fig1 - 4 illustrate a surface mounted electrode and applicator gun 70 of the prior art which are more fully set forth in u . s . pat . nos . 4 , 274 , 419 and 4 , 311 , 152 . these patents are commonly owned by the assignee of the present invention and are incorporated herein as if fully set forth below . the prior art electrodes of fig1 - 4 are described herein to provide a better understanding of the differences in structure and function of the prior art electrodes and the present invention . the prior art electrode shown in fig1 - 4 generally consists of a circular sheet member 10 having an annular cutout portion 12 in the center thereof into which a collar 14 is inserted . the collar 14 is shaped to hold an electrically conductive member 16 therein . a ring member 18 is further employed to clamp around the upper portion of the collar 14 . the sheet member 10 is coated on one side with a skin adhesive layer 20 . the adhesive is protected during storage with a protective cover 22 . a spongy abrasive member 24 ( see fig2 ) is provided with an electrolyte gel thereon and is placed in contact with the conductive member 16 . the abrasive member 24 is protected during storage with the protective cover 24 . the prior art collar 14 of fig1 - 4 has the general configuration of an inverted hat with a flat base surface 28 and a vertical wall surface 30 which is normal and integral with the flat base surface 28 and which terminates in a contoured flange 32 . the flat base surface 28 has an annular opening 34 in the center thereof with a diameter less than the diameter of the inner wall 30 . around the annular opening 34 , is a vertical wall 36 having slots 38 cut therein about every 90 degrees . the walls 30 and 36 extend above the plane of the base 28 leaving a channel 40 therebetween . the collar 14 is generally molded from a semi - flexible , nonconductive plastic material such as an acetate - based material , nylon , polyester , polyethylene or polypropylene . the wall 36 is made sufficiently thin so that it can be flexed under pressure . the diameter of the collar 14 is substantially greater than its height . the inner periphery of the wall 36 is provided with a ridge 42 which functions to retain the conductive member therein . the prior art electrically conductive member 16 of fig1 - 4 is adapted to be snapped into the collar 14 . the electrically conductive member 16 may be manufactured from a synthetic resin impregnated with carbon from a suitable electrically conductive metal or metal containing material or other suitable electrically conductive material . as shown in fig2 and 3 , the electrically conductive member 16 includes a lower portion 44 having a textured convex lower surface 45 and a thickness substantially equal to the depth of the cup formed by the flange 32 , wall 30 and base 28 of the collar . integral with the lower portion 44 is an upper portion 46 of reduced diameter relative to the lower portion . the upper portion 46 has a diameter equal to that of the annular opening 34 in the collar 14 . the circumference of the upper portion has a slot 48 therein which is interrupted by detents 50 positioned normal to the slot 48 . the slot 48 of the conductive member 16 receives the ridge 42 in the wall 36 of the collar 14 to prevent the conductive member from moving vertically within the collar . the detents 50 of the conductive member 16 engage in the slots 38 in the flexible wall 36 of the collar 14 to prevent the conductive member from being rotated except by the predetermined torque / force of the applicator gun 70 . a downwardly extending stud 52 provided on the bottom of the conductive member 16 preferably includes a polygonal outer surface 54 so that the coupler of the applicator gun can be drivingly secured over the stud to rotate the conductive member 16 . the prior art penetrating means for abrading or penetrating the epidermal layer of skin is a separate porous abrasive member 24 as illustrated in fig2 a and 4 . the abrasive member 24 is a generally fibrous pad incorporating abrasive fibers and having a convexly curved surface 60 and a diameter substantially the same as the diameter of the lower portion 44 of the conductive member 16 . a flange 58 is folded against the edges of the abrasive member 24 to clamp the abrasive member 24 in the conductive member 16 . the prior art abrasive member 24 is loaded with electrolyte gel so that when the electrode is applied to the skin , the electrolyte gel provides electrical contact between the skin and the conductive member 16 . the assembled collar 14 , conductive member 16 and abrasive member 24 are snapped together and placed in the annular opening 12 of the adhesive coated sheet member 10 . the adhesive coating 20 contacts the upper surface of the flange 32 of the collar 14 to secure the collar 14 in place relative to the sheet member . a snap ring 18 as shown in fig1 is snapped over the wall 30 of the collar . the snap ring 18 is held in place by a ridge 62 extending around the outer terminating edge of the wall 30 of the collar 14 . fig3 and 4 generally illustrate the prior art applicator gun 70 which is used with the electrode described above as well as the present invention described below . the applicator gun 70 generally includes a housing 72 within which is mounted an electric motor 74 driven by ac or dc current from a suitable current source . the motor illustrated is driven by a rechargeable battery 76 held in place in a quickly disconnectable case 78 which also serves as the handle of the applicator . the lower end of the case includes recessed electrical contacts 79 for battery recharging . the motor has a shaft 80 to which a coupler 88 is attached . the coupler 88 includes a polygonal recess 90 thereon which is shaped to receive the specifically shaped stud 52 of the electrode therein . fig5 - 11 are illustrative of the preferred forms of the present invention . the electrode 110 of the present invention is preferably a radiolucent