Patent Publication Number: US-7214107-B2

Title: Electrical connector apparatus and methods

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the field of electrical connectors and connection apparatus, and particularly to an electrical connector apparatus useful in, inter alia, biomedical applications. 
   2. Description of Related Technology 
   In certain electrical connector applications, multiple (often competing) design and performance requirements exist, thereby significantly constraining the selection of connector technology for use in that application. This is especially true of certain clinical or biomedical applications such as impedance cardiography (ICG) and electrocardiography (ECG), wherein it is highly desirable to have a connector which is low cost, clinically rugged and robust, yet which provides both acceptable electrical performance (including low impedance) in a stable and repeatable manner. ICG and ECG connector assemblies have been historically characterized by high cost and substantial complexity of design. Unfortunately, such high cost tends to steer the clinician (or medical facility) using the connector away from disposing of these devices on a routine basis, as well as creating significant barriers to adoption of the technology in the first place. 
   Ideally, ICG/ECG connectors would be very simple in construction and low in cost, thereby allowing routine replacement and more ubiquitous use of these techniques in general. 
   Operational simplicity is another important consideration. Preferably, no complex or difficult operations would required in order to connect or disconnect the connector, yet the engagement (or disengagement) would be positive and rapid. 
   A great variety of different electrical connector designs (biomedical and otherwise) are known in the prior art, the following being generally representative. 
   Swiss Patent No. 48,890 to Cuendet issued July 1909 discloses a metallic loop element with aperture adapted for mating with a spark plug electrode. The loop is expanded by biasing two portions of the loop toward one another against a spring force. 
   U.S. Pat. No. 1,212,821 to Schade discloses a device for spring fastening a wire device to an electrical conductor. 
   U.S. Pat. No. 2,082,279 to Fore discloses a clip insulator adapted to be placed over the uninsulated portion of a conductor terminal. 
   U.S. Pat. No. 2,758,947 to Feighner discloses a method of clamping a spring loaded clip onto wires, terminals or other electrical conductors. 
   French Patent No. 964,611 to Ford issued August 1950 discloses a metallic loop element with aperture adapted for mating with a spark plug electrode. The loop is expanded by biasing two portions of the loop toward one another. 
   U.S. Pat. No. 3,774,143 to Lopin discloses an adapter for use in making an electrical connection between an electrode and a cable connected to a monitoring instrument. 
   U.S. Pat. No. 4,040,697 to Ramsay, et al. issued Aug. 9, 1977 entitled “Electrical connector” discloses an electrical connector that has a resilient, stamped, metallic leaf contact defining a narrow neck contact entrance area and having reversely bent ends on either side of said area. A plastic body section embeds the ends and spans the area to provide two side by side lever legs arranged to act so that pressure on the legs resiliently opens the narrow neck to allow entrance of a second body contact. Relaxation of pressure on the legs causes resilient action of the connector to provide gripping of the second contact with a positive three point grip. 
   U.S. Pat. No. 4,178,052 to Ekbom, et al. issued Dec. 11, 1979 entitled “Medical terminal clip member for attachment to patient electrodes” discloses a medical terminal clip that has a body member with a longitudinal axis and a pair of laterally spaced leg members extending in approximately the longitudinal direction and pivotally connected for relative movement. The respective spaced leg members form a variably spaced electrode receptacle on one side of the pivotal connection. A beryllium copper conductive member is embedded in the body member and is formed from a strip of metal bent into approximately an M-shape with side flanges on the leg members to ostensibly provide additional strength. A shield or barrier member extends at least between the approximate ends of the leg members on the other side of the pivotal connection while permitting relative movement of the leg members. The shield member is designed to close longitudinal access to the space between the leg members and thereby prevent any dislocation of the terminal clip member by catching onto exterior objects such as other terminal wires. 
   U.S. Pat. No. 4,206,960 to Tantillo, et al. issued Jun. 10, 1980 entitled “Electrical connector” discloses an electrical connector for engaging a terminal stud that has first and second insulating spring arms each carrying a conductive metal contact with the metal contacts defining through holes for electrically contacting a shank of a terminal stud. The metal contacts normally are in opposed spaced relationship to each other but are superimposed over each other and resiliently biased to their original position when the spring arms are squeezed toward each other by finger pressure. Release of the pressure causes the contacts to grasp the shank of a terminal stud over which the contacts are positioned. An electrical connector is formed by positioning a preformed end piece over an insulated wire and then molding a plastic connector end in abutting relationship with at least a portion of said preform whereby the molding and forming temperature used does not adversely affect the insulation of said wire. 
   U.S. Pat. No. 4,220,387 to Biche, et al. issued Sep. 2, 1980 entitled “Medical clip” discloses a medical terminal, particularly for use in connecting a lead wire or conductor to an electrode conventionally secured to the skin surface of a human or animal. The electrode comprises a male projection of the buttontype with an enlarged diameter head portion disposed within a recessed area of the electrode. The clip is generally V or wishbone shaped and includes a pair of support arms secured together at one end and normally spaced from each other at the other end. The arms carry resilient conductive loops normally biased out of overlapping condition but movable upon the application of external force into an overlapped condition wherein the clip may be applied over the head portion of the electrode. The support arms have offset depending shoulder portions from which the conductive loops extend and which are positionable within the recessed area of the electrode when the arms are moved toward each other. The support arms are integrally formed of resilient dielectric plastic material in an initial unstressed generally V-shape, with a female socket embedded in the plastic and electrically connected by conductor means to the conductive loops. Replaceable or interchangeable identification means is removably mounted on the clip in the area of the female socket, and a strain relief cover is removably positionable on the clip over said female socket and over said identification means to provide strain relief for the connection to a lead wire, and the cover is at least in part transparent to provide visual observation of the identification means. 
   German Patent No. DD 257 145 discloses a contact terminal clamp designed for use in medical applications, which provides a connection to dish-shaped electrodes on a patient. A double loop terminal element is coupled around a terminal stud, with the loop aperture being opened by grasping two opposing free ends of the terminal element and compressing them together. 
