US3826246A

US3826246A - Apparatus for sensing physiological potentials

Info

Publication number: US3826246A
Application number: US00337262A
Authority: US
Inventors: W Raddi; R Johnson
Original assignee: ESB Inc
Current assignee: ESB Inc
Priority date: 1973-03-07
Filing date: 1973-03-07
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30
Also published as: FR2220227A1; CA995765A; GB1445261A; DE2322835A1; IT990332B; JPS49119494A; NL7314117A; FR2220227B1; BE803004A

Abstract

Apparatus is provided for sensing physiological potentials of a living body. There is provided a first band for at least partially encircling a part of the living body and having a first electrode mounted thereon. The first electrode is adapted for connection to an instrument for amplifying the physiological potentials of the living body. A second band is provided for at least partially encirling another part of the living body and has a second and a third electrode located thereon. The second and third electrodes each are adapted for connection to the instrument for amplifying the physiological potentials of the living body.

Description

United States Patent [191 Raddi et al.

[111 3,826,246 [451 July 30,1974

1 1 APPARATUS FOR SENSING PHYSIOLOGICAL POTENTIALS [75] Inventors: William J. Raddi, Philadelphia;

Robert William Johnson, Levittown,

21 App]. No.: 337,262

[52] US. Cl. l28/2.06 E, l28/2.06 B, l28/DIG. 4 [51] Int. Cl A6lb 5/04 [58] Field of Search 128/206 E, 2.06 B, 2.06 R, 128/212, 2.] R, 2.05 R, DIG. 4, 2.1 E, 410,

687,916 11/1936 -Gcrmany 128/21 R OTHER PUBLICATIONS Silcocks et al., High-fidelity electrode/preamplifier for cardiography, Journal for the Advancement of Biomedical Instrumentation, Vol. 5, No. 3, May, 1971 Primary ExaminerRichard A. Gaudet Assistant Examiner-Lee S. Cohen [5 7 ABSTRACT Apparatus is provided for sensing physiological potentials of a living body. There is provided a first band for at least partially encircling a part of the living body and having a first electrode mounted thereon. The first electrode is adapted for connection to an instrument for amplifying the physiological potentials of the living body. A second band is provided for at least partially encirling another part of the living body and has a second and a third electrode located thereon. The second and third electrodes each are adapted for connection to the instrument for amplifying the physiological potentials of the living body.

9 Claims, 8 Drawing Figures LEFT WRIST RIGHT WRlST APPARATUS FOR SENSING PHYSIOLOGICAL POTENTIALS BACKGROUND OF THE INVENTION 7 This invention relates to improvements in sensing means and electrode systems. More specifically, the invention relates to sensing means and electrode systems for detecting or picking up physiological potentials of a living body and as such sensing means and electrode systems are used in conjunction with a recording or measuring instrument or with an amplifier, which may form a part of such an instrument, and which is used to amplify the physiological potentials. I

It may be explained here that the present method for obtaining quality electrocardiograms in patients requires the use of a special electrode jelly or conductive cream to minimize the contact impedance'between the metal electrodes placed in contact with the body of the patient and the skin surfaces of the patient. This special jelly or cream is usually administered by a qualified In a co-pending US. application Ser. No. 337,261 assigned to the same assignee as the instant application and filed concurrently herewith there is described a monitor apparatus for monitoring electrical signals, either natural, i.e., electrocardiographic signals, or artificial, i.e., resulting from a, heart pacer stimulating the heart of a patient, via a communication link. Briefly, the monitor'apparatusdisclosed in the above identified application comprises a transducer including electrode means which are used to sense the physiological signals of the patient. The transducer processes the sensed signals for transmission over a communication link, as for example, a standard telephone communication network. A receiver, typically located at a remote telephone station such as a cardiologists office, receives the transmitted information which is thereafter used by the cardiologist for diagnostic purposes.

The transducer of the monitor apparatus just described is usually situ'ated with the patient in his home and must, therefore, be operated by the patient us ually without the assistance of a trained physician or technician. To this end, the transducer of the above identified application utilizes a pair of stretch arm band electrodeswhich can be utilized quite easily by the patient without assistance.

SUMMARY oF THE INVENTION technician.

