Monitoring Physiological Signals During External Electrical Stimulation

Abstract

Electrodes and circuitry for monitoring and stimulating the exterior of the human body, comprising delivering stimulation pulses to stimulation electrodes applied to the exterior of the body, detecting an electrical potential at monitoring electrodes applied to the exterior of the body, positioning at least a first and second monitoring electrode at locations at which an electrical artifact caused by the electrical stimulation pulses is substantially cancelled in a signal formed from the electrical potentials detected at the first and second monitoring electrodes.

What is claimed is: 
     
         1 . A multi-electrode assembly for cardiac stimulation and monitoring, the assembly comprising:
 a monitoring electrode configured to monitor electrical potential on the chest of a patient;   a stimulation electrode configured to deliver one or more stimulating pulses to the chest of a patient;   an electrode cable having first and second cable ends, the first cable end configured for connection to an external cardiac device and the second cable end configured for connection to the monitoring electrode and to the stimulation electrode; and   a non-linear circuit element electrically interposed between the second cable end and the stimulation electrode, the non-linear circuit element being configured to conduct during delivery of the stimulating pulses and to block conduction in the presence of a residual potential on the stimulating electrode following delivery of a stimulation pulse.   
     
     
         2 . The electrode assembly of  claim 1  wherein the non-linear circuit element comprises one or more diodes or gas discharge tubes. 
     
     
         3 . The electrode assembly of  claim 1  wherein the non-linear circuit element comprises at least two non-linear circuit elements forming parallel paths between the cable and the stimulation electrode, and with the polarity of the elements being opposite along the two paths, so that a biphasic stimulation waveform can be delivered to the stimulation electrode, with current flowing through one of the paths in one polarity of the waveform and through the other of the paths in the other polarity of the waveform. 
     
     
         4 . The electrode assembly of  claim 3  wherein conductance in the presence of a residual potential on the stimulation electrode is blocked along one of the parallel paths by setting the net offset potential of the one or more elements in that path to greater than the expected residual potential. 
     
     
         5 . The electrode assembly of  claim 1  wherein the non-linear circuit element comprises one or more transistors. 
     
     
         6 . The electrode assembly of  claim 1  wherein the non-linear circuit element generally blocks current flow in one direction and permits current flow in the opposite direction. 
     
     
         7 . The electrode assembly of  claim 1  wherein the electrode cable comprises a single conductor, and the first and second cable ends are first and second ends of the single conductor. 
     
     
         8 . The electrode assembly of  claim 1  further comprising a high-impedance element that is positioned in the electrical path between the electrode cable and the monitoring electrode and configured to reduce the level of current flowing to the monitoring electrode during delivery of a stimulation pulse to the stimulating electrode.