Electrode for detecting an electric biological signal, in particular an electrocardiographic signal

Abstract: An electrode (7, 8) for detecting an electric biological signal, in particular an electrocardiographic signal, and presenting a metal conducting disk (15, 16) and a rigid net (18, 19) of constant thickness (D) and superimposed on the metal disk (15, 16). A small amount of conducting fluid (30) is poured on to and spreads throughout the net (18, 19) to form a layer of conducting fluid (30) superimposed on the metal disk (15, 16) and presenting a constant thickness (D).

Description: The present invention relates to an electrode for detecting an electric biological signal, in particular an electrocardiographic signal. Currently known instruments for detecting electrocardiographic signals present at least two external electrodes, which are applied to portions of the human body (e.g. one on the left and one on the right arm) for detecting electric biological body signals generated by the action of the heart. The electrodes are substantially flat, and are normally applied to the body by means of straps or adhesive means on the electrode itself; and, to improve electrical contact between the electrode and the body, a thin layer of conducting gel is normally applied between the two. The layer of conducting gel, however, which is not applied evenly over the electrode and therefore varies in thickness, fails to provide for an optimum distance between the electrode and the body. In particular, on certain parts of the electrode, the thickness of the gel may be such as to present a contact resistance unsuited to the characteristics of the electrocardiographic signal detecting instrument. Moreover, the above means of securing the electrodes fail to provide for rigidly connecting the electrically contacting parts, and permit relative movements resulting in noise in the electric signal, even to the extent of impairing the outcome of the electrocardiogram. Document FR-A-2 581 855 discloses a device according to the preamble of claim 1. It is an object of the present invention to provide an electrode for detecting an electric biological signal, in particular an electrocardiographic signal, designed to overcome the above drawbacks typically associated with known electrodes. According to the present invention, there is provided an electrode for detecting an electric biological signal, in particular an electrocardiographic signal, as claimed in Claim 1. A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a view in perspective of an instrument for detecting an electric biological signal, in particular an electrocardiographic signal, featuring electrodes in accordance with the teachings of the present invention; Figure 2 shows a cross section of an electrode in accordance with the present invention. Number 1 in Figure 1 indicates a pocket instrument for detecting an electrocardiographic signal, and comprising a substantially parallelepiped outer casing 2, and a known electronic processing circuit 3 (shown schematically) housed inside casing 2. More specifically, casing 2 presents a flat rectangular wall 4 fitted with a display 5 and two input signal detecting electrodes 7, 8. Circuit 3 is supplied with and processes an electrocardiographic electric signal, and itself supplies various information, shown on display 5, relative to cardiac activity (e.g. the number of beats per minute, electrocardiographic trace, etc.). Electrodes 7, 8 communicate with circuit 3 over respective electric wires 9, 10, and circuit 3 communicates with display 5 over an electric line (bus) 11. Wall 4 presents two cylindrical dead holes 12, 13, each housing a respective electrode 7, 8; and each electrode 7, 8 according to the present invention (Figure 2) comprises a circular conducting disk 15, 16 housed inside hole 12, 13, and a rigid net 18, 19 superimposed on disk 15, 16. Each conducting disk 15, 16 presents a first circular face 15a, 16a contacting the bottom of cylindrical dead hole 12, 13, and a second face 15b, 16b to which net 18, 19 is applied; and net 18, 19 is circular in shape, presents a constant thickness D, is made of synthetic insulating material, e.g. Nylon, and is fixed stably, e.g. by means of adhesive, to conducting disk 15, 16, which is made of metal material, in particular chloridized silver. The bottom of each cylindrical dead hole 12, 13 presents a through hole 23, 24 engaged by electric wire 9, 10 extending from first face 15a, 16a to electronic circuit 3. In actual use, a small amount of conducting fluid 30, in particular chlorinated water, is poured on to and spreads evenly throughout net 18, 19 to form a layer of fluid of constant thickness D retained by net 18, 19 and superimposed on conducting disk 15, 16. The user (not shown) of instrument 1 then places two parts 21, 22 of the body on respective electrodes 7, 8. More specifically, the user (not shown) grips outer casing 2, places the right and left thumb 21, 22 on respective electrodes 7, 8, and with the ball of the thumb presses on nets 18, 19. The layer of conducting fluid 30 thus provides for ohmic contact between portions 21, 22 and respective conducting disks 15, 16 to connect portions 21, 22 to electric wires 9, 10 and transfer the biological body signal to circuit 3. Since net 18, 19 is in no way deformed by the pressure applied by the user, the thickness D of the layer of conducting fluid remains constant. The advantages of the present invention will be clear from the foregoing description. In particular, electrode 7, 8 provides for ohmic connection of a conductor (disk 15, 16) and a portion of the body (portion 21, 22) via a conducting means (conducting fluid) performing the same function as the gel used on known electrodes, but which presents a constant thickness regardless of the position of the body portion on the electrode. Moreover, net 18, 19 presents a thickness D corresponding to the optimum distance between the body portion and the conductor; and, even in the event of the body portion moving in relation to the electrode, the thickness of the conducting means remains unchanged, so that no noise is produced in the detected electric signal. Clearly, changes may be made to the electrode as described and illustrated herein without, however, departing from the scope of the present invention. For example, as opposed to chlorinated water, any other liquid solution with similar conducting characteristics may be used for achieving ohmic contact as described above.

Claims: An electrode (7, 8) for detecting an electric biological signal, in particular an electrocardiographic signal, comprising: substantially flat conducting means (15, 16); characterised by comprising: substantially flat net means (18, 19) superimposed on said conducting means (15, 16) and presenting a substantially constant thickness (D); said net means (18, 19) receiving a conducting fluid (30), which spreads evenly through the net means (18, 19) to form a layer of conducting fluid (30) superimposed on said conducting means (15, 16), retained by said net means (18, 19), and presenting a substantially constant thickness (D); said net means (18,19) being undeformable by the pressure applied by the user. An electrode as claimed in claim 1, characterized in that said conducting means (15, 16) comprise at least one flat conductor; said net means (18, 19) being located contacting a first face (15b, 16b) of said flat conductor. An electrode as claimed in claim 2, characterized by comprising connecting means (9, 10) for connecting said conducting means (15, 16) to processing means (3); said connecting means (9, 10) communicating with a second face (15a, 16a) of said flat conductor. An electrode as claimed in claim 2 or 3, characterized in that said net means (18, 19) are fixed by means of adhesive material to said first face of said flat conductor (15, 16). An electrode as claimed in any one of the foregoing claims, characterized in that said net means (18, 19) are made of insulating material. An electrode as claimed in any one of the foregoing claims, characterized in that said conducting means (15, 16) comprise at least a metal portion made of chloridized silver.

Inventors: CASTELLI ARRIGO, CASTELLI, ARRIGO
Applicants: CASTELLI ARRIGO, CASTELLI, ARRIGO
Application year: 1996
Main classification: A61B5
IPC codes: A61B5