1. Field of the Invention
The present invention relates to electrodes for sensing signals such as electrocardiograph signals and, more particularly, this invention relates to electrode elements or conductors adapted for use in such electrodes to interconnect an electrolyte with suitable signal processing or monitoring equipment.
2. Description of the Prior Art
U.S. Pat. Nos. 3,696,807 and 3,701,346 illustrate medical electrodes which are known in the prior art and to which the present invention is applicable. In these patents an electrolyte applied to the skin of a human or other animal subject is interfaced to electrocardiograph monitoring equipment by a solid metal conductor such as silver contacted to the electrolyte. Electrodes of this type are known to function adequately to meet the needs of the medical profession but are also relatively expensive because the preferred metal for electrolyte contact is silver. Even though the amount of silver used in such electrodes is not great, the cost of the silver used in the electrode represents a significant cost factor. Aside from the cost of the raw metal, difficulties encountered in forming or shaping solid metal contribute to the cost of electrode manufacture. Because of the cost of the manufacture, commercially available electrode configurations are to some extent limited.
U.S. Pat. No. 3,566,860 teaches an electrode conductor for interconnecting between an electrolyte and electrocardiograph monitoring equipment, the conductor comprising a dispersion of finely divided carbon in plastic. Such a conductor is desirably inexpensive but is also found to be relatively ineffective when compared with electrode devices which utilize metal conductors. In particular it is found that the signal which such an electrode can transmit to associated monitoring equipment is so erratic (wandering base line, irregular trace) that the informational signals available at the skin surface of the subject being monitored are distorted and sometimes entirely obscure.
It has also been known to produce electrode elements comprising a layer of silver on a copper support. Electrocardiograph traces obtained with the use of such electrodes frequently reveal a base line irregularity and the failure to provide proper repetitive wave forms, particularly after an extended period of contact with an electrolyte. Even when great care is employed in producing the silver layer, there is a distinct likelihood that the electrolyte will contact the underlying copper through minute pores in the silver layer. It is believed that when the electrolyte has invaded the silver layer so as to engage the underlying copper, the electrocardiograph monitoring equipment is seeing the product of two electrodes, one being silver contacted by the electrolyte and the other being copper contacted by the electrolyte, and it is further believed that reactions occur between these dissimilar metals which disturb the signals received by the monitoring equipment.