Another object of the invention is to provide an improved sensing means and electrode system which allows the patient to substantially completely relax while monitoring of the physiological potentials of the patient is effected.

tials of the patient without the aid of a physician or Briefly, the present invention achieves the foregoing objects by providing apparatus for sensing physiological potentials of a living body. The apparatus comprises: a first band for at least partially encircling a part of the living body and having a first electrode located thereon, the first electrode being adapted for connection to an instrument for amplifying the physiological potentials of the living body; and a second hand for at least partially encircling another part of the living body and having a second and a third electrode located thereon, the second and thirdelectrodes each being adapted for connection to the instrument for amplifying the physiological potentials of the living body.

The invention will be fully and comprehensively understood with other objects and advantages which will become subsequently apparent as the details of construction and operation thereof are more fully hereinafter described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 diagrammatically" illustrate prior art electrode systems and are useful to explain possible problems associated with their use;

FIG. 3 is a diagrammatic illustration of the modification to one of the two wrist band electrodes in accordance with the invention to facilitate the three electrode configuration of FIG. 2;

FIGS. 4, 5, and 6 show an actual implementation of the stretch wrist band electrode system in accordance with the invention; and

FIGS. 7 and 8 diagrammatically illustrate modifications to the electrode system of FIGS. 3-6 in accordance with the invention.

DESCRIPTION OF THE PREFERRED A EMBODIMENTS the skin surfaces of the patient during a lead 1 ECG A measurement using a two input terminal amplifier 22.

The amplifier 22 has input terminals 24 and 26 between which physiological voltage signals are sensed and a pair of output terminals 28 and 30 between which the amplified physiological voltages appear or where voltage measurements are taken, as for example, cardiographic signals (E Note that terminal 26 and terminal 30 are electrically identical. The effect of common mode voltages on the quality of measurements will now be described. A common mode voltage (E may be characterized as that voltage that exists between the chassis of the measuring instrument, that is, the amplifier, and the patient. I I

Assume the following typical values for the parameters in FIG. 1: I

2, (Skin to electrode impedance utilizing a =l000 ohms conductive cream between electrodes l8 and 20 and the skin of the patient) -Continued Z (amplifier input impedance) =l megohm Z (impedance between amplifier chassis =l000 megohm and patient) E (common mode voltage between =l volts amplifier chassis and patient) E (cardiac voltage measured between =2 millivolts amplifier output terminals 28 and 30) The percentage error in voltage measurement E caused by the input impedance Z, of the amplifier 22 in given approximately by the following formula (1):

Percent Error due to Z,-,, i 2 22 /2, Z X I00 Substituting the above values in formula (1) provides a percentage error in the voltage measurement of E of approximately 0.2 percent or 0.004 millivolts.

The percentage error in voltage measurements of E caused by the common mode voltage E is given Substituting the above values in formula (2) provides a percentage error in the voltage measurement of E of approximately 0.5 percent or 0.01 millivolts.

Consider now the situation if no conductive cream were used to reduce the impedance of Z,. Typically Z, would increase to 100,000 ohms and possibly as high as 1 megohm. With Z, being equal to l megohm, the percentage error caused by the input impedance Z,-,, of the amplifier 22 utilizing formula (1) would now be approximately 67 percent or 1.34 millivolts. This error could be reduced, however, bysimply increasing the input impedance Z to 1,000 megohm which is easily obtainable utilizing a Field Effect Transistor (F ET) amplifier.

But with Z, equal to l megohm, the percentage error in voltage measurement of E caused by the common mode voltage E utilizing formula (2) would now be approximately 500 percent or millivolts. This latter error cannot be'mitigated by increasing the impedance Z of amplifier 22.

However, by utilizing a three terminal input amplifier 31, as depicted in FIG. 2, having a positive input terminal 32, a negative input terminal 34 and a signal ground terminal 36, with the amplifier 31 signal ground terminal 36 connected to, for example, the right ankle of the patient via an electrode-37, a reduction in error proportional to the common mode rejection capability of the amplifier 31 is realized. Assume now, however, that the interface impedance Z, between the right ankle electrode 37 and the right ankle is also 1 megohm, therefore, the common mode percentage error in voltage measurement of E would be 10 millivolts as before. Now, however, the amplifiers common mode rejection capability, typically 60 db or greater will reduce this percentage error by 60 db, or by a factor of 1,000 to 0.01 millivolts. Thus, the electrode 37, commonly called an indifferent electrode, is to physically and electrically connect the signal ground terminal 36 of amplifier 31 to the patient so as to reduce the common mode voltage existing between the patient and the amplifier 31.

