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UBC Theses and Dissertations

A spherical polarcardiograph computer Poole, Edward Graham 1955

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A SPHERICAL POLARCARDIOGRAPH COMPUTER by Edward Graham Poole B.AoScoj , U n i v e r s i t y of B r i t i s h Columbia;, 1954 A t h e s i s submitted i n p a r t i a l f u l f i l m e n t of the requirements f o r the degree of Master of A p p l i e d Science i n the Department of E l e c t r i c a l E n g i n e e r i n g We accept t h i s t h e s i s as conforming to the standard r e q u i r e d from candidates f o r the degree of Master of A p p l i e d S c i e n c e Members of the Department of E l e c t r i c a l E n g i n e e r i n g The U n i v e r s i t y o f B r i t i s h Columbia December, 1955 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my depart-ment or, i n h i s absence, by the U n i v e r s i t y L i b r a r i a n . I t i s understood that any copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p ermission. ABSTRACT U n t i l r e c e n t l y , the major p o r t i o n of the study of the e l e c t r i c a l a c t i v i t y of the heart has been done wit h the a i d of electrocardiograms and vectorcardiograms. However, such i n f o r m a t i o n as t h e v a r i a t i o n of the magnitude and angle of t h e heart v e c t o r with time i s not d i r e c t l y d i s c e r n i b l e from e i t h e r of these r e c o r d i n g s . A p o l a r c a r d i o g r a p h was developed by W.K.R. Park to p r e s e n t the plane p r o j e c t i o n of the h e a r t v e c t o r i n magnitude and angle as a continuous f u n c t i o n of time. The p o l a r c a r d i o g r a p h proved to be u s e f u l but i t was not s u f f i c i e n t l y s t a b l e . An e l e c t r o n i c device which would be s t a b l e and a t the same-time present the heart v e c t o r i n three dimensions, magnitude, f r o n t a l angle and p o l a r angle as continuous f u n c t i o n s of time, would be u s e f u l i n e l e c t r o c a r d i o g r a p h i c r e s e a r c h . The design of such a computer, the " s p h e r i c a l p o l a r c a r d i o g r a p h " , i s d e s c r i b e d i n t h i s t h e s i s . The s p h e r i c a l p o l a r c a r d i o g r a p h , which must compute the s p h e r i c a l p o l a r c o o r d i n a t e s of p o i n t s from t h e i r r e s p e c t i v e . C a r t e s i a n c o o r d i n a t e s , has been developed u s i n g analog m u l t i p l i e r s , s u b t r a c t e r s and adders as w e l l as a two-phase s i n u s o i d a l v o l t a g e source and a device f o r generating a v o l t a g e p r o p o r t i o n a l to the phase d i f f e r e n c e of two s i n u s o i d a l s i g n a l s . With the exception of the t h i r d coordinate computat-i o n and the gated feedback c i r c u i t r y , . t h e system i s s i m i l a r i i to t h a t used by Park. Automatic b a l a n c i n g of the c i r c u i t occurs f o r a s h o r t i n t e r v a l d u r i n g the r e s t p e r i o d of the h e a r t . The s p h e r i c a l p o l a r c a r d i o g r a p h has not been c o n s t r u c t e d i n f i n a l form but t e s t s on the i n d i v i d u a l u n i t s i n d i c a t e t h a t the instrument w i l l be w e l l w i t h i n the accuracy r e q u i r e d f o r normal e l e c t r o c a r d i o g r a p h i c purposes. i i i TABLE OF CONTENTS Page XiX S% Of XXXllS'bX>&'*t'X 0X1S o o o o o o o o o o o o o o o o o o o o o o o o o o o o o * ; V A.CklXOWXGCLgGSlOH'bo 0 0 0 0 0 « a » 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 « 0 0 0 0 0 0 0 0 0 0 9 VI X CHAPTER X XU*bl?OcLllC "bX OH o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o X I I The P r i n c i p l e of the S p h e r i c a l P o l a r c a r d i o g r a p h Computer e . . . . . . . . . . . . . . . . . . . 8 I I I Automatic B a l a n c i n g with Gated Feedback...... 13 IV Frequency C o n s i d e r a t i o n s . . . . . . . . . . . .........<> 20 V Computation of the T h i r d Coordinate.......... 22 VI Voltage and Current Requirements............. 26 VII The Operating Adjustments.................... 28 ATX X X Pliy S X C EL X Lfl/y O U"b « o o o - o o o o o o o o * o o o o o o o o o o o o o o o o o 34 XX ConeXusxoii o 0 0 0 * 0 * 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 35 i v LIST OP ILLUSTRATIONS F i g u r e Page 1. R e l a t i o n s h i p of the Coordinate Systems to the Body* ....•.•••.«.'•..........•. 1 2. S i m p l i f i e d Model of the Heart and Body . 2 3o E l e c t r o c a r d i o g r a m s and A s s o c i a t e d E l e c t r o d e P o s i t i o n s . To f O X X O W o a o o o o o o e « o e o o o a « o o o o o o o o o o o o o o 4 3 4. Plane Vectorcardiograms and the A s s o c i a t e d E l e c t r o d e P o s i t i o n s . T O J ? O X X O W o o o o o o o o o o e o Q * o o o o o o o o o o o o » O Q » o 6 5 5 . Elementary Block Diagram of the S p h e r i c a l P o l a r c a r d i o g r a p h . T O f O . X X O W o e « « o o o o o o o o o a * « o o a « o a b o o o o o o « o o 9 6. P h i l b r i c k Model K2-W O p e r a t i o n a l A m p l i f i e r . T O f O l l O W o D O O O O O « O O O O Q O B O D O O A « O D O O O O O O e O O 14 7. Gated Feedback C i r c u i t . To f O X X O W o 0 0 » O 0 0 O 0 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 O O 0 O » 0 6 X5 8. O s c i l l a t o r and i t s Output C i r c u i t s . T O f O X X O W o o o o o o o o o o o o o o o o o o o o o o o o e o o o o o o o 20 9 . Adder C i r c u i t , High-Pass F i l t e r and Band-Pass A m p l i f i e r . To f O X X O W o e o o o o o o o o o o o e o o o o o o o o o o o o o o o o o o 2X 10. Free-Running M u l t i v i b r a t o r f o r C a l i b r a t i o n . T O i O X X O W o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o * 30 11. Back Panel Wiring Diagram. T O f O X X O W o a o e o o o o o o e o o o a o o o o a o o o o o u o o o o v a 34 12. Block Diagram of the S p h e r i c a l P o l a r c a r d i o g r a p h . To £O X X O W oOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 34 13. D e f l e c t i o n A m p l i f i e r , M u l t i p l i e r , S u b t r a c t o r and Feedback C i r c u i t . T O f O X X O W o g o o o o o o o o o o o e e o o o o o o c o o o o o o o o o o 34 14. Cathode-Coupled C l i p p e r or Squaring C i r c u i t . T O f O X X O W o o o o o o o o o o o o o o o o o o e o o o o o o o o o o o o o 34 V LIST OP ILLUSTRATIONS (cont'd) F i g u r e Page 15. D i f f e r e n t i a t i n g A m p l i f i e r and F l i p - P l o p . T O f O X X O W o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 34 16. Z-axis C a r r i e r - S i g n a l F i l t e r , Magnitude Output and P o l a r Angle Output. T O f O l l O V o o o o o o e e o o f t o e o o o o o o e o o o o o o o o o 34 17a. Delay C i r c u i t and Clamp-Pulse Generator. T O £ O X X O W o o o o o o o o v a e o o o o o e o o o o o o o o o o o o 34 17b. Switch f o r S e l e c t i n g T r i g g e r Pulse f o r Generator. T O fOllOWo o...o.o.ao«aoo.oooa«.«o..«ao. 34 18. Cathode-Ray-Tube C i r c u i t and i t s View-Selector Switch. T O f O X X O V o o o o o o o o o o e o e e o e t o o o o o o o o a o o * 34 19. Input Rotary Switch. T O f O X X O W o o o o o o o o o o o o o o o o o o o o o o o o o o e o © 34 20. Proposed U n i t P o s i t i o n s . T O «C O X X O W o O O O O O O O O O O O Q O O O O O O O O O O O D O O O t t 34 v i ACKNOWLEDGEMENT The author expresses h i s indebtedness to members of the Department of E l e c t r i c a l E n g i n e e r i n g at the U n i v e r s i t y of B r i t i s h Columbia, e s p e c i a l l y to Dr. A. D. Moore f o r h i s guidance throughout the re s e a r c h p r o j e c t . The s p h e r i c a l p o l a r c a r d i o g r a p h was developed with the a s s i s t a n c e of Dr. G. E. Dower, f o l l o w i n g h i s suggestion t h a t such a device might be u s e f u l i n e l e c t r o c a r d i o g r a p h i c r e s e a r c h . The p r o j e c t was supported by the Medical Board Fund of the Vancouver General H o s p i t a l . The author's post-graduate s t u d i e s were made p o s s i b l e through the B r i t i s h Columbia Telephone Company Graduate S c h o l a r s h i p i n Engi n e e r i n g and P h y s i c s , which he was awarded i n 1954. v i i 1. A SPHERICAL POLARCARDIOGRAPH COMPUTER I INTRODUCTION The instrument to be d e s c r i b e d , the s p h e r i c a l p o l a r -cardiograph, i s a computer which transforms e l e c t r i c a l v o l t a g e s p r o p o r t i o n a l to the C a r t e s i a n c o o r d i n a t e s x, y_, and z to v o l t a g e s p r o p o r t i o n a l to the r a d i u s r , the p o l a r angle © and the azimuthal or f r o n t a l angle 0 i n s p h e r i c a l p o l a r c o o r d i n a t e s . The s p h e r i c a l p o l a r c a r d i o g r a p h w i l l be used i n the study of the e l e c t r i c a l a c t i v i t y of the heart, and i t i s hoped t h a t i t w i l l overcome the shortcomings of the e l e c t r o c a r d i o g r a p h and the v e c t o r c a r d i o g r a p h which are instruments used a t present f o r t h i s purpose. The r e l a t i o n s h i p between the c o o r d i n a t e systems used i n t h i s a p p l i c a t i o n i s shown i n F i g u r e 1. F i g u r e 1. R e l a t i o n s h i p of Coordinate Systems to the Body. 2, The p o t e n t i a l d i f f e r e n c e s which appear a t the surface of the body were f i r s t explained by Einthoven"'" using the s i m p l i -f i e d model of the heart and body appearing i n F i g u r e 2. The Lead 11 r e s i s t i v e medimm Fi g u r e 2. S i m p l i f i e d Model of the Heart and Body f o l l o w i n g assumptions, although i n e r r o r , have been u s e f u l i n understanding the p o t e n t i a l differences,. 