   U.S. Pat. No. 4,671,591 to Archer issued Jun. 9, 1987 entitled “Electrical connector” discloses a connector for establishing electrical connection between a conductor and a patient engaging electrode that includes a conductive post extending from the electrode. The post has a proximal portion, a distal portion, and an intermediate portion having a diameter smaller than the diameter of the distal portion. The connector comprises insulation means shaped to form a socket open at one end, a pair of first spring members, a pair of second spring members, and means for electrically connecting the conductor to the second spring members. The first spring members are laterally positioned with respect to one another in the socket, and the second spring members are laterally positioned with respect to one another in the socket closer to said one end than the first spring members. The first and second spring members are positioned and constructed such that when the post is inserted in the socket, the second spring members grip the proximal portion of the post, and the first spring members and the intermediate and distal portions of the post comprise a detent mechanism that resists removal of the post from the socket. 
   U.S. Pat. No. 5,277,613 to Neward issued Jan. 11, 1994 entitled “Electrode junction assembly” discloses an electrical junction block particularly for use with a fetal electrode and electronic monitor. The junction block comprises a housing having a cavity therein, and a substantially U-shaped spring disposed in the cavity. The spring has legs which are biased outwardly by a suitable coil spring. The housing contains electrical contacts and wires connected thereto, and the U-shaped spring can be depressed to provide openings for receiving electrode wires. A mounting pad can be disposed on the housing for facilitating mounting of the assembly on a person during use. 
   U.S. Pat. No. 5,895,298 to Faupel, et al. issued Apr. 20, 1999 entitled “DC biopotential electrode connector and connector condition sensor” discloses an electrode connector and connector condition sensor for a biopotential sensing apparatus. A plurality of electrodes are connected to individual output leads for individual electrode channels by a connector which does not abrade the surface of the electrode button contact and does not require that pressure be applied to the electrode during connection. Two spring biased conductive arms for the connector are spread apart by the cam surface of an actuator button to receive the button contact and are contoured to engage substantially the peripheral surface of the button contact when the actuator button is released. The biopotential sensing apparatus includes a processor which senses the loss of signal in any electrode channel during a test period and activates an indicator to provide a warning indication. 
   U.S. Pat. No. 6,142,949 to Ubby issued Nov. 7, 2000 entitled “Lead protection and identification system” discloses a lead protection and identification system for a medical diagnostic device. Electrodes are placed on predetermined locations of a patient, and the system includes clips for attaching to the electrodes. The system identifies a lead and provides information to a user as to which one of the electrodes the lead should be connected to. Potentially dangerous signals are prevented from being inputted to a clip when the clip is not connected to an electrode and prevents the patient from being injured. 
   United States Patent Publication No. 20030068914 to Merry, et al. published Apr. 10, 2003 entitled “Precordial electrocardiogram electrode connector” discloses an electrocardiogram electrode connector for connecting an electrode to an electrocardiogram device. The connector of the present invention comprises a lower portion having an electrode end and an ECG end, and an upper portion pivotally connected to the lower portion. The upper portion likewise has an electrode end and an ECG end. The connector also comprises a spring between the lower portion and the upper portion to bias the electrode ends together to clamp about an electrode. Further, the connector comprises an electrical assembly having an elastomeric electrical connector to provide electrical continuity between the electrode and the ECG device when the electrode ends of the lower portion and the upper portion of the connector are biased together. 
   United States Patent Publication No. 20040039275 to Sato, et al. published Feb. 26, 2004 entitled “Biological electrode and connector for the same” discloses a conductive member adapted to be attached onto a living tissue to detect a bioelectrical signal. A retainer retains the conductive member on the living tissue. A lead member is partly brought into contact with the conductive member to lead out the bioelectrical signal to a connector. A waterproof sheet covers the lead member in a watertight manner, while exposing a portion of the lead member from which the biological signal is led out. 
   United States Patent Publication No. 20040072475 to Istvan published Apr. 15, 2004 entitled “Electrode connector” discloses an electrode connector for connecting a conventional tab electrode or sensor to a lead assembly for use with a physiological data collection system. The electrode connector includes a lead connecting portion for attaching the electrode connector to a lead assembly and a tab connection portion for attaching the electrode connector to a tab electrode or sensor. During use, the electrical signals corresponding to physiological data of the patient pass from the tab electrode or sensor, through the electrode connector, and to the lead assembly. 
   United States Patent Publication No. 20040106964 to Fischer, et al. published Jun. 3, 2004 entitled “Implantable Medical Device with Multiple Electrode Lead and Connector with Central Fastener” discloses an implantable medical device such as a cardiac stimulator, a multi-electrode lead attached to the device, and a connector coupling the device to the lead. The lead has multiple electrodes, each electrode connected to a wire extending though the lead. The electrodes may be circumferential coils or rings, for example. The lead has a connector that fits into a recess on a surface of the device or apparatus. A bottom wall of the recess has an array of apparatus connections deployed around a threaded bore. The connector is attached to the apparatus by a screw with a threaded shaft and an enlarged head. The screw passes through a central bore in the connector. Electrical connections form a regular pattern, such as a rectangular or square grid, or a radial pattern, around the central bore. A pair of O-rings or seals surround the connections. A gasket, mounted on male connections or contacts, fits around female connections that may be on either the apparatus or the connector. 
   Despite this broad variety of different designs, none of the foregoing prior art connectors are particularly well adapted to meeting the tandem goals of excellent electrical performance and stability, simplicity of design, low cost, and ease of operation. The prior art solutions (exemplified by those of U.S. Pat. No. 5,895,298 to Faupel discussed above) are either too complex and costly too manufacture, provide poor electrical performance, and/or are not well suited to biomedical applications. Spiraling health care costs further underscore the urgent need for lower cost (and disposable) connector form factors for use in, e.g., ICG/ECG monitoring and evaluation. 
