US3505993A - Electrocardiograph electrodes with surface convexities - Google Patents

Description

April 14, 1970 D. s. LEWES ET AL 3,505,993

ELECTROCARDIOGRAPH ELECTRODES WITH SURFACE CONVEXITIES Filed Dec. 17, 1965 FIG. 7.

o o o 0 5 61- o 0 0 o o F162. 3 2 7 OZ United States Patent US. Cl. 128.-2.06 3 Claims ABSTRACT OF THE DISCLOSURE An electrocardiograph electrode having a form such that skin preparation prior to application of the electrode can be dispensed with in most cases. The electrode comprises :a rigid metal sheet applied to the skin and making with it a multiplicity of small area contacts by means of points or edges which are distributed uniformly over the area of application and which press into the skin without penetrating 'beyond the epidermis.

This invention relates to electrodes for making electrical contact to the living body of a person, and is particularly concerned with electrodes for use in electrocardiography.

In electrocardiography the condition of the heart of a human subject (or of an animal in Veterinary practice) 'is investigated by making recordings of electrical signals generated in the body of the subject as a result of the heart beat. In order to pick up the electrical signals it is necessary to make satisfactory electrical contacts with the body surface at appropriate locations, and forthis purpose it is the normal practice to use skin contact electrodes. Such an electrode comprises a metallic member, so shaped that it may be brought into contact over an appreciable and appropriate skin area, and which is provided with a terminal for making connection to a lead extending from the recording instrument; hitherto such electrodes have been provided with smooth contact surfaces, and in some cases the contact surf ce is covered with a cloth impregnated with saline solution or alcohol. Two types of electrode are in normal use, one having a fiat or concave contact surface suitable for application to the limbs and the other having a flat contact surface or a circular contact ring in the form of a hollow metal cone suitable for application to the chest; in use the limb electrode is maintained in position by a perforated rubber band or nylon-grip cloth encircling the limb and passing over or attached to the electrode, or by a spring clip attachment, while the chest electrode is maintained in position by a suction device or by a rubber band encircling the chest.

When using conventional skin contact electrodes with modern electrocardiographs it is necessary, if satisfactory recordings are to be obtained Without appreciable delay after the applictaion of the electrodes, to carry out preliminary skin preparation at the relevant locations in order to reduce the natural skin resistance; for this purpose it is still common practice to use a substance known as electrode jelly, which contains both an electrolyte (usually in high concentration) and a finely divided abrasive. The use of electrode jelly is time-consuming and inconvenient, and could in fact cause fatal delay in certain cardiac emergencies (for example in clinical arrest of the heart from coronary thrombosis, where the time factor is vital and an electrocardiogram is essential to decide upon appropriate treatment). Further disadvantages of the use of electrode jelly are that it is costly, it may be aesthetically repugnant from the point of view of a subject, and it eventually results in some degree of corrosion of the metallic electrodes and apparatus and leads to premature deterioration of associated rubber bands due to the necessary frequent cleansing.

It is therefore an object of the present invention to provide electrodes having a form such that the need for preliminary skin preparation can be avoided in most cases.

In its broadest aspect the present invention provides an electrocardiograph electrode, comprising a metallic structure provided with a terminal for making connection to a lead and shaped so that it may be applied to the skin of the body over an appreciable area, the metallic structure having a multiplicity of convexities disposed and shaped so that when the structure is appropriately applied to the skin and held firmly in contact the convexities will press into the skin without penetrating beyond the epidermis.

In one form of electrode according to the invention, the convexities are constituted by small pointed projections distributed over the surface area which is to be applied to the skin. It has been found that by using electrodes of this form it is possible in most cases (including those in whom the limbs are hairy or the skin is unnaturally dry) to obtain satisfactory electrocardiograms without appreciable delay after the application of the electrodes and without any preliminary skin preparation. Such electrocardiograms are strictly comparable with those obtained in the same subject using conventional electrodes and electrode jelly. Controlled observations on which the invention is based have been carried out primarily with electrocardiographs having high input impedances (of the order of several megohms) but it has been shown by controlled experiment that lim-b electrodes provided with small pointed projections could equally well be used with recording instruments of lower input impedance, including the string galvanometer of relatively very low impedance (2,0003,000 ohms). It would appear that the efiicacy of the pointed projections results from their penetrating through the superficial insulating layer of the skin (the stratum corneum) which contributes the major part of the natural skin resistance, thereby making intimate contact at a number of points with the underlying layer of the epidermis. It will of course be appreciated that the form and distribution of the projections should be such that the penetration of the skin is insuflicient to cause any substantial discomfort or injury to the subject when the electrode is applied. An arrangement utilising projections of length 1.5 mm. distributed 36 to each square cm. of the contact area has been found suitable, provided that care is taken not to apply the electrode in the region of a superficial -bony prominence; it is not thought that these figures are particularly critical. Firm but uniform pressure of the electrode upon the skin surface is important for ensuring intimate skin contact.

