A TRANSISTORIZED SPHERICAL POLARCARD10GRAPH by PATRICK JOHN RONALD HARDING B.A.Sc, The U n i v e r s i t y of B r i t i s h Columbia, 19 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED 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 r e q u i r e d standard THE UNIVERSITY OP BRITISH COLUMBIA May, 1963 In presenting th i s thesis in p a r t i a l fulf i lment of the requirements for an advanced degree at the. Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make i t free ly avai lable for reference and study. I further agree that per-mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying, or p u b l i -cation of this thesis for f i n a n c i a l gain sha l l not be allowed without my written permission. Department of <<^ The Univers i ty of B r i t i s h Columbia, Vancouver 8, Canada. ABSTRACT The design of a two—dimensional p o l a r c a r d i o g r a p h and the use of two such two-dimensional devices to c a l c u l a t e the t h i r d p o l a r coordinate together w i t h the c i r c u i t r y necessary to d e r i v e and amp l i f y a s e t of 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 coordinates x, y, and z i s d e s c r i b e d . Although the technique used f o r o b t a i n i n g the p o l a r coordinates i s s i m i l a r to that used i n other instruments, the c i r c u i t r y i s somewhat d i f f e r e n t . This i s d i c t a t e d i n p a r t by the f a c t t h a t t h i s d e v i ce i s completely t r a n s i s t o r i z e d . Both the Prank and RAPE networks are a v a i l a b l e f o r the tr a n s f o r m a t i o n from p a t i e n t s i g n a l s to a set of s i g n a l s p r o p o r t i o n a l to the C a r t e s i a n coordinates x, y, and z. R e s t o r a t i o n of the b a s e - l i n e at the optimum time dur i n g the c a r d i a c c y c l e i s achieved through a system of gated f e e d -back which i s a c t i v a t e d by a p r e d i c t o r c i r c u i t . The pre -d i c t o r i s t r i g g e r e d by an automatic t r i g g e r s e l e c t o r . A t h r e s h o l d c i r c u i t i s a s s o c i a t e d with each angle out-put i n order to set the output to some predetermined value when the input s i g n a l l e v e l i s so small as to make the angle output indeterminate. i i ACKNOWLEDGEMENT The author would l i k e to thank Dr. A.D. Moore, the s u p e r v i s i n g p r o f e s s o r , f o r h i s help and guidance throughout t h i s r e s e a r c h p r o j e c t and Dr* G»E. Dower whose r e s e a r c h has demonstrated that a t r a n s i s t o r i z e d p o l a r c a r d i o g r a p h 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 y * The author i s also indebted to the t e c h n i c i a n s i n the E l e c t r i c a l E n g i n e e r i n g shop f o r t h e i r a s s i s t a n c e on t h i s p r o j e c t . The p r i n c i p a l p a r t of t h i s r e s e a r c h was c a r r i e d out under the Na t i o n a l Research C o u n c i l Block Term Grant BT-68. A d d i t i o n a l a s s i s t a n c e was giv e n under a grant from the B r i t i s h Columbia Heart Foundation* v i TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS i v ACKNOWLEDGEMENT v i 1. I n t r o d u c t i o n I 2. P r i n c i p l e of the Computer 6 3* A m p l i f i e r s and Lead-system Networks ................. 12 4. B a s e - l i n e Clamping 16 4.1 General D e s c r i p t i o n 16 4.2 The Automatic T r i g g e r S e l e c t o r ................. 20 4.3 The Clamp Advance C i r c u i t 22 5. The Two-dimensional Computer 26 5.1 General D e s c r i p t i o n 26 5.2 The M u l t i p l i e r s ................................ 26 5.3 The C a r r i e r Generator ............*..........*.. 28 5.4 The Low-pass F i l t e r ..••....................*... 31 5.5 Magnitude D e t e c t i o n «•••........................ 33 5.6 Angle D e t e c t i o n (phase comparison) ............. 35 5.7 The C l i p p e r 36 5.8 The Threshold C i r c u i t 37 6. The Three-dimensional Computer 40 7. Test R e s u l t s 42 8. Conclusions 49 Appendix 50 References 63 i i i LIST OP ILLUSTRATIONS F i g u r e Page 1.1 Coordinate systems i n e l e c t r o c a r d i o g r a p h y . 2 1.2 Types of electrocardiograms 3 2*1 Two-dimensional t r i g o n o m e t r i c computer .... 7 2*2 Three-dimensional t r i g o n o m e t r i c computer .. 9 3.1 A m p l i f y i n g and clamping c i r c u i t ........... 14 4.1 T y p i c a l e l e c t r o c a r d i o g r a p h i c waveform ..... 17 4.2 Clamp system used i n the previous p o l a r -cardiograph «••..••••••.................... 18 4*3 Clamp system used i n t h i s p o l a r c a r d i o g r a p h 19 4.4 Automatic t r i g g e r s e l e c t o r ................ 21 4.5 Clamp advance c i r c u i t ......«...*«......... 23 4.6 Waveforms generated i n the clamp advance c i r c u i t 24 5*1 Block diagram of the two-dimensional t r i g o n o m e t r i c computer as c o n s t r u c t e d ..... 27 5*2 C i r c u i t diagram of a m u l t i p l i e r ........... 28 5*3 C a r r i e r generator output waveforms ........ 29 5.4 4-Kc c a r r i e r generator .................... 