1 0 I t i s assumed that onduction i s c o n f i n e d w i t h i n the body and that the surface of the body can be represented by a sphereo 2 0 I t i s assumed t h a t the limb e l e c t r o d e s are l o c a t e d e l e c t r i c a l l y on the sphere at the corners of an e q u a t o r i a l plane of the sphere, t h i s plane being c a l l e d the fron i / a l planeo lW0 Einthoven, G„ Fahr, A. De Waart ( i n E n g l i s h ) , "Uber di e Eichtung und d i e Manifeste Gibsse der Potentialschwan-kungen im Menschlichen Herzen und liber den E i n f l u s s der Herzlage auf d i e Form des Elektrokardiogramme," American Heart J o u r n a l , 1950, XL, 163o 3. 3. I t i s assumed that the body i s a homogeneous, i s o -t r o p i c , r e s i s t i v e medium. 4. I t i s assumed t h a t the e l e c t r i c a l sources w i t h i n the heart can be represented by a s i n g l e c u r r e n t d i p o l e or heart v e c t o r of v a r i a b l e s t r e n g t h and o r i e n t a t i o n , but f i x e d i n p o s i t i o n at the centre of the s p h e r i c a l conducting medium. The graphic r e c o r d i n g s of the v o l t a g e s between e l e c t r o d e s on the body as f u n c t i o n s of time are c a l l e d e l e c t r o c a r d i o g r a m s . Graphs or t r a c i n g s I, II and I I I , of Fi g u r e 3, represent t y p i c a l v o l t a g e v a r i a t i o n s o c c u r i n g between limbs as obtained with a standard e l e c t r o c a r d i o g r a p h . A f t e r the p i o n e e r i n g work of Einthoven, i t was found t h a t a study of the v o l t a g e s appear-i n g at the f r o n t and back of the chest ( s a g i t t a l a x i s ) r e -ve a l e d f u r t h e r i n f o r m a t i o n about the h e a r t not found i n re c o r d i n g s from the f r o n t a l plane. To o b t a i n a r e f e r e n c e 2 p o t e n t i a l f o r v o l t a g e s from the chest, Wilson , u s i n g Einthoven's e q u i l a t e r a l - t r i a n g l e hypothesis, connected three equal r e s i s t o r s from the limbs to a common t e r m i n a l (Wilson's C e n t r a l T e r m i n a l ) . With t h i s p o i n t as a r e f e r e n c e , an ex-p l o r i n g e l e c t r o d e i s used to o b t a i n the remaining nine t r a c i n g s of F i g u r e 3. The three graphs obtained by p l a c i n g the e x p l o r -i n g e l e c t r o d e on the r i g h t arm, l e f t arm and l e f t l e g are the augmented waveforms AVE, AVL and AVF, r e s p e c t i v e l y . The use of the electrocardiogram i n t h i s manner presents c e r t a i n disadvantages. To i l l u s t r a t e some of the shortcomings, F. No Wilson, F. D. Johnston, A„ G„ MacLeod, P. S. Barker, " E l e c t r o c a r d i o g r a m s t h a t Represent the P o t e n t i a l V a r i a t i o n s of a S i n g l e E l e c t r o d e , " American Heart J o u r n a l , 1934, IX, 447. l e t us again c o n s i d e r the twelve electrocardiograms taken with the lead system i n Fi g u r e 3. I t i s apparent t h a t there i s a grea t d i f f e r e n c e i n wave shapes obtained from the p o i n t s VI to V6 although the e l e c t r o d e p o s i t i o n s are i n c l o s e p r o x i m i t y . Hence, we may conclude that the waveforms are s e n s i t i v e f u n c -t i o n s of e l e c t r o d e p o s i t i o n . When i n t e r p r e t i n g e l e c t r o c a r d i o -gram changes i n consecutive t r a c i n g s , the c a r d i o l o g i s t must bear i n mind the f a c t t h a t some of these changes may be due to e r r o r i n e l e c t r o d e p o s i t i o n i n g . When d e s c r i b i n g the graphs, the magnitude and s i g n must be l i s t e d f o r each of the segments shown i n I I I of F i g u r e 3 f o r each of the twelve graphs. The c a r d i o l o g i s t i s faced with the d i f f i c u l t t ask of forming an o v e r a l l p i c t u r e of the heart a c t i v i t y from these numerous elements of i n f o r m a t i o n . The preceding d i s c u s s i o n g i v e s l i t t l e j u s t i f i c a t i o n f o r the assumption t h a t v o l t a g e s p r o p o r t i o n a l to the C a r t e s i a n p r o j e c t i o n s of the heart v e c t o r can be found on the surface 3 4 of the body. I t has been shown ' th a t such v o l t a g e s do e x i s t by us i n g concept of the image s u r f a c e . The assumptions upon which the image surface i s based are that e l e c t r i c a l c o nduction'within the body i s a l i n e a r phenomenon and that the heart v e c t o r i s f i x e d i n p o s i t i o n at the o r i g i n of the 3 H. Co Burger and J , B 0 van Milaan, "Heart Vector and Leads, P a r t I I I , " B r i t i s h Heart J o u r n a l . 1 9 4 8 , X,-:229, 4 Ernest Prank, "The Image Surface of a Homogeneous Torso," American Heart J o u r n a l , 1 9 5 4 , XLVII, 7 5 7 , 5. c o o r d i n a t e systems; the i n a c c u r a c i e s i n the assumptions are minor. The image surface i s the locu s of the t i p s of v e c t o r s c" such t h a t the s c a l a r product c»r, where r i s the heart v e c t o r , g i v e s the p o t e n t i a l d i f f e r e n c e s between p o i n t s on the surface of the body and the o r i g i n o f the co o r d i n a t e system. There i s a one-to-one correspondence between p o i n t s on the image surface and p o i n t s on the body. Then f o r any p a i r of p o i n t s on the surface of the body with mappings c^ and Cg on the image s u r f a c e , the p o t e n t i a l d i f f e r e n c e i s v^ - Vg B (c"1 - c'g)/'?. Hence, i t i s apparent that by suitably pro-portioning the p o t e n t i a l d i f f e r e n c e s between c e r t a i n p o i n t s on the body, s i g n a l s p r o p o r t i o n a l to the Cartesian p r o j e c t i o n s of r may be obtained. The.science of v e c t o r c a r d i o g r a p h y 5 has been developed to exploit the f a c t t h a t the orthogonal p r o j e c t i o n s of the he a r t v e c t o r can be observed simultaneously, thereby surmounting some of the d i f f i c u l t i e s encountered i n e l e c t r o c a r d i o g r a p h y and o b t a i n i n g more i n f o r m a t i o n from a s i n g l e o b s e r v a t i o n . In plane v e c t o r c a r d i o g r a p h y , two orthogonal components are a p p l i e d simultaneously to the d e f l e c t i o n p l a t e s of a cathode-ray tube. The r e s u l t i n g f i g u r e , with a time s c a l e obtained by p e r i o d i c modulation of the beam, i s known as a vectorcardiogram. An 6 example of vectorcardiograms and e l e c t r o d e p o s i t i o n s from which they are d e r i v e d i s shown i n Fi g u r e 4. Note t h a t , i n 5 P. W. Duschosal, R. S u l z e r , La Vect o r c a r d i o g r a p h i e s S. Karger, New..York, N. I . , 1949. g.. „ .... _ . . . G. E. Dower, J . A. Osborne, "Comments on V e c t o r c a r d i o -g r a p h ^ Lead Systems:A New System Proposed,*' forthcoming p u b l i c a t i o n . F r o n t a l S a g i t t a l Transverse ( L o n g i t u d i n a l and Coronal) ( S a g i t t a l and L o n g i t u d i n a l ) (Coronal and S a g i t t a l ) F i g u r e 4« Plane Vectorcardiograms and the A s s o c i a t e d E l e c t r o d e P o s i t i o n s . 6. the l e a d system shown, the s a g i t t a l e l e c t r o d e i s p o s i t i o n e d i n the c e n t r e o f the c h e s t so as t o make i t e a s i e r t o p l a c e c o r r e c t l y . The v e c t o r c a r d i o g r a p } groups the i n f o r m a t i o n o f the e l e c t r o c a r d i o g r a m s i n t o t h r e e r e c o r d i n g s and a t t h e same time i n t r o d u c e s the d i r e c t i o n of t h e p l a n e p r o j e c t i o n of t h e h e a r t v e c t o r . However, an e x a m i n a t i o n o f F i g u r e 4 shows t h a t much of the i n f o r m a t i o n r e g a r d i n g t h e s l o w l y v a r y i n g waveforms . i s o b l i t e r a t e d around the o r i g i n . As an example of t h e i n f o r m -a t i o n l o s t i n t h i s manner, c o n s i d e r the d e v i a t i o n s of t h e S-T segment (shown i n F i g u r e 3) from the b a s e - l i n e o r o r i g i n o i the e l e c t r o c a r d i o g r a m . Such d e v i a t i o n s may i m p l y i m p o r t a n t a b n o r m a l i t i e s such as m y o c a r d i a l i n f a r c t i o n s ( d e a t h o f a r e g i o n o f the h e a r t muscle due t o poor blood s u p p l y ) . I t i s common f o r h e a r t a i l m e n t s to a l t e r t he slowl,} v a r y i n g segments o f the waveforms, which are l o s t i n the v e c t o r c a r d i o g r a m , l e a v i n g the r a p i d l y v a r y i n g segments i n t h e i r normal forms. T h r e e - d i m e n s i o n a l or s p a t i a l v e c t o r c a r d i o g r a p h y has, i n p r i n c i p l e a t l e a s t , advantages over p l a n e v e c t o r c a r d i o g r a p h y i n t h a t a l l of the i n f o r m a t i o n can be viewed a t once but i t s u f f e r s from the same d i f f i c u l t i e s as p l a n e v e c t o r c a r d i o g r a p h y . To p r e s e r v e the advantages o f the e l e c t r o c a r d i o g r a m , w h i c h g i v e s good d e f i n i t i o n of the s l o w l y v a r y i n g waveforms, and of the v e c t o r c a r d i o g r a m which g i v e s d i r e c t i o n , the p o l a r -7 3 c a r d i o g r a p l : computer ' has been developed to t r a n s f o r m 7- . -Ro McFee, "A T r i g o n o m e t r i c Computer w i t h E l e c t r o c a r d i o -g r a p h i c A p p l i c a t i o n s , " Review of S c i e n t i f i c I n s t r u m e n t s , 1950, XXI, 420o -8 . . . . Wo K. Ro Park, "A P o l a r c a r d i o g r a p h Computer," M.A.