The impracticability of using a three electrode system configuration as depicted in FIG. 2 with an unaided patient is obvious. The sensing means or electrode system in accordance with the invention acquires 5 the same performance capability of the three discreet electrode configuration of FIG. 2 using only two discreet electrodes.

FIG. 3 is a diagrammatic illustration of the modification to one of the two electrodes 18 and20 in accordance with the invention, to facilitate the three electrode configuration of FIG. 2. This modification to one of the electrodes l8 and 20 provides two independent connections, one for the amplifier negative input terminal 34 and one for the amplifier signal ground terminal 36.

There is diagrammatically shown in FIG. 3, a shielded cable 40 interconnecting the left wrist of the patient to the positive input terminal 32 of amplifier 31 and a second shielded cable 42 interconnecting the right wrist of the patient to the negative input terminal 34 of the amplifier 31. The shielded

cables

40 and 42 each comprise an inner electrical conductor 62 and a braided outer electrical conductor 64 which are insulated from one another. It will be noted that the braided conductors 64 of shielded

cables

40 and 42 are interconnected by lead wire 44 and that each of them are in turn connected to the signal ground terminal 36 of amplifier 30 via lead 37.

The

electrodes

18 and 20 are shown in FIG. 3 in the form of arm or wrist bands and each comprises a metallic stretch band similar to watch band having its opposite ends interconnected by an electrode assembly 52. The wrist or

arm bands

18 and 20 and assemblies 52 are each arranged for contact with the skin surfaces of the arms or wrists of the patient. Each assembly 52 comprises an upper metallic plate portion 54 and a lower metallic plate portion 56. It will be noted, however, that the electrode assembly 52 of arm or wrist band 20 differs slightly from that of arm or wrist band 18. The electrode assembly 52 of arm or wrist band 20 is provided with an opening in the upper metallic plate 54 and interposed between the upper plate 54 and the lower plate 56 is a member or piece of electrically insulating material 58 which is also provided with an opening 60 therethrough. The insulating material 58 is not present in arm or wrist band 18 and the upper and

lower portions

54 and 56, respectively, are physically and electrically connected to each other and to the stretch band 50.

As shown in FIG. 3, the braided outer conductor 64 of shielded cable 40 is not electrically connected to the stretch band 50 nor to the electrode assembly 52 and only the inner electrical conductor 62 is electrically connected to the electrode assembly 52 and thus to the stretch band 50. However, the braided outer conductor 64 of shielded cable 42 is electrically connected via lead 66 tothe stretch band 50 and the inner electrical conductor 62 is electrically connected to the lower metallic plate 56. With such an arrangement, at the right arm or wrist of the patient, there is in effect two separate electrical connections between the amplifier 31 and right wrist of the patient, namely, an electrical connection is made between the input terminal 34 and the right arm or wrist of the patient via conductor 62 and lower plate 56 of electrode assembly 52, and another electrical connection is made between the signal ground terminal 36 of amplifier 31 and the right arm or wrist of the patient via lead 37, braided conductor 64,

lead 66, upper plate 54, and stretch band 50. Thus, the requirement for a separate right ankle electrode as depicted in FIG. 2, which is normally required in a lead l ECG, is eliminated because the electrical connection between the signal ground terminal 36 of amplifier 31 and the right'arm or wrist of the patient via lead 37, braided conductor 64, lead 66, upper plate 54, and stretch band 50 is electrically equivalent to the indifferent electrode (electrode 37) connection of FIG. 2.

Referring now to FIGS. 4, 5, and 6, there is shown an actual implementation of the stretch arm or wrist band electrode system in accordance with the invention. Each of the arm or wrist band electrodes 18 and are constructed identically except for an electrical connection for the indifferent electrode and therefore, only the arm or wrist band electrode 20 is illustrated in FIGS. 4, 5, and 6.

