TECHNICAL FIELD

This application relates to the construction of "hands-free" defibrillation electrodes.

BACKGROUND

External defibrillators frequently include a pair of "hands-free" disposable electrodes  which are essentially flexible pads that are adhered to the skin of a patient having a cardiac event (i.e.  used transcutaneously). By "hands-free " we mean electrodes of the type that are adhered to a patient  rather than paddles that are held by a rescuer during defibrillation. Hands-free disposable electrodes typically include a non-conductive backing layer  a conductive metal layer  formed from a thin sheet of metal (e.g. tin or silver) or a conductive ink (e.g. silver-chloride) printed on a substrate  and a liquid or solid electrically conductive gel covering the metal layer so that electrical current passes through the gel to the patient""s body. The area of contact between the gel and the patient""s body where current is delivered is referred to herein as the "treatment area". Because such electrodes use a thin sheet of metal  flexibility is limited and cracking results from repeated use. Wire mesh or expanded metal have been proposed as a solution to this problem  but wire mesh provides for extraneous "noise" in ECG monitoring and expanded metal is also prone to cracking. Metal cracking results in arcing or failure to deliver therapy as required. As a result such typical electrodes are not reusable  requiring purchase of electrodes after use and consequently  increased costs.

External defibrillators also routinely use paddle electrodes  such as disclosed in Scharnberg U.S. Patent No. 4 779 630. These paddle electrodes are not "hands-free". Typically  the rescuer applies a liquid gel to the metallic surface of the paddles  and presses the gelled surface against the chest of the patient during delivery of the defibrillation shock. Scharnberg also discloses an alternative construction in which disposable  gel-containing pads are secured to the metallic surface of the paddles. But the paddles with attached pads must still be held against the chest by the rescuer.

One important property of electrodes is that the material used in the metal layer depolarize quickly (within seconds) after a defibrillating pulse ("shock") is delivered to a patient. Otherwise  the electrode is not capable of sensing a signal that will allow the defibrillator to generate a clear ECG and determine whether another shock should be delivered within a short period of time.

US Patent Application Publication No. 2008/0221631  the disclosure of which is herein incorporated by reference  discloses that stainless steel  and other metals that polarize during a defibrillating pulse  can be used as the conductive metal layer in a defibrillating electrode  provided that the defibrillator with which the electrode is used is configured to deliver to the patient a defibrillation waveform that is capable of rapidly depolarizing the electrode. Stainless steel is an advantageous material for the conductive layer  as it is resistant to corrosion  thereby providing a long electrode shelf life. Stainless steel is also strong  and thus its use in the conductive layer reduces the likelihood that the electrode will be damaged by mishandling.

Such depolarizing waveforms include biphasic waveforms  e.g.  those which are discussed in detail in U.S. Patent No. 5 769 872  the disclosure of which is incorporated herein by reference. As disclosed in the earlier application  it is believed that the negative phase of a biphasic waveform reduces or eliminates the electrical charge  allowing the electrode to rapidly depolarize after the defibrillating pulse is delivered.

SUMMARY

In a first aspect  the invention features a reusable component of a hands-free defibrillation electrode  the reusable component comprising a flexible nonconductive element  and a flexible metallic element supported by the flexible nonconductive element  wherein the flexible metallic element comprises a plurality of substantially inflexible metallic elements interconnected by flexible metallic linking elements  and wherein the majority of the flexibility of the metallic element is provided by the flexible metallic linking elements  wherein the flexible metallic element has an exposed surface on one side of the reusable component and the exposed surface is configured to be adhered to a disposable coupling portion  and wherein the reusable component is configured to accept an electrical defibrillation pulse and spread the electrical pulse across the exposed surface area  from which it is delivered to the patient""s chest through the disposable coupling portion.