In an alternative form of electrode according to the invention the convexities are constituted by the edges of small holes distributed over the surface area which is to be applied to the skin, means being provided for applying suction to the skin via the holes. In this case it would appear that there is no complete penetration of the stratum corneum, but the drawing of the skin surface into the holes as a result of the suction causes the skin to be stretched around the edges of the holes so that at these edges the stratum corneum is appreciably thinned, with a consequent improvement in electrical contact with the epidermis. The holes may suitably be of circular form with a diameter of the order of one mm., and may be distributed about 25 to each square cm. of the contact area.

Various illustrative embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a side view of an electrode suitable for application to a human limb;

FIGURE 2 is an underneath plan view of the electrode in FIGURE 1;

FIGURE 3 is a sectional view of one form of electrode suitable for applictaion to the human chest; and

FIGURE 4 is a sectional view of a second form of electrode suitable for application to the human chest.

The electrode shown in FIGURES 1 and 2 comprises a stainless steel sheet 1 which is curved to have the form of a portion of a cylinder and which has formed integral with it an outwardly projecting tongue 2 whose free end is curled round so as to constitute a socket suitable for receiving a plug (not shown) attached to an electrocardiograph lead. The sheet 1 is of similar form to a conventional limb electrode and may suitably have a radius of curvature of 4 cms., and a surface area for each main face of 30 square cms. To the concave face of the sheet 1 is secured (for example, by soldering, welding or rivetting) a thin metal sheet 3 which is bent to conform to the curvature of the sheet 1 and which has been perforated by a series of uniformly distributed holes so formed as to leave a small number of triangular teeth 4 projecting from the periphery of each hole in a direction perpendicular to the surface of the sheet 3, the sheet 3 being secured to the sheet 1 so that the teeth 4 project on the side of the sheet 3 remote from the sheet 1. Suitable materials for the sheet 3 are tin-plated soft iron and the alloy known as German silver and a suitable arrangement for the holes is to have nine holes per square cm., each hole having a diameter of two mms. and providing four teeth which project 1.5 mm. from the general surface of the sheet 3.

In use the electrode is applied to a fleshy part of the forearm or lower leg so that the teeth 4 press into the skin, the electrode being held firmly in position by a rubber band (not shown) encircling the limb and passing over the electrode, the band being provided with slots which engage with the tongue 2.

Turning now to FIGURE 3, the electrode shown therein comprises a metal disc 5 to one main face of which is secured a circular metal sheet 6 which has been perforated in a similar manner to the sheet 3 to provide teeth 7 projecting from the sheet 6 on the opposite side to the disc 5. The sheet 6 may suitably have a diameter of 2.5 cms., and from the point of view of efliciency in overcoming natural skin resistance it may be desirable to provide a somewhat larger number of teeth per unit area in this case than is the case for the sheet 3, it being relevant in this connection that the skin contact area must necessarily be confined in chest lead electrocardiography (in contrast to limb lead electrocardiography in which the skin contact area is relatively unimportant). The disc 5 is formed integral with a hollow boss 8 which projects from the main face of the disc 5 opposite the sheet 6, the boss 8 being internally threaded and screwing on to a threaded portion of a terminal post 9 in which is formed a circular hole 10 adapted to receive a plug (not shown).

The terminal post 9 extends perpendicularly through the base of a circular cylindrical cup 11 of insulating material so that the disc 5 and sheet 6 are disposed within the cup 11 with the points of the teeth 7 slightly recessed with respect to the rim of the cup 11, the terminal post 9 being secured in position with a nut 12. The cup 11 has a side tube 13 which is connected by flexible tubing 14- to a conventional exhausting bulb 15.

In use of the electrode, the cup 11 is applied so that the whole of its rim is in contact with the chest, and suction is applied to the interior of the cup 11 by operating the bulb 15 so that the cup 11 is firmly held in place and the skin is drawn into contact with the points of the teeth 7. Slight complication may arise where the electrode is applied to a subject who is particularly hirsute or has a particularly dry skin, since in these cases it may be difficult to obtain adequate suction to maintain the electrode firmly in contact with the skin; the difliculty may be overcome in the first case either by applying to the skin an inocuous abrasive-free lubricating jelly of low electrolyte content or by shaving the relevant parts of the chest, and in the second case by moistening the skin with a damp sponge.

