Biomedical Body Electrode

Abstract

A biomedical body electrode is provided having a nonconductive housing with an apertured face for application to a body surface. A metallic element is mounted within the housing, the element and the face defining a cavity therein. An electrolyte fills the cavity and a membrane is secured to the face to cover the apertures, thereby sealing the electrolyte within the cavity. A lead is connected to the metallic element for connecting the electrode to external instrumentation.

Description

The present invention relates to electrodes, and more particularly to an improved electrode for application to a body surface. Such electrodes, commonly called body electrodes, are used with electromedical diagnostic and therapeutic apparatus, such as electrocardiographs, pacemakers and other devices, as input and output terminals for transferring electrical signals to and from a living body.

One early form of body electrodes comprised a metallic plate secured in direct contact with a patient's skin. Such an electrode however, had several distinct drawbacks, a first being that the metal plate-to-skin contact of the electrode generated unwanted contact potentials. A second drawback with this form of electrode was that even the slightest movement between the metal plate of the electrode and the patient's skin caused substantial variations in the contact impedance of the electrode, these contact impedance variations being commonly known in the medical profession as motion artifacts.

In order to eliminate contact potentials generated by direct metal-to-skin contact, body electrodes were subsequently developed in which a metallic plate or element was positioned in spaced relation to a patient's skin. To establish electrical contact with the patient's body, these latter electrodes required the application of a layer of electrolyte, in the form of a paste or gel, to that area of the body surface to which the electrode was to be applied. The electrolyte thereby provided the electrical conductive path between the electrode's metallic plate and the patient's body. This type of electrode, however, was very sensitive to mechanical disturbances of the electrolyte material at the metal-electrolyte interface as resulted from motion of the electrode on the patient's skin, and motion artifacts were produced as a consequence thereof.

Aside from motion artifacts, use of these latter electrodes had the added disadvantage that skin irritation often resulted therefrom. This skin irritation caused patient discomfort and resulted since patients skins were frequently quite sensitive or allergic to the layer of electrolyte paste or gel which necessarily had to be applied with the use of these electrodes. In order to minimize such patient discomfort, in certain cases it was necessary to periodically relocate the point of electrode attachment, and in certain other instances it was even necessary to limit the use of therapeutic or diagnostic apparatus requiring the attachment of body electrodes to a patient's body.

In is accordingly, an object of the present invention to provide an improved body electrode which, in situ, does not irritate a patient's skin, has a low and stable contact impedance which is substantially unaffected by motion artifacts, and generates contact potentials which are negligible.

It is a further object of the present invention to provide body electrode as set forth, suitable for use in a dynamic environment wherein a patient may perform physical activities characterized by being lightweight, inexpensive to manufacture, and readily attachable to a patient's body for comfortable wear.

In accomplishing these and other objects, there has been provided in accordance with the present invention a body electrode having a nonconductive housing with a metallic element mounted therein. With the electrode in situ on a patient's body surface, the housing supports the metallic element in spaced relation to the patient's skin. The space within the housing between the metallic element and the patient's skin is filled with an electrolyte, and the electrolyte is sealed in the housing by means of a membrane secured across a face of the housing. The face of the housing contacts the patient's skin when the electrode is situ and an electrical conductive path is established from the patient's skin through the membrane, through the electrolyte, and to the metallic element of the electrode.

A better understanding of the invention may be had from the following detailed description when read in connection with the accompanying drawings in which:

FIG. 1 is a view of the base of an electrode according to the present invention, with the line 2-2 denoting the plane on which FIG. 2 is taken; and

FIG. 2 is an exploded vertical section view of the electrode of FIG. 1.

Referring to the drawings in more detail, there is shown a housing 1 having a base or face 2, apertures 3 in the base 2, and a top surface 4. The top surface 4 has a small opening therein to accommodate the passage of an electrical lead 5. Mounted within the housing 1 in parallel spaced relation to the base 2, and adjacent to the top surface 4 is a metallic element 6. The lead 5 is connected to the upper surface of the metallic element 6, as shown in the FIG. 2. A cavity in the housing 1 is defined, respectively, on its upper and lower boundaries by the metallic element 6 and the base 2, and the cavity is filled with a suitable electrolyte 16. It is here noted that in FIG. 1, the periphery of base 2 is indicated by the dotted circle 11. Further, it is noted that in an electrode constructed in accordance with the present invention, the housing 1 may be made of a nonconductive lightweight material, such as a plastic, and the metallic element 6 may be a silver/ silver chloride tablet of the type described in U.S. Pat. No. 3,137,291 issued to Phipps et al.