Preferred implementations of this aspect of the invention may incorporate one or more of the following. The reusable component may be combined with a flexible disposable coupling portion  wherein the flexible disposable coupling portion may comprise a conductive layer configured to be in electrical contact with the chest of the patient on one of its surfaces and in electrical contact with the exposed surface of the metallic element of the reusable component on the other of its surfaces. The reusable component and disposable portion may be configured to be stored as separate elements  and may be adhered together when used to defibrillate a patient. The reusable component and disposable portion when adhered together may form an electrode capable of being flexed simultaneously in more than one direction of curvature in order to conform to the shape of the patient""s chest. The flexible metallic linking elements may be narrower than the substantially inflexible metallic elements  and wherein the majority of the flexibility of the metallic element may be provided by flexure of the narrower flexible metallic linking elements. The substantially inflexible metallic elements and flexible metallic linking elements may be cut from the same sheet of metal. The flexible metallic element may be made from stainless steel. The flexible metallic element may be made from stainless steel. The flexible metallic element may be encapsulated by the flexible nonconductive element by molding the flexible nonconductive element around portions of the flexible metallic element. The flexible metallic element may be encapsulated by the flexible nonconductive element by molding the flexible nonconductive element around portions of the flexible metallic element. The flexible nonconductive element may comprise an elastomeric material. The conductive layer of the coupling portion may comprise a conductive viscous liquid. The conductive viscous liquid may comprise an electrolyte. The conductive layer of the coupling portion may comprise a solid conductive gel. The conductive layer may comprise hydrogel. The disposable coupling portion may include a first peripheral adhesive region configured to adhere to the periphery of the reusable component. The disposable coupling portion may include a second peripheral adhesive region on the surface opposite the surface carrying the first peripheral adhesive region  and the second peripheral adhesive region may be configured to adhere to the chest of the patient. The first and second peripheral adhesive regions may be generally peripherally outside of the area through which electrical current flows from the exposed surface of the reusable component through the conductive layer of the coupling portion to the chest of the patient. The conductive layer of the coupling portion may comprise a solid conductive gel with adhesive properties sufficient to adhere the coupling portion to the chest of the patient. The electrode may further comprise first and second release liners that  prior to assembly of the coupling portion to the reusable component  cover the first and second peripheral adhesive regions  respectively. The electrode may further comprise first and second release liners  and wherein  prior to assembly of the coupling portion to the reusable component  the first release liner may cover the first peripheral adhesive region and the second release liner may cover the solid conductive gel. The reusable component may be combined with a sensor that provides an output from which information about the depth of CPR chest compressions can be obtained. The sensor may comprise an accelerometer. The reusable component may be combined with a sensor tat provides an output from which information about the force applied to the chest during CPR chest compressions can be obtained. The reusable component may be combined with a sensor that provides an output from which information about the rate of CPR chest compressions can be obtained. The exposed surface of the metallic element may comprise exposed portions of each of the inflexible metallic elements. The metallic linking elements may be fully encapsulated within the nonconductive element so that the exposed surface comprises a plurality of exposed metallic areas separated by nonconductive areas. Each of the plurality of exposed metallic areas may project beyond the surface of the surrounding nonconductive element.

In other aspects of the invention  an electrode may comprise a composite structure  wherein the composite structure comprises a conductive metal component that is partially encapsulated in a non-conductive matrix. The electrode may further comprise a coupling layer. The non-conductive matrix may be flexible. The non-conductive matrix may be an elastomer. The non-conductive matrix may be selected from the group consisting of rubbers  silicone rubber  synthetic rubbers  polychloroprene  thermoplastic elastomers and thermoplastic vulcanizates. The conductive metal component may be comprised of a metal selected from the group consisting of stainless steel alloys  tin  silver  silver chloride  aluminum and copper.

Stainless steel alloys may be selected from the group consisting of 302  316 and 316L. The conductive metal component may be flexible. The conductive metal component may comprise an array of two or more plates connected to each other by bridges. The conductive metal component may comprise a three by three array of nine plates connected to each other by bridges. The plates may be substantially inflexible. The bridges may be flexible. The electrode may be a medical electrode. The portions of the conductive metal component that are not encapsulated by the non-conductive matrix may be on the surface of the electrode that faces a patient. The portions may be planar or circular or both. The portions may project beyond the surface of the non-conductive surface. The treatment area associated with the electrode may be at least 15 sq. cm. The combined treatment area of an apex electrode and a sternum electrode when used in combination may be at least 45 sq. cm. The treatment area associated with the electrode may be at least 50 sq. cm. The combined treatment area of an apex electrode and a sternum electrode when used in combination may be at least 150 sq. cm. The metal component may be connected to an external source of electrical current. The portions of the conductive metal component that are not encapsulated may be circular in shape. The conductive metal component may be comprised of a single stamped component. The coupling layer may be comprised of an electrolyte. The coupling layer may be comprised of a hydrogel. The composite structure may be reusable. The coupling layer may be disposable. The coupling layer may be releasably attached to the composite structure. The coupling layer may comprise a hydrogel that may be attached around its perimeter to an adhesive ring. The adhesive ring may be attached to the composite structure outside of the treatment area. The coupling layer may be configured to be adhered to the skin of a patient. The coupling layer may be packaged between two releasable liners prior to attachment to the composite structure. The electrode may be configured for one or more of defibrillation  electrical signal monitoring  ECG monitoring  cardiac pacing and cardioversion. The coupling layer may include an additional metallic layer in order to enable cardiac pacing. The portions of the conductive metal that are not encapsulated by the non-conductive matrix may be in a 3 by 3 array. The electrode may be attached to a sensor constructed to acquire data indicative of the depth and rate of CPR compressions. The sensor may be an accelerometer or one or more of feree and pressure monitors. The data may be processed by a defibrillator to provide CPR feedback.

