Method for Use of Depolarizing Pre-Pulses to Increase the Maximum Comfortable Stimulation Level of Neurostimulation
Publication Date: 2003-Jan-09
The IP.com Prior Art Database
Depolarizing Pre-Pulses (DPPs) disable Dorsal Root (DR) fibers, thereby enabling a broad effective range of stimulation of Dorsal Column (DC) fibers. Spinal Cord Stimulation (SCS) systems generally target DC fibers for stimulation. However, neighboring DR fibers are generally more responsive to the stimulation, and limit the threshold for comfortable stimulation. Long duration sub-threshold depolarizing pre-pulses cause the effective h-gate of the sodium channels of the DR fibers to close, but do not cause the effective m-gate of the sodium channels of the DR fibers to open. Because the DC fibers are less responsive than the DR fibers (primarily due to their closer proximity to the stimulating electrodes), the sub-threshold pulses do not cause the effective h-gate of the sodium channels of the DC fibers to close. Normal stimulation pulses may then be applied over a broad range of stimulation levels without undesirable side effects associated with DR fiber stimulation.
Background and Summary
A spinal cord stimulation system treats chronic pain by providing electrical stimulation pulses through the electrodes of an electrode array placed epidurally near a patient=s spinal cord. The maximum comfortable stimulation level is the stimulation level at which any increase in stimulation level results in discomfort to the patient independent of the pain being treated. The maximum comfortable stimulation level is important because it is effectively a limit to the range of adjustment allowed to a patient to meet varied pain relief/paresthesia requirements during the patient=s daily activities.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an Implantable Pulse Generator (IPG), electrodes, electrode lead, and optional electrode lead extension. The IPG generates electrical pulses that are delivered to the dorsal column and dorsal root fibers in the spinal cord through the electrodes. The electrodes are implanted along the dura of the spinal cord. Individual electrode contacts (the Aelectrodes@) may be arranged in a desired pattern and spacing in order to create an electrode array. Individual wires connect with each electrode in the array. These wires are encased within an insulating material, and thus encased are referred to as a lead. The lead exits the spinal cord and, usually, attaches to an electrode lead extension. The electrode lead extension, in turn, is typically tunneled through the torso of the patient to a subcutaneous pocket where the IPG is implanted.
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 biocompatible material is provided as a carrier on which a plurality of electrodes are formed. The electrodes are connected by a conductor, e.g., a lead body, to an RF receiver, which is also implanted, and which is controlled by an external controller.
In United States Patent No. 3,822,708, another type of electrical SCS device is taught. The device disclosed in the >708 patent has five aligned electrodes which are positioned longitudinally on the spinal cord. Current pulses applied to the electrodes block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes have a repetition rate of from 5 to 200 pulses per second. A patient-operated switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the stimulation pulses, so that the a...