Method and System for Controlling Electrical Conditions of Tissue II

Abstract

A method for controlling electrical conditions of tissue in relation to a current stimulus. A first current produced by a first current source is delivered to the tissue via a current injection electrode. A second current drawn by a second current source is extracted from the tissue via a current extraction electrode. The second current source is matched with the first current source so as to balance the first current and the second current. A ground electrode which is proximal to the current injection electrode and the current extraction electrode is grounded, to provide a ground path for any mismatch current between the first current and second current. A response of the tissue to the current stimulus is measured via at least one measurement electrode.

1 . A method for controlling electrical conditions of tissue in relation to a current stimulus, the method comprising:
 delivering to the tissue via a current injection electrode a first current produced by a first current source;   extracting from the tissue via a current extraction electrode a second current drawn by a second current source, the second current source being matched with the first current source so as to balance the first current and the second current;   grounding a ground electrode which is proximal to the current injection electrode and the current extraction electrode, to provide a ground path for any mismatch current between the first current and second current; and   measuring via at least one measurement electrode a response of the tissue to the current stimulus.   
     
     
         2 . The method of  claim 1  wherein the ground electrode is connected to ground throughout application of a stimulus by the first and second current sources. 
     
     
         3 . The method of  claim 1  wherein the ground electrode is disconnected, or floating, during some or all of the application of the stimulus. 
     
     
         4 . The method of  claim 1  wherein the ground electrode and the measurement electrode are located outside a dipole formed by the current injection electrode and the current extraction electrode. 
     
     
         5 . The method of  claim 1  wherein the ground electrode is grounded to a distal patient ground electrode. 
     
     
         6 . An implantable device for controlling electrical conditions of tissue in relation to a current stimulus, the device comprising:
 a plurality of electrodes including at least one nominal current injection electrode, at least one nominal current extraction electrode, at least one nominal ground electrode which is proximal to the current injection electrode and the current extraction electrode, and at least one nominal measurement electrode, the electrodes being configured to be positioned proximal to the tissue to make electrical contact with the tissue;   a first current source for producing a first current to be delivered to the tissue by the current injection electrode;   a second current source for producing a second current to be extracted from the tissue via the current extraction electrode, the second current source being matched with the first current source so as to balance the first current and the second current;   an electrical ground for grounding the ground electrode, to provide a ground path for any mismatch current between the first current and second current; and   measurement circuitry for measuring via the at least one measurement electrode a response of the tissue to the current stimulus.   
     
     
         7 . The implantable device of  claim 6  wherein the ground electrode and the measurement electrode are located outside a dipole formed by the current injection electrode and the current extraction electrode. 
     
     
         8 . The implantable device of  claim 6  wherein the ground electrode is grounded to a distal patient ground electrode.