Connection arrangement for monitoring fetal heart rate
This a division of application Ser. No. 08/201,772 entitled &#34;CONNECTOR DEVICE FOR USE IN MONITORING FETAL HEART RATE&#34;, now U.S. Pat. No. 5,373,843. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates no a connection arrangement for monitoring fetal heart rate. The arrangement electrically interconnects a remote fetal monitoring device with bipolar fetal electrodes. 
     U.S. Pat. No. Re 28,990, which is incorporated herein by reference, discloses the bipolar fetal electrode assembly commonly used to monitor fetal heart rate during birth. In use of that assembly, a doctor inserts the forward end of a curved guide tube through the mother&#39;s vagina and cervix until the forward end of the guide tube makes contact with the fetal head or other portion of the fetus. Holding the forward end of the guide tube stationary, the doctor then pushes the rear end of a flexible driving tube forwardly until a spiral fetal electrode at the forward end of one wire of a twisted wire pair makes contact with the fetal epidermis. The forward end of the other wire has a spade-like maternal electrode which is electrically isolated from the spiral fetal electrode. 
     The doctor then rotates the flexible driving tube clockwise about one full turn while maintaining the forward end of the guide tube against the fetal head. This will screw spiral electrode into the fetal epidermis. Thereafter, the doctor removes his fingers from the mother&#39;s vagina, grasps the outer ends of the driving tube and the guide tube, and slides these tubes as a unit off the wires, leaving only the bipolar electrodes and the two twisted wires within the mother. 
     The outer ends of the wires are then connected to a suitable apparatus for monitoring fetal heart rate. Such an apparatus is discussed in U.S. Pat. No. 4,632,121, the contents of which are also incorporated by reference and which also shows a cable assembly for effecting electrical connection between the electrodes and the fetal monitor. A galvanic potential difference may then be measured between the bipolar electrodes. The wires connected to the electrodes are twisted about each other so that any induced voltages caused by external electromagnetic interference will be the same in each and therefore will not adversely affect the measurement of the galvanic potential difference between the electrodes. 
     In practice, the ends of the twisted wires are left uninsulated, e.g. by as much as 5/8 inch to 3/4 inch, to allow connection to the monitor and to enable removal of the guide and driving tubes from the twisted wires. 
     Manually connecting the uninsulated ends of the twisted wire pair to the base plate is somewhat cumbersome and creates the possibility that the wires may unintentionally short each other. If shorted, the wires will be unable to transmit correct signals from the fetal electrodes. 
     It would therefore be desirable to effect electrical interconnection between the fetal and maternal electrodes and a remote fetal monitoring device without handling uninsulated ends of wires. 
     SUMMARY OF THE INVENTION 
     The present invention is directed at an arrangement for establishing electrical connection between fetal and maternal electrodes and a remote fetal monitoring device. The arrangement includes a connector holding one end of a twisted wire pair, fetal and maternal electrodes at the other end of the twisted wire pair, and a removable driving tube which may be pulled over the connector. 
     It is preferred that the end of the connector which faces the driving tube be tapered and that an open ended, cone-like driving handle be arranged at the rear end of the driving tube to facilitate removal of the driving tube by pulling. The driving tube may be pulled off together with the guide tube, which surrounds the driving tube. 
     The connector has electrical terminals which are in electrical contact with the wires of the twisted wire pair. The connector is insertable into an opening of a housing of a leg plate so as to establish contact between the terminals and biased electrical connectors in the housing. 
     The input electrical connectors, as well as a ground electrode held by the leg plate, are electrically interconnected with output leads that are in electrical connection with a remote fetal monitoring device. 
     Preferably, the housing is rotatably secured to a base which contains the ground electrode. The leg plate may be either disposable or reusable. If disposable, then the base has an adhesively coated flexible pad through which extends the ground electrode. The pad is adhered to the mother&#39;s leg. If reusable, the base has a ground plate as the ground electrode and a belt attached to the base is wrapped around the mother&#39;s leg to hold the base in position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, reference is made to the following description and accompanying drawings while the scope of the invention will be pointed out in the appended claims. 