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia, 1954. 7. signals representing the Cartesian projections of the heart vector i n two dimensions to an equivalent representation i n polar coordinateso The polar coordinates (plane d i r e c t i o n and magnitude) are displayed on continuous recordings as functions of time to preserve the d e t a i l l o s t i n the vector-cardiogram- The palarcardiograph developed by Park was t e s t -ed under c l i n i c a l conditions at the Vancouver General Hospital by Drs. Dower and Osborne. Although the results were d i f f i -c u l t to obtain, nevertheless the p r i n c i p l e was proved. The main d i f f i c u l t y encountered i n the polarcardiograph was i t s i n s t a b i l i t y and time-consuming balancing procedure. This d i f f i c u l t y proved that i f a three-dimensional computer were to be developed s t a b i l i z i n g c i r c u i t s would be required. 8. II THE PRINCIPLE OP THE SPHERICAL POLARCARDIOGRAPH COMPUTER To develop a general mathematical analysis, i t w i l l be assumed that there exists within the body a heart vector or dipole with instantaneous magnitude r, f r o n t a l angle 0 , and polar angle Q. Further, i t w i l l be assumed that the Cartesian components x, y_> a n d _z of this heart vector can be obtained by suitably combining the potential differences from three pairs of electrodes on the surface of the body» Let H and the front-a l angle 0 represent the instantaneous projection of v on the fr o n t a l plane so that the Cartesian coordinates i n that plane are given by x = H cos 0, and y = H sin 0„ The solutions for H and g5 are H = y 2 , A N D ^ - 1 V 0 = taa A £ 0 x By combining the solution for H with the t h i r d Cartesian co-ordinate zt the f i n a l magnitude r_ and the polar angle Q are found to be JT„2 , 2 .Pi 2 2 = \E + z = \jx + y + z , and n , ~ 1 z 9 = cot —o r The spherical polarcardiograph computer i s a device intended to transform input voltages proportional to x, y_, and z to output voltages proportional to r_, 0, and 0 . In carrying out thi s transformation, H and 0, the com-ponents i n the fr o n t a l plane, are computed f i r s t , and then H 9 . i s combined with z to o b t a i n r and 0 according to the above equations. A block diagram of an elementary c i r c u i t intended to give these r e s u l t s i s shown i n F i g u r e 5. At t h i s time i t i s impossible to use e l e c t r o m e c h a n i c a l r e s o l v e r s because of the frequency requirements. The p r i n c i p l e used i s b a s i c a l l y t h at of Park's p o l a r -cardiograph computer. That i s . a p a i r of guadrature s i n u -s o i d a l s i g n a l s of equal amplitude are f i r s t generated; these w i l l be represented by e^ S B E s i n (tot + T) 9 and e g = E s i n (wt + T + 90°) = E cos (tot + r ) , where to represents the f o u r - k i l o c y c l e - p e r - s e c o n d c a r r i e r frequency. M u l t i p l i c a t i o n of e^ and eg by v o l t a g e s propor-t i o n a l to x and y_ r e s p e c t i v e l y , and a d d i t i o n of the products, g i v e s a r e s u l t i n g sum S so t h a t S = x e 1 + y e 2 , = E s i n (wt + r)°H cos 0 + E cos (wt + r)°H s i n 0, = HE s i n (wt + T + 0) o The m u l t i p l i c a t i o n of the C a r t e s i a n c o o r d i n a t e s and the c a r r i e r - s i g n a l component i s accomplished by two p e n t a g r i d tubes of the normal frequency-conversion type. The s i g n a l s from the two tubes must be su b t r a c t e d f o r proper m u l t i p l i -c a t i o n , and the s u b t r a c t o r outputs from the x - a x i s and y - a x i s channels must be added to o b t a i n S. Simple c i r c u i t s e x i s t f o r c a r r y i n g out the a d d i t i o n and s u b t r a c t i o n s t e p s . Park, op_. c i t . , p. 11. y - a x i s channel m u l t i p l i e r e2 = E cos (wt + r ) f + 4 5 5 - j e, = E sin (wt + D x — m u l t i p l i e r x - a x i s channel E s i n (wt + T -t z — 0) [ m u l t i p l i e r z-axis channel f r o n t a l - p l a n e channel ./ HE; s i n (wt + T + 0) f i l t e r 90 v sq. cct. d/dt sq. cct, d/dt f i l t e r -HE cos (wt + T + 0) E r s i n (wt + T + 0 +9) + f i l t e r sq. c c t r e c t . rect< J f - f |—»• 0_ 6 F i g u r e 5 . Elementary Block Diagram of the S p h e r i c a l P o l a r c a r d i o g r a p h . 10. At t h i s p o i n t the waveform representing S contains many unwanted components that were introduced by the m u l t i p l i e r s e c t i o n s . Hence the modulated s i g n a l must be f i l t e r e d before a true representation of 5! i s obtained. That £5 i s the d e s i r e d s o l u t i o n i n the f r o n t a l plane can be seen by noting that the amplitude o i S i s p r o p o r t i o n a l to the magnitude H and that the phase of j3 d i f f e r s from that of e^ by the f r o n t a l angle 0. To obtain the f r o n t a l angle 0, the waveform representing j5 i s fed through a cathode-coupled c l i p p e r c i r c u i t to produce square waves. The square waves are then d i f f e r e n t i a t e d and c l i p p e d , leaving, a negative pulse marking the t r a i l i n g edge. At the same time, a reference s i g n a l p r o p o r t i o n a l to s i n (wt + T) i s s i m i l a r l y operated upon. The time delay between the two negative pulses represents the phase d i f -ference 0 of the two waveforms. The pulses fed to a f l i p -f l o p or b i s t a b l e m u l t i v i b r a t o r c i r c u i t so as to t u r n a tube a l t e r n a t e l y o f f and on. The r e s u l t i n g conduction time of the tube w i l l be p r o p o r t i o n a l to the f r o n t a l angle g5» The reference s i g n a l e^ to be fed to the z-channel m u l t i -p l i e r i s obtained by f i l t e r i n g the c l i p p e d wave derived from Sf the f r o n t a l - p l a n e s i g n a l . I f S3 i s of s u f f i c i e n t magnitude to produce a square wave i n the c l i p p i n g c i r c u i t , then e^ w i l l be of constant magnitude and can be made to have the magnitude £. That i s , e 3 = E s i n (wt + T + 0)„ The waveform representing £> from the frontal-p]ane channel i s s h i f t e d ninety degrees and added to the product of e„ and 11. JZ to form e 3z + HE s i n (tot + T + 90°) = zE sin(wt + T + 0) + HE s i n (wt + T + 0 + 90°), .= zE sin(wt + T + 0) + HE cos (wt + T + 0 ) , = Eifz 2+ H2[I « Z n sin(wt + T + 0) .+ i , . H „ cos(wt + T + 0) 1 | jB + IT / Z VH 2 J = Er cos 0 sln(wt + P + 0) + s i n © cos(wt + T +0) , = Er sin(wt + T + '0 + ©), where © = c o t " —; r =yz + H . This i s the d e s i r e d r e s u l t since the amplitude i s p r o p o r t i o n a l to the heart-vector magnitude, and the phase of the s i n u s o i d d i f f e r s from that of 6g by the p o l a r angle ©. As was the case i n the f r o n t a l -plane channel, a f i l t e r i s required to obtain a waveform which i s a true r e p r e s e n t a t i o n of the s i n u s o i d Er sin(wt + T.+0 + ©). To obtain a voltage p r o p o r t i o n a l to the po l a r angle ©, the s i n u s o i d i s f i r s t fed through a cathode-coupled c'.ipper c i r c u i t to obtain a square wave which i s added to the square wave from the f r o n t a l - p l a n e phase-comparison c i r c u i t . The output of the adder c i r c u i t i s c l i p p e d to r e j e c t the negative p o r t i o n of the waveform. The width of the remaining p o s i t i v e pulse i s a l i n e a r f u n c t i o n of ©_, the phase d i f f e r e n c e of the two sinusoids being compared. An electromechanical recorder which i s s e n s i t i v e to the quasi-dc components gives an i n d i c a t i o n of ©... The polarcardiograph computer developed by Park operated on the same p r i n c i p l e as th a t described above except t h a t , since the z-axis was not considered, the only components needed.were those necessary to produce the f r o n t a l - p l a n e outputs H and 0. 12. Experience w i t h the polarcardiograph showed that i n s t a b i l i t y due to various causes was the most severe l i m i t a t i o n on the e f f e c t i v e n e s s of the equipment. P r i n c i p a l among these sources of i n s t a b i l i t y arc a m p l i f i e r and mul-t i p l i e r d r i f t and f l u c t u a t i n g voltages of p o l a r i z a t i o n on the p a t i e n t e l e c t r o d e s . Therefore, i n designing the present computer, i n a d d i t i o n to adding the z-axis input to get a three-dimensional representation, s p e c i a l c i r c u i t r y was developed to remove or c o r r e c t such causes of i n s t a b i l i t y . The p r i n c i p a l means by which t h i s has been done i s a gated feedback c i r c u i t which a u t o m a t i c a l l y rebalances the system once during each heart beat. I t i s hoped t h a t , with these a d d i t i o n s , the computer w i l l be s u f f i c i e n t l y accurate to be of s u b s t a n t i a l a i d i n diagnosing heart d i s o r d e r s . 