   SUMMARY OF THE INVENTION 
   The present invention satisfies the aforementioned needs by providing an improved electrical connector apparatus and associated methods of use and manufacturing. 
   In a first aspect of the invention, an improved electrical connector apparatus is disclosed. In one exemplary embodiment, the connector apparatus comprises: a unitary spring element having first and second substantially opposing portions, first and second connecting portions coupled to respective ones of said first and second opposing portions, and a variable geometry portion coupled to both said connecting portions and comprising a variable size aperture, said aperture being configured to receive a terminal when properly expanded; and a housing element having first and second movable bias portions, said movable bias portions communicating with respective ones of said opposing portions. The connector is configured such that by biasing at least one of said first and second bias portions, said aperture expands in size. 
   In another embodiment, the connector comprises: a bias element having a movable portion and a stationary portion, first and second connecting portions coupled to respective ones of said movable and stationary portions, and a variable geometry portion coupled to both said connecting portions and comprising a variable size aperture, said aperture being configured to receive a terminal; and a housing element having a housing bias portion, said movable bias portion communicating with said movable portion of said spring element. When the housing bias portion is biased, said aperture expands in size. 
   In yet another embodiment, the connector comprises an ultra-low cost device having the unitary conductor (spring) element previously described, along with a flexible and electrically insulating covering disposed over the conductor element. This configuration obviates the rigid housing and actuators of other embodiments, thereby reducing the cost of the connector as a whole (and hence increasing its clinical “disposability”). 
   In a second aspect of the invention, an improved method of manufacturing a connector is disclosed. In one embodiment, the method comprises: providing a conductor element; providing a housing; providing at least one actuator adapted to move within said housing; providing at least one electrical conductor; deforming said conductor element into a shape having at least one bias portion and at least one connection portion having an aperture; disposing said deformed conductor element and said at least one actuator at least partly within said housing; and terminating said deformed conductor element to said at least one electrical conductor. 
   In a third aspect of the invention, an improved method of operating a biomedical connector is disclosed. In one embodiment, the method comprises: disposing a biomedical electrode in a desired location on a subject; coupling said connector to said electrode; passing at least one electrical signal through said electrode and connector; and removing said connector and said electrode as a unit from said location. A patch electrode having one or more terminals is disposed on the exterior of said subject, and said act of coupling comprises mating said connector onto one of said terminals by applying a substantially normal force to said connector so as to snap it onto the terminal of the patch. 
   In another embodiment, the biomedical connector has at least two substantially opposing bias portions and at least one fulcrum portion, and the method comprises: biasing said at least two bias portions toward each other so as to expand an aperture proximate to said at least one fulcrum portion, said aperture being shaped to receive said terminal; inserting said terminal at least partly into said aperture; and unbiasing said bias portions, said unbiasing allowing said fulcrum portion to contract said aperture around said terminal. 
   In yet another embodiment, the connector has a bias element comprising first and second substantially opposing portions adapted to move relative to one another, first and second coupling portions coupled to respective ones of said first and second opposing portions, and a connection portion coupled to said coupling portions and comprising a variable size aperture, and the method comprises: disposing an electrode apparatus having one or more shaped terminals proximate to a living subject; disposing said connector proximate to at least one of said terminals; biasing said connector onto said at least one shaped terminal, said act of biasing comprising expanding said aperture at least temporarily to accommodate a first portion of said shaped terminal and subsequently contracting said aperture to accommodate a second portion of said shaped terminal. After said acts of at least temporarily expanding and subsequently contracting have been completed, said connection portion and said at least one shaped terminal cooperate to maintain said connector in a substantially constant orientation with respect to one another. 
   In a fourth aspect of the invention, a variable geometry conductor element for forming an electrical connection with a terminal is disclosed. In one embodiment, the contact element comprises: first and second substantially opposing portions; first and second connecting portions coupled to respective ones of said first and second opposing portions; and a variable geometry portion coupled to both said connecting portions and comprising a variable size aperture, said aperture being configured to receive a terminal when properly expanded. Upon biasing at least one of said first and second substantially opposing portions, said aperture expands in size. 
   In a fifth aspect of the invention, a low-force electrical connector is disclosed. In one embodiment, the connector comprises: a bias element having first and second substantially opposing portions adapted to move relative to one another, first and second connecting portions coupled to respective ones of said first and second opposing portions, and an aperture portion coupled to both said connecting portions and comprising a variable size aperture, said aperture being configured to receive a terminal; and a housing element substantially containing said bias element, said housing having an opening formed therein substantially coincident with said aperture. Upon biasing said connector onto said terminal, said aperture at least temporarily expands in size to receive said terminal in a frictional engagement. 
   In a sixth aspect of the invention, a biomedical evaluation system is disclosed using the aforementioned connector(s). In one embodiment, the system comprises an impedance cardiography (ICG) device adapted to use the connectors to electrically connect the system to patch-type electrodes disposed on the thorax of the subject being evaluated. In one variant, the signals to and from the various electrodes are passed from and to the system, respectively via a ganged cable element having a plurality of conductors and associated connectors at their distal ends. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, objectives, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein: 
       FIG. 1   a  is an exploded perspective view of a first exemplary embodiment of the connector apparatus of the present invention. 
       FIG. 1   b  is a top elevational view of the connector of  FIG. 1   a.    
       FIG. 1   c  is a bottom perspective view of the connector of  FIG. 1   a.    
       FIG. 2   a  is a top elevational view of a first embodiment of the variable geometry conductor element useful with the connector of  FIGS. 1   a – 1   c.    
       FIG. 2   b  is a front elevational view of the conductor element of  FIG. 2   a.    
       FIG. 2   c  is a top perspective view of the conductor element of  FIG. 2   a.    
       FIG. 2   d  is a side elevational view of the conductor element of  FIG. 2   a , showing a button-type electrode terminal received therein. 