In FIGS. 4, 5, and 6, the arm or wrist electrode is again shown generally at 20; the stretch band isshown at 50; the shielded cable at 42; the inner conductor of the shielded cable at 62 which terminates at one end in an amplifierconnector 70, and at the opposite end in a lug connector 71; the outer braided conductor at 64 which terminates at one end in an amplifier connector 72 and at the opposite end in a lug connector 73; and the electrode assembly generally at 52 comprising the upper metallic plate 54, the lower metallic plate 56 and the insulation material as block 58. The upper plate 54 is fastened to the insulating block 58 at its upper portion by means of

screws

74 and 75. Lower plate 56 is fastened to insulation block 58 at its lower portion by means of a threaded pin 76 formed with the plate 56or welded thereto, and a nut 78. Interposed between nut 78 and the surface 80 of insulation material 58 is a metallic lock washer 81 and an electrical connector 82 onto which lug connector 71 is snapped or otherwise secured. Another metallic lock washer 83 and an electrical connector 84 is shown interposed between the upper plate 54 and the surfaces 85 of a recessed portion 86 provided in the left side of the insulation material 58 as viewed in FIGS. 5 and 6. The connector 72 of braided conductor 64 is snapped onto orotherwise secured to electrical connector 84.

As stated above, the arm or

wrist electrodes

18 and 20 are identical, however, in the arm or wrist electrode 18 the braided conductor 64 is cut off as at point 88 in FIG. 4 and, therefore, is not connected to the electrical connector 84. In fact, the electrical connector 84 is not present or utilized in the arm or wrist electrode 18.

From the foregoing it will be understood, that the arm or wrist electrode described with reference to FIGS. 4, 5, and 6, is an actual implementation of the arm or

wrist electrodes

18 and 20 described with reference to FIG. 3.

Referring now to FIG. 7, there is diagrammatically illustrated a modification to the electrode system of the invention wherein a pair of resistors R and R, are eIec-- trically connected between the shielded conductors 64 and the stretch'bands 50. While the insulation material 58, the wrist bands 50 and the shielded cable 42 are illustrated somewhat differently in FIG. 7 than in FIGS. 3-6, they are electrically equivalent to those. shown in FIGS. 3-6. Also, in FIG. 7, both arm or wrist band electrodes are identical, that is, they are both identical to that shown at 20 in FIG. 3.

The values of the resistors R and R need not necessarily be the same but the sum of the two must be large compared with the impedance of the patient between his right arm and left arm, as for example, R plus R must be greater than 500 ohms which typically represents the body fluid impedance between the right arm and left arm of the patient neglecting contact impedance (2,) between the electrodes and the skin surfaces of the patients body. However, the sum of R, and R must be low enough to be effective to reduce the common mode voltage. Typically R plus R should be in the range from about 1,000 ohms to about 20,000 ohms.

Referring now to FIG. 8, there is diagrammatically illustrated a modification of the electrode system of the invention shown in FIG. 7 wherein the pair of resistors R and R are electrically connected between the braided conductors 64 of shielded cable 42 and the stretch wrist bands 50 at the amplifier end via signal ground terminal 36 and leads and 82 connected, respectively, between the braidedconductors 64 of the left and right stretch bands 50. Electrically, the embodiment shown in FIG. 8 is the equivalent of that shown in FIG. 7.

The advantages of the embodiments of the invention shown in FIGS; 7 and 8 are that should anyone of the ground connections between the patient and the amplifier 31 fail or become reduced because of corrosion or dirt or other failure, as for example, one of the arm or wrist stretch bands 50 not making effective contact, then the alternative arm or

wrist electrode

18 or 20 ground connection will function to provide an alternate ground path or connection between the patient and the amplifier 31.

It should also be pointed out here that both R, and R may be replaced by a short circuit if a sufficient resistance is present due to the contact impedance between the stretch bands 50 and the skin surfaces of the patient, but, since the contact resistance or impedance between the stretch bands 50 and the skin surfaces of the patient cannot be assured of being of any given value, the use of resistors R and R is preferred.

