Full report

Original page 1

General Disclaimer One or more of the Following Statements may affect this Document This document has been reproduced from the best copy furnished by the organizational source. It is being released in the interest of making available as much information as possible. This document may contain data, which exceeds the sheet parameters. It was furnished in this condition by the organizational source and is the best copy available. This document may contain tone-on-tone or color graphs, charts and/or pictures, which have been reproduced in black and white. This document is paginated as submitted by the original source. Portions of this document are not fully legible due to the historical nature of some of the material. However, it is the best reproduction available from the original submission. Produced by the NASA Center for Aerospace Information (CASI)

Original page 2

„^- X-207-71-32 PREPRINT i. J.5 Z/ FINAL TECHNICAL REPORT ON ELECTROC A RDIOGRAPHIC ELECTRODES FOR RAPID APPLICATION JANUARY 1911 (4, ^l ----- GODDARD SPACE FLIGHT CENTER GREENBELT, MARYLAND N'71.1684Q (ACCESS[ ON UNN MBER)U oc ( GES) 5 0^ D (CODE)- (NSA CR OR 1MX OR AD NUMBER) (CATEGORY(

Original page 3

X-207-71-:3`l FINAL TECHNICAL ltI:PORT ON ELECTROCARDIOGRAPHIC ELECTRODES FOR RA PTD APPLICATION Mitchell Weisberg Rolfe D. White January 1971 Warner H. Miller Technical Advisor Information Processing Division GODDARD SPACE FLIGHT CENTER Greenbelt, Maryland

Original page 4

PREFACE. The technical results presented here represent a ten week effort by its authors during the Summer Institute for Biomedical Research sponsored by the Technology Utilization Office at the Goddard Space Flight Center. Their challenge was to apply NASA developed technology toward the solution of this particular problem and to demonstrate its usefulness to other problems in medical diagnostic monitoring instrumentation. This report has been published and made available for general use so that others in both the technical and medical communities might benefit from the work of these individuals. AveF/ Chen, Coordinator Summer Institute for Biomedical Research Technology Utilization Office iii

Original page 5

III IN ^r TI F

Original page 6

INTRODUCTION The title of our project and its goal is the development of an electrode lotrapid application and a method of rapidly applying the new electrode. The need for the apparatus to he developed is apparent in both Multitest Screening facilities and Emergency Situations where a 12-lead scalar electrocardiogram would be desired and time is the governing parameter for application. In the multitest screening unit, minutes saved add up in terms of elimination of a possible backlog at the FCG rotation and wi increased number of patients covered per hour. In an emergency situation where a patient may be suffering from a myocardial infarction, it is of the utmost importance to have as complete an assess ►nent of his condition to submit to the doctor so that he may direct proper treatment on the way to the hospital in an attempt to save some of the 60 percent of the heart attack victimtr that die before getting to the hospital or on arrival because proper treatment could not be given, due to a lack of an adquate diagnosis. The first part of any research project involves a literature search to find out, who has done similar research. In this phase of the project we employed the National Library of Medicine's Computerized Search System, Medlar, and the National Aeronautics and Space Administration's Computerized Search System, Recon. After the search, at the risk of spreading ourselves too thin, we decided to retain both aspects of our project; i.e., the electrodes and the application. It was at this stage that we fully realized the handicap we would be under with only 10 weeks to complete our full project. Various designs for the electrodes and the harness were discussed, however, only a few of those chosen could be constructed and tested. We tried to carry as many of the ideas as we could to the testing state, however, at tl,-s date we have not yet completed our evaluation. The goals of the electrode phase of our project is to incre :se the quality of ECG recordings to the required accuracy for complete analysis. Much research r was done to find a method of applying dielectric, material to the surface of the electrode. We had to be careful in choosing the dielectric material; a dielectric constant too low — not enough capacitance for electrode to work while a dielectric constant too higli — distortion due to aid bubbles or surface discontinuities beneath the electrode. Silver plate copper dishes were used for high conductivity. In addition to anoidized Tantalum Electrodes we contacted Mr. David Robertson, of Surface Technology, Incorporated in Mountain View, California to tap his resource of knowledge in the area of thin film dielectrics. After much coaxing he agreed to squeeze a few samples of sputtered (quartz (siiicon dioxide), and 1