       FIGS. 3   a – 3   d  are top, bottom, side, and front elevational views, respectively, of the exemplary bottom housing element of the connector of  FIGS. 1   a – 1   c.    
       FIG. 3   e  is top perspective view of the exemplary bottom housing element of the connector of  FIGS. 1   a – 1   c.    
       FIGS. 4   a – 4   d  are top, bottom, side, and front elevational views, respectively, of the exemplary top housing element of the connector of  FIGS. 1   a – 1   c.    
       FIG. 4   e  is a bottom perspective view of the exemplary top housing element of the connector of  FIGS. 1   a – 1   c.    
       FIGS. 5   a – 5   c  are top, side, and front elevational views, respectively, of the exemplary actuator element of the connector of  FIGS. 1   a – 1   c.    
       FIG. 5   d  is cross-sectional view of the exemplary actuator element of the connector of  FIG. 5   c , taken along line  5   d – 5   d.    
       FIGS. 6   a – 6   c  are top perspective, bottom elevational, and side elevational views, respectively, of an exemplary embodiment of an electrode patch useful with the connector of the present invention. 
       FIG. 7   a  is a top elevational view (partial cutaway) of another embodiment of the connector apparatus of the invention. 
       FIG. 7   b  is a side elevational view (partial section) of the connector apparatus of  FIG. 7   a.    
       FIGS. 8   a – 8   d  are top, side rear, and front elevational views of the conductor element of the connector of  FIGS. 7   a – 7   b.    
       FIG. 9  is a bottom perspective view of yet another embodiment of the connector apparatus of the invention, illustrating the use of a flexible covering. 
       FIG. 9   a  is a cross-sectional view of the connector of  FIG. 9 , taken along line  9   a – 9   a.    
       FIG. 10  is a logical flow diagram illustrating one exemplary embodiment of the method of manufacturing the connector apparatus according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference is now made to the drawings wherein like numerals refer to like parts throughout. 
   As used herein, the terms “user”, “caregiver”, and “clinician” are used interchangeably to refer to a person positioning, using, actuating, or removing the connector or associated components, or practicing the methods disclosed herein, whether for monitoring or treatment of another subject or themselves. 
   As used herein, the term “biomedical” includes any application for which the transfer of an electrical current or potential is useful in providing treatment or otherwise assessing a biological subject, including without limitation impedance cardiography (ICG), electrocardiography (ECG), and electroencephalography. 
   As used herein, the terms “subject” and “living subject” refer not only to human beings, but also any other species which may benefit from biomedical analysis, evaluation or treatment. 
   As used herein, the term “unitary” refers generally to a single functional structure or component, such structure or component which may comprise one or more sub-components. 
   It will be appreciated that the terms “upper”, “lower”, “top”, “bottom”, “front”, “rear”, and the like are used herein generally to describe position with respect to other components of the invention or associated structures, as opposed to connoting any sort of absolute position, location or relationship. For example, a “lower” housing element may actually be above the “upper” housing element when the connector is installed in an inverted orientation. 
   Overview 
   In one salient aspect, the present invention provides an improved connector apparatus for use in biomedical applications such as ICG and ECG monitoring. This connector is optimized for high electrical performance, low manufacturing cost, and ease of operation. In one exemplary embodiment, the connector comprises a single electrical conductor element which is deformed into a shape that allows easy operation by the user (simply be pressing portions of it between their fingers), and is extremely simple to manufacture. The connector firmly engages a corresponding (e.g., “button” type) electrode terminal, and allows for rotation of the connector around the axis of the terminal so to provide operational flexibility to the clinician. 
   The particular attributes of the shape into which the conductor element is deformed also allow it to be “tuned” to provide the desired physical properties, including in one variant the ability to be snapped onto an electrode terminal without actuating the connector&#39;s actuating buttons. Similarly, the connector (when properly adapted) can be removed from the terminal through the proper application of force in a given direction. Hence, the same basic connector form factor can adopt a number of differing physical characteristics as required for each different application. 
   In another variant, the external housing an actuators of the connector are replaced with a simple flexible covering, thereby even further simplifying the connector and lowering its cost of manufacture. 
   Detailed Description of the Exemplary Embodiments 
   Referring now to  FIGS. 1   a – 5   d , a first exemplary embodiment of the connector apparatus of the invention is described. It will be recognized that while described herein primarily in terms of a connector apparatus adapted for biomedical applications such as ICG or ECG, the connector may also readily be adapted to other applications, whether biomedical or otherwise. All such adaptations and alternate embodiments will be readily understood by those of ordinary skill given the present disclosure, and are considered to fall within the scope of the claims appended hereto. 
   As shown in  FIGS. 1   a – 1   c , the exemplary connector apparatus  100  generally comprises a substantially symmetric, contoured connector body  101  with an electrical cable  114  issuing from one end thereof. As will be described in greater detail below, the cable  114  provides the electrical interface between the connector  100  and an external system (e.g., ICG or ECG monitoring system, not shown). 
   The connector body comprises top and bottom connector housing elements  102 ,  104 , as well as two opposed actuator elements  106  which are pivoted at their one end  107  so as to allow the opposing or distal end to move with respect to the housing elements  102 ,  104 . Each of these components comprise a molded polymer such as ABS (acrylonitrile butadine styrene), although other materials such as polyethylene, fluoropolymers (e.g., ETFE), and the like may be used. ABS is selected in the illustrated embodiment for its comparatively high strength and other excellent mechanical properties, as well as comparatively low cost and ease of handling. 