     FIG. 1 is a perspective view of the forward end of a bipolar fetal electrode assembly in accordance with the prior art. 
     FIG. 2 is a perspective view of the improved connector incorporated in a fetal monitoring system and illustrating a leg plate which may be either disposable or reusable; 
     FIG. 3 is an enlarged cross sectional view taken along the line 3--3 of FIG. 2 of an embodiment which has a reusable housing detachably connected to a disposable adhesive pad; 
     FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 3; 
     FIG. 4a is a cross-sectional view taken along the line 4a--4a of FIG. 4. 
     FIG. 5 is a longitudinal cross-section of the electrode assembly showing the guide and driving tubes being removed from the connected electrode. 
     FIG. 6 is a top view of a reusable leg plate with provisions for the attachment of monitor and fetal electrode leads. 
     FIG. 7 is an elevation view of the leg plate of FIG. 6. 
     FIG. 8 is an enlarged cross-sectional view as if taken along the line 3--3 of FIG. 2, except that for this embodiment, the housing and adhesive pad are fixed to each other. 
     FIG. 9 shows an alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the forward end 2 of a conventional fetal electrode product in accordance with U.S. Pat. No. Re. 28,990. The fetal electrode product includes a guide tube 4, driving tube 6 which is of a smaller diameter than that of the guide tube and a twisted pair of wires 8 the ends of which are connected respective fetal and maternal electrodes 10, 12. A nonconductive plastic holder 14 electrically insulates the fetal and maternal electrodes 10 and 12 from each other. 
     The fetal electrode 10 is in the form of a spiral electrode having a pointed end which is driven into contact with the fetal epidermis. The maternal electrode 12 is engageable by slots 16 at the forward end of the driving tube 6 to enable the pointed end of the fetal electrode 10 to rotate and be driven into the fetal epidermis E (see FIG. 5) by rotation of the driving tube 6. 
     After the spiral electrode 14 has engaged the fetus, guide and driving tubes 4, 6 may be pulled and removed from the mother, leaving the electrode head and twisted wire pair 8 in the birth canal. In the prior art, the proximal ends (not shown in FIG. 2) of the twisted wire pair were uninsulated bare wire for enabling connection to electrical terminals on a leg plate. 
     FIGS. 2-4 show a connector 20 attached to the proximal ends of the twisted wire pair 8 in accordance with the invention. The connector 20 has electrically conductive ring-shaped terminals 22, 24 which are connected to uninsulated ends 26, 28, respectively (see FIG. 4) of the twisted wire pair 8. The terminals 22, 24 may extend around the entire circumference of the connector 20 and are spaced apart from each other to electrical contact therebetween. 
     A drive handle 18 defines a passage 19 (see FIG. 5) communication with the inner passage defined by the driving tube 6. The driving tube 6 is jam fit into handle 18 along an inner taper of handle 18 that extends toward a stepped surface of the handle 18 (see FIG. 5). 
     Handle 18, which has a cone-like shape facing rearwardly, facilitates pulling of the driving tube 6 off the twisted wire pair 8. The distal end 21 of the connector 20 is tapered fit within the open end of handle 18 and thereby travel with the driving tube 6 without jamming. 
     A leg plate 30 (FIG. 2) includes a housing 32 with is opening 34, which is adapted to receive the connector 20 after the driving and guide tubes are removed. Concavely curved finger grips 36 are provided on either side of the housing 32. These grips 36 facilitate holding of the housing while inserting the connector 20 into the opening 34. The bottom of the housing 22 is integrally formed or attached to a circular plate 35. 
     The outside diameter (e.g., 0.125&#34;) of the connector body 20 is smaller than the inside diameter (e.g. 0.146&#34;) of driving tube 4. Thus, the guide and driving tubes 4, 6 may pulled together over the connector 20 and thereby removed from B twisted wire pair 8 prior to connecting to leg plate 30. 
     As an additional feature, an opening 37 may be provided along the top of the housing 32. This opening 37 provides access for facilitating cleaning of the electrical connections and further allows one to visually verify that electrical connection has been made. 