member which consists generally of an electrically conductive center member 112 which is received in a circumferential housing 114 . the housing 114 includes a flexible screen member 116 received therein on the side of the housing 114 opposite to the center member 112 . as with the prior art electrode described above , the electrode 100 of the present invention may further include an adhesive coated sheet member 118 surrounding a retaining ring 150 . the sheet member 118 is preferably formed of a cross linked polyethylene foam having an adhesive thereon to facilitate the attachment of the electrode 100 to the skin of the patient . prior to use , the adhesive surface of the sheet member 118 is protected by a paper - like protective cover 120 , and the surface of the electrode is further protected in a tray - like package ( not shown ) or by a further protective cover 121 . in the preferred form of the present invention , the center member 112 is preferably a plastic carbon member having a thin silver plated layer thereon which has been treated with silver chloride to enhance ion flow therethrough as well as to form a low impedance point of connection with the wires ( not shown ) of the electrode . alternately , the center member may be formed of a metal or other material to provide the desired conduction of the physiological signal from the skin of the patient to the signal acquisition device as shown in fig5 and 6 , the center member 112 of the present embodiment includes a generally flat first surface 122 which faces the skin of the patient in use . the center member 112 includes a circularly shaped outer circumference having a diameter which is greater than the diameter of the aperture 134 in the housing 114 as described below . as shown in fig6 the second surface 124 of the center member 112 faces away from the skin of the patient in use and preferably includes a pair of post members 126 and 128 extending therefrom . the post members 126 and 128 preferably each include a tapered surface 129 thereon which extends from the second surface 124 of the center member 112 . the tapered surface 129 of each post member 126 and 128 preferably includes a slight rib 130 thereon and decrease in circumference to form a snap area 132 on each of the post members 126 and 128 . the snap areas are contacted and engaged by a snap type of electrode connector ( not shown ) to supply physiological signals which originate from the same location for use by a plurality of signal acquisition devices . the rib 130 is shaped to frictionally contact a portion of the housing 114 described below . unlike the prior art post member 52 shown above in fig1 - 4 , the post members 126 and 128 of the present invention are preferably not hexagonally or otherwise particularly shaped to receive reciprocal motion from the prior art applicator gun 70 ( fig4 ) thereon although the tip of the applicator gun may be readily modified to engage and rotate the pair of post members 126 and 128 as described above . the circumferential housing 114 of the present embodiment is preferably formed of a rigid plastic or similar material . as shown in fig6 the housing 114 includes an aperture 134 extending therethrough and first and second surfaces 136 and 138 respectively . the aperture 134 is formed to frictionally receive the center member 112 therein . the first surface 136 of the housing 114 is best shown in fig5 . the first surface 136 includes an outer circumferential rib 140 which forms the outer periphery of the housing 114 and an inwardly positioned annular ring shaped surface 142 having a plurality of channels 144 formed therein . during assembly , the circumferential rib 140 is crimped or otherwise formed to retain the screen member 116 thereon as shown in fig6 . a recessed area 146 is also located inwardly of the annular surface 142 to surround the aperture 134 and receive the first and second surfaces 122 and 124 of the center member 112 therein . the second surface 138 of the housing 114 preferably includes a generally flat contact surface 148 which is shaped to receive a portion of the retaining ring 150 thereagainst in a manner similar to the contact between the collar 14 and the conductive member 16 as shown in fig2 . the sidewall surface 154 of the housing 114 extends outwardly from the contact surface 148 and includes a circumferential recess 152 therein . the circumferential recess 152 is sized to frictionally receive a portion of the retaining ring 150 therein . as with the collar 14 shown in fig2 the retaining ring 150 of the present invention extends between the outer surface of the housing 114 and the sheet member 118 to retain the housing 114 , center member 112 and screen member 116 while allowing relative movement between the housing 114 and retaining ring 150 . additionally , a snap ring 158 is positioned between the outer surface of the retaining ring 150 and the sheet member 118 to prevent movement between the sheet member 118 and the retaining ring 154 . the screen member 116 of the present invention is preferably constructed of a flexible silicon carbide or other abrasive material . the screen member 116 is sized so that when the outer circumference of the screen member 116 is positioned generally inwardly from and adjacent to the crimped outer circumferential rib 140 , the screen member 116 contacts the annular ring surface 142 of the housing 114 and is bowed slightly outwardly therefrom . this orientation is particularly useful to provide consistent abrasion of the skin of the patient because if the user of the applicator gun presses too hard during the preparation of the skin of the patient , the screen member 116 will preferably flex to decrease the abrasion of the skin . the flexibility of the screen member 116 and the orientation of the screen member 116 with respect to the housing 114 and center member 112 may also be particularly important during the use of the electrode . the electrolyte gel ( not shown ) is preferably