Clasp Structure for Biomedical Electrodes

This invention relates to improved electrical clasp structures for transferring biomedical electrical signals.

This invention is concerned with a biomedical clasp structure and especially, although not exclusively, with one capable of universal use, i.e., use with both kinds of external skin contacting electrode sensors (tab and snap types) now in use for substantially interference-free transfer of body or cardiovascular (CV) signals to electrocardiographic equipment for making ECG measurements, producing displays or for providing electrical stimulation to the body of a patient.

Disposable external electrode sensors for ECG readings are placed in contact with a patient at selected locations about the torso and limbs. These sensors are held adhesively to the skin surface and include a conductive gel or membrane that chemically reduces the resistance presented by the skin and thereby promotes the transmission of CV electrical impulses from the body of the patient via the electrodes to the associated detecting means. Two types of external disposable electrode sensors are in general use. The selection of either type is dependent on measuring conditions. One type used with the patient in a prone position for short-term measurements is a thin sheet form of electrode with an exposed planar tab for transferring sensed electrical signals. An alligator clip with jagged-edge gripping means has typically been used on an exposed planar contact tab. Another type of electrode generally used for longer-term measurements, for example, when the patient is exercising and/or being monitored for prolonged time periods, has a central metallic contact such as a male lug or nut.

As seen in FIG. 3 of U.S. Pat. No. 4,640,563 to LeBlanc, a prior art alligator clip includes jagged edge jaws at its working end and a handle for opening the jaws. As a part of the prior art connector structure, a lead wire is electrically connected by solder to one arm of the alligator clip. At the opposite longitudinal end of the lead wire, a female receptacle is provided for receiving a male member for electrical connection to the measuring equipment.

However, such an alligator clip has certain disadvantages and, in particular, cannot provide desired electrical contact and stability with a snap style contact stud. Because of the differing types of sensors and connectors, delays have occurred due to inferior and/or loose connections resulting in much frustration for the EKG operator since such connections can ruin the recording and prevent the machine from properly performing the test. Thus, it would require repeat tests and manual resecuring of prior art connections to the patient.

Because of the exposed lead wire, and other aspects of prior connectors, they could not be sterilized for use in a sterile environment, had short-term life expectancy in non-sterile environments and, in general, did not provide optimum recovery of the low-energy-level patient signals available.

The present invention overcomes these problems and disadvantages by providing a single type of electrical clasp structure for obtaining accurate ECG measurements from the planar tab type electrode structures used for sensing patient signals, and allows for easy and rapid connection of a male connector leading to an electrical measuring and indicating device.

U.S. Pat. No. 4,061,408 describes a connector having an L-shaped lever arm. In the development of the present invention, it was found that such a lever is often awkward to use and is therefore not fully acceptable from a human engineering standpoint. In developing the present invention, it was noticed that the direction of lever rotation in U.S. Pat. No. 4,061,408 opposes the natural motion of the clasp itself as it is attached and later disconnected from the electrode. In addition, the patented clasp is only suited for the tab type of planar electrode. One important objective of the present invention is to overcome these deficiencies.

In contrast to the prior art, the present invention is well adapted for use with both the planar tab-type external electrode and the snap-type electrode in any type of patient monitoring or stimulation environment. It also provides a streamlined configuration. The structure can also be usefully employed, as well, in any so-called tab TENS (muscle stimulating electrode) environment and with other stimulation electrodes.

In order to establish electrical contact with a biomedical electrode, a preferred embodiment of the invention provides a clasp structure with a pair of jaws and a lever for closing the jaws when the lever is moved toward the end of the clasp where the jaws are located. Optionally, the clasp has a stud-receiving opening in which the stud of an electrode is held when the lever is moved to an operative position.

The invention will be better understood by reference to the figures and detailed description which illustrate by way of example a few of the various forms of the invention within the scope of the claims.

FIG. 1 is a perspective view of the new clasp just before the jaws are closed on a planar tab-type of external electrode which has been in general use;

FIG. 2 is a view similar to FIG. 1 with the clasp jaws in the closed position;

FIG. 3 is a vertical, longitudinal sectional view of a preferred embodiment of the present invention (substantially enlarged) with the jaws positioned in the non-operative open mode;

FIG. 4 is a vertical, longitudinal sectional view of the embodiment of FIG. 3, with the clasp in the operative mode, i.e., closed;

FIG. 5 is a top plan view of the clasp structure of FIG. 4 when in the operative mode;

FIG. 6 is a plan view of the bottom portion of the clasp with the spring and lead wire installed;

FIG. 7 is a bottom view of the invention;

FIG. 7A is a bottom view of an opening in the bottom of the clasp as it appears when a stud of the snap-type electrode is inserted therein;

FIG. 8 is a vertical cross-sectional view taken on line 8--8 of FIG. 3;

FIG. 9 is a vertical cross-sectional view taken on line 9--9 of FIG. 3;

FIG. 10 is a plan view of the spring;

FIG. 11 is a left-end view of the spring;

FIG. 12 is a vertical cross-sectional view of the spring taken on line 12--12 of FIG. 10;

FIG. 13 is a right-end elevational view of the spring; and

FIG. 14 is a bottom view of the spring.