   The housing elements  102 ,  104  when assembled form an interior cavity in which a variable geometry conductor element  110  is received. The conductor element  110  comprises the electrical interface between the conductor(s) of the cable  114  and the electrode terminal  610  (see  FIGS. 6   a – 6   c ) to which the connector  100  is mated during use. Herein lies a primary feature of the present invention; i.e., the use of a unitary conductor element which greatly simplifies the connector over prior art designs, and also significantly reduces its cost. Rather than having to form a number of precision components, the conductor element  110  of the illustrated embodiment can be formed simply by properly deforming a single piece of conductor wire. The shape and material of the conductor element  110  cooperate to provide the element with a resiliency when deformed (i.e., “spring” action) without use of any springs or other such components which may ultimately fail or become dislodged under impact or stress. This spring action also provides a very positive engagement between the conductor element  110  and the terminal  610  which it is mated with. 
   As best shown in  FIG. 1   a , outward portions of the conductor element  110  are received within grooves  506  ( FIG. 5   b ) formed on the interior surfaces of the actuator elements  106 , thereby allowing force applied to the outer surfaces of the actuators  106  to be transmitted directly to the conductor element  110 . As will be described in greater detail below, this force transmission allows the connector to open and close for mating to (or removal from) the electrode terminal  610 . 
   The housing elements  102 ,  104  of the illustrated embodiment are a “snap-together” type construction, thereby further reducing costs and obviating any fasteners. It will be recognized, however, that such fasteners (either alone or in conjunction with the snap-together functionality), may be used consistent with the invention if desired. 
     FIGS. 2   a – 2   d  illustrate a first exemplary embodiment of the variable geometry conductor element  110 , which is shown without the housing elements  102 ,  104  or other such components. In this embodiment, the conductor element  110  comprises a single metallic wire having an effective spring constant (when deformed) of k and electrical conductivity 1/ρ. The metal used for the wire comprises Type 302 Stainless Steel (0.036 in. nominal diameter) having a nickel plating for added ruggedness and low friction. The passivated nature of the stainless steel (i.e., Chromium content) avoids corrosion or oxidation of the conductor element after formation; e.g., while it is sitting on the shelf waiting to be used. Such corrosion or oxidation might cause undesirable changes in the electrical properties of the conductor element, thereby reducing the accuracy and stability of the monitoring system as a whole. This is especially true considering the relatively small electrical potentials being measured in the typical ICG or ECG system. Furthermore, such corrosion and oxidation can increase the roughness of the surface of the conductor element  110 , thereby providing increased resistance to rotation of the connector  110  around the terminal  610  during use. 
   The illustrated conductor element  110  is formed from a wire having a substantially circular cross-section. This shape is selected for a variety of reasons, including (i) a smooth, low friction interface with the rounded terminal head; (ii) symmetry in deformation (i.e., so as to avoid any issues relating to particular handling orientations of the wire blank used to form the conductor element; and (iii) minimizing creation of stress risers on the deformed wire which may result in premature failure (e.g., under high cyclic or fatigue loading). Stated simply, a round wire can be most easily handled, and will generally have the lowest friction and highest reliability. 
   The aforementioned circular cross-section, in conjunction with the substantially rounded head and skirt region of the terminal  610 , allows the conductor element  110  (and hence connector  100 ) to rotate around the terminal axis without encountering significant friction or galling the terminal skirt. 
   It will be appreciated, however, that other materials and cross-sectional profiles may be used for the conductor element  110 . For example, another alloy such as Cu—Ni or Inconel (Ni—Cr—Fe), plated or unplated, may be used with the same or another profile (such as octagonal or hexagonal). A square or rectangular cross-section may even be used with proper handling. Myriad other variations and combinations are possible, as will be recognized by those of ordinary skill in the metallurgical arts. 
   As previously noted, the shape of the conductor element  110  is specially selected to provide a number of functions and features, including inter alia: (i) spring action which returns the element  110  to its original shape after being biased; (ii) a multi-planar configuration such that the bias portions  202 ,  204  of the conductor element  110  are disposed in a plane different than the terminal-receiving aperture  220  which receives the electrode terminal  610 ; (iii) significant lateral and longitudinal space conservation (thereby allowing the connector  100  to be smaller); (iv) the creation of a loop fulcrum  212  which allows the aperture  220  to expand and contract with relatively minimal bias force, yet which keeps the terminal securely engaged within the aperture when no bias force is applied. 
   As further shown in  FIGS. 2   a – 2   d , the exemplary embodiment of the conductor element  110  is comprised generally of a connection portion  210  set on a lower plane  260  of the element  110 , and a bias or actuation portion set on an upper plane  262  of the element  110 . This multi-planar approach allows the connector to be spatially efficient, since the terminal head  610  is received within the volume formed between the two planes  260 ,  262  as shown in  FIG. 2   d . The difference in elevation between these two planes  260 ,  262  (which need not be parallel in orientation) is controlled substantially by the connecting portions  206 ,  208  of the element  110 , which in the illustrated embodiment are substantially perpendicular to both planes  260 ,  262 . It will be recognized, however, that these connecting portions may assume literally any shape, and need not per perpendicular or vertical in orientation. 
   Furthermore, the exemplary conductor element  110  “loops back” on itself, thereby minimizing the overall length of the element  110 . It will also be noted that the overall diameter of the element  110  (when viewed from above as in  FIG. 2   a ) is minimized, with the compressed diameter being even smaller than that of the uncompressed (unbiased) state. There is also a good correspondence between the points of application of the bias force  202 ,  204  and the center of the aperture  220 , thereby avoiding the situation where the bias force is longitudinally offset from the aperture (which would make operation of the connector mechanically awkward). 
   The use of a unitary component for the element  110  also reduces weight, since no supporting, interfacing, or bonding components are needed to provide the various functions of the element  110 . However, in any of the embodiments of the present invention, it will be appreciated that the variable geometry conductor element  110  may also be composed of more than one piece of wire. For example, the conductor element  110  may comprise a plurality of wires bonded or otherwise coupled together, such as in a stranded or rope-lay fashion. Alternatively, the materials and/or physical properties and dimensions of the conductor element may vary over its length, whether through use of a unitary (“raw”) blank or one composite in nature. For example, where it is desired to have different materials form the bias portions  202 ,  204  and opposed to the lower connection portion  210 , the two components can be joined (e.g., at the connecting portions  206 ,  208 ) via welding, brazing, etc. It will be appreciated that the connection portions  206 ,  208  and even other portions of the conductor element  110  are not critical in terms of strength or fatigue resistance, and hence a sturdy joint can be tolerated if desired. 
