Liquid Electrode Material

Abstract

A novel electrode material for use with medical diagnostic potentiometric devices having a wire lead extending therefrom to be secured to the skin of a patient, is provided. The electrode material is a viscous, adhesive, electrically conductive liquid which dries on the skin. Upon application the electrode material will envelope the wire lead, and after drying will assure that dependable and durable electrical contact between skin and wire lead has been made.

Description

This invention relates to devices for measuring small electrical voltages generated in the human body as is commonly done in medical diagnosis, and more particularly to an improved electrode for use with electrocardiographic, oscilloscopic-monitoring and like recording devices.

The heart, muscles and brain of the human skin generate small voltages which are measurable on the skin of a person. The precise and accurate recording of these voltages form the basis of electrocardiography, electromyography, and electroencephalography, respectively. The recorded potentials are valuable aids in the diagnosis of normality and disease of the tissues from whence they originate. It is sometimes necessary to continue such measurements for prolonged periods of time, sometimes three days or longer. Specifically, long-term monitoring of bioelectrical potentials originating from the heart has provided lifesaving in patients who have had or are suspected of having had a myocardial infarction (heart attack). In addition, there is a need for continuous recording of heart rate and heart rhythm and changes thereof in humans subjected to the stresses of exercise, aerospace, ocean depths and supersonic speeds.

In making such measurements, a potentiometric device for receiving and recording electrical signals is employed. A wire lead between the device and patient is required for purposes of conducting the signal from patient to device, and the wire lead terminates at an electrode, the term "electrode" in this context signifying the means by which electrical connection between wire lead and skin of the patient is made.

Standard clinical electrodes currently in use with electrocardiographic, oscillographic-monitoring, and recording devices are usually large and cumbersome metal plates, mesh, or recessed wells in which electrical contact with the skin is made by means of hypertonic salt solution in the form of a paste or gel. Mechanical contact with the skin is maintained by elastic straps, suction cups, adhesive tape, or other mechanical means. The conductive paste or gel dries up after several minutes or hours and electrical resistance between the skin and metal plate increases. In electrocardiography this may result in spurious electrical signals, or motion artefacts. If the patient is connected to a monitor-alarm system in a coronary care unit, frequent false alarms may be initiated which falsely simulate an absence of electrical activity of the heart or a serious cardiac arrhythmia. This results in frequent harassment of patient, physician and nursing personnel.

Such electrodes are also unsuitable in the unrestrained and ambulatory subject. As the subject moves, there is considerable variation in the area of direct contact between the skin and the metallic electrode as well as variation in the amount of electrolyte paste or gel between the skin and the electrode. Thus the electrical resistance between the skin and electrode varies considerably with body movement and the desired bioelectrical potential is obscured by reduced voltage and unwanted electrical noise and artefact. Heavy shielded leads and cables and constricting bands, straps and adhesive tape as used in all prior devices all lead to patient discomfort and inconvenience. It is necessary to clean and reapply electrode paste to such electrodes at relatively frequent intervals. Adhesive tapes which have been use to bind metal electrodes to skin tend to lose their adhesiveness under conditions of patient perspiration, humid environment or when the electrode paste has wet them. In many patients, particularly with prolonged usage, the hypodermic salt solution incorporated into the electrode paste is an irritant to the skin resulting in considerable discomfort and even inflammation and ulceration of the skin. Needle electrodes make good electrical contact with the body but are painful to the patient and hence their use is undesirable in the critically ill coronary patient. They are impractical in the ambulatory subject because of pain attendant upon muscle movement, and because needles penetrate the skin there is always a risk of infection.