initially placed in the housing 114 to fill the space between the first surface 136 of the housing 114 , the first surface 122 of the center member 112 and the screen member 116 . when the electrode is applied to the skin of the patient , the sheet member 118 encircles the periphery of the housing 114 such that the electrolyte gel is trapped therein to provide for the electrical conduction of the physiological signal from the skin of the patient to the center member 112 and the signal acquisition device . during certain procedures such as ecg stress tests , the patient is exercising or otherwise moving around . this movement may cause the skin which is in contact with the various electrodes to stretch or contract according to the movements of the patient . during this movement , the skin may press against or move away from the prior art electrodes . this movement between the electrode and the skin of the patient may cause muscle artifact and may even break the signal between the patient and the signal acquisition device . during use of the electrode of the present embodiment , the electrolyte gel forms a gel column in the electrode which responds to the movement of the skin of the patient to ensure that the electrolyte gel maintains electrical contact between the skin of the patient and the center member 112 . although , the use of a gel form of the electrolyte is preferred , a solid or wet gel may also be used to maintain contact between the center member 112 and the skin of the patient . the area between the circumferential rib 140 and the annular surface 142 on the first surface 136 of the housing 114 functions basically as a reservoir area 160 for the electrolyte gel in the present embodiment . for example , if the skin of the patient presses against the slightly flexed or raised center of the mesh screen , the electrolyte gel is pushed back into the recess of the housing and is forced to flow to the outer periphery of the housing 114 through the channels 144 in the annular surface 142 to the reservoir area 160 of the housing 114 between the circumferential rib 140 and the annular surface 142 . when the skin of the patient draws away from the electrode , the electrolyte gel is drawn from the reservoir area 160 of the housing 114 through the channels 144 and into the recessed area 146 to ensure that a continuous column of electrolyte gel extends between the skin of the patient and the center member 112 . fig7 and 8 are illustrative of a further embodiment of the present invention wherein the pair of post members 126 and 128 are operatively connected to individual center members 166 and 168 rather than the common center member 112 as shown in fig5 and 6 . in this embodiment , the electrode assembly includes a pair of electrodes each having center members , housings , snap rings and the other components described above , all of which are commonly connected to a single sheet member 118 which retains the electrodes in a fixed and spaced apart relationship with respect to each other so that research and comparative studies performed with this electrode assembly may have a variability of a known quantity between each of the acquisition sites to allow the researcher and / or study coordinator to eliminate the effect of the distance between the signal acquisition sites as a variable in the study . the electrode assembly of this embodiment operates generally in the same manner as the preferred embodiment ; and , therefore , like numbers have been added to like members , and the features common to each embodiment are not separately repeated herein . fig9 - 11 are illustrative of a further variation of an alternate form of electrode assembly 170 of the present invention wherein the electrode assembly includes a pair of center members 172 and 174 each having their own post members thereon , 176 and 178 , respectively . as shown in fig9 the center members 172 and 174 are preferably oriented horizontally along the electrode assembly 170 . as shown in fig1 , the center members 172 and 174 are in operative and conductive contact with a recess 180 on the surface of the electrode assembly 170 which contacts the skin of the patient in use . the electrode assembly 170 of this embodiment consists of the sheet member 118 with an adhesive on one surface thereof ; the recess 180 which is shaped to receive a conductive material such as an electrolyte gel 182 therein and the center members 172 and 174 each having a post member 176 and 178 thereon . this embodiment is particularly adapted for use as a low cost electrode assembly 170 and includes the electrically conductive center members 172 and 174 operatively connected to a common centrally located recess area 180 which may be of nearly any desired shape . the center members 172 and 174 are preferably positioned on a relatively small sheet member 118 and are spaced apart from each other a relatively small distance so that the snap connectors ( not shown ) may be connected thereto while the physiological signals are received from a common recess area 180 via the electrolyte gel 182 so that the acquisition devices are provided with physiological signals from a common source on the skin of the patient . the foregoing is intended to be illustrative of the currently preferred forms of the present invention which are defined by the following claims .
a medical electrode and skin preparation device is adapted to be secured to the skin of a patient and is designed to allow the user to acquire physiological signals for use by a plurality of signal acquisition devices and optionally to also reliably prepare the skin of the patient by abrasion or penetration of the epidermal layer of the skin which is in conductive contact with the conductive member of the electrode assembly . the electrode assembly includes a plurality of post members capable of conducting physiological signals received from the skin of the patient for acquisition , recording and / or analysis by one or more external devices .