     FIGS. 3   a – 3   e  illustrate the exemplary bottom housing element  104  of the connector  100  of  FIG. 1   a . As previously described, this housing element comprises an ABS or comparable material molded to the desired shape. This shape includes a central aperture  302  for receiving the terminal  610  therein during use, as well as a channel  310  adapted to place and retain the conductor element  110  and its terminated cable  114 . Two pivot points  318  (e.g., recesses to receive the actuator element pins  502  described subsequently herein with respect to  FIG. 5 ) are also provided in order to facilitate the desired rotation of the actuator elements  106  within the housing body  101 . An interior volume  315  or basin is also formed within the housing element  104  in order to seat and retain the conductor element  110  when received in the housing. 
     FIGS. 4   a – 4   e  illustrate the exemplary configuration of the top housing element  102  of the connector  100  of  FIG. 1   a . As shown in the Figures, this component  102  comprises a generally planar structure having a plurality of snap risers  408 ,  410  which correspond to the grooves  308 ,  306  formed in the bottom element  104 , such that the two housing elements  102 ,  104  snap together. The top housing element  102  also includes two pivot features  418  which receive the tope ends of the pins  502  of the actuator elements  106 , comparable to those for bottom element  104  previously described. The outer surface of the of top element  102  also contains a recess  117  which can optionally receive a label  116  or other indication mechanism. For example, the label  116  might be used to identify the connector placement (e.g., “L” for Left, “R” for right), or otherwise provide instructions on use, cautions/warnings, manufacturer information, compatibility information, expiration date of the connector, etc. 
     FIGS. 5   a – 5   d  illustrate an exemplary configuration of the actuator elements  106  of the connector of  FIG. 1 . As shown in  FIG. 5   a , the actuators  106  each comprise a molded (e.g., ABS) arm with a pivot pin  502  at one end and an eccentric load-bearing region towards the other end. The load-bearing region includes a projection which is used by the operator to bias the conductor element  110  together, as subsequently described herein. 
   As shown in  FIG. 5   b , the interior surface of the actuator arm  106  includes a slot or groove  506  which is adapted to receive the respective bias portion  202 ,  204  of the conductor element  110  therein. This relationship helps retain the conductor element  110  in the proper orientation within the connector housing body  101 , and provides a firm and tightly coupled interface between the actuators  106  and the bias portions  202 ,  204  to prevent the latter from moving significantly with respect to the former when a bias force (load) is applied to each actuator  106  during use. Note also that the housing elements  102 ,  104  are configured such that their rigid coupling to one another, and the receipt of the pins  502  within their respective recesses  318 ,  418 , provide actuators  106  with a stable platform for biasing the bias portions of the conductor element  110 . Stated simply, the actuators  106  are prevented from skewing within the housing body  101  during loading by the cooperation of these various design features. 
     FIGS. 2   d  and  6   a – 6   c  illustrate one exemplary embodiment of an electrode patch  600  that can be used consistent with the invention. It will be appreciated that the connector of the present invention can be used with literally any type of electrode or terminal shape, so long as it fits within the aperture  220  of the conductor element  110  when the latter is compressed. While a button-type or shaped terminal  610  is illustrated, the invention can operate with other terminal profiles, and clearly can be scaled as necessary to accommodate different sizes of terminals. Furthermore, the cross-sectional profile of the conductor element  110  wire can be varied so as to optimize the interface between the selected terminal profile and the connector, as described elsewhere herein. 
   In the illustrated embodiment, the exemplary electrode terminal element  610  ( FIGS. 2   d  and  6   a – 6   c ) comprises an electrically conductive material such as extruded metal or metal-coated polymer, and having a top or head portion that is larger in diameter than the middle or skirt portion. The electrodes also include a conductive interface (e.g., gel shape) on its lower face to provide an electrical interface between the upper terminal  610  and the subject being monitored. Exemplary configurations of such “spot” electrodes particularly useful with the invention herein are described in U.S. Pat. No. 6,636,754 to Baura, et al. issued Oct. 21, 2003 and entitled “Apparatus and method for determining cardiac output in a living subject” as well as in U.S. design Pat. Nos. D475,138 entitled “Electrode for use on a living subject with removable protective electrode carrier”, and Nos. D471,281 and D468,433 each entitled “Electrode for use on a living subject”, each of the foregoing assigned to the Assignee hereof and incorporated by reference herein in its entirety. 
     FIGS. 7   a – 8   d  illustrate another embodiment of the connector apparatus  700  of the invention. As shown, this embodiment comprises two directly opposed actuators  706  which act against corresponding bias portions  802 ,  804  of the conductor element  710 . Here, the conductor element  710  uses two substantially parallel bias portions  802 ,  804  as opposed to the divergent configuration of the element  110  of  FIGS. 2   a – 2   d . The general operating principles of the is element  810  are the same, however. Notably, the actuators  706  of the present embodiment are not pivoted per se, but rather travel linearly inward and outward from the connector  700  during use, their alignment maintained substantially by the surrounding portions of the housing  702 ,  704  and the bias portions  802 ,  804  of the conductor element  110 . 
