System and method for determining a stimulation threshold for closed loop spinal cord stimulation

Abstract

System and methods are provided for determining a stimulation threshold for closed loop spinal cord stimulation (SCS). The system and methods provide a lead coupled to an implantable pulse generator (IPG). The system and methods deliver SCS pulses from the IPG to the lead electrodes in accordance with an SCS therapy and determine an evoked compound action potential (ECAP) amplitude based on an ECAP waveform resulting from the SCS therapy. The system and methods increase the SCS therapy by increasing at least one of an amplitude, a duration, and number of the SCS pulses associated with the SCS therapy. The system and methods also include iteratively repeat the delivering, determining and increasing operations until the ECAP amplitude exhibits a downward trend divergence. The system and methods define a stimulation threshold based on the ECAP amplitude at the trend divergence.

What is claimed is: 
     
         1 . A method for determining a stimulation threshold for closed loop spinal cord stimulation (SCS), the method comprising:
 providing a lead coupled to an implantable pulse generator (IPG), the IPG having a processor, wherein the lead includes at least one lead electrode and is configured to be implanted at a target position proximate to or within nerve tissue of interest, and further wherein the processor of the IPG is programmed to perform following steps:   delivering a series of SCS pulses from the at least one lead electrode to the nerve tissue of interest, the series of SCS pulses programmed to form a plurality of SCS waveforms, wherein each SCS waveform has a different stimulation amplitude;   measuring evoked compound action potential (ECAP) waveforms resulting from application of the plurality of SCS waveforms, each ECAP waveform corresponding to a respective SCE waveform; and   defining a stimulation threshold based on at least one of a slope and a time delay associated with a respective peak corresponding to each of the ECAP waveforms.   
     
     
         2 . The method of  claim 1 , wherein the stimulation threshold is defined further based on:
 comparing the time delays of the respective peaks of the ECAP waveforms;   determining that an increase in the time delays is above a predetermined threshold; and   identifying the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform with a particular time delay resulting in the increased time delay as the stimulation threshold.   
     
     
         3 . The method of  claim 2 , wherein the time delays of the respective peaks of the ECAP waveforms are measured from a respective stimulation spike associated with each ECAP waveform. 
     
     
         4 . The method of  claim 1 , wherein the stimulation threshold is defined further based on:
 measuring a slope for each ECAP waveform with respect to the peak of the ECAP waveform and a predetermined baseline potential associated with the ECAP waveform;   comparing the slopes of the ECAP waveforms to determine a change in the slopes associated with the corresponding peaks; and   identifying the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform having a slope reduced by a predetermined threshold as the stimulation threshold.   
     
     
         5 . The method of  claim 4 , wherein the predetermined baseline potential is defined by a common ground voltage of the IPG. 
     
     
         6 . The method of  claim 1 , wherein the SCS waveforms comprise waveforms having stimulation amplitudes increasing over time. 
     
     
         7 . The method of  claim 1 , wherein the SCS waveforms comprise at least one of tonic stimulation waveforms, biphasic stimulation waveforms and burst stimulation waveforms. 
     
     
         8 . The method of  claim 1 , wherein each ECAP waveform is measured proximate to an Aβ sensory fiber of the nerve tissue of interest. 
     
     
         9 . The method of  claim 1 , further comprising transmitting an alert notification responsive to defining the stimulation threshold. 
     
     
         10 . An apparatus for determining a stimulation threshold for closed loop spinal cord stimulation comprising:
 a lead having at least one lead electrode, the lead configured to be implanted at a target position proximate to or within nerve tissue of interest;   an implantable pulse generator (IPG) coupled to the lead, the IPG configured to deliver SCS pulses to the lead electrodes in accordance with an SCS therapy;   the IPG including sensing circuitry configured to measure an evoked compound action potential (ECAP) waveform resulting from the SCS therapy;   the IPG further including a processor in communication with the sensing circuitry, the processor programmed, in response to instructions stored on a non-transient computer-readable medium, to perform:
 delivering a series of SCS pulses from the at least one lead electrode to the nerve tissue of interest, the series of SCS pulses programmed to form a plurality of SCS waveforms, wherein each SCS waveform has a different stimulation amplitude; 
 measuring evoked compound action potential (ECAP) waveforms resulting from application of the plurality of SCS waveforms, each ECAP waveform corresponding to a respective SCE waveform; and 
 defining a stimulation threshold based on at least one of a slope and a time delay associated with a respective peak corresponding to each of the ECAP waveforms. 
   