13 I I I AUTOMATIC BALANCING WITH GATED FEEDBACK With maximum input s i g n a l s of the order of one m i l l i -v o l t , the computer must be stable t o be of any p r a c t i c a l use. A measure of the s t a b i l i t y of the computer i s the extent to which manual balancing must be c a r r i e d out each time the instrument i s t o be used. The procedure requires such adjustments as balancing the two pentagrid tubes of each m u l t i p l i e r s e c t i o n to give zero output f o r zero i n p u t , and e q u a l i z i n g the various channel gains. Although the computer i s balanced p r i o r to i t s use, the instrument w i l l not maintain t h i s c o n d i t i o n to the required extent. Hence, i f v a l i d r e s u l t s are t o be obtained, the procedure must be repeated every few minutes. The time consumed wi t h such operation emphasizes the heed f o r automatic balancing. The obvious time f o r automatic balancing i s during the i s o e l e c t r i c p e r i o d marking the r e s t time between heart beats. The problem now becomes t h r e e f o l d , namely: where should the s i g n a l f o r feedback be obtained; how should the s i g n a l be d i r e c t e d to the proper p o i n t f o r c o r r e c t i o n ; how should the s i g n a l be reintroduced to the c i r c u i t f o r proper c o r r e c t i o n ? To begin the i n v e s t i g a t i o n , a study was made to determine the necessary loop gain to provide at l e a s t a twenty-to-one reduction i n the error during feedback. The computer design i s such that the input a m p l i f i e r s to each channel are the equivalent of those i n the normal e l e c t r o -cardiograph. I t was a l s o found necessary to include a cathode-ray tube so as to present vectorcardiograms of any 14. two d e s i r e d channels and to a i d i n the balancing procedure. To o b t a i n s u f f i c i e n t d e f l e c t i o n on the face of the cathode-ray tube, a double-ended d e f l e c t i o n a m p l i f i e r w i t h a gain of f i f t e e n i s required f o l l o w i n g the i n p u t a m p l i f i e r . To adjust the s i g n a l amplitude to that r e q u i r e d f o r the pentagrid tubes which m u l t i p l y , f o r example, e^ and x, a t h i r t y - t o - o n e reduction i s necessary. Since the e f f e c t i v e gain through the m u l t i p l i e r s e c t i o n i s approximately u n i t y , the forward gain from the d e f l e c t i o n - a m p l i f i e r input to the m u l t i p l i e r output i s seen to be 15/30 or 0.5. Therefore, i f feedback i s taken from the m u l t i p l i e r output, the back-ward path w i l l r e q u i r e a gain of 20/0.5 or f o r t y . To e l i m i n a t e the need f o r a d d i t i o n a l feedback a m p l i f i e r s , i t was attempted to o b t a i n the feedback s i g n a l from a p o i n t f u r t h e r on i n the c i r c u i t r y . By doing t h i s , another problem was introduced. Although the gain was s u f f i c i e n t , the modulated component s i g n a l had been combined and i t was therefore necessary t o supply feedback to four inputs from one s i g n a l . Various types of phase-sensitive detectors were designed and t e s t e d but the d i f f i c u l t y of s l i g h t phase s h i f t s i n the preceding c i r c u i t r y caused the idea t o be abandoned. I f the feedback s i g n a l i s to be obtained before the component s i g n a l s are combined, separate subtractors w i l l be r e q u i r e d f o l l o w i n g the two tubes of each m u l t i p l i e r s e c t i o n . Since the external c i r c u i t of the a m p l i f i e r shown i n Figure 6 can be designed to add and subtract i n one operation, separate subtractors i n the backward path were considered. The required gain of a subtractor a m p l i f i e r i n 2 . 7 8 H IH 1 3 4 in -300 gnd, Rl R2 R3 .22 M .22 M 1.0 R4 2.2 M M R5 R6 R7 R8 R9 RIO .47 M 10 K .22 M .22 M .27 M .68 M Rll 4.7 M Cl 7.5 uuf, C2 500 " C3 7.5 " General S p e o i f i c a t i o n a GAIN i 15,000 do, open loop POWER REQUIREMENTS! 4.5 ma, at +300Vdo 4.5 m&, at -300Vdo 0.6 amperes at 6.3V TUBE COMPLEMENTt 2 12AX7 OUTPUT CURRENTi -1 ma. INPUT IMPEDANCEl VOLTAGE RANGEt Above 100 megohms -50 Vdo to +50 OUTPUT IMPEDANCEi .; . . Vdo, at output Less than 1 K open-loop and both inputs below 1 ohm fully fed baok INPUT CURRENTSt DRIFT R A T E I / l e s s than 0.1 5_mv. per day, referred . raicroamp for to the input either input to +1 ma. over f u l l voltage range. Figure 6. Philbrick Model K2-W Operational Amplifier 15 the backward path would,be f o r t y plus that needed tooyercome the losses i n the d e t e c t i o n c i r c u i t . I f t h i s high gain were used i n the o p e r a t i o n a l a m p l i f i e r t h a t was t o be employed as a subtractor, the a m p l i f i e r would be d r i v e n beyond i t s l i n e a r range. I f the output of the s u b t r a c t e r were not l i n e a r l y dependent upon i t s i n p u t , the s i g n a l f e d to the d e f l e c t i o n -a m p l i f i e r inputs would not be p r o p o r t i o n a l to the e x i s t i n g e r r o r . Since, i n t h i s case, the feedback would not balance the computer p r o p e r l y , the idea of a high-gain subtractor a m p l i f i e r i n the feedback path was discarded. A subtractor f o r each m u l t i p l i e r c i r c u i t was f i n a l l y put i n t o the forward path and the o p e r a t i o n a l a m p l i f i e r t h a t was formerly to be used as both an adder and subtractor c i r c u i t i s now used only as an adder. So t h a t the subtractor c i r c u i t w i l l not be overdriven, i t s g a i n ; i s lowered to s i x . The s u b t r a c t o r using t h i s low gain I s i n h e r e n t l y so s t a b l e t h a t a manual balance i s not r e q u i r e d . The feedback s i g n a l which comes from the subtractor output i s given a gain of twenty by a separate a m p l i f i e r i n the feedback, path. Since the feedback s i g n a l , f o r proper c o r r e c t i o n , must be a p p l i e d to one of two i n p u t s , a phase-sensitive detector i s r e q u i r e d . Figure 7 shows the complete automatic balancing c i r c u i t . An e r r o r i n the m u l t i p l i e r s e c t i o n produces a modulated s i g n a l output from the s u b t r a c t o r . This s i g n a l operates the detector c i r c u i t so as to r a i s e the p o t e n t i a l of one g r i d or the other of the d e f l e c t i o n a m p l i f i e r . The reference s i g n a l appearing at the cathodes of the vacuum diodes i s derived through a step-up transformer from the +300 Vdc F i g u r e 7. Gated Feedback C i r c u i t . 16. local oscillator which generates e and eg of the multiplier section. The centre-tap of the transformer secondary winding is connected to the plate of the diode through a one-megohm resistor. The error signal is fed from the feedback amplifier, through an isolating resistor, to the diode plate. When the reference signal i s of such a phase as to hold the cathode positive with respect to the centre-tap, and hence with respect to the plate, the tube w i l l not conduct. On the other hand, when the cathode is forced negative with respect to the centre-tap and diode plate, the tube conducts and thus lowers the potential of the plate. For complete detection, the effect of the reference signal on the plate circuit must be greater than that of the error signal. There are two possible conditions which may arise in the plate circuit of the diode. Either the error signal is in phase with the reference signal or i t is 180 degrees out o f phase. If the latter exists, the diode w i l l conduct whenever the error signal is positive. Hence the plate potential w i l l never rise above a previously set level. However, i f the former case prevails, the diode w i l l conduct during the negative half-cycle of the error signal but w i l l be turned o f f during the positive half-cycle. Here the diode plate poten-t i a l , which w i l l be used in the feedback, follows the positive half-cycle of the error signal. The problem of reintroducing the signal to the system was one of charging the input capacitors of the deflection amplifier. Tests showed that the circuit was highly receptive to the carrier frequency of four kilocycles per second which, 1 7 . during feedback, r e s u l t e d i n a l i n e pn the cathode-ray tube. To charge an input c a p a c i t o r and to attenuate the f o u r - k i l o -cycle-per-secpnd s i g n a l , a high-u t r i o d e was connected from the d e f l e c t i o n - a m p l i f i e r g r i d to ground with a choke i n the cathode c i r c u i t . The choke causes s u f f i c i e n t degeneration to reduce the r a t i o of c a r r i e r to r e c t i f i e d dc component by a f a c t o r of b e t t e r than twenty to one. The er r o r s i g n a