   “Snap” Variants 
   In another aspect, an exemplary streamlined apparatus and method of operating the connector(s) described herein are disclosed. Specifically, typical biomedical (e.g., ICG) electrodes such as those of U.S. Pat. No. 5,895,298 discussed previously herein require affirmative actuation of the connector (e.g., depressing the buttons on the sides) for both attachment and removal of the connector to the electrode terminal. In an alternate embodiment of the present invention, the connector is configured so as to permit a rapid “snap on” to the electrode terminal simply by the application of sufficient downward force (e.g., by the user grasping the connector housing, placing the bottom terminal aperture over the head of the terminal, and pressing down). This functionality is somewhat akin to a snap button on a garment or the like, and is facilitated through the use of a conductor element having a rounded (e.g., circular, elliptical, or similar) cross-section in the region where it engages with the (rounded) head of the terminal  610  (see  FIGS. 2   d  and  6   c ). Specifically, as the user presses downward on the connector housing, the aperture of the connection portion  210  of the conductor element  110  is opened slightly by the terminal head acting to spread the aperture as the terminal  610  penetrates. The rounded, substantially smooth surfaces of the terminal head and the conductor element  110  facilitate reduced friction, and sliding of the components past one another. Once the conductor element aperture is expanded sufficiently, the broadest portion of the head or the terminal  610  is passed through the aperture  220 , and the connection portion  210  and aperture  220  contract around the shank or skirt of the terminal  610 , thereby locking the terminal in place within the conductor element  110 . 
   It will be appreciated that the geometry, materials, and/or dimensions of the conductor element  110  may be selected so as to provide literally any degree of desired compliance. Hence, for the typical biomedical application, it would be desirable to configure the connector such that only a fairly minimal downward force or normal is required to cause the terminal head to penetrate the aperture  220  and be fully engaged therein. This minimal force profile helps prevent any bruising or other deleterious effects which may result from the excessive application of pressure to an electrode that is already disposed on the subject being monitored. 
   It is also noted that since the conductor  110  (and hence connector  100 ) can rotate around the skirt or shank of the terminal  610  without reducing electrical continuity, the force applied by the contact portions of the conductor element  110  forming the aperture  220  against the terminal skirt need not be as high as might otherwise be required if the connector were not allowed to rotate. For example, where a patient or clinician inadvertently tugs or jerks the conductor wire  114 , the connector  110  will rotate around the terminal shaft as needed to help mitigate the stress, while still maintaining electrical continuity. The connector  110  would rather rotate around the electrode terminal than dislocate the terminal out of the aperture, at least in most cases. 
   Obviously, the actuator buttons may also be retained on this device so as to provide a fully manual mode (i.e., where the user does not want to exert any appreciable downward force on the subject, or the terminal post head is not sufficiently rounded to permit easy “snap-on” engagement). Alternatively, the actuator buttons  106  can be completely obviated in favor of a purely snap-on/snap-off functionality, thereby reducing cost of the connector. The “hybrid” variant of  FIGS. 9–9   a  discussed elsewhere herein may also be used in this regard; this configuration is the nexus of low cost (i.e., no actuator buttons  106  and a low cost pliable housing) and actuator functionality (i.e., the sides of the connector body can be depressed to actuate the connector as previously described with respect to the embodiment of  FIG. 1   a ). 
   In terms of removal of the “snap-on” device, the user can use any number of approaches. In one variant, the user simply actuates the button(s) on the connector (or depresses the sides in the case of the variant of  FIG. 9 ) to expand the aperture  220  and allow removal of the connector from the terminal stud  610 . 
   Alternatively, the user can simply remove the connector and the electrode patch as a unit, such as by grasping the connector and applying a torsional and/or shear stress to the connector (without actuating the buttons) so as to dislodge the patch from being adhered on the subject. Similarly, the user can pull up one corner of the patch, with connector attached, and then simply peel up the remainder of the patch. 
   As yet another alternative, the connector (where properly adapted) can be rotated out of the plane of its normal orientation (i.e., out of a plane roughly parallel with that of the electrode patch  600 ) so as to slightly distort the conductor element  110  of the connector to open sufficiently in order to remove the terminal  610 . As will be noted by inspection of  FIGS. 2   a – 2   d , the longitudinal axis of the connection portion  210  of the conductor element  110  represents a path of least resistance for expanding the aperture  220 . Hence, if the user rotates the connector out of the aforementioned normal orientation along this axis, such as by grasping the conductor wire and pulling upward and forward toward the front of the connector housing body  101 , the conductor element  110  within the connector  100  will be in effect pried open by the terminal head  610  acting against the sides of the aperture  220  (assuming the electrode patch is sufficiently restrained during the prying action). If the conductor element  110  is sufficiently compliant, this removal can be accomplished with fairly minimal force. Hence, especially in embodiments of the connector where no actuator buttons are present, this mode of removal may be readily used. 
   One-Button Variants 
   It will be appreciated that while the foregoing embodiments of the connector apparatus of the invention generally employ two (2) opposing actuators or buttons, the connector apparatus may be practiced with equal success using one (1) button, or even no (zero) buttons. Specifically, in the case of the one-button variant, the conductor element  110  merely requires sufficient biasing force to move the two opposing members  202 ,  204  toward one another so as to open the aperture  220 . Since only relative motion between the two opposing portions  202 ,  204  is required, one of the portions can be in a substantially fixed disposition (e.g., seated within a recess or groove on the interior of the housing body  101 ), while the other opposing portion  202 ,  204  is actuated by an actuator  106  (e.g., button or the like) as previously described. The compressive bias force is generated as the user squeezes the one side of the housing body  101 , and the single actuator  106  on the other side of the body  101 , together. The penetration  302  in the lower housing  104  can be made slightly larger to accommodate the small degree of lateral translation of the aperture  220  of the conductor element  110  in such a configuration. This approach even further simplifies and reduces the cost of the connector  100 . 
   Ultra-Simplified Variants 
   Referring now to  FIGS. 9–9   a , yet another exemplary embodiment of the connector apparatus  900  of the invention is described. As shown in  FIGS. 9–9   a , the connector  900  comprises a central variable geometry conductor element  910  similar to that of  FIGS. 2   a – 2   d  (or  8   a – 8   d ) disposed within a simplified molded-on or pliable housing jacket  930 . The housing jacket  930  purposely has no actuator elements  106 , yet replaces these with finger recesses  917  disposed proximate to the bias portions  902 ,  904  of the conductor element  910 . The user then simply biases the finger recesses  917  inward against the bias portions of the conductor element, thereby actuating the latter. The thickness of the covering  930  in the region of the bias portions  902 ,  904  can be adjusted as desired in order to make the connector  900  easy to operate yet provide sufficient electrical performance (including insulation level between the user and the conductor element  910 ). An aperture  925  is formed in the bottom of the covering coincident with the aperture  920  of the conductor element  110  so as to permit ingress and egress of the terminal  610 . A cable  914  with molded strain relief is also provided. 