In still other aspects of the invention  the electrode may have a reusable component. The reusable component may comprise a composite structure  wherein the composite structure comprises a conductive metal component that is partially encapsulated in a non-conductive matrix. The non-conductive matrix may be flexible. The non-conductive matrix may be an elastomer. The non-conductive matrix may be selected from the group consisting of rubbers  silicone rubber  synthetic rubbers  polychloroprene  thermoplastic elastomers and thermoplastic vulcanizates. The conductive metal component may be comprised of a metal selected from the group consisting of stainless steel alloys  tin  silver  silver chloride  aluminum and copper. Stainless steel alloys may be selected from the group consisting of 302  316 and 316L. The conductive metal component may be flexible. The conductive metal component may comprise an array of two or more plates connected to each other by bridges. The conductive metal component may comprise a three by three array of nine plates connected to each other by bridges. The plates may be substantially inflexible. The bridges may be flexible. The electrode may be a medical electrode. The portions of the conductive metal component that are not encapsulated by the non-conductive matrix may be on the surface of the electrode that faces a patient. The portions may be planar or circular or both. The portions may project beyond the surface of the non-conductive surface. The treatment area associated with the electrode may be at least 15 sq. cm. The combined treatment area of an apex electrode and a sternum electrode when used in combination may be at least 45 sq. cm. The treatment area associated with the electrode may be at least 50 sq. cm. The combined treatment area of an apex electrode and a sternum electrode when used in combination may be at least 150 sq. cm. The metal component may be connected to an external source of electrical current. The portions of the conductive metal component that are not encapsulated may be circular in shape. The conductive metal component may be comprised of a single stamped component. The reusable component may further be used with a disposable component which comprises a coupling layer. The coupling layer may be comprised of an electrolyte. The coupling layer may be comprised of a hydrogel. The coupling layer may be releasably attached to the composite structure. The coupling layer may comprise a hydrogel that may be attached around its perimeter to an adhesive ring. The adhesive ring may be attached to the composite structure outside of the treatment area. The coupling layer may be configured to be adhered to the skin of a patient. The coupling layer may be packaged between two releasable liners prior to attachment to the composite structure. The electrode may be configured for one or more of defibrillation  electrical signal monitoring  ECG monitoring  cardiac pacing and cardioversion. The coupling layer may include an additional metallic layer in order to enable cardiac pacing. The portions of the conductive metal that are not encapsulated by the non-conductive matrix may be in a 3 by 3 array. The electrode may be attached to a sensor constructed to acquire data indicative of the depth and rate of CPR compressions. The sensor may be an accelerometer or one or more of feree and pressure monitors. The data may be processed by a defibrillator to provide CPR feedback.

In another aspect of the invention  the electrode may be configured to be used as a "hands-free" electrode and to deliver a defibrillating pulse to the patient. In alternative implementations  electrodes are configured to also monitor electrical signals from the patient""s body  and to deliver a defibrillating pulse comprising a waveform configured to substantially depolarize the metal. By "substantially depolarize " we mean that polarization is eliminated  or reduced sufficiently so that a clear ECG can be read by the defibrillator.

Other features and advantages of the invention will be found in the detailed description  drawings  and claims.

BRIEF DESCRIPTION OF DRAWINGS

Figs. 1A-1E are front  back and side views of a composite electrode structure in accordance with one implementation of the invention.

Figs. 2A-2B are illustrations of how a coupling assembly can be attached to the composite structure.

Figs. 3A-3I are illustrations of various aspects of a conductive metal component (including the ability of the component to be flexed simultaneously in more than one direction of curvature in order to conform to the shape of the body).

Figs. 4A-4E are illustrations of various aspects of an alternative metal component.

Figs. 5A-5B are illustrations of an alternative metal component.

Figs. 6A-6C are illustrations of how a coupling layer can be connected to a composite structure.

Figs. 7A-7C are illustrations of electrodes in an alternative implementation of the invention  in which a sensor is incorporated into the electrode assembly.

Fig. 8 is a waveform that may be used in conjunction with the electrodes of the invention.

Fig. 9 is a diagram of a circuit suitable for generating the waveform of Fig. 8.

DETAILED DESCRIPTION

There are a great many possible implementations of the invention  too many to describe herein. Some possible implementations that are presently preferred are described below. It cannot be emphasized too strongly  however  that these are descriptions of implementations of the invention  and not descriptions of the invention  which is not limited to the detailed implementations described in this section but is described in broader terms in the claims.

As discussed above  a hands-free electrode typically includes a non-conductive backing layer  a conductive layer  formed from a thin sheet of metal or a conductive ink printed on a substrate  and a coupling layer  typically liquid or solid electrically conductive gel or other electrolytic material  covering the metal layer so that electrical current passes through the gel (or other electrolyte) to the patient""s body. A lead connecting the electrode to a defibrillator is also included. It is well known that defibrillators utilize two electrodes  commonly referred to as sternum and apex electrodes.

The implementation of the electrode disclosed below differs from the electrode described above in that it includes a reusable component having a composite structure comprising a conductive metal component that is partially encapsulated in a non-conductive matrix material (e.g.  by molding the non-conductive material around at least portions of the conductive metal component). A disposable coupling portion is adhered to the reusable component to form the hands-free electrode for delivering defibrillation currents to a patient.