l i s introduced at the gating-tube g r i d through an i s o l a t i n g r e s i s -t o r from the diode d e t e c t o r . To c o n t r o l the per i o d i n which feedback occurs, a square wave i s introduced at the centre-tap of the reference transformer of the de t e c t i o n c i r c u i t . This gating pulse o r i g i n a t e s i n a cathode-coupled delay m u l t i v i b r a t o r w i t h c o n t r o l l a b l e delay, the f i r s t stage of which i s t r i g g e r e d from a p o s i t i v e - g o i n g p o r t i o n of the input waveform. The t r i g g e r p u l s e , with the a i d of a r o t a r y switch, may be taken from any one of the s i x d e f l e c t i o n - a m p l i f i e r p l a t e s . The p o s i t i v e square wave of f i x e d width, at some v a r i a b l e time a f t e r the t r i g g e r pulse, i s fed to the centre-tap of the reference transformer to c o n t r o l the b i a s of the gating tube. To c o n t r o l the voltage l e v e l s , the square wave i s f e d through a cathode f o l l o w e r whose cathode i s returned, through a r e s i s t o r , to a p o t e n t i a l below th a t of ground. A diode catcher on the p o t e n t i a l d i v i d e r feeding the cathode f o l l o w e r governs the l e v e l to which the cathode may r i s e . Between pulses the cathode f o l l o w e r output, because of the negative voltage r e t u r n , becomes h i g h l y negative. The gating-tube g r i d l e v e l s are set so that when the pulse i s a p p l i e d the g r i d p o t e n t i a l 18. i of the gating tube r i s e s to j u s t below c u t o f f , p e r m i t t i n g feedback i f there i s s i g n a l from the subtracter output. The gating pulse amplitude and width i s f i x e d , but the delay time i s adjustable by the operator to ensure that feedback takes place e x a c t l y during the r e s t p e r i o d of the heart. The proper delay time may be obtained by a d j u s t i n g the delay c o n t r o l u n t i l the clamp pulse occurs during the r e s t p e r i o d of the heart, as i n d i c a t e d e i t h e r by spot-brightening on the cathode-ray tube or by temporarily superimposing the clamp pulse on one of the normal electrocardiograph outputs. During one stage of the work on feedback, complete balance caused both gating tubes to conduct an equal amount. The in-phase components, i f given f u l l d e f l e c t i o n - a m p l i f i e r g a i n , would have been s u f f i c i e n t to s h i f t the m u l t i p l i e r tubes beyond t h e i r l i n e a r range. To compensate f o r t h i s , i t was found necessary to redesign the d e f l e c t i o n a m p l i f i e r s t o give a high in-phase r e j e c t i o n r a t i o . The common cathode r e s i s t o r i n the d e f l e c t i o n - a m p l i f i e r c i r c u i t of Figure 7 accomplishes t h i s r e s u l t . With the present design, the in-phase components do not a r i s e to the same extent i n the feedback s i g n a l ; however, the d e f l e c t i o n a m p l i f i e r c a t h o d e - c i r c u i t design i s r e t a i n e d to compensate f o r the in-phase components which do a r i s e . As w i l l be discussed l a t e r , the operation of the z-axis channel depends upon there being a component of the heart v e c t o r l y i n g i n the f r o n t a l plane. That i s , i f the f r o n t a l -plane c i r c u i t r y i s completely balanced, feedback on the z-axis channel w i l l be of no use. However, i t i s hoped t h a t , since the balancing a c t i o n takes place very r a p i d l y , the z-axis channel 19. can be balanced i n a s i m i l a r manner. I f , a f t e r f i n a l c o n s t r u c -t i o n i s complete, i t i s found t h a t the z-axis channel does not balance with normal feedback, the f o l l o w i n g recommendations are made. The feedback time may be d i v i d e d so t h a t the z-axis channel i s balanced f i r s t . This may be done by a p p l y i n g a sh o r t time delay to the square wave i n i t i a t i n g the feedback to the f r o n t a l - p l a n e c i r c u i t r y . I f the l a t t e r a l s o proves i n -s u f f i c i e n t , a separate s i g n a l may be a p p l i e d t e m p o r a r i l y to the m u l t i p l i e r tubes and the feedback r e f e r e n c e transformer of t h e z-ax i s channel during feedback. The two l i n e s f e e d i n g s i g n a l from the f r o n t a l - p l a n e c i r c u i t r y to the z - a x i s channel must be broken d u r i n g t h i s p e r i o d . T h i s method w i l l be adequate, but the complexity of the necessary c i r c u i t r y suggests that i t be used only i f a b s o l u t e l y r e q u i r e d . 20. IV FREQUENCY CONSIDERATIONS The s p h e r i c a l p o l a r c a r d i o g r a p h , l i k e the present-day-e l e c t r o c a r d i o g r a p h s , i s s e n s i t i v e to in p u t f r e q u e n c i e s up to 100 c y c l e s per second. To allow f o r t h i s frequency range and +100 c y c l e s per second o s c i l l a t o r d r i f t i t i s seen t h a t a bandwidth of 400 c y c l e s per second i s r e q u i r e d . A c a r r i e r frequency of f o u r k i l o c y c l e s per second, as was used by Park, was chosen so t h a t the band-pass a m p l i f i e r and d e t e c t i o n c i r c u i t s c o u l d be e a s i l y designed and so t h a t the s t r a y capacitance e f f e c t would not be too g r e a t . The o s c i l l a t o r which produces the c a r r i e r - f r e q u e n c y s i g n a l i s a r e s i s t i v e - c a p a c i t i v e twin-T type (Figure 8), which gives good frequency s t a b i l i t y and low harmonic content. The cathode f o l l o w e r on the o s c i l l a t o r output feeds s i g n a l d i r e c t l y t o the reference-phase c i r c u i t of the f r o n t a l - p l a n e channel and through i s o l a t i n g transformers t o the feedback d e t e c t i o n c i r c u i t s and the m u l t i p l i e r s e c t i o n s . The r e f e r e n c e -phase c i r c u i t contains an R-C p h a s e - s h i f t i n g network to compensate f o r any phase s h i f t i n the f i l t e r i n g c i r c u i t s . To adapt the s p h e r i c a l p o l a r c a r d i o g r a p h f o r r e c o r d i n g vectorcardiograms, i t i s d e s i r a b l e t o apply time markers t o the cathode-ray tube p r e s e n t a t i o n by i n t e n s i t y modulation. Although the present design does not i n c o r p o r a t e the time-marker c i r c u i t , p r o v i s i o n has been made to l o c a t e the time-marker generator near the o s c i l l a t o r . . This has been done so t h a t the o s c i l l a t o r may be used as a source of s y n c h r o n i z i n g s i g n a l . Vlb 1 3 ^ E l E2, E3, R7, E8 E4 R5, E9 R6 E10 E l l E12 E13, E14 E l 5 , E16 22 kilohmn 0.47 megohm 0.2 " 2.2 kilohra 0.5 megohm 0.1 " 0-250 kilohm 0 - 1 0 11 0-30 " 27 " CI, C3 04, C5, C6 VI C2 C8 C7 100 uuf. 200 " 0.005 uf 0.01 0.001 12AX7 II it C9, CIO 0.001 Fi g u r e 8. The O s c i l l a t o r and i t s Output C i r c u i t s 21. The m u l t i p l i e r tubes, as was pr e d i c t e d by Park, introduce many unwanted frequency components which must be r e j e c t e d . These components are r e j e c t e d by passing the s i g n a l through the high-pass f i l t e r and double-tuned a m p l i f i e r of Figure 9. The f i l t e r i s necessary t o prevent the low-frequency components from overloading the a m p l i f i e r tube. The T-net-work of standard slug-tuned chokes i s the equivalent c i r c u i t of a transformer. By a d j u s t i n g the shunt r e s i s t o r s and the chokes, a pass-band a m p l i f i c a t i o n constant w i t h i n three per cent i s obtained between 3800 and 4200 cycles per second. Loc. c i t . F i g u r e 9. Adder C i r c u i t , High-Pass F i l t e r , and Band-Pass A m p l i f i e r 22. V COMPUTATION OF THE THIRD COORDINATE Instruments such as the p o l a r c a r d i o g r a p h compute the angle and magnitude of the plane p r o j e c t i o n of the he a r t v e c t o r . The p r i n c i p l e of computation of the three s p h e r i c a l p o l a r c o o r d i n a t e s r_, 6 and §b of the heart v e c t o r has been d e s c r i b e d i n chapter I I . The s i g n a l s used i n t h i s extension are the f r o n t a l - p l a n e output HE., s i n (tot + T + 0) and the t h i r d i n p u t s i g n a l The computation could proceed by r e c t i f i c a t -i o n of the f r o n t a l - p l a n e s i g n a l and by combination v i t h z i n p r e c i s e l y the same way as was done f o r the x and v_ i n p u t s . However, the e x t r a d i s t o r t i o n i n t r o d u c e d and the a d d i t i o n a l c i r c u i t r y r e q u i r e d d i d not seem j u s t i f i a b l e s i n c e t h e r e i s a simpler method. The c a r r i e r - f r e q u e n c y s i g n a l f o r the z-axis m u l t i p l i e r s e c t i o n i s obtained by f i l t e r i n g the output of the c i r c u i t which produces square waves from t h e f r o n t a l - p l a n e s i g n a l . The s i g n a l i s a d j u s t e d so t h a t i t i s p r o p o r t i o n a l to E sin(tot + T + 0) . The frontal-plane s i g n a l , HE sin(tot + T + 0) , i s s h i f t e d n i n e t y degrees and added to the z-axis m u l t i p l i e r output to give zE sin(tot + T + 0) + HE cos(tob + T + 0) = E r