Original page 7

Tantalum oxide (TiYY on a stainless steel substrate for us. As of last night, work had not yet been completed on these samples. We were able, to have silver plated copper disks coated with a 500 Angstrom layer of Silicon Monoxide. This procedure, clone in the optical plating lalmratory, consists of placing the electrodes substrates in a vacuum chamber and vaporizing silicon monoxide in the same chamber by c-Jectrically heating it. The vapors then condense on all available surt'aces. The thickness of the coating is time dependent. Also being tested are silver plate electrodes with a silicon monoxide film 1000 Angstroms, the result of the SiO electrode is viewgraph number 8. From the original viewgraph number 7 standpoint of trying to simply mount an operational amplifier on a standard commercial electrode or on a dic e cut ►netal disk we have come a long way. With our stepping into the area of a eapicative coupling with the kody we encountered a whole g low of electrical problems. The output impedance of the electrode plate was now quite formidabic. On theoretically the order of 10 10 ohms, it was felt that the operational amplifiers that were available could not reduce this value enough to be acceptable for low resistance transmission. A Field Effect transistor (FET) ti'as used in a voltage follower configuration to cope with the impedance. In this arrangement (viewgraph) the voltages seen from the source follows that observed at the gate of the FET. The output impedance of the FET is u: ► the order of 4 k olms which is acceptable to present electrocardiograph machines. This design utilized state-of-the-art circuiting. Although we are not really ready to present a finished, tested and approved final electrode, we do have one prototype silver/S'0 2 electrode complete with circuitry, potteed in a stainless steel cup. The actual final size of the electrode, complete with circuitry, will lye much smaller — we plan to eventually use a small integrated circuit chip simply mounted to the electrode disk. It was the time element alone that prevented us from reaching fruition of this phase of the project. Springs with a constant coefficient of expansion were also considered, but rejected bcc;ause of their unavailability. Commercially available elastic bandage seemed to be the material best suited for this harness attempt. 2

Original page 8

July 7, 1970 The purpose of our project, as we see it to date, is (1) to reduce noise, i.e. extriuit-ous signals on EKG recordings and (2) to develop a method for rapid application of the pre-cordial EKG leads. We are attacking the project from four angles: the electrodes, the electrode-skin interface, uses of amplifiers cuid cables from the electrodes to the machi ►ic. At present we have no plans to modify existing EK(; machines. A restriction on the projeci is that our outputs must be of the same style as present F:KG outputs. The low noise level is required since an eventual goal is the digitalization in con ► f)uter analysis and diagnosis of F:KG recordings. in the area of electrodes we arc' studying existing models with respect to materials of which they are constructed. We are weighing advantages of those with high conductivity with disadvantages of corrosion and/or polarization in order to find an optimum. We are planning to carry out a comparison of large electrode surfaces which imply high capacitance and lower impedance to small electrodes which are producing more accurate recordings, but must be positioned more accurateiy. We also hope to determine whether the shape of the electrode has any effect reference point on the Xiphisternal f:oint and/or on the anterior axial line. These devices niust be able to compensate for the chest expansion due to breathing. The final product of our research should he an integrated system composed of electrodes, amplifiers, cables and " EKG machine with the noise level of the recordings reduced to within the desirable limits. Studies in the area of electrode-skin interface deals mostly with the impedance seen by the electrode. Possibly, these car be removed through signal amplification. Perspiration, w1jich increases skin conductivity, also presents a difficult problem since this impedance may be changing during the time of our recordings. A point of present confusion s whether the body can be represented as a resistor or a capacitor, or sonic combination of these devices, but with two leads of the EKG. By direct contact electrodes, the impedance has wide variability, not only between patients, but between electrode sites of the same patient. Patient studies also show that the skin-t--electrode implies variability with frequency. Once study shows that at a frequency of ten hertz (average frequency for the 3

Original page 9

majority of (dItS complexes) impod: ► nce variability from (-.500 ohms) to over 2uo K ohms. This variability is at present :r Inrgv so o rc a of error in I-:Kt recordings, The uses of operational amplifiers to inyrove the yu:rlity of readings is being attempted. A buffer aniplihor characterized by a high input impedance an► I :t lo%%• output impedance, is to be placed on the actual electrode with the purpose of redueing the impedance in the long-cord (six foot) reacting IJIeWeen the electrode and the 1 •:K(; machine. 'Thus. lowering the amount of noise picked up in this lead in response to 0h m's La%k . sr 1 iu,tr,• F rr1l,!r Vnu ► A method must also he found to reduce artifacts clue to muscle movement. We are also going to attempt the elimination of the right-leg-driven grt ►und. possibly by grounding the amphl'ier to the I*orwarcl point suppIv. This would eliminate the two micro Volts to 50 microvolts frmn this electrode. At present we are testing an operational amplil• ier of the following circuit design: + 15V -15V Operational Amp!,fier Circuit D-agram from EKG Electrode Design Number One We are Using a Burr Brown 1C operational arrrphHer model 3050/01, chosen arbitrarily. We plan to study the operating range of this amplifier reducing the hwid idth to 200 cycles, to determine the offset voltages for up to 500 mili Volts front this electrode. %Vc are also considering ti ►e use of other designs emlJoying fet's c► r mosfet's. 4