     After insertion of the connector 20 into the opening as shown in FIGS. 3 and 4, the spring biased electrical connectors 38, 40 within the housing 32 electrically contact ring-shaped terminals 22, 24, respectively at their distal ends. The proximal ends of the electrical connectors 38, 40 holding clamps which hold uninsulated ends of leads 42, respectively. The leads 42, 44 extend through ribbon cable (see FIG. 2) to a signal receiving socket of a fetal monitoring device via interengaging socket and plug connectors 48, 50, cord 52 and plug 54, which is adapted to be plugged into the fetal monitor. In a similar manner, leads 41, 43, 45 (see FIG. 6), which will be described later, extend through the ribbon cable 46. 
     FIGS. 2 and 3 also show a base 56 snapped to the underside of the housing 32 via a stud 58 within a snap compartment 60. The base 56 may be an adhesively coated flexible pad made from foam material. In FIG. 3, the stud 58 is pushed between an opening periphery 62 in the underside of the snap compartment until its top rounded end 64 clears the opening periphery 62 and then the stepped transition area 66 of the stud 58 engages the opening periphery 62. During insertion, the opening periphery 62 bends against the stud 58 into the position shown. The bottom 68 of the stud 58 extends radially outward as to sandwich the base 56 between itself and the underside the snap compartment 60. 
     The housing 32 is freely rotatable about the stud 58 with respect to the base 56 in either the clockwise or counterclockwise directions indicated by double arrow 69 (see FIG. 2). This rotation allows the housing 32 to be oriented into any desired angular orientation. This rotatable connection helps to avoid inadvertent disconnection of the removable connector 20 from the leg plate 30 when, for instance, a doctor brushes against the twisted wire pair 8. 
     FIG. 5 shows the manner of removal of the guide and driving tubes 4, 6 from the connector 20 and twisted wire pair 8. The spiral electrode 10 is in contact with the fetal epidermis E. The tubes 4, 6 are removed by pulling the driving handle 18 and guide tube 4 in the direction indicated by the direction arrows, i.e., in a direction away from the fetal and maternal electrodes 10, 12. After removal of the tubes, the connector 20 is accessible for its insertion into a leg plate. 
     FIG. 6 shows three leads 42, 43, 44 in electrical connection with leads 70, 72 and 74, respectively (see also FIG. 3). Another two leads 41, 45 (not shown in FIG. 3 for sake of brevity but are arranged similar to that shown FIG. 6) are unterminated to serve as shield wires to help shield against stray induced voltages from electromagnetic interference and are electrically connected to a chassis (not shown) of the monitoring device. The unterminated leads 41, 45 act like an antenna to pick up stray voltages in the vicinity and route them to the chassis, rather than allow the stray voltages to follow the path of the other wires. Leads 41, 45 also distribute capacitance from the other three leads 42, 43, 44 via ribbon cable 80 to the chassis. 
     FIGS. 6 and 7 also show a leg plate 76, which has the same housing 32 as that for the leg plate 30 of FIG. 3, except that the housing is attached to a larger rectangular belt plate 78, rather than to an adhesive pad 56. The belt plate 78 of FIG. 6 has a ground plate 80 welded onto the base 68 (see FIG. 3) of the stud 58. 
     The belt plate 76 has a slot 82 for holding one end of a belt 84 as shown on one side and holed projections 86 with a pin 88 extending through the holes in projections 86 for holding the other end of the belt 84. The belt plate 76 snaps into the underside of the housing 32 in the same way as does the base 56 so as to enable the housing 32 to rotate about the stud 58. Since the belt 84 is only snugly fie around the mother&#39;s thigh and not too tight as to cause restriction of blood flow, the ground plate 80 must be larger than the base 68 of the FIG. 3 embodiment needs to be in order to ensure that contact with mother&#39;s leg is maintained. 
     The belt plate 76 is exemplified by Corometrics Medical Systems as part of leg plate model no. 260800A, C. A suitable leg plate belt 84 is exemplified by Corometrics Medical Systems as model no. 202300AA. 