sin(cot + T + 0 + 0). The a d d e r - c i r c u i t output must be f e d through a f i l t e r to r e j e c t the unwanted components i n t r o -duced i n the m u l t i p l i e r s . Half-wave r e c t i f i c a t i o n produces a quasi-dc component which may be i n t e r p r e t e d (by us i n g an ele c t r o m e c h a n i c a l r e c o r d e r ) , as an i n d i c a t i o n of the mag-ni t u d e r_ of the heart v e c t o r . The z - a x i s channel s i g n a l d i f f e r s i n phase from the 23. f r o n t a l - p l a n e s i g n a l by the p o l a r angle 0. Since the p o l a r angle © v a r i e s between zero and 180 degrees, a s i g n a l propor-t i o n a l to © may be obtained by adding the square wave r e s u l t i n g from HE s i n (tot + T + 0) to the square wave r e s u l t i n g from r E sin(wt + T + 0 + © ) . The output of the adder c i r c u i t , i f c l i p p e d so as to r e t a i n only the p o s i t i v e p o r t i o n of the s i g -n a l , i s a square wave of width p r o p o r t i o n a l to the p o l a r angle 6. An i n d i c a t i o n of 6 i s obtained by f e e d i n g the square wave to an ele c t r o m e c h a n i c a l r e c o r d e r which i s s e n s i t i v e only t o the quasi-dc component of s i g n a l . One apparent disadvantage of t h i s system i s t h a t the z-a x i s channel w i l l be no n - o p e r a t i o n a l i f the f r o n t a l - p l a n e s i g n a l i s i n s u f f i c i e n t to produce a square wave a t the phase meter. The r e s u l t i s a c y l i n d r i c a l volume i n the space i n which the heart v e c t o r l i e s w i t h i n whieh the output from the z-a x i s channel w i l l have no meaning. Thinking of the whole volume i n which the heart v e c t o r may l i e as a sphere, there i s an "apple-core" surrounding the p o l a r a x i s ; no i n f o r m a t i o n can be obtained f o r heart v e c t o r p o s i t i o n s w i t h i n the apple-core. Tests have shown t h a t the r a t i o of the r a d i u s of the c y l i n d e r to the maximum magnitude of the heart v e c t o r i s approximately one to t h i r t y with the equipment t h a t has been b u i l t . Thus, f o r heart v e c t o r s of maximum amplitude, accurate i n f o r m a t i o n w i l l be obtained f o r p o l a r angles g r e a t e r than two degrees. Since i t i s not thought l i k e l y t h a t the h e a r t -v e c t o r d i r e c t i o n w i l l c o i n c i d e w i t h t h a t of the z- a x i s or s a g i t t a l a x i s very f r e q u e n t l y , the l o s s of i n f o r m a t i o n through t h i s apple-core e f f e c t i s not considered s e r i o u s . I f such cases do a r i s e , a change of co o r d i n a t e axes w i l l supply the 24. missing information. The indicated direction of the heart vector has l i t t l e meaning when the magnitude i s small. This fact has prompted the development of a threshold control to suppress the frontal-angle output when the frontal-plane magnitude is too.low. A threshold control was added to Park's polarcardiograph shortly after i t was completed. In the present design of the polar-cardiograph, a triode replaces the vacuum diode which formerly rectified the differentiated square-wave pulses. The square wave i s taken from the second stage of the squaring circuit, integrated and applied through an amplifier to the. grid of the rectifying triode. The pulses which mark the t r a i l i n g edge of the square wave are normally passed to the f l i p -flop because the peak of the triangular wave (integrated square wave) is applied to the grid of the triode at the same time, thus allowing the triode to conduct. However, i f .the magnitude becomes too small to develop a triangular wave of sufficient height to cause,the triode to conduct, the angle reading is suppressed. The threshold control as described here is only partially successful, mainly because i t is too c r i t i c a l to adjust. The threshold control designed ibr the spherical polar-cardiograph uses the same basic principle with the exception that a sine wave is used in place of the triangular wave. It is -bought that the circuit w i l l not be as c r i t i c a l l y sensitive to a slight difference between the times of arrival of the peak of the sine wave and of the pulse at the rectifying triode as i t i s in the former control. A sinusoid, obtained 25. f r o m t h e f i l t e r f e e d i n g t h e z - a x i s m u l t i p l i e r c a r r i e r s i g n a l , i s s h i f t e d n i n e t y d e g r e e s , g i v e n h a l f - w a v e r e c t i f i c a t i o n , a n d a p p l i e d t o t h e r e c t i f y i n g - t r i o d e g r i d . T h e n i n e t y - d e g r e e p h a s e s h i f t e n s u r e s t h a t t h e p e a k o f t h e s i n e w a v e w i l l o c c u r s i m u l t a n e o u s l y w i t h t h e t r a i l i n g e d g e o f t h e s q u a r e w a v e i n t h e p h a s e - m e t e r c i r c u i t . T h e s p h e r i c a l p o l a r c a r d i o g r a p h c o m p l e t e l y s p e c i f i e s t h e h e a r t v e c t o r w i t h o u t p u t v o l t a g e s p r o p o r t i o n a l t o r , 0, a n d 0 a n d a t t h e same t i m e s u p p r e s s e s t h e s e r e s u l t s w h e n t h e y h a v e n o m e a n i n g . 26. VI VOLTAGE AND CURRENT REQUIREMENTS The low input s i g n a l l e v e l and the l i m i t e d l i n e a r range of many of the tubes of the computer imposes a need f o r v o l t a g e r e g u l a t i o n . The unbalance r e s u l t i n g i n the plane p o l a r c a r d i o -graph from s l i g h t v o l t a g e v a r i a t i o n s has emphasized t h i s 'requirement. The c i r c u i t s t h a t r e c e i v e r e g u l a t e d v o l t a g e are those r e q u i r i n g great s t a b i l i t y and drawing a constant c u r r e n t , the input a m p l i f i e r s use f i f t y m i l liamperes a t +300 v o l t s dc and f o r t y m i l l i a m p e r e s a t -300 v o l t s dc, both r e g u l a t e d . The heaters of these u n i t s and the m u l t i p l i e r tubes are f e d i n s e r i e s by a r e g u l a t e d dc supply. The u n i t s c o n t a i n i n g the d e f l e c t i o n a m p l i f i e r , the m u l t i p l i e r s e c t i o n , the s u b t r a c t o r and the feedback c i r c u i t draw n i n e t y m i l l i a m p e r e s a t +300 v o l t s r e g u l a t e d and 14 mill i a m p e r e s a t -300 v o l t s r e g u l a t e d . The adder, f i l t e r , and double-tuned a m p l i f i e r c i r c u i t s use a t o t a l of f o r t y m i l l i a m p e r e s a t +300 v o l t s r e g u l a t e d and nine milliamperes a t -300 v o l t s r e g u l a t e d . In a d d i t i o n , a r e g u l a t e d +300-voIt supply i s needed f o r the o s c i l l a t o r (two m i l l i a m p e r e s ) , and f o r the u n i t p r o v i d i n g the magnitude out-put, p o l a r angle output and the f i l t e r f o r the z-axi s c a r r i e r s i g n a l ( fourteen m i l l i a m p e r e s ) ; the l a t t e r u n i t a l s o uses f i v e m i l l i a m p e r e s a t -300 v o l t s r e g u l a t e d . The remaining u n i t s r e q u i r i n g only an unregulated +300-volt supply are the cathode-coupled c l i p p e r . o r squaring c i r c u i t (25 m i l l i a m p e r e s ) , the f r o n t a l - c h a n n e l phase meter (35 m i l l i a m p e r e s ) , and the delay clamp-pulse generator (two m i l l i a m p e r e s ) . The t o t a l ' c u r r e n t requirements are 196 mi l l i a m p e r e s a t +300 v o l t s r e g u l a t e d , 62 milliamperes at +300 v o l t s unregulated 27 and_78 milliaraperes a t -300 v o l t s regulate,d 0 The ac heater requirements t o t a l 21 amperes a t 6.3,volts. To d i s s i p a t e the heat, the c h a s s i s has been designed w i t h s i d e f l a p s which, are to be l e f t open d u r i n g o p e r a t i o n . The r e g u l a t i o n of the supply v o l t a g e f o r the more c r i t i c a l c i r c u i t s w i l l a i d the s p h e r i c a l p o l a r c a r d i o g r a p h i n m a i n t a i n i n g i t s balanced c o n d i t i o n f o r longer p e r i o d s than d i d the plane p o l a r c a r d i o -graph. Coupling the r e g u l a t i o n with the gated feedback, r e s u l t s i n a s t a b l e computer. 28. VII THE OPERATING ADJUSTMENTS Before t a k i n g any t r a c i n g s with the s p h e r i c a l p o l a r -cardiograph, the computer z e r o - l e v e l must.be e s t a b l i s h e d , each m u l t i p l i e r s e c t i o n balanced f o r zero s i g n a l output f o r zero input and the channel gains equalized. The balancing procedure, i f the computer i s f i r s t allowed to become warm, heed only be performed once. Any subsequent unbalances w i i l be compensated f o r by the gated feedback. When performing the balancing procedure on, f o r example, the x-axis channel, the y - a x i s and z-axis channels must have feedback a p p l i e d to avoid i n t e r f e r e n c e . The z e r o - l e v e l of the channel i s set by a d j u s t i n g the x-axis c e n t r i n g c o n t r o l f o r zero d e f l e c t i o n and then the corresponding m u l t i p l i e r p a i r i s balanced to show zero magnitude output. A s i m i l a r method i s used on the y-axis channel but a d d i t i o n a l precaut-ions must be taken when balancing the z-axis channel. A c a r r i e r s i g n a l must be a p p l i e d to the m u l t i p l i e r s and the f r o n t a l - p l a n e s i g n a l disconnected before the z-axis channel i s adjusted. A f t e r i n i t i a l channel adjustments, channel gains are equalized by applying equal s i g n a l s to the x and y_ inputs and then to the y_ and z inputs and a d j u s t i n g channel gains so as to produce a 45-degree d e f l e c t i o n on the cathode-ray tube i n each case. Then the gains as f a r as t h e d e f l e c t i o n - a m p l i f i e r outputs w i l l be equal so t h a t the cathode-ray tube presents a v a l i d vectorcardiogram. The i n i t i a l balancing must be followed by the c a l i b r a t i o n of the instruments used to record angle and magnitude outputs. 