In FIG. 1 a flexible, planar tab-type biomedical electrode sensor 12 is shown by way of example as a thin sheet of plastic 13 with a plated electrically conductive silver layer 14. The conductive layer 14 has a signal-sensing portion 12a and a signal transfer tab 16. On the lower surface of silver layer 14 is an electrically conductive hydrogel layer 15 which bonds to the skin of the patient and forms electrical contact therewith. The laterally extending signal transfer tab 16 is accessible for transfer of electrical signals sensed by the gel portion 15 which is in contact with the skin of the patient.

In the side and top views of the clasp connector of the present invention (FIGS. 4 and 5), a typical planar electrode 12 is shown with the signal transfer tab portion 16 in locking engagement with the present clasp structure indicated generally at 20a.

In FIGS. 1 and 3, an enlarged view of the clasp 20 is depicted in the non-operative mode, i.e., the clasp jaw opening 20a is not in clamping electrical contact with electrode 12. The clasp body 20 has a front or jaw end at the right and a rear end at the left as shown in the figures. Clasp 20 includes a flat leaf spring 30 with a pair of elongated arms 23 and 24 which serve as jaws, with aligned clasp surfaces presenting integral electrical contact surfaces 32, 33 confronting each other. The contact surfaces 32, 33 are normally biased by the elasticity of spring 30 in an open spaced apart relationship as shown.

When the clip arms or jaws 23, 24 are biased in a spaced-apart posture, they will admit the insertion of the tab 16 of a biomedical electrode like 12 of FIG. 1. If desired, the inner electrical contact surfaces 32, 33 can be serrated for good electrical contact and mechanical gripping of inserted electrodes. Most preferably, the upper contact surface 32 is provided with a pair of laterally spaced, downwardly and inwardly projecting teeth or barbs 31 (FIGS. 3, 10 and 12-14) formed by making a V-shaped cut in the spring 30 for more reliably gripping the signal transfer tab 16.

The inner contact surfaces 32, 33 of the jaw portions of the clip arms 23, 24 are configured to grasp the signal transfer tab 16. This is accomplished by forcing the contact surfaces 32, 33 toward one another to provide a firm grip on the tab 16 of electrode 12.

Spring 30 is metallic for conductive purposes, preferably being of plated, annealed spring steel (1050.degree. grade, heat treated to Rockwell 45 hardness) or stainless steel and is completely sterilizable upon disconnection from the electrode 12 between uses. The spring 30 has a gauge of 0.012".+-.0.00075" and is plated first with copper and then with laboratory grade nickel. As shown, the contact surfaces 32, 33 are well spaced apart until ready to clasp the electrode 12.

Affixed above the intermediate portion of upper clip arm 23 is a thumb-length jaw operating lever 40 which rotates forwardly on laterally extending aligned pivots 48 between a lever-up inoperative position (FIG. 3) and a lever-down operating position (FIG. 4) in line with the clasp body. In the latter position, the electrode 12 is gripped tightly between the contact surfaces 32, 33 of clip arms 23, 24. It should be noted that during the jaw closing operation, the free end 54 of lever 40 swings forwardly toward the jaw opening 20a. This permits it to be easily operated with the finger or thumb, tending to move the open clasp 20 toward engagement with the electrode 12 rather than away from it. This gives the clasp 20 superior closing characteristics from a human engineering standpoint.

The lower end 46 of lever 40 has a protrusion or cam 49 which engages the top of spring 30 (FIGS. 4 and 5). In the lever-up inoperative position of FIGS. 1 and 3, the protrusion 49 allows the contact surfaces 32, 33 of clip arms 23, 24 to be spaced apart. In the in-line or operating lever position, the cam 49 biases the upper portion 36 downwardly, clamping the contact surfaces 32, 33 of clip arms 23, 24 on the tab 16 as in FIG. 4.