     FIG. 6 also shows a plug 90 from which extends ribbon cable 46 and which is fitted into a socket 92 of the leg plate 76. This differs from the hard wiring of leads 70, 72, 74 from ribbon cable 46 of FIG. 3. 
     FIG. 8 shows a view similar to that of FIG. 3 except that the stud 94 has an undercut 96 in which is resiliently biased a snap spring 98. Spring 98 is retained in the snap compartment 60 and is ring-shaped to define an opening there-through. 
     In order to snap the stud 94 into place, the top rounded end 100 of the stud 94 is inserted through the opening defined by the snap spring 98 and into the compartment 60. A cap 102 is on the top rounded end 100 of the stud 94. During this insertion, the snap spring 98 is forced to elastically expand outward by the cap 102 pressing against the snap spring 98 until the spring 98 clears the downwardly facing end 104 of the cap 102. The snap spring 98 thereafter resiliently closes against the undercut 96 to retain the stud 94 in position. If attempt is made to pull the stud 94 out of the compartment 60, withdrawal of the stud 94 is prevented by the holding force of the spring 98. Thus, a permanent mechanical snapping securement is obtained. 
     A conductive gel 105 is applied to the base 106 of the stud 94. This gel will contact the thigh of the mother. Although not shown in the other embodiments, the gel 105 is applied to the bases of each of the other embodiments as well. The bases 68, 106 or ground plate 80 serve as ground electrodes. 
     In both FIGS. 3 and 8 embodiments, the snap compartment 60 is electrically conductive and is in electrical contact with the stud 58 or 94, which is also electrically conductive. Lead 72 has an uninsulated end which is soldered to the snap compartment 60. 
     In the embodiments of FIGS. 2-4 and 8, the flexible adhesive pad 56 may conform to the shape of the mother&#39;s leg when adhered to the leg. A removable sheet (not shown) may cover the adhesive on the underside of the pad 56 and then removed when the pad 56 is to be applied to the mother&#39;s leg. The adhesive pad 56 (see FIG. 8) may include a foam material 108 secured to a sturdier element 110, such as vinyl. 
     As should be apparent, for any embodiment, the ribbon cable 46 may be either hard wired to the leg plate or may be plugged into a socket in the leg plate. Also, either embodiment may employ either the permanent or detachable snap connection. The advantage of using the detachable snap connection is that the housing may be reused; only the base which is in direct contact with the patient will be discarded. Thus, any base is interchangeable with another. 
     For all the leg plate embodiments, it is desireable angle the incline of the opening 34 in the housing 32 for receiving the connector 20 at about eighteen degrees relative the horizontal plane (or of the adhesive pad 56 or belt plate so that insertion of the connector 20 will not get in the way of the mother&#39;s leg. The side of the leg plates which receive the connector may be considered an input and the side which effects connection with the remote monitoring device may be considered an output. 
     Preferably, the electrodes and electrical contacts and conductors are made of nickel or gold plated copper or else gold plated over nickel plated copper. High density polyethylene (such as 12 melt Arco #7120 or Chevron #9160 or petrothene LS 606 8 melt, density 0.96) is recommended as the material for the guide and driving tubes 4, 6 handle 18 and the housing 32. The conductors are preferably jacketed with polyvinylchloride. All components may be made from the same materials as are described for their counterparts in the patents previously mentioned that are incorporated herein by reference. 
     The outer diameter of the guide tube 4 must be small enough to avoid harming the mother during its insertion, such as about 0.315 inches. The inner diameter of the driving tube 6 is about 0.146 inches. Thus, the width of the connector 20 must be smaller than 0.146 inches to fit within the driving tube 6. 
     A further embodiment utilizes a printed circuit board which is fitted in the bottom of the housing. All interconnection leads are then soldered directly to contacts 114 on the printed circuit board 112 below. The board is preformed so that all leads will be in alignment with respective contacts 114 after placing the board in the housing. The printed circuit board 113 may interconnect the appropriate contacts 114. 
     If desired, the housing may be prevented from rotating relative to the base by providing projections from the base which block the housing from rotating. 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various changes and modifications may be made without departing from the spirit and scope of the present invention.