Original page 10

I'lioCEDURE: Dimc to be anodized is placed in A molar II 1 SO 4 , as the anode of' the circuit. The cathode is mule- of the same material as the anode (in this case — both are made of tantalum). An ammeter is placed in the circuit and n power supply capable of supplying 160 volts compIctes the set up. The voltage is e1w%ly supplied so that the current never exceeds 1 rniIliamp her square centimeter. When the volt:μ;(- reaches 160 volts, the circuit is left for an hour. .Ater an hour the power is shut oIf an(I the discs are removed and dried. POWER SUPPLY A Field Effect 'Transistor (FF:T) circuit was designed in a standard voltage follower configuration and nnounted on the back of' the neH r1ectrode discs for the purlx)sc of' lowering the transmission line impedance and making a low enough output impedance to be acceptable to standard EKG inachines. The circuit is: GATEt^ ELECTRODE DISC + 15 VOLTS nAIN 's'COURC 0.47 pf -^ EKG 4.7 K SZ On several evenings we rode on tits , "Heartmobile," a cardiac emergency vehicle sponscred by the Montgomery County Heart Fund. The purpose of these excursions was to explore the applicability of our harness to an emergency situation. Our conclusion is that our harness can be used in such a situation. u'e contacted a Mrs. Mary Beth l.agoey to ride in the heartmobile (Montgome ry County Heart Association). P RFMING PAGE; MANX NOT FII.hf pj1 6

Original page 11

\k a questioned the necessity of n 12-lead FCG enronrte and decided that the present halt of Landoll's would not he suitable, due to the weight of it. A person having; a heart attack would not w mit the► weight on his rhect. Another s ystem is neccsSM—y for a close electrode skin contact. Several clays were slmii tenting and trouble shooting our electrodes and circuits. ^k 0 are also attempting impedan ce measurements. A Alechanical aria Fystem was considered to be run either manually or by motor. Ilowever, time limits caus d us to reject this ides. e W e tried spraying inflatable bladders out of f i licon rubber WIN and M^igicvvlc ruhher, but both of these attumpts led to failures. We sprayed the rubber onto an aluminum mold and removed them after they were dry. All the bladders exploded upon inflation. The silicon rubber• WIN did not have the Imped:ur ce Circ uit desired stretch for our use. It was found nuecssary to test impedance somehow at the electrode site for a comparable basis. The first circuit tricot (see Index) was unsuccessful because? we ware forced to use DC equipment - what was available - LSpach's Test, and there is, according to one advisor, an AC capacitance present at the skin. However, we died manage to use anoth%. r test: with a Hewlett-Packard Vector Impedance Meter. See Index. This proved to be very efficient. The only readings we were able to take prior to our presentation are as follows: Capacitance @ 3" Impedance @ 100 Hz Silver/Silver Chloride Electrodes .025 of 2.3 kilohms Silicon Dioxide Electrodes .005 of 1.5 kilohms This set up was discovered the day of the presentation. 7

Original page 12

Further research skill be made parlicularly in comparing impedances on some ohmic electrexies ( platinum, silver / silver chloride, silver over stainless steel, etc.) with FET circuits on the back of them. One particularly interesting side light is that we took a GE electrodedisposable (Ualay) and mounted a circuit on the back of this. This electrode was obtained from Miss Siebelt. It retails for $ .70 a piece. A F ET can be purchased individually at $ .56 a piece. The cost of our capacitor and resistor aia negligible. It is extremely possible to have very soon available commercially, a disposable dry electrode. We are just beginning; to lest these as well as the others. The t-ntalum electrodes and silver electrodes (SiO) are described in the index. The vacuum plating of the Si O, is described herd also. The dielectric was '100A oez theS'02.Below are comparable readouts of our different EKG elect roues . SILVER 500 A ELECTRODE 929/70 SILVEk 500 8/24/70 ... ... ...^... a .... .... }....t :. ^ ♦ iii' •^^:_ ^.... .^.. ^ TANTALUM FLFCT P nDE 8/25/70 tit tt 8

Original page 13

(See Index for llarness pictures) HARNESSES The above is a model employing; the elastic cloth idea of' Landoll's (and approximately his proportional distances). The plexi-glass is just a support mechanism. The ends are fastened with velcro. a I This is the copper (beryllium) spring; clamped to the chest. Hopefully, we hope to employ an inflatable bladder with imbedded electrodes in it (V r and V2 would be built up). See Index for schematics. 9