When the clasp 20 is to be employed with electrodes already in place on a patient's body, and while the contact surfaces 32, 33 are still in the open posture, they are slipped over the electrode tab 16 and then closed with a finger or thumb by rotating lever 40 forwardly, i.e., toward free ends 27, 28 of the jaws and the electrode 12 itself, causing the protrusion 49 to compress the middle portion of spring 30 so as to move the upper arm 23 downwardly into locking closure on the electrode 12 (see FIG. 4). The electrode 12 is then secured against normal jostling or cable flexure, until the clasp 20 is purposefully released by prying lever 41 upwardly and rearwardly.

In a preferred embodiment (FIG. 3), the spring 30 is generally U-shaped and has a closed end 30a as seen at the left in FIGS. 3 and 4. The clasp 20 includes an upper body portion 25 and a lower body portion 26. During assembly, the spring 30 is dropped onto the clasp lower body portion 26 and after assembly its free ends 27, 28 rest snugly against adjacent clasp inner pocket 26a (FIGS. 1 and 6). The closed portion, i.e., the left end 30a of the spring 30 is also provided with a centrally-positioned, rearwardly extending, rigid, trough-shaped, electrically conductive lug 58. An electrical lead 78 has its inner end contacting the surface of the lug 58 and is preferably soldered to it.

The upper and lower portions 25 and 26 of the clasp 20 are of a molded material, preferably plastic resin which has electrical insulating properties, typically of nylon or polycarbonate plastic which is completely sterilizable. The upper portion 25 has a forwardly facing, upwardly opening, central cavity 25a to receive the lever 40 (FIG. 5). The lower portion 26 has an upwardly facing recess 26a aligned beneath it to receive the spring 30. On either side of the spring 30 are upwardly extending lever supporting posts 68, 70 which have laterally aligned central openings 68a, 70a to receive the pivots 48 of the lever 40 (FIG. 8). During assembly, the lever 40 is mounted by forcing the upper ends of the supporting posts 68, 70 apart slightly and then allowing them to snap back toward one another to enclose the pivots 48 of lever 40. The upper portion 25 of the clasp 20 is then forced downwardly onto the lower portion 26, causing the tops of the posts 68, 70 to enter openings 25c and 25d (FIG. 5) as a peripheral snap connection 29 (FIGS. 5, 8 and 9) locks the upper and lower portions 25, 26 together. The posts 68, 70 are then held permanently in the openings 25c, 25d which act as retaining means so that they can no longer be spread apart. The lever 40 will, therefore, resist being dislodged by a force many times the force required to separate snap connection 29. When the lever 40 is pivoted forwardly, the posts 68, 70 hold it securely in place. It is not the snap connection 29 which holds it since the entire load exerted by the lever 40 is carried by the posts 68, 70. This feature of the invention provided by the advantage of having the load carried by posts 68, 70 makes it possible to assemble the invention without the necessity of welds which reduces manufacturing costs. The posts 68, 70 will, in fact, hold a force applied to the lever 40 that is twenty times that which is needed to open the clasp 20 at the snap connection 29.

An insulating sleeve 79 surrounds an insulated electrically conductive cable or lead 78 which is also connected at its distal end to a meter or other measuring means or source of current for stimulation (not shown). The lead 78, 79 is shown passing through a central opening 61 in the clasp 20 (FIGS. 6, 8 and 9). The vertical sectional views of FIGS. 8 and 9 show the clasp body 20 provided with a discrete U-shaped internal channel 61 therethrough, in which the inner terminal length of lead 78 rests. The lead 78, 79 is held in a serpentine passage between staggered pins including two upper retaining pins 76 and two lower retaining pins 74. The pins 74, 76 act as a maze which serves as a strain relief function and are fabricated as a part of the upper and lower portions 25, 26 of the clasp 20.

The operative mode of the clasp 20 is depicted in FIGS. 2 and 4, in which a planar signal transfer tab 16 (FIG. 1) is firmly gripped between the contact surfaces 32, 33 of clip arms 23, 24. Lever 40 has been rotated forwardly to be in line with the longitudinal dimension of clasp 20, causing cam 49 to rotate clockwise as seen in FIG. 4 and bias downwardly the upper arm 36 of spring 30 to hold the jaws in clamping position.

The free length of lead 78, 79 is retained in operative contact by the crimping of retaining pins 74, 76 in the channel 61 and conductor 78 is soldered to lug 58 (FIG. 3).