Against the foregoing background, it is the primary object of this invention to provide a novel electrode material and technique for use in the recording of bioelectrical potentials. The electrode material which we provide is a viscous, adhesive, electrically conductive liquid which dries on the skin, bonding firmly to the skin and to a lead wire from the recording device. The consistency of the liquid electrode material should be such that it is easily applied to the skin from a tube or by any applicator stick. It is contemplated that the electrode material be applied on top of an exposed end of a flexible wire lead and to the adjacent skin, where it will dry in a short period of time forming a firm mechanical bond between the skin and the wire lead. As an example, we have found collodion, with carbon particles suspended therein to provide an effective electrode. Collodion is available in "flexible" and "nonflexible" grades. When the term collodion is used herein, we mean the "flexible" grade. The solvent in the collodion quickly evaporates on exposure to air. Other liquid substances which are nontoxic to human tissues yet which upon drying adhere firmly to human skin may also be employed in place of collodion and conductive particles of materials other than carbon may be used as will be dealt with more fully hereafter.

Another object herein is to provide an improved wire lead terminus structure which is especially useful in connection with our inventive electrode material.

How these and many other objects are to be achieved by employment of the present invention will become clear through a consideration of the accompanying drawings wherein:

FIG. 1 is a top view of our novel wire lead terminus structure;

FIG. 2 is a sectional view taken at 2-2 in FIG. 1;

FIG. 3 depicts a wire lead between a receiving and recording device for electrical signals, and the body of a patient when the embodiment of FIG. 2 is employed; and

FIG. 4 is a top view of a second embodiment of our novel wire lead terminus structure;

FIG. 5 is a section at 5-5 of FIG. 4;

FIG. 6 depicts a wire lead in place upon the skin of a patient as it may appear after the second embodiment of our novel wire lead terminus as shown in FIGS. 4 and 5 has been employed.

In the drawings the symbol "P" represents any standard potentiometric device used in medical diagnosis such as an EKG. or ECG. machine. Interconnection between machine P and the body of a patient, 10, is made by means of wire lead 11. A terminal structure for such a wire lead 11 which we provide is shown in FIGS. 1 and 2 which show such a terminal structure prior to application to the skin of the patient.

Wire lead 11 is sandwiched between two layers of tape 12 and 13 by means of an adhesive layer 14. Adhesive layer 15 is also provided at the under surface of bottom tape 13. So that the tackiness of adhesive 15 will be maintained until it is desired to attach the end of the wire lead to the body of a patient, nontacky protective strips 16 and 17 are placed upon adhesive layer 15. Flaps 20 and 21 are integral parts of protective strips 16 and 17 respectively and provide finger grips whereby the protective strips 16 and 17 may readily be removed when desired. An aperture 22 through tapes 12 and 13 is provided, and a portion 23 of wire lead 11 crosses such aperture.

An electrode 24, in accordance with our present invention, is provided to make contact between the skin of a patient and the terminus of a wire lead 11, and thus the measuring device P. The procedure for connecting patient and measuring device is first for the operator to grasp flaps 20 and 21 and by manipulating such flaps, pull away protective strips 16 and 17, thus exposing adhesive 15 at the bottom of tape 13. The terminus of wire lead 11 is then brought into close proximity with the body of the patient by placing the sandwich consisting of tapes 12 and 13 against the patient's body, and then assuring that the wire leads terminus remains in position by pressing the sandwich against the patient's body whereupon adhesive 15 will hold the wire lead terminus close to the body. Dependable electrical contact, of course, between the patient's skin and wire lead terminus is not thus made. To make such electrical contact viscous liquid electrode material is disposed over the sandwich consisting of tapes 12 and 13, and particularly in aperture 22, there reaching the skin of the patient and also engulfing portion 23 of wire lead 11. The solvent in the conductive electrode material will quickly evaporate, electrode 24 will result, and thereupon connection between measuring device P and patient is achieved, which connection will serve to provide accurate measurements of electrical voltages for extended periods of time. For long-term use, it is desirable that the wire lead be taped to the body of the patient at point 25 located between electrode 24 and device P (preferably near electrode 24) to prevent unnecessary tension thereon.