Figs. 1A-1E shows one implementation of a composite structure noted above. In Figure IA  the composite structure 100 includes an electrically non-conductive matrix 105 (one implementation of the "flexible nonconductive element" referred to elsewhere) that encapsulates a portion of a conductive metal component. The composite structure has an encapsulated high voltage lead 150 for connection to an electrical source such as a defibrillator. The lead may connect via an eyelet or other connecting means as discussed below to the metal component. The conductive metal component will be described separately in further detail below. Those portions 110 of the metal component not encapsulated in the matrix are on the top surface (the patient side) of the composite structure and deliver electrical current to a patient via an electrolyte or other conductive viscous liquid (not shown) that is between the composite structure and a patient. Accordingly  these portions 110 may be referred to herein as the "exposed surfaces" or "current delivery surfaces". The contact area of a current delivery surface may be inflexible and the uppermost surface may be planar. The composite structure is configured such that the treatment area (exemplified by the area 115 within the dotted line in Fig. IA) is may be at least 2.33 sq. inches (15 sq. cm)  with a combined treatment area associated with two electrodes (the sternum electrode and the apex electrode) of 6.98 sq. inches (45 sq. cm) for pediatric electrodes; and 7.75 square inches (50 square cm)  with a combined treatment area associated with two electrodes (the sternum electrode and the apex electrode) of at least 23.25 square inches (150 square cm) for all other electrodes  in accordance with AAMI DF-80 and international requirements. In a preferred implementation the treatment area associated with each pediatric electrode is 7.56 sq. inches (22.5 sq. cm) and for all other electrodes 11.63 square inches (75 square cm.) per electrode. The area outside of the treatment area 115 (which is comprised of the non-conductive matrix) should be of sufficient dimensions as to prevent lateral discharge of current to the outer edge of the electrode and to enable attachment of an adhesive ring to which a coupling layer such as hydrogel is attached. As can be seen in Figure IB  which shows the bottom surface of the composite structure (opposite the patient side)  the conductive metal component is completely covered with the non-conductive material of sufficient thickness such that no electrical current passes through the bottom surface. Figure 1C shows an end-on side view of the composite structure. Figure ID shows a side view of the composite structure. Figure IE shows an expanded view of circled section B in Figure ID. As can be seen (and will be discussed in greater detail below)  the current delivery surfaces 110 of the composite structure 100 may protrude beyond the surface of the non-conductive matrix 105. As can be seen by the dashed lines in Figs. ID and IE (in expanded detail)  the conductive metal component 120 (described in greater detail below) may be partially embedded in the non-conductive matrix 105. The portion of the current delivery surface that extends beyond the surface of the non-conductive matrix corresponds to step 375 (shown in Fig. 3D). Thus non-conductive matrix may extend up to the top of step 365 (shown in Fig. 3) or as shown by indicia 120.

Alternative dimensions (length and width) for the metal component  treatment area and composite structure are set forth below. It is noted that these dimensions reflect composite structures (as well as metal components) with equal length and width  which is preferred for manufacturing and packaging. However  the invention is not limited to such dimensions  and is applicable to electrodes of any dimension (whether or not the length and width are equal) or shape (e.g. circular  oval  rectangular or other shapes well known in the art)  provided that the treatment area is sufficiently large for defibrillation or cardioversion and the minimum treatment area standards noted in AAMI DF-80 and required by regulation are met. For example instead of having an electrode configured for a treatment area that is 2 inches by 2 inches  the electrode could be configured for a treatment area that is one inch by four inches. Of course the apex and sternum electrodes may be of dissimilar size and shape.

Table 1 shows non-limiting examples of possible dimensional ranges (length and width) for pediatric electrodes and Table 2 shows non-limiting examples of possible dimensions ranges (length and width) for other  non-pediatric  electrodes.

TABLE 1

TABLE 2

It is noted that the dimensions of the treatment area in any length and/or width direction is preferably not greater than the dimensions of the composite structure in those same one or more directions.

Table 3 below illustrates alternative thicknesses for the composite structure. The thickness of the structure should take into consideration at least the following: (a) the thickness of the non-conductive material should preferably be sufficient to prevent the passage of current (e.g. current only comes out of the electrode at the current delivery surfaces; (b) the electrode should preferably be thin enough to be flexible  yet thick enough to be durable; (c) the wall thickness should preferably be sufficiently thick for molding of the composite structure; and (d) sufficient surface area for the metal to bond to the non-conductive matrix. The thickness may taper to the outer edge of the composite structure.

TABLE 3

Figures 2 A and 2B illustrate an implementation of the above described electrode that shows how the composite structure connects with a coupling layer. As shown in Figure 2A (exploded view) coupling assembly 200 (one possible implementation of a "disposable coupling portion" referred to elsewhere)  comprised of an adhesive ring 210 and containing hydrogel 220  may be adhered to composite structure 230. The assembled electrode structure is shown in Figure 2B. The adhesive ring 210 may also include adhesive on a patient side for attachment of the electrode to a patient. It is noted that the coupling assembly 200 may be disposable  while the composite structure may be reusable  as will be discussed in greater detail below.