   This configuration  900  provides an extremely low cost solution yet retains the general functionality of the connector  100  of  FIG. 1   a . It can also be adapted for “snap-on” operation as previously described herein if desired. 
   Method of Manufacture 
   Referring now to  FIG. 10 , an exemplary embodiment of the method of manufacturing the connector of the present invention is described in detail. It will be appreciated that while the following method is described primarily in terms of the connector embodiment of  FIGS. 1   a – 5   d , the method can be readily adapted to any of the embodiments shown herein (and in fact others) by those of ordinary skill in the manufacturing arts. 
   As shown in  FIG. 10 , the method  1000  comprises first providing a conductor element  110  (step  1002 ). As previously described herein, the conductive element comprises a metallic (e.g., alloy) conductor having a selected cross-section (e.g., round, elliptical, rectangular, etc.). In step  1004 , one or more housing components  102 ,  104  are formed, such as via a molding process (e.g., injection, transfer, or the like). Included within the housing components are the actuator elements  106  (e.g., buttons). 
   Per step  1006 , an electrical conductor  114  (e.g., an insulated 24 AWG wire having one or more individual conductor strands) is provided. This conductor may also be prepared by stripping the insulation from one end to facilitate subsequent termination to the conductor element  110 . A stress relief device  112  is also optionally attached to the conductor  114  in preparation for subsequent assembly of the housing per step  1008 . 
   Next, per step  1010 , the conductor element  110  is deformed into a shape having the bias portions  202 ,  204  and at least one connection portion  210  (including the aperture  220 ) as previously described herein. This deformation is accomplished via a bending machine or other such process well known in the manufacturing arts. When completed, this step  1010  produces a conductor element such as that shown in  FIGS. 2   a – 2   d  or  8   a – 8   d  (or even another configuration, depending on the particular application). 
   Once the conductor element  110  has been deformed, it is then terminated to the electrical conductor (wire)  114  per step  1012  using any number of well known termination processes including, e.g., soldering, brazing, welding, crimping, wire wrapping, etc. The conductor element  110  may optionally be notched, have a loop or terminal, serrated teeth, etc. to further facilitate positive electrical and mechanical engagement between the wire and the deformed element  110 . 
   Next, the deformed and terminated conductor element  110  is disposed within the bottom housing  104  with the actuator button(s)  106  per step  1014 . As previously described, the actuator buttons  106  are configured to engage their corresponding bias portions  202 ,  204  of the conductor element, such as by having these portions fit within a slot  506  formed within the interior surface of the actuators  106 . The actuators  106  are also optionally fitted with a pivot structure (e.g., opposed pins  502 ) that engage corresponding portions of the housing  102 ,  104  so as to permit the buttons to move pivotally with respect to the housing portions  102 ,  104 . 
   Hence, when assembling the conductor element  110  (with stress relief and cable), the housing body  101 , and actuators  106 , the actuators  106  are first fit onto the conductor element, and then the assembly disposed into one half (e.g., lower portion  104 ) of the housing body  101 , such that the components each fit into their proper features within the lower housing  104 . 
   Lastly, per step  1016 , the top portion of the housing  102  is positioned over top of the lower portion  104  which contains the aforementioned components, and the two housing components  102 ,  104  mated so as to capture the various components within the housing body  101 . In the exemplary embodiment, this capturing comprises snapping the two housing components together using the molded-in locking tabs  408 ,  410  and corresponding recesses  308 ,  306  to keep them in a firm cooperation; however, the housing portions  102 ,  104  can also be held in the desired relative position using adhesives, threaded fasteners, rivets, friction or heat-staked pins, metal clips, or any number of other mechanisms well known to those of ordinary skill in the mechanical arts. 
   The assembled connector may then be mechanically tested (step  1018 ); e.g., by actuating the buttons, straining the strain relief, etc. The connector can be electrically tested as well; e.g., by mating the connector to a terminal or other electrically conductive device and performing electrical continuity or resistance testing thereof. For example, since the electrical characteristics of the connector are potentially critical in certain applications, the connector may be mated to an actual electrode of the type with which it will be used (e.g., ICG “patch” or spot electrode) and tested in this fashion, thereby most closely approximating actual operating conditions. The conductor  114  (or even the connector itself) may also be tested for voltage withstand or other electrical, mechanical or insulating properties. Myriad other testing and/or quality assurance techniques may be applied as desired. 
   In an alternate embodiment of the method, the housing is molded or otherwise disposed over top of the deformed conductor element  910  as previously described with respect to  FIGS. 9–9   a . Specifically, in one variant, the actuators  106  of  FIG. 1   a  are obviated in favor of a substantially flexible covering  930  (such as a PVC, elastomer, or other such material) that permits the user to apply inward bias pressure directly to the bias portions of the conductor element simply by grasping the two recesses  917  formed in the covering  930 . Hence, during manufacturing, the flexible covering is applied after the deformed conductor element  910  has been terminated to the cable, such as by either (i) pre-forming the covering and stretching it over the conductor element  910 , or (ii) molding the covering  930  directly onto the conductor element/wire assembly. Such techniques (and other comparable approaches) are well known to those of ordinary skill in the manufacturing arts, and hence not described further herein. 
   It will be recognized that while certain aspects of the invention have been described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the invention, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the invention disclosed and claimed herein. 
   While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the invention. The foregoing description is of the best mode presently contemplated of carrying out the invention. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.