To assemble the clasp 20, the conductor 78 is first soldered to lug 58. The lead 78, 79 is then threaded through channel 61 between the pins 74, 76. Lever 40 is then snapped into place on the posts 68, 70. The upper and lower outer insulator casing portions 25, 26 are then snapped together at 29 and the assembled clasp 20 with its coupled cable 78, 79 is ready for use.

In FIG. 5 is shown a top plan view of the clasp 20 with the lever 40 in the operating mode. In this mode the lever 40 is thrown forwardly into the upwardly opening cavity 25a which receives the free end 54 of the lever 40, providing a clasp that is free of projections and has a smoothly contoured surface. Extending laterally across the open end of the cavity 25a is a lever support bar 25e.

The feature of the invention used for holding a snap-type electrode will now be described in connection with FIGS. 4 and 7.

Near the center of the bottom portion 26 of the clasp 20 is an oblong opening 26h which is slightly larger at its forward end as shown in FIG. 7. Around the opening 26h is an upwardly and centrally tapered surface 26h'. Aligned above it is a similarly shaped opening 30h in the lower arm 24 of the spring 30. The spring 30 is also provided with two pairs of openings 30l and 30L' in the lower arm 24. The openings 30l are placed over aligned locating pins that project upwardly from the lower surface of the lower portion 26 of the clasp 20 for holding the spring 30 in place. The openings 30L' receive the barbs 31 when the jaws 20a are closed. The forward portion of the opening 26h and the forward portion of the opening 30h of the spring 30 are large enough to accommodate the stud 17a of a snap-type electrode 18 shown in FIG. 4. When the stud 17a is introduced into the forward enlarged end of the opening 30h in the spring 30 through opening 26h, it can do so because the opening is large enough at its forward end to accommodate the stud 17a. However, when the lever 40 is thrown forwardly and downwardly to the operating position, a keel 40k provided as an integral part of the lever 40 exerts a rearward force on a downwardly projecting tab or finger 30T which extends downwardly from the upper spring arm 23, causing tab 30T to be deflected rearwardly so as to shift the lug or stud 17a of the snap-type electrode 18 rearwardly in the oblong opening 30h, thereby locking it in place. The stud 17a is shown shifted rearwardly to its locked position at 17a' in the opening 30h in FIG. 7A. It will be noticed that the upper end of the stud 17a is slightly enlarged. This enlargement will prevent the stud 17a from being withdrawn once the locking tab 30T is deflected rearwardly by the downward pressure applied by the keel 40k (FIG. 4). The tab or finger 30T also acts as a means for establishing electrical contact with the stud 17a.

Because the clasp of the present invention will handle both a tab-type electrode (FIG. 1) or a snap-type electrode as shown in FIG. 4, the clasp of the present invention can be considered a universal clasp, i.e., it will handle both types of biomedical electrodes now in use. It is therefore is much more convenient and provides an additional safety factor since it is ready for use with either type of electrode now employed in hospitals and clinics.

The present invention is also adapted for use and reuse in a sterile environment. The clasp 20 can be repeatedly sterilized in a steam autoclave. The capability of sterilizing the entire clasp structure in a steam autoclave is an advantage which was not available with certain prior art structures because of the lead wire construction.

In practice, the spring 30 can be fabricated from low carbon, cold-rolled steel having a nominal thickness of about 0.012". The entire structure is coated by medical-grade plating with nickel, so that no portion of the clasp is subject to rusting. Preferably an initial copper flash coating is applied, followed by a coating of laboratory grade nickel. In the alternative, stainless steel is used with no plating. A typical embodiment has an overall length of about 3.5 cm and a height of about 0.7 cm. The length of lever 40 is about 1.2 cm.

The forward movement of the lever 40 toward the jaw-end of the clasp 20 at the right in FIGS. 1-4 provides a surprising improvement over the prior art since the movement of the finger or thumb in closing the jaws automatically pushes the clasp 20 in the correct direction to move the jaws onto the tab 16 or, in the case of a snap, to move the lug 17 toward the back of the opening 26h. It was discovered that this provides a surprising advantage from a human engineering standpoint. It should also be noticed that the reverse movement of the lever 40 has the same effect with the clasp 20 is being disconnected from the electrode. That is to say, the lever action helps to move the clasp 20 away from the electrode 12. This is particularly important since the opening and closing of the clasp 20 is carried out with one hand as one hand holds the clasp with the lead wire 78, 79 extending away from the clasp 20 in a line parallel with a person's arm. Since everything is accomplished with one hand, human engineering advantages of the invention are particularly significant and beneficial.

Many variations of the present invention within the scope of the appended claims will be apparent to those skilled in the art once the principles described herein are understood.