Figure 3 A shows an implementation of a structure of conductive metal component 300. Conductive metal component 300 includes nine circular plates 310 in a three by three array wherein each plate is connected via a metal bridge 320 (one possible implementation of a "metallic linking element" referred to elsewhere) to one or more adjacent plates. The dimensions 350  355  360  370  380 and 390 of the array are determined by the overall size of the electrode and the width of the area outside of the treatment area 115 (shown in Fig. IA). The bridges may be flexible. An eyelet 330 may be attached to one or more of the plates or bridges. This eyelet allows for attachment of a high voltage lead for defibrillation  and in alternative implementations electrical signal monitoring  ECG monitoring  cardiac pacing and/or cardioversion. Flanges 340 may be added to the edges of the plates to increase the footprint of the metal embedded in the non-conductive matrix. Figure 3B shows a side view of the array of Figure 3A; with Figs. 3C and 3D showing expanded versions of the encircled areas. As can be seen from Figs. 3B-3D  the plates have a stepwise structure  with steps 365 and 375. While a single step could be used (resulting in the surface of the metal component being flush with the non-conductive surface)  the use of multiple steps offers certain advantages such as improved attachment of the metal component to the non-conductive matrix (which can fill in the area under the metal component and the area between each plate (over the bridges) up to the top of step 365) and easier overmolding of the metal component with the non-conductive matrix. Step 375 allows the plate to protrude above the level of the non-conductive matrix which provides for improved contact with the coupling layer and improved fixation of the coupling layer to the composite over the treatment area. In particular  in certain aspects  the height of the second step (375) correlates with the thickness of the adhesive ring holding the coupling layer such that the surface of the coupling layer that is in contact with a patient is level  thus ensuring uniform current application across the treatment area.

In a non-limiting example  with reference to Figures 3A-3D  dimensions 355 and 350 are each three inches; dimension 360 (the diameter of a current delivery surface) is 0.813 inches (2.065 cm); dimension 370 is 0.063 inches (0.160 cm) and dimension 380 is 0.25 inches (0.635cm). Dimensions 315  325  335  345 and 355 which are the thickness of the metal at selected points on the array are equal to 0.005 (0.013 cm) inches. The height of step 365 is 0.063 inches (0.160 cm) and height of step 375 is 0.031 inches (0.787 cm).

Figures 3E-3I illustrate the flexibility of the three by three array metal component described above. As described above  flexibility of the metal component may be achieved via the flexibility of the bridges.

The metal component is not limited to the specific implementations described above  rather a metal component may have two or more current delivery surfaces. For example  Fig. 4A shows one implementation of a structure of conductive metal component 400 that includes three substantially inflexible circular plates 410 wherein each plate is connected via a metal bridge 420 to one or more adjacent plates. The bridges may be flexible. An eyelet 430 may be attached to one or more of the plates or bridges. This eyelet allows for attachment of a high voltage lead for defibrillation. In certain implementations  the same lead may be used for electrical signal monitoring  ECG monitoring  cardiac pacing and/or cardioversion. Other means of attaching leads for defibrillation  ECG monitoring  cardiac pacing and/or cardioversion may be utilized. Flanges may be added to the edges of the plates to increase the footprint of the metal in the non-conductive matrix.

Figures 4B-4E illustrate the flexibility of a conductive component having three plates. In these figures it can be seen that the flexibility derives from the bridges between the plates.

The thickness of the metal in the metal component may be on the order of 0.004 - 0.008 inches (0.010 - 0.020 cm). In one implementation the thickness is 0.005 inches (0.013 cm). The metal should be thick enough so as to provide durability and ease of manufacture  yet thin enough to allow flexibility of the composite structure sufficient to conform to a patient""s body. The spacing between the plates should be close enough such that  when used in conjunction with a coupling layer  the lateral conductivity of the coupling layer produces a substantially uniform current distribution at the interface of the coupling agent and the patient""s skin over the treatment area (e.g. the electrode "functions" as a single plate instead of as  for example with reference to Figure 3 A  nine distinct plates). As indicated above  the treatment area should have a surface area that is sufficiently large for defibrillation or cardioversion.

In one implementation  the metal component is comprised of stainless steel. Suitable stainless steel alloys include  for example  302  316  316L and alloys having similar composition. Other metal alloys may be used. The metal component may also be made of tin  silver  aluminum  silver chloride  copper or other metal or metal combinations (e.g. silver coated copper)  and may be in the form of a metallic or conductive ink (e.g. silver-chloride) disposed on a suitable substrate such as polyester  as known to those skilled in the art. In an alternative implementation  the metal component is comprised of any metal that polarizes during a defibrillation pulse is delivered. Where such a metal is used  it is preferred to use it in conjunction with a waveform that substantially depolarizes the electrode within 6 seconds of the delivery of the defibrillation pulse.

The metal component can be a single stamped piece and be annealed for flexibility and to minimize the presence of brittle joints. The use of a single stamped piece facilitates handling and overmolding and eliminates the need for welding or soldering of the bridges and/or plates. On the other hand  the component may be made of multiple plates that are welded or soldered together  or that are mechanically connected.

In another alternative implementation  wires can be connected directly to individual current delivery surfaces. This would lead to good flexibility of the composite structure  but would be more complex to manufacture. The wires could be arranged in a network to optimize connectivity by making redundant connections without compromising flexibility. The wires would be connected to the high voltage lead at a common node.

In another alternative implementation  a flexible circuit with a printed conductive element can be used instead of the metal component described above.

