 13, 1982 | Kosugi et al. |
4340630 | July 20, 1982 | Doty |
4431002 | February 14, 1984 | Maurer et al. |
4442839 | April 17, 1984 | Maurer et al. |
4453548 | June 12, 1984 | Maurer et al. |
4520825 | June 4, 1985 | Thompson et al. |
4535777 | August 20, 1985 | Castel |
4541432 | September 17, 1985 | Molina-Negro et al. |
4556064 | December 3, 1985 | Pomeranz et al. |
4565200 | January 21, 1986 | Cosman |
4640286 | February 3, 1987 | Thomson |
4671286 | June 9, 1987 | Renault |
4723552 | February 9, 1988 | Kenyon et al. |
4735204 | April 5, 1988 | Sussman et al. |
4759368 | July 26, 1988 | Spanton et al. |
4790319 | December 13, 1988 | Slovak |
4793353 | December 27, 1988 | Borkan |
4887603 | December 19, 1989 | Morawetz et al. |
4907589 | March 13, 1990 | Cosman |
4917092 | April 17, 1990 | Todd et al. |
4922908 | May 8, 1990 | Morawetz et al. |
4929865 | May 29, 1990 | Blum |
4938223 | July 3, 1990 | Charters et al. |
RE33420 | November 6, 1990 | Sussman et al. |
4977895 | December 18, 1990 | Tannenbaum |
4989605 | February 5, 1991 | Rossen |
5036850 | August 6, 1991 | Owens |
5052391 | October 1, 1991 | Silberstone et al. |
5058605 | October 22, 1991 | Slovak |
5063929 | November 12, 1991 | Bartelt et al. |
5109847 | May 5, 1992 | Liss et al. |
5117826 | June 2, 1992 | Bartelt et al. |
5233515 | August 3, 1993 | Cosman |
5330515 | July 19, 1994 | Rutecki et al. |
5342409 | August 30, 1994 | Mullett |
5350414 | September 27, 1994 | Kolen |
5370672 | December 6, 1994 | Fowler et al. |
5417719 | May 23, 1995 | Hull et al. |
5433739 | July 18, 1995 | Sluijter et al. |
5478303 | December 26, 1995 | Foley-Nolan et al. |
5562717 | October 8, 1996 | Tippey et al. |
5569242 | October 29, 1996 | Lax et al. |
5571147 | November 5, 1996 | Sluijter et al. |
5573552 | November 12, 1996 | Hansjurgens |
5584863 | December 17, 1996 | Rauch et al. |
5643330 | July 1, 1997 | Holsheimer et al. |
5658322 | August 19, 1997 | Fleming |
5690692 | November 25, 1997 | Fleming |
5702428 | December 30, 1997 | Tippey et al. |
5702429 | December 30, 1997 | King |
5759158 | June 2, 1998 | Swanson |
5800481 | September 1, 1998 | Loos |
5814092 | September 29, 1998 | King |
5817139 | October 6, 1998 | Kasano |
RE35987 | December 8, 1998 | Harris et al. |
5908444 | June 1, 1999 | Azure |
5913882 | June 22, 1999 | King |
5925070 | July 20, 1999 | King et al. |
5938690 | August 17, 1999 | Law et al. |
5948007 | September 7, 1999 | Starkebaum et al. |
5951546 | September 14, 1999 | Lorentzen |
5983141 | November 9, 1999 | Sluijter et al. |
6035236 | March 7, 2000 | Jarding et al. |
6161044 | December 12, 2000 | Silverstone |
6275735 | August 14, 2001 | Jarding et al. |
3151180 | August 1982 | DE |
000811395 | December 1997 | EP |
WO8501212 | March 1985 | WO |
WO9400188 | January 1994 | WO |
WO9713550 | April 1997 | WO |
WO974953 | December 1997 | WO |
WO984888 | November 1998 | WO |
- Cosman & Cosman, “Methods of Making Nervous System Lesions,” Neurosurgery, pp. 2490-2499.
- Cosman et al., “Theoretical Aspects of Radiofrequency Lesions in the Dorsal Root Entry Zone,” Neurosurgery, vol. 15, No. 6, pp. 945-950, 1984.
- Guttman et al., “Squid Axion Membrane Response to White Noise Stimulation,” Biophysical Journal, vol. 14, pp. 941-955, 1974.
- Radionics, “RFG-3C Graphics: RF Lesion Generator System with Graphics,” 1996.
- Salkoff & Kelly, “Atmospheric Electricity and Sun-Weather Relationships,” Nature, vol. 273, No. 5658, pp. 3-5, May 11, 1978.
- Terman, Frederick Emmons, “Radio Engineering,” New York, Mcgraw-Hill Book Company, Inc., 1947.
- International Search Report: PCT/US 97/11145, Oct. 13, 1997.
Type: Grant
Filed: Jun 12, 2003
Date of Patent: Dec 15, 2009
Assignee: Covidien AG (Neuhausen am Rheinfall)
Inventors: Menno E. Sluijter (Amsterdam), William J. Rittman, III (Lynnfield, MA), Eric R. Cosman (Belmont, MA)
Primary Examiner: Michael Peffley
Application Number: 10/460,506
International Classification: A61F 2/00 (20060101);