A membrane 7 and annulus or attaching means 8 are adhered to the electrode base by a suitable adhesive. The membrane 7 is impermeable to the electrolyte 16 and is so secured to the base 2 to cover the apertures 3, thereby sealing the electrolyte 16 within the housing 1. In FIG. 1, the periphery of the membrane 7 is indicated by the dotted circle 9, and the inner and outer periphery of the annulus 8 are indicated, respectively, by the solid circles 10 and 15, the annulus 8 surrounding the area of the membrane 7 covering the apertures 3. The annulus 8 has an adhesive surface on the side thereof to be applied to a patient's body surface or skin 17. Thereby the electrode when in situ will adhere to the patient's body as a result of the action of this adhesive surface of the annulus 8. The electrode may be stored with a protective covering, not shown, placed over the annulus 8 and the membrane 7 in order to protect the membrane 7 and to prevent the adhesive surface of the annulus 8 from drying prior to electrode use. While in the electrode described herein, the annulus 8 was used as attaching means to attach the electrode housing 1 to the patient's body, other attaching means known in the art could easily be substituted therefor, e.g. a suitable belt may be used to strap the electrode to the patient's body.

Before application of an electrode constructed in accordance with the present invention to the patient's body surface, the membrane 7 may be wetted with a selected wetting agent which permeates the membrane 7, and which is electrically conductive or will become conductive upon contact with the patient's skin 17. Thereby the conductivity of the membrane 7 is enhanced, and it is insured that a low resistance path will be offered to current flowing between the electrolyte 16, and the patient's skin 17. In an exemplary electrode, the membrane 7 was polytetrafluorethylene imbedded with fiber glass and a drop of water was used as the selected wetting agent to wet the membrane 7 to enhance its conductivity. Water, if it is not already conductive due to the presence of impurities, becomes conductive upon contact with the body salts present on the patient's skin. After wetting the membrane 7, the base 2 of the electrode may be then applied to the skin 17 with the annulus 8 serving to secure the electrode thereto. The membrane 7 which is flexible, conforms with the patient's body surface, thereby making smooth and continuous contact with the skin 17, even in a dynamic environment in which the patient is performing bodily activities. The lead 5 of this electrode may then be connected to diagnositc or therapeutic apparatus, as desired, whereupon electrical signals may be transferred to or from the patient's body.

While with the exemplary electrode the membrane therein was dampened with a drop of water in order to enhance its conductivity, this procedure may not be necessary in all situations. For example with a body surface already wet, such as from a patient's perspiration it may then be unnecessary to further dampen the membrance.

Thus, there has been provided an improved body electrode which makes electrical contact with a patient's body surface by means of a flexible membrane which conforms to the body surface. The improved body electrode provides an electrical contact with the patient's skin characterized by a low and stable contact impedance which is substantially unaffected by motion artifacts, the generation of minimal contact potentials, and its nonirritating effect on the patient's skin. Further, the improved electrode is lightweight, inexpensive to manufacture due to its simplicity, and readily attachable to a patient's body for comfortable wear. The ease of attachment and lightweightedness of this electrode, coupled with its low and stable contact impedance substantially unaffected by motion artifacts, makes this electrode suitable for use in dynamic environments wherein a patient is performing physical activities.

Claims

The embodiments of the invention in which I claim an exclusive property or privilege are defined as follows:

1. An electrode for establishing electrical contact with a body surface of a living organism, said electrode comprising:

a nonconductive housing having a face at one end for contacting said body surface, said face having an aperture therein;

a metallic element mounted at the other end within said housing in spaced parallel relation to said face whereby said metallic element and said face define a cavity within said housing;

an electrolyte filling said cavity; a membrane secured to said face to cover said aperture, said membrane being impermeable to said electrolyte thereby to seal said electrolyte within said housing, said membrance being permeable to at least one selected wetting agent, for dampening said membrane whereby to enhance the electrical conductivity thereof; and

an electrical lead connected to said metallic element for connecting said electrode to external instrumentation.

2. The electrode as recited in claim 1 wherein said face has a plurality of apertures therein, and said membrance is secured to said face to cover all of said several apertures.

3. The electrode as recited in claim 1 including means for attaching said electrode to said body surface.

4. The electrode as recited in claim 3 wherein said attaching means comprises an annulus, said annulus being secured to said face surrounding the area of said membrance covering said aperture whereby to expose said membrane area to said body surface, said annulus having an adhesive surface on the side thereof to be applied to said body surface.

5. The electrode as recited in claim 1 wherein said membrane is polytetrafluorethylene embedded with fiber glass.

6. The electrode as recited in claim 5 wherein said housing in nonconductive plastic and said metallic element is a silver silver chloride tablet.

7. The electrode as recited in claim 6 wherein said face has a plurality of apertures therein and said membrance is secured to said face to cover all of said several apertures.

8. The electrode as recited in claim 7 including means for attaching said electrode to said body surface, said attaching means comprising an annulus, said annulus being secured to said face surrounding the area of said membrance covering said apertures whereby to expose said membrane area to said body surface, said annulus having an adhesive surface on the side thereof to be applied to said body surface.