An additional implementation is illustrated in Figures 5A and 5B. As shown in Figure 5B  individual (non-circular; though any shape may be used) conductive plates 510 are attached to a conductive backing layer 520 (that may be flexible) via attachment points 530. A connection point 540 for a wire connection to a defibrillator is within the conductive backing layer 520.

As indicated above  the metal component is partially encapsulated in an electrically non-conductive matrix. This may be accomplished by molding the metal component within an elastomer. Molding the metal component within an elastomer may be accomplished via any suitable process known to those skilled in the art. Such processes may include injection molding  overmolding and insert molding. The composite may also be made by sandwiching the metal component between two (or more) non-conductive matrix pieces  and adhering the non-conductive matrix pieces together. The metal may be passivated to remove any surface contamination  a heat activated adhesive (e.g. Chemlock 608  available from Lord Corporation  Cary  NC  USA) is added to the metal at locations where the elastomer will be in contact with the metal  and an elastomer is bonded to the metal in a hot vulcanization process.

Any flexible elastomer or rubber may be utilized as the non-conductive matrix. These materials may have one or more of the following properties: flexibility  durability  resistance to chemicals such as cleaning and disinfecting materials (e.g. bleach  alcohol and gluteraldehyde)  resistance to temperature extremes  biocompatibility (e.g. ISO 10993 compliant)  and good adhesion to the metal. Such materials may include  but are not limited to silicone rubber (e.g. Class VI Elastomer C6-150  available from Dow Corning Corporation  Midland  MI USA)  synthetic rubbers (e.g. Neoprene polychloroprene available from DuPont Performance Elastomers  Wilmington  DE  USA)  thermoplastic elastomers (e.g. Sarlink plastics resins available from DSM Thermoplastic Elastomers  Inc. Heerlen  NL); or thermoplastic vulcanizates (TPVs) (e.g. Santoprene TPV available from ExxonMobil  (Houston  TX  USA)).

A coupling layer may be disposed on the patient side of the electrode. In one implementation  the coupling layer is attached to an adhesive ring that is configured to adhere the electrode to a patient""s skin and the coupling layer to the electrode. The coupling layer may also be sandwiched between two adhesive rings. The coupling layer and adhesive ring together form a modular coupling assembly. The coupling assembly is generally configured to be disposable  i.e.  to be discarded after a single use. The adhesive ring may include a pressure sensitive adhesive that releasab Iy joins the coupling assembly to the non-conductive matrix outside of the area where the metal component protrudes through the non-conductive matrix. The perimeter of the adhesive ring may correspond to the perimeter of the composite that is outside the treatment area 115 (see Fig. IA)  which  in some implementations may be about 3A of an inch wide. It is noted that the adhesive ring may function  in this respect  as a mask around the treatment area. In one implementation the adhesive ring can be comprised of 5 mil low density polyethylene (LDPE) (DV216-127A available from Lohmann Therapy Systems  West Caldwell  NJ) or 1/32 inch polyethylene (PE) foam (Part No. 22116 also available from Lohmann Therapy Systems). Both the LDPE and PE as provided from Lohmann Therapy Systems are coated with a medical grade pressure sensitive adhesive (MTC 611 solvent based acrylic adhesive). In an alternative  coupling layer may be sandwiched between the above disclosed LDPE layers or PE layers or combinations thereof. After a used coupling assembly is removed  it can be replaced by a new one  allowing the composite structure to be re-used. The composite structure may be used for 100 uses or more providing for significant cost savings over pre-existing electrodes. Accordingly  the adhesive and non-conductive matrix materials should be selected so as to provide sufficient adhesion to the non-conductive matrix  but minimize residue on the non-conductive matrix after removal of the coupling assembly  to allow for re-use of the electrode. A coupling assembly may have a removable release sheet on one or both sides to protect the coupling layer prior to use.

Figures 6A-6C illustrate the above in greater detail. Figure 6A shows an exploded view of an electrode prior to attachment of the coupling assembly. In particular  coupling layer 630 is attached to adhesive ring 640  then sandwiched between removable liners (also referred to as release sheets) 620 and 650. The sandwich structure allows for separate packaging of the coupling assembly  which allows for the coupling assembly to be purchased separately (as a disposable item) from the composite structure which  as indicated above  may be reusable. In practice  the disposable coupling assembly is removed from its packaging  liner 620 is removed  and the adhesive ring carrying the coupling layer is adhered to the composite structure. Liner 650 is them removed and the electrode is attached to the patient.

The coupling layer may be any type of electrolyte (or other conductive material) in gel or liquid form  and may be optionally attached to a carrier. In some implementations the coupling layer comprises a high viscosity electrically conductive gel (often referred to as a "solid" gel) or hydrogel. Such hydrogels may include FW340 hydrogel (available from First Water Ltd.  Wilshire  UK); AG604 hydrogel (available from Axelgaard Manufacturing Co.  Fallbrook  CA); and RG63T hydrogel (available from Ludlow Manufacturing  Chicopee  MA . Alternatively  a foam  cloth or sponge layer saturated with an electrically conductive liquid (e.g. saline) or gel may be used. When an electrode is to be used for cardiac pacing  an additional metallic material  (such as tin) should be added to the coupling layer between the electrolyte and the surface of the composite.