29 In g r e a t e r d e t a i l , the b a l a n c i n g procedure i s as, f o l l o w s . F i r s t ground a l l i n p u t s by p l a c i n g the i n p u t r o t a r y switch to p o s i t i o n n i n e . Open switch one so t h a t the f i n a l tube of the clamp generator i s t u r n e d o f f and a l l feedback loops are c l o s e d . By means-of-the cathode-ray tube rotary, switch, observe d e f l e c t i o n s i n the f r o n t a l p lane. Open the feedback loop of the x-axis channel by p l a c i n g switch two i n p o s i t i o n two, thereby lowering the g r i d of t h e corresponding g a t i n g t r i o d e below c u t - o f f p o t e n t i a l . Return the spot on the cathode-ray tube to the v e r t i c a l l i n e with the x - c e n t r i n g c o n t r o l , thus e f f e c t i v e l y t i e i n g the s i g n a l g r i d s of t h e m u l t i p l i e r tubes together. The v a r i a b l e p l a t e l o a d r e s i s t o r of the m u l t i p l i e r s i s then adjusted u n t i l the magnitude T reads zero. At t h i s p o i n t , the x - a x i s channel balance i s com-p l e t e so t h a t switch two may be returned to i t s normal p o s i t i o n ( p o s i t i o n one). The procedure i s repeated w i t h the y - a x i s channel u s i n g switch three to break the f e e d -back loop and the y - c e n t r i n g c o n t r o l on the cathode-ray tube to set the zero l e v e l of the channel. Since the z-axis channel o p e r a t i o n depends upon a c a r r i e r s i g n a l from the f r o n t a l - p l a n e being f e d to the m u l t i p l i e r s , the i n p u t r o t a r y switch must be moved to p o s i t i o n e i g h t so t h a t s i g n a l i s a p p l i e d to the y - a x i s i n p u t . Switch one i s r e t u r n e d to i t s normal p o s i t i o n to remove a l l feedback. Open switch f i v e to prevent the f r o n t a l - p l a n e s i g n a l , HE s i n (cot + V + 0), from e n t e r i n g the z-axis channel. The cathode-ray tube p i c t u r e must 30 be changed to present the x-z plane. The z - c e n t r i n g c o n t r o l i s used to r e t u r n the spot to the x - a x i s . The m u l t i p l i e r i s a d j u s t e d t o give zero magnitude output. At t h i s stage, the zero l e v e l or o r i g i n of the computer has been set and the three m u l t i p l i e r s e c t i o n s have been balanced. Before a d j u s t i n g the x-, y_-, and £-axis channel gains of the instrument, i t i s necessary to check t h a t switches one to f i v e are i n t h e i r normal p o s i t i o n s . The i n p u t r o t a r y switch i s p l a c e d i n p o s i t i o n seven so t h a t one m i l l i v o l t i s a p p l i e d to one s i d e of each i n p u t , the other s i d e s remaining grounded. The i n p u t a m p l i f i e r g a i n c o n t r o l s are adjusted u n t i l x-y and x-z p r e s e n t a t i o n s show 45-degree d e f l e c t i o n s on the f a c e of the cathode-ray tube. The gains to the d e f l e c t i o n - a m p l i f i e r outputs are now equal and the m u l t i p l i e r s are balanced so t h a t the instrument i s ready to be c a l i b r a t e d . The angle c a l i b r a t i o n i s accomplished by a p p l y i n g a o n e - m i l l i v o l t s i g n a l a t approximately one c y c l e per second to v a r i o u s i n p u t s . The c a l i b r a t i o n s i g n a l i s taken from the f r e e - r u n n i n g m u l t i v i b r a t o r shown i n F i g u r e 10. By a p p l y i n g the c a l i b r a t i n g s i g n a l to v a r i o u s combinations of t h e s i x a v a i l a b l e i n p u t s , the f r o n t a l and p o l a r angles can be c a l i b r a t e d i n 45-degree s t e p s . P o s i t i o n s i x of the r o t a r y switch a p p l i e s s i g n a l to one i n p u t of the x - a x i s channel which r e s u l t s i n a f r o n t a l - a n g l e output a l t e r n a t -i n g between zero and 180 degrees. P o s i t i o n f i v e maintains the s i g n a l i n p u t to the x - a x i s channel and a p p l i e s the same R l , R2 68 kilohms R3, R5 4.7 megohms R4 1.5 kilohms CI, C2 0.05 uf. VI, V2 VR 90 V3 12AX7 R6 H7 1 megohm 0-100 ohm Fi g u r e 10. Fre.e-Runni.ng M u l t i v i b r a t o r For C a l i b r a t i o n . 31. s i g n a l to one input of the y - a x i s channel to show a f r o n t a l angle of 45 and 225 degrees. I f the x- a x i s channel inputs are grounded with the s i g n a l remaining on the y - a x i s ( p o s i t i o n f o u r ) , the f r o n t a l angle w i l l r e g i s t e r n i n e t y and 270 degrees. P o s i t i o n three of the r o t a r y switch r e t a i n s t h e s i g n a l on the y - a x i s channel and simultaneously a p p l i e s the s i g n a l to the opposite input of the x - a x i s channel as was p r e v i o u s l y used. The r e v e r s a l of the x- a x i s channel i n p u t s changes the instantaneous p o l a r i t y so t h a t the f r o n t a l - a n g l e reading w i l l be s h i f t e d n i n e t y degrees from t h a t of p o s i t i o n f i v e to give 135 and 315 degrees. The f r o n t a l - a n g l e output i s now c a l i b r a t e d i n 45-degree steps f o r 360 degrees. N o n - l i n e a r i t y i n the c a l i b r a t i o n of the f r o n t a l - a n g l e output should be c o r r e c t e d by a d j u s t i n g the adder c o n t r o l f o r t h i s channel. C a l i b r a t i o n of the p o l a r - a n g l e r e c o r d i n g s can be performed d u r i n g the f r o n t a l - a n g l e c a l i b r a t i o n . With f r o n t a l - p l a n e s i g n a l and with no z-axi s s i g n a l , the p o l a r angle w i l l r e g i s t e r as n i n e t y degrees. I f a s i g n a l i s a p p l i e d to e i t h e r i n p u t of the x~ o r y_-axis and the same s i g n a l i s a p p l i e d "to one i n p u t of the z - a x i s , the p o l a r -angle output w i l l a l t e r n a t e between 45 and 135 degrees. The r o t a r y switch allows f o r t h i s c a l i b r a t i o n i n p o s i t i o n s f i v e and f o u r r e s p e c t i v e l y . Any n o n - l i n e a r i t y a r i s i n g i n the p o l a r - a n g l e c a l i b r a t i o n should be c o r r e c t e d by a d j u s t -i n g the z-axis adder c o n t r o l . A summary of the b a l a n c i n g and c a l i b r a t i n g procedure i s as f o l l o w s : 32. 1. Place the in p u t r o t a r y switch i n p o s i t i o n nine, open switch one, apply the x-y plane to the cathode-ray tube, p l a c e switch two i n p o s i t i o n two and zero the x-coor d i n a t e of the spot on the tube f a c e ; a d j u s t the mul-t i p l i e r s to show zero magnitude output and r e t u r n switch two to p o s i t i o n one. 2. With the in p u t r o t a r y switch s t i l l i n p o s i t i o n n i n e , repeat 1. using the y - a x i s c e n t r i n g c o n t r o l and switch t h r e e . 3. Place the in p u t switch i n p o s i t i o n e i g h t , change switch one to i t s normal o p e r a t i n g p o s i t i o n and open switch f i v e ; w i t h the cathode-ray tube p r e s e n t i n g the x-z plane, centre the spot on the f a c e of t h e tube and a d j u s t the m u l t i p l i e r c o n t r o l f o r zero magnitude output. 4. Check t h a t switches one to f i v e are i n the normal o p e r a t i n g p o s i t i o n s . 5. Place the input switch i n p o s i t i o n seven and a d j u s t the input a m p l i f i e r gains of the x and y axes t o show 45 degrees on the cathode-ray tube. 6. Adju s t the z-axi s input a m p l i f i e r g a i n c o n t r o l u n t i l the cathode-ray tube p r e s e n t a t i o n , which shows the x-z plane, reads 45 degrees. 7. Place the i n p u t r o t a r y switch i n p o s i t i o n s i x and note the zero- and 180-degree f r o n t a l angles. 8. Turn the in p u t switch to p o s i t i o n f i v e and note the 45- and 2 2 5 - f r o n t a l angles. A l s o note the n i n e t y -degree p o l a r angle. 9. With the input switch i n p o s i t i o n f o u r , note the 33 90- and 270-degree f r o n t a l angles and the 45- and 135-degree p o l a r a n g l e s . 10. Place the i n p u t switch i n p o s i t i o n t h r e e and note the 135- and 315-degree f r o n t a l angles. 