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Publication Date: 2004-Feb-12

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A neural stimulation system automatically corrects or adjusts the stimulus parameters in order to maintain a comfortable and effective stimulation therapy. Changes in dCSF, the distance indicating the stimulating electrode position relative to the target nerves, can be measured by measuring body conductor field potentials which are affected by the conductivity of surrounding tissue matter. Measured changes in dCSF can be used to adjust stimulation parameters in a feedback loop system for the most comfortable and efficacious stimulation. In addition, obtaining dCSF can help the clinician place an in-line lead array close to the physiological mid-line.

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The present invention relates to neural stimulation systems and, more particularly, to an output control system used with such neural systems that automatically maintains the output of the stimulation system at a comfortable and efficacious level.

The present invention may be used in spinal cord stimulation therapies in which a neurostimulator is used to stimulate dorsal column nerves. Spinal cord stimulation (SCS) systems treat chronic pain by providing electrical stimulation pulses through the contacts of an electrode array placed epidurally near a patient’s spinal cord. SCS is a well-accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an Implantable Pulse Generator (IPG) coupled to an array of contacts at or near the distal end of an electrode lead. An electrode lead extension may also be used, if needed. The IPG generates electrical pulses that are delivered to neural tissue, e.g., the dorsal column fibers within the spinal cord, through the contacts of the electrode array. In an SCS system, for example, the electrodes are implanted proximal to the dura mater of the spinal cord. Individual electrode contacts (the “electrodes”) may be arranged in a desired pattern and spacing in order to create an electrode array. Individual wires, or electrode leads, connect with each contact in the array. The electrode leads exit the spinal column and attach to the IPG, either directly, or through one or more electrode lead extensions. The electrode lead extension, in turn, when used, is typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted.

The electrical pulses generated by the SCS system, or other neuro-stimulation system, are also referred to as "stimulation pulses". In an SCS system, the stimulation pulses typically have the effect of producing a tingling sensation, also known as a paresthesia. The paresthesia helps block the chronic pain felt by the patient. The amplitude of the stimulation pulses affects the intensity and location of the paresthesia felt by the patient. In general, it is desirable to have the amplitude of stimulation comfortably set to a level which produces paresthesia to block pain but not above a level that may actually result in pain apart from the native pain. Moreover, the stimulus amplitude should be set to a stimulus level lower than that which can recruit reflex motor nerves that can cause involuntary muscle contractions.

SCS and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in United States Patent No. 3,646,940 that provides timed, sequenced electrical impulses to a plurality of electrodes. As another example, United States Patent No. 3,724,467, teaches an electrode implant for neuro-stimulation of the spinal cord. A relatively thin and flexible strip of biocom...