In another implementation  the adhesive ring is omitted and the coupling layer may be directly attached to the treatment area of the electrode. In an alternative implementation  liquid gel could be applied either directly on the electrode or directly on the patient prior to placing the electrode on the patient. Tape could then be used to attach the electrode to the body.

The electrodes described herein may be configured to be a multi-purpose defibrillator electrode  i.e.  capable of monitoring electrical signals from the patient  as well as delivering defibrillation  pacing and cardioversion. For example  after a defibrillating pulse is delivered  the electrode is configured to monitor a signal that can be used to generate an ECG.

An additional implementation is illustrated in Figures 7A-7C. Note that the perspective on these Figures is from the non-patient side of the electrode. As such  the ghost outlines in Fig. 7A of the metal component and wire bundles is for illustrative purposes only. In this implementation  (see Figs. 7 A and 7B)  a sternum electrode 700 having the characteristics described above  and configured for one or more of electrical signal monitoring  ECG monitoring  defibrillation  pacing and/or cardioversion is connected a sensor (or sensors) 710 constructed to acquire data indicative of the depth and rate of CPR compressions. The sensor can be one or more of an accelerometer or force and pressure monitors. The system is enabled to provide CPR feedback (in one mode in real time) to a caregiver. The functionality of the electrode and an accelerometer is as described in US Patent Application Publication 2006/0009809  the disclosure of which is herein incorporated by reference. The CPR sensor may be molded together with the composite structure using the molding processes describe above. The wiring 720 necessary for the CPR feedback functionality can be molded into the non-conductive matrix material connecting the sensor 710 to the electrode 700  and bundled with the high voltage wiring 730 for connection via combination bundle 740 to a defibrillator (not shown). It is noted for the purposes of this implementation  that the apex electrode 780 illustrated in Fig. 7C does not have the additional CPR feedback functionality.

As indicated above  the electrodes described hereinabove may be used with any type of waveform known in the art. One such waveform is a biphasic waveform. An example of a biphasic waveform is shown in Fig. 8. The biphasic waveform 80 shown in Fig. 8 includes a generally rectilinear positive phase 82 having a sawtooth ripple 84. The current of the positive phase is approximately 9 amps. The positive phase has a duration of approximately 6 milliseconds. The positive phase is followed by a negative phase 86. The negative phase has a duration of approximately 4 milliseconds and has an initial current of approximately -8 amps. The transition 88 between the positive and negative phases is generally very short  e.g.  0.1 millisecond or less.

The waveform shown in Fig. 8 is simply one example of a suitable waveform. Other waveforms having different characteristics may be used  including both biphasic waveforms having other shapes and other types of waveforms. It is preferred that the waveform used in conjunction with the herein described electrode is capable of depolarizing the electrode

(i.e.  either completely depolarizing the electrode or reducing the polarization to a level where a clean ECG can be obtained) within a few seconds  e.g.  4-6 seconds or less  after the pulse is delivered as described in US Patent Application Publication 2008/0221631 noted above. This allows the rescuer to continue treatment on a patient without interruption.

The waveform may be generated in any desired manner  e.g.  using the circuitry described in U.S. Patent 5 769 872. Referring to FIG. 9 herein  which is a reproduction of Fig. 2 of U.S. 5 769 872  a storage capacitor 20"" (115 µF) is charged to a maximum of 2200 volts by a charging circuit 22"" while relays 26"" and 28"" and the H-bridge are open  and then the electric charge stored in storage capacitor 20"" is allowed to pass through electrodes 21 "" and 23"" and the body of a patient 24"". In particular  relay switches 17"" and 19"" are opened  and then relay switches 26"" and 28"" are closed. Then  electronic switches 30""  32""  34""  and 36"" of H-bridge 48"" are closed to allow the electric current to pass through the patient""s body in one direction  after which electronic H-bridge switches 30""  32""  34""  and 36"" are opened and H-bridge switches 38""  40""  42""  and 44"" are closed to allow the electric current to pass through the patient""s body in the opposite direction. Electronic switches 30 ""-44"" are controlled by signals from respective opto-isolators  which are in turn controlled by signals from a microprocessor 46""  or alternatively a hard- wired processor circuit. Relay switches 26""  and 28""  which are also controlled by microprocessor 46""  isolate patient 24"" from leakage currents of bridge switches 30 ""-44""  which may be about 500 micro-amps. Relay switches 26"" and 28"" may be relatively inexpensive because they do not have to "hot switch" the current pulse. They close a few milliseconds before H-bridge 48"" is "fired" by closure of some of the H-bridge switches.

Optionally  a resistive circuit 50 that includes series-connected resistors 52  54  and 56 is provided in the current path  each of the resistors being connected in parallel with a shorting switch 58  60  and 62 controlled by microprocessor 46. The resistors are of unequal value  stepped in a binary sequence to yield 2n possible resistances where n is the number of resistors. During the initial "sensing pulse " when H-bridge switches 30""  32""  34""  and 36"" are closed  all of the resistor-shorting switches 58  60  and 62 are in an open state so that the current passes through all of the resistors in series. Current-sensing transformer 64 senses the current passing through the patient 24""  from which microprocessor 46 determines the resistance of the patient 24"".