From the foregoing it will be understood to those skilled in the art that the invention in its broadest aspects comprises apparatus for sensing or picking up physiological potentials of a living body which when used in conjunction with an instrument for amplifying or measuring these potentials provides three independent electrical connections between the living body and the instrument utilized, but does so utilizing only two discreet sensing or pick-up means. Further while the wrist or

arm electrodes

18 and 20 including the stretch bands 50 and the electrode assemblies 52 have thus far been described as metallic, if desired, they may be completely or partially be fabricated of any suitable electrically conductive material, as for example, an electrically conductive plastic material or carbon. Also, the stretch bands 50 of wrist or

arm electrodes

18 and 20 may be in the form of flexible bracelets for only partially encircling the wrists or arms of the patient, and, for that matter, are not restricted for use on the arms or wrists of the living body but may be constructed and arranged to wholly or partially encircle any appropriate part of the living body. As for the stretch bands 50 themselves, they may actually be fabricated of an electrically insulating material such as a rubber band for completely encircling a body part or a rubber bracelet for only partially encircling the body part. In these latter situations one of the rubber bands or bracelets, i.e., the equivalent of 18, would have an electrically conductive electrode, such as the electrode 52, mounted thereon for contact with the skin surfaces of the living body and the electrode would be provided with any suitable electrical connector for electrical connection to the instrument being utilized; in the case of the other rubber band or bracelet, i.e., the equivalent of 20, there would be mounted thereon for contact with the skin surfaces of the living body, two spaced apart electrically conductive electrodes, such as 56 and each of the electrodes would be provided with any suitable electrical connector for electrical connection via electrical conductors, such as shielded

cables

40 or 42, appropriately connected to the instrument being utilized. Again, in these latter situations with both arm or

wrist band electrodes

18 and 20 being identical, the resistors R and R may be utilized as they are described with reference to FIGS. 7 and 8.

Also from the foregoing, it will be understood that with respect to the electrode system, we have provided an electrode system wherein a patient can record his own ECG without the aid of a physician or technician. The electrode system of the invention is especially useful with the monitor apparatus described in the above identified co-pending application. The electrode system of the invention permits the patient to completely relax while physiological measurements are being taken as there is nothing that the patient must hold or grasp during the measurement process. Thus, much of the electrical noise introduced into the measurement process due to the normal requirement that a patient grasp electrodes, which noise emanates from muscle tension of the patient, is eliminated. Also, use of the electrode system of the invention permits the patient freedom of movement which may be required for obtaining other measurements.

While we have herein described and shown illustrative embodiments of our invention, it is to be understood that the invention is not limited thereto, but may comprehend other constructions, arrangements of parts, details and features without department from the spirit of the invention.

Having thus described our invention, we claim:

'1. An electrode system for use with an instrument constructed and arranged for the measurement of physiological potentials of a patient wherein the instrument has at least three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprising:

a. a first band for encircling a part of the body of the patient and having a first electrode located thereon;

b. a first electrical conductor having opposite ends,

one end of the first electrical conductor being electrically connected to the first electrode and the opposite end thereof being connected to the positive input terminal of the instrument;

c. a second band for encircling another part of the body of the patient and having a second and third electrode located thereon; and

d. second and third electrical conductors, each having opposite ends, one end of the second electrical conductor being electrically connected to the second electrode and the opposite end thereof being electrically connected to the negative input terminal of the instrument, one end of the third electrical conductor being electrically connected to the third electrode and the opposite end thereof being electrically connected to the signal ground terminal of the instrument.

2. Apparatus as defined in claim 1 wherein the first band is fabricated of electrically conductive material with the first electrode being electrically connected thereto.

3. Apparatus as defined in claim 1 wherein the second band is fabricated of electrically conductive material with the second electrode being electrically connected thereto, a piece of electrically insulating material, the third electrode being electrically insulated from the second band by the piece of electrically insulating material.