11. I f n o n - l i n e a r i t y i s apparent i n the angle i n d i c a t -i o ns i t i s necessary to c o r r e c t the corresponding adder c o n t r o l s . With the s p h e r i c a l p o l a r c a r d i o g r a p h completely balanced and c a l i b r a t e d , the i n p u t r o t a r y switch i s returned to p o s i t i o n one, i t s normal o p e r a t i n g c o n d i t i o n . P o s i t i o n two of the r o t a r y switch i s p r o v i d e d as a f r o n t a l - p l a n e quadrant s h i f t . The s h i f t i s necessary because of the ambiguity of the phase meter at the 180-degree mark. I f the preceding i n s t r u c t i o n s are f o l l o w e d c a r e f u l l y , the computer can be used t o o b t a i n accurate i n f o r m a t i o n concerning the e l e c t r i c a l a c t i v i t y of the h e a r t . 34. VIII PHYSICAL LAYOUT The computer, with the exception of the power supply, i s designed so as to be housed i n an 11" x 14" x 20" Hammond c a b i n e t . When i n use, the instrument w i l l r e s t on a push-cart w i t h the power supply on a lower s h e l f . With t h i s arrangement, the computer can e a s i l y be moved to the p a t i e n t ' s bedside. For an instrument of t h i s s i z e and complexity, s e r v i c -i n g i s an important f a c t o r . The apparatus has been designed f o r c o n s t r u c t i o n i n u n i t s so as to s i m p l i f y the t e c h n i c i a n ' s ta s k . I f t r o u b l e i s suspected i n any p o r t i o n of the equip-ment, the a p p r o p r i a t e u n i t can be withdrawn and t e s t e d independently of the remainder of the i n s t a l l a t i o n . Connections t o the u n i t s are to be made through s i x t e e n -t e r m i n a l p l u g - i n connectors. A l l of the i n t e r - u n i t w i r i n g w i l l be housed on a back panel (Figure 11) to which the u n i t s connect. F i g u r e 12 shows a complete block diagram of the s p h e r i c a l p o l a r c a r d i o g r a p h . F i g u r e s 13 to 19 i n c l u s i v e show the c i r c u i t diagrams and element values of the remaining u n i t s . For the suggested u n i t p o s i t i o n s c o n s u l t F i g u r e 20. I t w i l l be noted t h a t s e v e r a l of the u n i t s i n the f i n i s h e d instrument w i l l be i d e n t i c a l . CI, C2 0.001 uf. A ' R3, R4 27K F- R l , R2 0-30K . A +300 V unreg . B +300 V reg C -300-V reg D a-c heater: * E ground ' F CRT hig h V F i g u r e 11. Back Panel Wiring Diagram, y-axxs_ ecg x - a x i s ecg det amp 1 -d e f l mult from any d e f l e c -t i o n a m p l i f i e r output delay z-axis ecg d e f l det_ +45~1 1^451 d e f l mult 1 det amp clam] mult 90© f i l t e j - sq cct d/dt t - c ~i f - f 0 sqcct d/dt filter 90° f i l t e r sqcct r e c t + — re c t © F i g u r e 1 2 . Block Diagram of the S p h e r i c a l P o l a r c a r d i o g r a p h R l , R2, R34 R3, R4 R5, R7, R16, R17 R8, RIO R9, R25 R l l , R23, R29 1 megohm 0.47 •" 2.2 " 2.2 kilohm 10 0-10 R19, R22 R24 R26 R27, R30 R28, R31 R33 R12, R14, R20, R21, R32 0,15 megohm R13 0-0.25 " R15, R18 0.5 4.7 megohm 0.5 kilohm 20 " 68 " 447 11 3.3 " CI, C2, C5, C6 0.1 uf. C3, C4 0.01 " L l , L2 130 mh. F i g u r e 13. D e f l e c t i o n A m p l i f i e r , M u l t i p l i e r , S u b t r a c t o r , and Feedback C i r c u i t . R l , R6, R12 6.8 kilohm R2, R7 100 « R3, R8, R20 68 R4, R5, R9, RIO, R15 2.2 megohm R l l 2.2 kilohm R13 33 " R16 220 « R17, R1T9 R18 R21, R22 C1, C2, C3, 06 07, 08, C9 VI, V2, V3 0-250 kilohm 10 " 6.7 " 04°, 05 0.001 Uf. 100 UUf. 6 Uf. 12AU7 Fi g u r e 14. Cathode-Coupled C l i p p e r or Squaring C i r c u i t :R15 13 Rl, R18 R2, R19 R3, R7, R8, R4, R17 R16 1 kilohm 270 ohran 10 kilohm 68 " 6 KO 0.2 megohm R6, R14, R15, R21 0.1 " R9, RIO, R13 ' * R l l , R12 ad. 6 CI, C8 C2, C7 C3, C6, C9 6AC7 V3 6AL5 V4 12AX7 V5 12AU7 22 kilohtnn 150 - " 0-1 megohm 0.25 " 8 uf. 0.1 " 0.01 " 50 uuf. Figure 15. Differentiating Amplifier and Flip-Flop V2a 14 C l IS— C4 IR14 8 C2 U ;R7 2 ,L1 R13 C5 xXSULSA^—^SULSLQj^ L2 L3 C8 C9 CIO R14 f»— R15 ZL23 R4 R l 15-R2 6 For P h i l b r i c k K2-W b i a s i n g arrangement see F i g u r e 9 R l , B 2 , R 3 y R4 100 kilohms LI 10 mh. R 7 , R8 , R9 1 megohm L2, L3 120 11 RIO 68 kilohms C l , C2, C3 500 uuf. B l l , R13 47 n 04, C5 0.015 Uf. R12 330 ohms C6, C7 0.01 « R14 100 kilohms C8, C9, CIO, C l l 0.001 " R15 B 1 6 , R17 R18 , R19 500 0-30 27 II it it VI V2 6AU6 6AL5 F i g u r e 16 . Z-axis C a r r i e r - S i g n a l F i l t e r , Magnitude Output, and P o l a r Angle Output. *~1 R l R2 R3 R5 R6, R7, R l l , R13 R8 R9, R14 RIO, R12 O-lOO kilohm . 500 " 10 megohm o.5 "" 0.15 " 0,5-3.0 " 10 kilohm 1 megohm R15 0-500 kilohm R16 0.68 megohm R17 0.22 CI 1 ufd. C2, C3 0.1 " VI, V2 V3 12AX7 6AL5 Figurel7a. Delay C i r c u i t and Clamp-Pulse Generator s i n g l e deck r o t a r y switch the numbers represent the t e r m i n a l s to which the d e f l e c t i o n - a m p l i f i e r outputs are connected F i g u r e 17b. Switch f o r S e l e c t i n g T r i g g e r Pulse f o r Generator R1, R2 - 150 Kilohms Transformer 214-60 R3 - 3.3 Megohms CRT RP1 R4 - 2.0 Megohms R5 - 1.0 Megohms R6 - 0.5 Megohms VI - 2X2 Figure 18. Cathode-Ray-Tube C i r c u i t and i t s View-Selector Switch. Figure 19, Input Rotary Switch. clamp generator t r i g g e r s e l e c t o r input a m p l i f i e r d e f l e c t i o n a m p l i f i e r m u l t i p l i e r s e c t i o n feedback c i r c u i t add, f i l t e r and band-pass a m p l i f i e r squaring c i r c u i t -phase meter and threshold c o n t r o l o s c i l l a t o r and time marker input a m p l i f i e r d e f l e c t i o n a m p l i f i e r m u l t i p l i e r s e c t i o n feedback c i r c u i t add, f i l t e r and band-pass a m p l i f i e r squaring c i r c u i t r e c t i f i e r , add, f i l t e r and band-pass a m p l i f i e r input r o t a r y switch c a l i b r a t i o n m u l t i v i b r a t o r input a m p l i f i e r d e f l e c t i o n a m p l i f i e r m u l t i p l i e r s e c t i o n feedback c i r c u i t squaring c i r c u i t view selector focus i n t e n s i t y Figure 20. Proposed Unit P o s i t i o n s IX CONCLUSION The s p h e r i c a l polarcardiograph i s an e l e c t r o n i c device v h i c h transforms voltages p r o p o r t i o n a l to the C a r t e s i a n p r o j e c t i o n s x, y_, and z of the heart vector to voltages p r o p o r t i o n a l to the s p h e r i c a l p o l a r coordinates r , 0, and 0. The gated feedback discussed i n chapter I I I and the voltage r e g u l a t i o n of the more c r i t i c a l u n i t s discussed i n chapter VI r e s u l t i n a s t a b l e computer. The feedback loop which i s cl o s e d between heart beats rebalances the instrument s u f f i c i e n t l y so t h a t the manual balance proce-dure need be c a r r i e d out only once a f t e r the computer i s warm. The method of i n t r o d u c i n g the t h i r d coordinate i s simple but i t leaves a c y l i n d r i c a l volume surrounding the po l a r a x i s i n which no information can be obtained. Although very l i t t l e information w i l l be l o s t i n t h i s r e g i o n , i t can be restored by exchanging the i n p u t s . Although the computer has not been constructed i n f i n a l form, t e s t s on the i n d i v i d u a l u n i t s have i n d i c a t e d t h a t the device w i l l be w e l l w i t h i n accuracy requirements. However, only prolonged c l i n i c a l t e s t s can determine the ul t i m a t e usefulness of the s p h e r i c a l polarcardiograph i n the f i e l d of medical research. 36. BIBLIOGRAPHY 1. Burger, H.C., and van Milaan, J.B., "Heart Vector and Leads, Part III,." B r i t i s h Heart J o u r n a l . 1948, X, 229. 2. Dower, G.E., Osborne, J.A., "Comments on Vector-c a r d i o g r a p h ^ Lead Systems: A New System Proposed," forthcoming p u b l i c a t i o n . 3. Dusehosal, P.W., Sulzer, R., La V e c t o r c a r d i o g r a p h ^ , S. Karger, New York, N.Y., 1949. 4. Einthoven, E., Fahr, G., de Waart, A. ( i n E n g l i s h ) , "Uber die r i c h t u n g und die Manifests Gr8sse der Potentialschwankungen im Menschlichen Herzen und fiber den E i n f l u s s der Herzlage auf die Form des Elektrokardiogramme," American Heart  J o u r n a l . 1950, XL, 163. 5. Florman, E.R., "Measuring Phase at Audio and U l t r a s o n i c Frequencies," E l e c t r o n i c s . 1949, XXII, 114. 6. Frank, Ernest, "The Image Surface of a Homogeneous Torso," American Heart J o u r n a l . 1954, XLVI I , 757. 7. Goldmuntz, L.A., and Kraus, H.L., "The Cathode-Coupled C l i p p e r C i r c u i t , " Proceedings of the I.R.E., 1948, XXXVI, 1172. 8. Koontz, P a u l , and Delatush, E a r l e , "Voltage-Regulated Power Supplies," E l e c t r o n i c s , 1947, XX, 119. 9. Kretzmer, E.R., "Measuring Phase at Audio and U l t r a -sonic Frequencies," E l e c t r o n i c s . 1949, XXII, 114. 10. McFee, R., "A Trignometric Computer w i t h E l e c t r o c a r d i o -graphic A p p l i c a t i o n s , " Review of S c i e n t i f i c  Instruments, 1950, XXI, 420. 11. Park, W.K.R., "A Polarcardiograph Computer," M.A.Se. Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1954. 12. Pressman, Ralph, "How to Design B i s t a b l e M u l t i v i b r a t o r s , " E l e c t r o n i c s . 1953, XXVI, 164. 13. Wilson, F.N,, Johnston, F.D., MacLeod, A.G., Barker, P.S., "Electrocardiograms that Represent the P o t e n t i a l V a r i a t i o n s of a Single Electrode," s  American Heart J o u r n a l . 1934, IX, 447. 14. Yu, Y.P., "Zero Intercept Phase Comparison Meter," E l e c t r o n i c s . 1953, XXVI, 178. 

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