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Nerve stimulator and methodRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Electrical Therapeutic Systems, Electrical Treatment Of PainNerve stimulator and method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060195158, Nerve stimulator and method. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application is a continuation of and claims the benefit of priority to U.S. patent application Ser. No. 10/853,590, filed on May 25, 2004. FIELD OF INVENTION [0002] This invention relates to the stimulation of nerves with invasive electrodes for targeted therapeutic interventions. BACKGROUND [0003] Nerve stimulators commercially available for targeted nerve therapies are exemplified by the NeuroTrace III (HDC Corp., Milpitas, Calif.), the Stimuplex (B.Braun America, Bethlehem, Pa.) and the Digistim III (NeuroTechnologies, Inc, Chennai, India), among others. These devices are constant current, monophasic, pulsed square waveform generators having pulse widths no longer than 200 microseconds in duration. These devices are connected to insulated hypodermic needles which are inserted through the skin and advanced toward the presumed position of a target nerve. Accurate localization of the needle tip is presumed when either a sensory paresthesia or a motor paresthesia is provoked by current outputs less than 0.5 mA. This work is derived from historical strength-duration curves. However, there are several problems with these devices. [0004] The following references will be used to discuss relevant prior art and inadequacies. [0005] 1. Cooper M S. Membrane Potential Perturbations Induced in Tissue Cells by Pulsed Electric Fields. Bioelectromagnetics 1995; 16:255-62. [0006] 2. Vloka J D and Hadzic A. The Intensity of the Current at Which Sciatic Nerve Stimulation Is Achieved Is More Important Factor in Determining the Quality of Nerve Block That the Type of Motor Response Obtained. Anesthesiology 1998; 88(5):1408-10. [0007] 3. Barthram C N. Nerve Stimulators for Nerve Location--Are They All the Same? Anaesthesia 1997; 52:761-4. [0008] 4. Pither, C. E., Raj, P. P., and Ford, D. J. The Use of Peripheral Nerve Stimulators for Regional Anesthesia: A Review of Experimental Characteristics, Technique and Clinical Applications. Reg Anesth 1985; 10(2):49-58. [0009] 5. Andres, J D. and Sala-Blanch, X. Peripheral Nerve Stimulation in the Practice of Brachial Plexus Anesthesia: A Review. Reg Anesth Pain Med 2001; 26(5):478-83. [0010] 6. Hadzic A; Vloka J, Hadzic N, Thys D M, Santos A C. Nerve stimulators used for peripheral nerve blocks vary in their electrical characteristics. Anesthesiology 2003; 98(4):969-74. [0011] 7. Urmey, W. F. Interscalene Block: The Truth About Twitches. Reg Anesth Pain Med 2000; 25(4):340-2. [0012] 8. Urmey, W. F.; Stanton, J.; O'Brien, S.; Tagariello, V.; Wickiewicz, T. L. Inability to Consistently Elecit a Motor Response Following Sensory Paresthesia During Interscalene Block Administration. Reg Anesth 23, 7. 1998. [0013] 9. Choyce A; Chan V W; Knight W J; Peng P; McCartney C J. What is the relationship between paresthesia and nerve stimulation for axillary brachial plexus block? Reg Anesth Pain Med 26[2], 100-104. 2001. [0014] 10. Hille B. Ionic Basis of Resting and Action Potentials. Brookhart, J. M., Mountcastle, V. B., and Kandel, E. R. The Nervous System Baltimore, Md.: Waverly Press, Inc; 1977. pp. 99-136. [0015] 11. Hodgkin A L and Huxley A F. A Quantitative Description of Membrane Current and Its Application to Conduction and Excitation in Nerve. J Physiol 1952; 117:500-44. [0016] 12. Cole K S, Membranes, ions, and impulses. Berkeley and Los Angeles: University of California Press; 1972. (Biophysics Series; 1). [0017] 13. Rall W. Core Conductor Theory and Cable Properties of Neurons. Brookhart, J. M., Mountcastle, V. B., and Kandel, E. R. Handbook of Physiology, section 1, The Nervous System Baltimore, Md.: Baltimore, Md.; 1977. pp. 39-97. [0018] Cooper (reference 1 above) developed a mathematical description of the necessary parameters of externally applied, pulsed electric fields for effective nerve stimulation. There are two important concepts that derive from his work. First, an adequate voltage gradient must be generated across the neuronal cell membrane for effective depolarization of the nerve cell to occur. Second, an externally applied electric field must have a pulse duration that is at least 0.5 times the neuronal cell membrane time constant to cause reproducible depolarization. [0019] Anesthesia literature is replete with papers concerning nerve stimulation. In all of these works, the applied current is seen as an important parameter (references 2-9). However, examination of the Hodgkin-Huxley equations reveals that current does not play a role in the opening of membrane sodium or potassium channels. Opening of these channels is required for nerve depolarization to occur (see references 10-12). The role that applied current plays in nerve depolarization is related to the associated voltage gradient required to drive the current through the load represented by the tissue impedance. At a first level approximation, the current to voltage relationship follows Ohm's Law, or E=IR, where E is voltage, I is current, and R is resistance. Clearly, at constant current, the voltage will vary directly with the load. During placement of a needle for nerve stimulation, the load varies with distance from the nerve, as shown by Nervonix experimental data in FIG. 1. Since the impedance decreases as the needle tip approaches the nerve, the applied voltage will also decrease, making the development of an adequate voltage gradient for depolarization unpredictable. [0020] An additional factor in achieving adequate voltage with constant current output is the resistance-capacitance (RC) nature of tissue. Tissue can be represented in equivalent electrical circuits as an RC circuit. When any RC circuit is exposed to a constant current pulse, the associated voltage shows a charging curve as depicted from Nervonix experimental data in FIG. 2. A constant current pulse was directed across tissue via a 22G insulated needle or a 24G insulated needle. These data demonstrate that the applied voltage only reaches its maximum toward the end of the 2.5 ms pulse. If the pulse had ended at 0.2 ms, as the commercially available nerve stimulators provide, the voltage would be well short of its maximum value. [0021] Finally, there are a many references regarding the time constant of motoneurons. Rall (reference 13) summarizes these studies, which show that motoneuron membrane time constants range from 3 ms to 7 ms. Based on Cooper's work, if a pulse is to be of adequate duration to reproducibly cause neuronal cell depolarization, it must be greater than 1.5 ms. The commercially available nerve stimulators operate well below this level. 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