Original page 14

This is an idea that we had for an ambulance situation rapid application belt. It employs elastic cloth and disposable elastic adhesive strips. Its disadvantage is that it needs skin for application. (The patient's clothes must be removed completely in the chcst area.) We have also done research on construction of small, inflatable bladders (latex), but have yet to come up with one strong enough to fit in a harness (cross section) as pictured in the index. f 10

Original page 15

Itr:FF11ENCES Ilerson, A. S. and l lipberger. ll. V. Electrode to Skirl Impedance Problems in ECG Recordings. t1Lnasi, John J. and Sch ►nitt, llr. (Xto 11. The Dependence of Skin-Tliru- Electrode Impedance to Individual Variations, Skin Preparation and Body Location. Geddes, L. A. and Baker, L. E. Distortion of Bioelectric Events by Electrodes. Morris, T. W. Skin Electrode Impedance of bong Term Eiectrodes. Arnazoon, P. G., Feldman, C. L., Moi.uzzi, It. L., and Beechle, R. G. Real Time Filter for Noisy Electrocardiogram. Spach, Madison, M. D., Barr, Roger C., B. S., lla y stad, James W., B. A. and Long, E. Croft, M. D., Ph.D. Skin Electrode Impedance and its Effect on Recording Cardiac Potentials. Richardson, Capt. Philip C. USAF, MC, Coombs, Franklyn K., B. S. and Adams, Robert M., M. A. Some New Electrode Techniques for Long-Term Physiologic Monitoring. Landoll, J. R., Winer, D. L., Jackson L. and Caceres, C. A. Electrode System for Automatic Recording of Electrocardiograms. Richardson, Philip C. and Coombs, Franklyn K. New Construction Techniques for Insulated Electrocardiographic Electrodes. Richardson, P. C. The Insulated Electrode: A Pastless Electrocardiographic Technique. 11

Original page 16

TASK 1 F.I.F.CTIM)CARDIOGRAPHIC ELECT110DES FOR RAPID APPI.ICATION COMMENTS MET110DOLOGY Report written for this project took tale form of a narrative in the laboratory notebook. It was not structured to a formal report style, but did have reasonable continuity. The project was identified and the scope of work stated in the introductor y section. The results of the NASA literature search were included in the report, but not the actual literature. Goals were stated along with methods of achieving the goals. The experts in the field of medical electrodes were sought out. Their work was reviewed and used to a large extent in the breadboarding of developments in the latest techniques in electrodes. Students were very resourceful in acquiring source material, either through manufacturers, medical facilities and governmental agencies (NITS). The scope of the project was accepted as one input by the students. It was then modified by other inputs during the course of study. 'Thus, a genuine contribution was made to the task. RESULTS This project allowed several solutions in the area of electrodes and electrode application. Several ideas were tried. Although students were not electrical engineers, buffer amplifiers and electrodes were constructed and breadboarded based on guidance of NASA mentor (an instrumentation engineer experienced in amplifier design). Procedures for fabrication of electrodes were noted, including an anodizing procedure of tantalum. They were able to place themselves in an environment of ECG's under various conditions; for example, first-hand experience in the heartmobile, a cardiac emergency vehicle sponsored by the Montgomery County Heart Vund. Interaction between students and NASA was evident. (Measurements for harness were taken on several NASA personnel.) The students' enthusiasm is exhibited by the number of persons contacted and the number of prototype circuits and harnesses fabricated. CONC LUSION No formal cenclusior_s were stated. Areas of future work were stated; for example, other belt arrangements, impedance investigation -md so on. 13 nR ^ '- , rVG pA^F T3 T.^ NI{ RTf17' 1'II Ar^j

Original page 17

Basic concepts of instrumentation and ECG amplifiers were not grasped (not instrumentation engineers). For example, is it necessary to quantify impedance, especially based on the wort: of others. What are the principles of' shielding and grounding and reason for right leg driven ground. Is it necessary to ground the subject. These point out areas which should be emphasized in the formal lectures. FUTURE APPLICATION/EXPANSION The technology of dry electrodes and techniques of' ECG instrumentation seem to be available. The problem is one of implementing a workable system of instrumentation at n reasonable cost. The Multitest Facility of the Department of Clinical Engineering does provide a 12-lead scaler ECG on one of the test procedures. The instrumentation for this testing station can be improved. Tangled leads, messy electrode paste and sixty cycle noise are the common problems that have existed for many years in electrocardiographic acquisition. Although no harness or electrode was developed, the contribution of the stateof-the-art review wi 11 provide the input for the further economical development of dry electrodes with appropriate instrumentation and perhaps a technique for application. 14