     
     
         11 . The apparatus of  claim 10 , wherein the instructions for defining the stimulation threshold further comprise instructions configured to:
 compare the time delays of the respective peaks of the ECAP waveforms;   determine that an increase in the time delays is above a predetermined threshold; and   identify the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform with a particular time delay resulting in the increased time delay as the stimulation threshold.   
     
     
         12 . The apparatus of  claim 11 , wherein the time delays of the respective peaks of the ECAP waveforms are measured from a respective stimulation spike associated with each ECAP waveform. 
     
     
         13 . The apparatus of  claim 10 , wherein the instructions for defining the stimulation threshold further comprise instructions configured to:
 measure a slope for each ECAP waveform with respect to the peak of the ECAP waveform and a predetermined baseline potential associated with the ECAP waveform;   compare the slopes of the ECAP waveforms to determine a change in the slopes associated with the corresponding peaks; and   identify the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform having a slope reduced by a predetermined threshold as the stimulation threshold.   
     
     
         14 . The apparatus of  claim 13 , wherein the predetermined baseline potential is defined by a common ground voltage of the IPG. 
     
     
         15 . The apparatus of  claim 10 , wherein the SCS waveforms comprise waveforms having stimulation amplitudes increasing over time. 
     
     
         16 . The apparatus of  claim 10 , wherein the SCS waveforms comprise at least one of tonic stimulation waveforms, biphasic stimulation waveforms and burst stimulation waveforms. 
     
     
         17 . The apparatus of  claim 10 , wherein each ECAP waveform is measured proximate to an Aβ sensory fiber of the nerve tissue of interest. 
     
     
         18 . The apparatus of  claim 10 , wherein the non-transient computer-readable medium further comprises instructions configured to transmit an alert notification responsive to defining the stimulation threshold. 
     
     
         19 . A tangible, non-transitory computer readable storage medium having program instructions stored thereon, which perform a determination of a stimulation threshold for closed loop spinal cord stimulation (SCS) when executed by a processor of an implantable pulse generator (IPG) having sensing circuitry, the IPG configured to be coupled to a lead including at least one lead electrode that is configured to be implanted at a target position proximate to or within nerve tissue of interest, the program instructions comprising:
 a code portion configured to facilitate delivery of a series of SCS pulses from the at least one lead electrode to the nerve tissue of interest, the series of SCS pulses programmed to form a plurality of SCS waveforms, wherein each SCS waveform has a different stimulation amplitude;   a code portion configured to measure evoked compound action potential (ECAP) waveforms resulting from application of the plurality of SCS waveforms, each ECAP waveform corresponding to a respective SCE waveform; and   a code portion configured to define a stimulation threshold based on at least one of a slope and a time delay associated with a respective peak corresponding to each of the ECAP waveforms.   
     
     
         20 . The tangible, non-transitory computer readable storage medium of  claim 19 , wherein the code portion configured to define the stimulation threshold further comprise instructions configured to:
 compare the time delays of the respective peaks of the ECAP waveforms;   determine that an increase in the time delays is above a predetermined threshold; and   identify the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform with a particular time delay resulting in the increased time delay as the stimulation threshold.   
     
     
         21 . The tangible, non-transitory computer readable storage medium of  claim 20 , wherein the time delays of the respective peaks of the ECAP waveforms are measured from a respective stimulation spike associated with each ECAP waveform. 
     
     
         22 . The tangible, non-transitory computer readable storage medium of  claim 19 , wherein the code portion configured to define the stimulation threshold further comprise instructions configured to:
 measure a slope for each ECAP waveform with respect to the peak of the ECAP waveform and a predetermined baseline potential associated with the ECAP waveform;   compare the slopes of the ECAP waveforms to determine a change in the slopes associated with the corresponding peaks; and   identify the stimulation amplitude of the SCS waveform corresponding to the ECAP waveform having a slope reduced by a predetermined threshold as the stimulation threshold.   
     
     
         23 . The tangible, non-transitory computer readable storage medium of  claim 22 , wherein the predetermined baseline potential is defined by a common ground voltage of the IPG. 
     
     
         24 . The tangible, non-transitory computer readable storage medium of  claim 19 , further comprising a code portion configured to transmit an alert notification responsive to defining the stimulation threshold. 
     
     
         25 . The tangible, non-transitory computer readable storage medium of  claim 19 , wherein the code portion configured to measure ECAP waveforms comprises program instructions configured to measure each ECAP waveform proximate to an Aβ sensory fiber of the nerve tissue of interest.