Management of stimulation safety limits in a neurostimulation system

Abstract

A neurostimulation system for management of stimulation safety limits. The system determines a tissue charge injection metric at each electrode, compares the metric to the hard stop charge limit, and prevents the neurostimulator from delivering stimulation energy to the tissue region in accordance based on the comparison. The hard stop limit may be user-programmable or may be automatically modified in response to detection of electrode characteristics. The system may quantitatively notify a user of a value of the injected charge injected into the tissue. The electrodes may be organized into different sets, in which case, the system may directly control tissue charge independently at each of the electrode sets. If current steering is provided, the system may displace the electrical stimulation energy along the tissue region in one direction, while preventing the charge injection value at each of the electrodes from meeting or exceeding the hard stop charge limit.

1 . A neurostimulation system for use with at least one electrode, comprising:
 a neurostimulator configured for delivering electrical stimulation energy to a tissue region in accordance with a stimulation parameter, thereby injecting a charge into the tissue region at the at least one electrode;   an external control device configured for allowing a user to modify the stimulation parameter;   memory storing a hard stop charge limit; and   control circuitry configured for determining a tissue charge density injection metric at the at least one electrode, comparing the tissue charge injection metric to the hard stop charge limit, and preventing the neurostimulator from delivering the electrical stimulation energy to the tissue region in accordance with the modified stimulation parameter based on the comparison.   
     
     
         2 . The neurostimulation system of  claim 1 , wherein the tissue charge density injection metric is one of a charge density per phase, a k-value, and a charge density per second. 
     
     
         3 . The neurostimulation system of  claim 1 , wherein the tissue charge density injection metric is in terms of one of a relative value, a normalized value, and an absolute value. 
     
     
         4 . The neurostimulation system of  claim 1 , wherein the external control device is configured for allowing the user to modify the hard stop charge limit. 
     
     
         5 . The neurostimulation system of  claim 1 , wherein the entirety of the control circuitry is contained in either the neurostimulator or the external control device. 
     
     
         6 . The neurostimulation system of  claim 1 , wherein a portion of the control circuitry is contained in the neurostimulator, and another portion of the control circuitry is contained in the external control device. 
     
     
         7 . The neurostimulation system of  claim 1 , wherein the neurostimulator is configured for monitoring a charge injected into the tissue region, and the control circuitry is configured for determining the tissue charge density injection metric based on the monitored charge. 
     
     
         8 . The neurostimulation system of  claim 1 , wherein the control circuitry is configured for estimating the tissue charge density injection metric based, at least in part, on the modified stimulation parameter. 
     
     
         9 . The neurostimulation system of  claim 1 , wherein the control circuitry is configured for preventing the neurostimulator from delivering the electrical stimulation energy to the region in accordance with the modified stimulation parameter if the tissue charge injection metric meets or exceeds the hard stop charge limit. 
     
     
         10 . The neurostimulation system of  claim 1 , wherein the memory stores a charge warning threshold, the control circuitry is configured for comparing the tissue charge injection metric to the charge warning threshold, and the external control device is configured for providing a user-discernible notification message to the user based on the comparison between the tissue charge injection metric and the charge warning threshold. 
     
     
         11 . The neurostimulation system of  claim 10 , wherein the external control device is configured for allowing the user to modify the charge warning threshold. 
     
     
         12 . The neurostimulation system of  claim 11 , wherein the external control device is configured for preventing the user from modifying the charge warning threshold to a value greater than the hard stop limit. 
     
     
         13 . A neurostimulation system for use with at least one electrode, comprising:
 a neurostimulator configured for delivering electrical stimulation energy to a tissue region, thereby injecting a charge into the tissue region at the at least one electrode; and   an external control device configured for being actuated to actively modify the characteristics of the delivered electrical stimulation energy, and for, in response to the modification of the delivered electrical stimulation energy characteristics, quantitatively notifying a user of a value of the charge injected into the tissue.   
     
     
         14 . The neurostimulation system of  claim 13 , wherein the external control device is configured for quantitatively notifying the user by textually conveying the value of the charge to the user. 
     
     
         15 . The neurostimulation system of  claim 13 , wherein the external control device is configured for quantitatively notifying the user by graphically conveying the value of the charge to the user. 
     
     
         16 . The neurostimulation system of  claim 13 , wherein the value of the charge is defined by one of a charge per phase, a charge density per phase, a k-value, a charge per second, and a charge density per second. 
     
     
         17 . The neurostimulation system of  claim 13 , wherein the value of the charge is in terms of one of a relative value, a normalized value, and an absolute value. 
     
     
         18 . The neurostimulation system of  claim 13 , wherein the external control device is configured for displaying the value of the charge relative to a charge warning threshold. 
     
     
         19 . The neurostimulation system of  claim 13 , wherein the external control device is configured for displaying the value of the charge relative to a hard stop charge limit. 
     
     
         20 . The neurostimulation system of  claim 13 , wherein the external control device is configured for displaying the value of the charge relative to a tissue damage threshold. 
     
     
         21 .- 54 . (canceled)