The liquid electrode material which we provide essentially comprises two constituents, a liquid component and particles of an electrical conductor suspended therein, the constituents being combined by mixing them together. A variety of liquid components may be used and different electrical conductor particles may also be used. The electrode material should be nontoxic, relatively quick drying, flexible when dry, and preferably of the viscosity of a thick free-flowing syrup. We have found the following to be suitable liquid components, and each will be seen to consist of a polymeric adhesive in a highly volatile solvent:

1, Collodion (A viscous solution of pyroxylin in a mixture of alcohol and ether).

2. Vinyl chloride and acetone (vinyl chloride 30 percent by weight).

3. Vinyl chloride and methyl ethyl ketone (vinyl chloride 30 percent by weight).

4. Natural rubber and hexane (natural rubber 35 percent by weight). The criteria for the electrical conductor employed is that it be available in comminuted form, that it be a good electrical conductor, that it be nontoxic, and that it not be unduly susceptible to polarization. The following are specific examples of suitable conductors:

1. Carbon

2. Nickel

3. German silver

4. Gold

5. Silver

6. Platinum

The electrode material should contain approximately 40-70 percent by weight conductor, with the balance being liquid adhesive.

Examples of electrodes embodying our invention which have been used and which gave consistently accurate reading over a period of five days, and from which patients suffered no toxic effects are:

Example 1. Adhesive: Collodion. Conductor: Carbon. Carbon 45 percent by weight in the mixture.

Example 2. Adhesive: Vinyl chloride and acetone (vinyl chloride 30 percent by weight). Conductor: Carbon. Carbon 53 percent by weight in the mixture.

Example 3. Adhesive: Collodion. Conductor: German silver. German silver 57 percent by weight in the mixture.

Example 4. Adhesive: Natural rubber and hexane (natural rubber 35 percent by weight). Conductor: Nickel. Nickel 50 percent by weight in the mixture.

While we have shown the use of a sandwich made up of top tape 12 and bottom tape 13 which it is contemplated will remain in place upon the skin of the patient during the measurement period, it is also possible that a single apertured tape could be employed and such tape removed after liquid electrode material had been applied and had dried. Such an embodiment is illustrated in FIGS. 4-5.

The second embodiment of our novel wire lead terminus structure has wire lead 27 which, it will be understood, is connected to a medical diagnostic potentiometric device, the portion of wire lead 27 crossing aperture 28 in tape 29 being designated 30. The terminal portion of wire lead 27 is held to the underside of tape 29 by adhesive layer 31. Protective strips 32 and 33 with flap portions 34 and 35 respectively overlay adhesive layer 31 to maintain tackiness until used. When the second embodiment in FIG. 4 is employed, protective strips 32 and 33 are first peeled away by grasping finger-grip portions 34 and 35 and pulling. Tape 29 is then placed against the body 10 of a patient, holding lead portion 30 against the skin. Our inventive liquid electrode material 36 is then applied at the aperture 28 in tape 29. When said material dries the liquid electrode tape 29 may be stripped away leaving an electrical connective condition as illustrated in FIG. 6.

In addition, of course, the end of a wire lead could be applied to the skin of a patient and maintained there solely by use of the electrode resulting upon unemployment of our novel electrode material. Thus, it is apparent that while we have shown specific embodiments of our invention, changes and modifications may be made therein without departing from the spirit thereof, and though so changed or modified the material and method of using it may still fall within the ambit of our invention.

Claims

We claim:

1. A liquid electrode material for use with medical diagnostic potentiometric devices having a wire lead extending therefrom, said electrode material consisting essentially of collodion and a comminuted, electrical conductor selected from the group consisting of carbon, nickel, German silver, gold, silver and platinum.

2. A liquid electrode material as claimed in claim 1 wherein said electrode material contains approximately 4040-70 percent by weight electrical conductor.

3. A liquid electrode material for use with medical diagnostic potentiometric devices having a wire lead extending therefrom, said electrode material consisting essentially of collodion and comminuted carbon.