4. An electrode system for use with an amplifier adapted for the measurement of physiological potentials of a patient wherein the amplifier has three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprising:

a. a first conductive band having its opposite ends electrically interconnected, the first conductive band being constructed and arranged for physical.

and electrical contact with the skin surfaces of a limb of the patient;

b. a first electrical conductor having opposite ends,

one end of the first electrical conductor being electrically connected to the first conductive band and the opposite end thereof being (for) electrically (interconnecting the first conductive band with the) connected to the positive input terminal of the amplifier,

. a second conductive band having its opposite ends interconnected by an electrode assembly, the second conductive band and the electrode assembly each being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the electrode assembly comprising:

i. an upper conductive plate:

ii. a lower conductive plate; and

iii. a member of electrically insulating material interposed between the upper and lower conductive plates; the upper conductive plate of the electrode assembly being electrically connected to the second conductive band.

d. a second electrical conductor having opposite ends, one end of the second electrical conductor being electrically connected to the lower conductive plate and the opposite end thereof being (for) electrically (interconnecting the lower conductive plate) connected to the negative input terminal of the amplifier; and

. a third electrical conductor having opposite ends, one end of the third electrical conductor being electrically connected to the upper conductive plate and the opposite end thereof being (for) electrically (interconnecting the upper conductive plate) connected to the signal ground terminal of the amplifier.

5. An electrode system as defined in claim 4 wherein the first conductive band has its opposite ends electrically interconnected by a first electrode assembly comprising:

i. an upper metallic plate; and ii. a lower metallic plate, the upper and lower metallic plates being electrically connected together.

6. An electrode system for use with an amplifier constructed and arranged for the amplification of physiological potentials of a patient wherein the amplifier has three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprisa. a first metallic stretch band having its opposite ends interconnected by a first electrode assembly,

the first metallic stretch band and at least one portion of the first electrode assembly being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the first electrode assembly comprising:

i. a first upper metallic plate portion;

ii. a first lower metallic plate portion; and

iii. a first block of electrically insulating material interposed between the first upper and lower metallic plate portions, the first upper metallic plate portion being secured to an upper portion of the block of insulating material and the first lower metallic plate portion being secured to a lower portion of the first block of insulating material, the first upper metallic plate portion being physically and electrically connected to the opposite ends of the first metallic stretch band;

b. a first cable having first and second electrical conductors, the first and second electrical conductors being insulated from one another, the first electrical conductor being electrically connected at one end thereof to the first lower metallic plate portion and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the positive input terminal of the amplifier,

. a second metallic stretch band having its opposite ends interconnected by a second electrode assembly, the second metallic stretch band and at least one portion of the second electrode assembly being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the second electrode assembly. comprising:

i. a second upper metallic plate portion;

ii. a second lower metallic plate portion; and

iii. a second block of electrically insulating material interposed between the second upper and lower metallic plate portions, the second upper metallic plate being secured to an upper portion of the second block of insulating material and the second lower metallic plate portion being secured to a lower portion of the second block of insulating material, the second upper metallic plate portion being physically and electrically connected to the opposite ends of the second metallic stretch band;

d. a second cable having first and second electrical conductors, the first and second electrical conductors of the second cable being insulated from one another, the first electrical conductor of the second cable being electrically connected at one end thereof to the second lower metallic plate portion and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the negative input terminal of the amplifier, the second electrical conductor of the second cable being electrically connected at one end thereof to the second metallic stretch band and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the signal ground terminal of the amplifier.

7. An electrode system as defined in claim 6 wherein the second electrical conductor of the first cable is electrically connected at one end thereof to the first metallic stretch band and is electrically connected at its opposite end to the signal ground terminal of the amplifier.

8. An electrode system as defined in claim 7 wherein the second electrical conductor of the first cable is electrically connected at said one end thereof to the first metallic stretch band via a first resistor and wherein the second electrical conductor of the second cable iselectrically connected at said one end thereof to the second metallic stretch band via a second resistor.

9. An electrode system as defined in claim 7 including a first resistor connected to the said opposite end of the second electrical conductor of the first cable, wherein the said opposite end of the second electrical conductor of the first cable is electrically connected to the signal ground terminal of the amplifier via said first resistor, and a second resistor connected to the said opposite end of the second electrical conductor of the second cable, wherein the said opposite end of the second electrical conductor of the second cable is electrically connected to the signal ground terminal of the amplifier via said second resistor.

Claims

1. An electrode system for use with an instrument constructed and arranged for the measurement of physiological potentials of a patient wherein the instrument has at least three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprising: a. a first band for encircling a part of the body of the patient and having a first electrode located thereon; b. a first electrical conductor having opposite ends, one end of the first electrical conductor being electrically connected to the first electrode and the opposite end thereof being connected to the positive input terminal of the instrument; c. a second band for encircling another part of the body of the patient and having a second and third electrode located thereon; and d. second and third electrical conductors, each having opposite ends, one end of the second electrical conductor being electrically connected to the second electrode and the opposite end thereof being electrically connected to the negative input terminal of the instrument, one end of the third electrical conductor being electrically connected to the third electrode and the opposite end thereof being electrically connected to the signal ground terminal of the instrument.