Other implementations of the invention are within the scope of the claims.

We Claim:

1. A reusable component of a hands-free defibrillation electrode  the reusable component comprising: a flexible nonconductive element  and a flexible metallic element supported by the flexible nonconductive element  wherein the flexible metallic element comprises a plurality of substantially inflexible metallic elements interconnected by flexible metallic linking elements  and wherein the majority of the flexibility of the metallic element is provided by the flexible metallic linking elements  wherein the flexible metallic element has an exposed surface on one side of the reusable component and the exposed surface is configured to be adhered to a disposable coupling portion  and wherein the reusable component is configured to accept an electrical defibrillation pulse and spread the electrical pulse across the exposed surface area  from which it is delivered to the patient""s chest through the disposable coupling portion.

2. The reusable component of claim 1 combined with a flexible disposable coupling portion  wherein the flexible disposable coupling portion comprises a conductive layer configured to be in electrical contact with the chest of the patient on one of its surfaces and in electrical contact with the exposed surface of the metallic element of the reusable component on the other of its surfaces.

3. The defibrillation electrode of claim 2 wherein the reusable component and disposable portion are configured to be stored as separate elements  and to be adhered together when used to defibrillate a patient.

4. The electrode of claim 2 wherein the reusable component and disposable portion when adhered together form an electrode capable of being flexed simultaneously in more than one direction of curvature in order to conform to the shape of the patient""s chest.

5. The electrode of claim 1 wherein the flexible metallic linking elements are narrower than the substantially inflexible metallic elements  and wherein the majority of the flexibility of the metallic element is provided by flexure of the narrower flexible metallic linking elements.

6. The electrode of claim 5 wherein the substantially inflexible metallic elements and flexible metallic linking elements are cut from the same sheet of metal.

7. The electrode of claim 1 wherein the flexible metallic element is made from stainless steel.

8. The electrode of claim 6 wherein the flexible metallic element is made from stainless steel.

9. The electrode of claim 1 wherein the flexible metallic element is encapsulated by the flexible nonconductive element by molding the flexible nonconductive element around portions of the flexible metallic element.

10. The electrode of claim 6 wherein the flexible metallic element is encapsulated by the flexible nonconductive element by molding the flexible nonconductive element around portions of the flexible metallic element.

11. The electrode of claim 9 wherein the flexible nonconductive element comprises an elastomeric material.

12. The electrode of claim 2 wherein the conductive layer of the coupling portion comprises a conductive viscous liquid.

13. The electrode of claim 12 wherein the conductive viscous liquid comprises an electrolyte.

14. The electrode of claim 2 wherein the conductive layer of the coupling portion comprises a solid conductive gel.

15. The electrode of claim 14 wherein the conductive layer comprises hydrogel.

16. The electrode of claim 2 wherein the disposable coupling portion includes a first peripheral adhesive region configured to adhere to the periphery of the reusable component.

17. The electrode of claim 16 wherein the disposable coupling portion includes a second peripheral adhesive region on the surface opposite the surface carrying the first peripheral adhesive region  and the second peripheral adhesive region is configured to adhere to the chest of the patient.

18. The electrode of claim 17 wherein the first and second peripheral adhesive regions are generally peripherally outside of the area through which electrical current flows from the exposed surface of the reusable component through the conductive layer of the coupling portion to the chest of the patient.

19. The electrode of claim 16 wherein the conductive layer of the coupling portion comprises a solid conductive gel with adhesive properties sufficient to adhere the coupling portion to the chest of the patient.

20. The electrode of claim 17 further comprising first and second release liners that  prior to assembly of the coupling portion to the reusable component  cover the first and second peripheral adhesive regions  respectively.

21. The electrode of claim 19 further comprising first and second release liners  and wherein  prior to assembly of the coupling portion to the reusable component  the first release liner covers the first peripheral adhesive region and the second release liner covers the solid conductive gel.

22. The electrode of claim 1 wherein the reusable component is combined with a sensor that provides an output from which information about the depth of CPR chest compressions can be obtained.

23. The electrode of claim 22 wherein the sensor comprises an accelerometer.

24. The electrode of claim 1 wherein the reusable component is combined with a sensor tat provides an output from which information about the force applied to the chest during CPR chest compressions can be obtained.

25. The electrode of claim 1 wherein the reusable component is combined with a sensor that provides an output from which information about the rate of CPR chest compressions can be obtained.

26. The electrode of claim 5 wherein the exposed surface of the metallic element comprises exposed portions of each of the inflexible metallic elements.

27. The electrode of claim 26 wherein the metallic linking elements are fully encapsulated within the nonconductive element so that the exposed surface comprises a plurality of exposed metallic areas separated by nonconductive areas.

28. The electrode of claim 27 wherein each of the plurality of exposed metallic areas project beyond the surface of the surrounding nonconductive element.