Turning now to FIGURE 4, the electrode shown therein comprises a cylindrical metal chamber 16 constituted by a cup 17 and a cover plate 18 secured to the cup 17, the plate 18 being provided with a tag 19 to which is soldered one end of an insulated lead 20 whose other end is connected to a terminal 21 providing a socket adapted to receive a plug (not shown). The base of the cup 17 is perforated cleanly with a regular array of small holes 22, and is provided with a projecting circular rim 23 which surrounds the perforated area. The cup 16 may suitably have an external diameter of about 3.5 cms., the base of the cup 17 having a thickness of one mm. and being perforated with circular holes of diameter one mm. distributed 25 per square cm. over a central circular area of diameter 2.5 cms.; the material of the cup 17 may again suitably be tin-plated soft iron or German silver. The plate 18 is provided with a tube 24 connected by flexible tubing 25 to an exhausting bulb 26.

In use the electrode is applied so that the whole of the rim 23 is in contact with the chest, and suction is then applied to the interior of the chamber 16 by operating the bulb 26 so that the electrode is held in position and the skin is drawn into contact with the exterior of the base of the cup 17 and partially into the holes 22. In some cases, particularly with hirsute subjects, it may be desirable to provide auxiliary means to assist in producing the necessary suction to hold the electrode firmly in position. This auxiliary means may take the form of an annular sheet of flexible material (not shown) whose inner part is secured to the electrode, for example being clamped between the cup 17 and the plate 18, and whose outer part bears against the chest around the electrode.

It will of course be appreciated that many alternative embodiments of the invention are possible. For example an electrode similar in form to the one shown in FIG- URES l and 2 could be provided with a spring clip device for maintaining it in position. Further, electrodes comprising a perforated sheet-like member similar to the base of the cup 17 in the electrode shown in FIG- URE 4 may have the contact surface curved instead of flat, and may be arranged to be maintained in position by means other than the suction device provided for drawing the skin into the holes.

We claim:

1, An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for making connection to a lead and incorporating a rigid sheetlike member shaped so that it may be applied to the skin of a subject over an appreciable area,

said member being formed so as to present to the skin a multipuicity of similar small convexities distributed in a substantially uniform pattern over the area applied to the skin,

the said convexities being disposed and shaped so that when said member is appropriately applied to the skin and held firmly in contact the convexities will press into the skin without penetrating beyond the epidermis,

said convexities being constituted by the edges af small holes formed in the sheet-like member, and

means being provided for applying suction to the skin via the holes.

2. An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for male ing connection to a lead and incorporating a rigid sheet-like member shaped so that it may be applied to the skin of a subject over an appreciable area,

said member being formed so as to present to the skin a multiplicity of similar small convexities distributed in a substantially uniform pattern over the area applied to the skin wherein the convexities are constituted by small pointed projections in the form of triangular teeth formed by perforating the sheet-like member and extending outwardly from one main face of the sheet-like member,

the said convexities being disposed and shaped so that when said member is appropriately applied to the skin and held firmly in contact the convexities will press into the skin without penetrating beyond the epidermis.

3. An electrocardiograph electrode comprising:

a metallic structure provided with a terminal for making connections to a lead and incorporating a rigid sheet-like member shaped so that it may be applied to the skin of the subject over an appreciable area,

said member being formed so as to present to the skin a multiplicity of similar small convexities distributed in a substantially uniform pattern over the area applied to the skin wherein the convexities are constituted by the edges of small holes formed in the sheetlike member,

the said convexities being disposed and shaped so that when said member is appropriately applied to the skin and held firmly in contact the convexities will press into the skin Without penetrating beyond the epidermis,

means being provided for applying suction to the skin via the holes, and

said metallic structure including a chamber to which suction may be applied, the chamber having a perforated Wall which constitutes said sheet-like member.

References Cited UNITED STATES PATENTS 872,688 1'2/ 1970 Saighrnan 128-417 X 1,889,271 11/1932 Zevne 128-416 1,935,138 11/1933 Windisch 128-418 X 2,580,628 1/ 1952 Welsh 128-404 2,660,175 11/1953 Thrasher et a1. 128-404 3,067,749 12/1962 Walters 128-418 3,295,515 l/1967 Kahn 128-206 WILLIAM E. KAMM, Primary Examiner

Images