4. An electrode system for use with an amplifier adapted for the measurement of physiological potentials of a patient wherein the amplifier has three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprising: a. a first conductive band having its opposite ends electrically interconnected, the first conductive band being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient; b. a first electrical conductor having opposite ends, one end of the first electrical conductor being electrically connected to the first conductive band and the opposite end thereof being (for) electrically (interconnecting the first conductive band with the) connected to the positive input terminal of the amplifier, c. a second conductive band having its opposite ends interconnected by an electrode assembly, the second conductive band and the electrode assembly each being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the electrode assembly comprising: i. an upper conductive plate: ii. a lower conductive plate; and iii. a member of electrically insulating material interposed between the upper and lower conductive plates; the upper conductive plate of the electrode assembly being electrically connected to the second conductive band. d. a second electrical conductor having opposite ends, one end of the second electrical conductor being electrically connected to the lower conductive plate and the opposite end thereof being (for) electrically (interconnecting the lower conductive plate) connected to the negative input terminal of the amplifier; and e. a third electrical conductor having opposite ends, one end of the third electrical conductor being electrically connected to the upper conductive plate and the oPposite end thereof being (for) electrically (interconnecting the upper conductive plate) connected to the signal ground terminal of the amplifier.

5. An electrode system as defined in claim 4 wherein the first conductive band has its opposite ends electrically interconnected by a first electrode assembly comprising: i. an upper metallic plate; and ii. a lower metallic plate, the upper and lower metallic plates being electrically connected together.

6. An electrode system for use with an amplifier constructed and arranged for the amplification of physiological potentials of a patient wherein the amplifier has three input terminals, one being a positive input terminal, one being a negative input terminal and one being a signal ground terminal, the electrode system comprising: a. a first metallic stretch band having its opposite ends interconnected by a first electrode assembly, the first metallic stretch band and at least one portion of the first electrode assembly being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the first electrode assembly comprising: i. a first upper metallic plate portion; ii. a first lower metallic plate portion; and iii. a first block of electrically insulating material interposed between the first upper and lower metallic plate portions, the first upper metallic plate portion being secured to an upper portion of the block of insulating material and the first lower metallic plate portion being secured to a lower portion of the first block of insulating material, the first upper metallic plate portion being physically and electrically connected to the opposite ends of the first metallic stretch band; b. a first cable having first and second electrical conductors, the first and second electrical conductors being insulated from one another, the first electrical conductor being electrically connected at one end thereof to the first lower metallic plate portion and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the positive input terminal of the amplifier, c. a second metallic stretch band having its opposite ends interconnected by a second electrode assembly, the second metallic stretch band and at least one portion of the second electrode assembly being constructed and arranged for physical and electrical contact with the skin surfaces of a limb of the patient, the second electrode assembly comprising: i. a second upper metallic plate portion; ii. a second lower metallic plate portion; and iii. a second block of electrically insulating material interposed between the second upper and lower metallic plate portions, the second upper metallic plate being secured to an upper portion of the second block of insulating material and the second lower metallic plate portion being secured to a lower portion of the second block of insulating material, the second upper metallic plate portion being physically and electrically connected to the opposite ends of the second metallic stretch band; d. a second cable having first and second electrical conductors, the first and second electrical conductors of the second cable being insulated from one another, the first electrical conductor of the second cable being electrically connected at one end thereof to the second lower metallic plate portion and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the negative input terminal of the amplifier, the second electrical conductor of the second cable being electrically connected at one end thereof to the second metallic stretch band and the opposite end thereof being (constructed and arranged for electrical connection) electrically connected to the signal ground terminal of the amplifier.

8. An electrode system as defined in claim 7 wherein the second electrical conductor of the first cable is electrically connected at said one end thereof to the first metallic stretch band via a first resistor and wherein the second electrical conductor of the second cable is electrically connected at said one end thereof to the second metallic stretch band via a second resistor.