30 5.5 Waveforms used to ensure c o r r e c t phasing of c a r r i e r generator outputs 32 5.6 Low—pass f i l t e r » . * * * * . . . . . . . . . . . . . o . • • » • • « . 33 5.7 Low-pass f i l t e r response curves ........... 34 5*8 Waveforms of the phase comparator ......... 35 5*9 Waveforms of the t h r e s h o l d c i r c u i t ........ 37 5*10 Block diagram shoving the t h r e s h o l d c o n t r o l c i r c u i t .«....*****•****.... * ............... 39 6*1 Block diagram of the three-dimensional p o l a r c a r d i o g r a p h 41 i v Page 7.1 P l o t of d e t e c t e d output as a f u n c t i o n of input f o r the two-dimensional computer . 44 7.2 P l o t of d e t e c t e d output as a f u n c t i o n of input f o r the three—dimensional computer .. 45 7.3 Recording of angle outputs of the two-dimensional computer f o r three d i f f e r e n t peak-to-peak i n p u t — s i g n a l l e v e l s , (a) 15 v o l t s , (b) 4 v o l t s , (c) 0.8 v o l t s 46 7.4 Recording of p o l a r angle output of the three-dimensional computer f o r three d i f f e r e n t peak—to—peak i n p u t - s i g n a l l e v e l s , (a) 15 v o l t s , (b) 4 v o l t s , (c) 0.8 v o l t s .. 47 7.5 Recording of angle output of the two-dimensional computer showing t h r e s h o l d c i r c u i t i n o p e r a t i o n f o r four d i f f e r e n t t h r e s h o l d l e v e l s , (a) 10$, (b) 3$, (c) 1.5$ 48 A . l C i r c u i t diagram f o r p r e a m p l i f i e r s ......... 53 A.2 C i r c u i t diagram f o r second and t h i r d stage a m p l i f i e r s ...••••••••••..••.........••«... 54 A.3 C i r c u i t diagram f o r Frank and RAFE l e a d systems 55 A.4 C i r c u i t diagram of c o u p l i n g network and re 1 ays «.«....»............................. 56 A.5 C i r c u i t diagram f o r automatic t r i g g e r s e l e c t o r .»••«••>••••••.......•.•.•....••.. 57 A.6 C i r c u i t diagram f o r clamp advance c i r c u i t . 58 A.7 C i r c u i t diagram f p r two-dimensional computer 59 A.8 C i r c u i t diagram f o r 4-Kc c a r r i e r generator 60 A*9 C i r c u i t diagram f o r t h r e s h o l d c o n t r o l 61 A.10 C i r c u i t diagram f o r f r o n t a l magnitude d e t e c t o r and p o l a r — a x i s delay ............. 62 v 1. INTRODUCTION The instrument to be d e s c r i b e d here i s an analogue computer which converts e l e c t r i c a l s i g n a l s p r o p o r t i o n a l to the C a r t e s i a n coordinates x, y, and z i n t o e l e c t r i c a l s i g n a l s p r o p o r t i o n a l to the plane and s p h e r i c a l p o l a r coordinates r» R, 0/ and 9. The r e l a t i o n s h i p between these coordinates i s shown i n Figure 1.1. Such a computer f i n d s an a p p l i c a t i o n i n e l e c t r o c a r d i o g r a p h y since 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 of a "heart v e c t o r " can be obtained by the proper arrangement of e l e c t r o d e s on a p a t i e n t ' s body. The heart produces an e l e c t r i c f i e l d w i t h i n the body v a r y i n g i n d i r e c t i o n and magnitude throughout the c a r d i a c c y c l e . This f i e l d g ives r i s e to 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. Continuous r e c o r d i n g s of such v o l t a g e s on a time sc a l e are ca.lled e l e c t r o c a r d i o g r a m s (Figure 1.2). In present—day e l e c t r o c a r d i o g r a p h y , a dozen e l e c t r o c a r d i o g r a p h i c r e c o r d i n g s are u s u a l l y taken, one a f t e r another, from a number of e l e c t r o d e p o s i t i o n s . As a f i r s t approximation, the heart's e l e c t r i c f i e l d may be considered to 1-3 a r i s e predominantly from a s i n g l e c u r r e n t d i p o l e . The d i p o l e moment i s known as the heart v e c t o r . The s i m p l i f i c a t i o n which the h e a r t - v e c t o r concept allows cannot o r d i n a r i l y be u t i l i z e d i n c l i n i c a l e l e c t r o c a r d i o g r a p h y because i t i s impossible to r e c o n s t r u c t the v e c t o r a c c u r a t e l y from the usual electrocardiograms even though they may be considered to a r i s e from i t . A much more accurate p i c t u r e of the heart v e c t o r i s 2 X F i g u r e 1.1 Coordinate system i n e l e c t r o c a r d i p g r a p h y T 3 -4-^—A E l e c t r o c a r d i o g r a m s - ^ r ~ 4 Vectorcardiograms Computer Polarcardiograms F i g u r e 1.2 Types of electrocardiograms 4 obtained by a p p l y i n g orthogonal l e a d s i g n a l s to the h o r i z o n t a l and v e r t i c a l p l a t e s of a cathode-ray tube and photographing the locus of the spot d u r i n g one heart c y c l e . This two-dimensional p r o j e c t i o n of the heart v e c t o r i s c a l l e d a v e c t o r -cardiogram (Figure 1.2), The same technique can be used i n 4 three dimensions by s t e r e o s c o p i c p r e s e n t a t i o n . Vectorcardiograms s u f f e r from the disadvantage that the e l e c t r i c a l phenomena they r e c o r d are not d i s p l a y e d on a time s c a l e . This leads to l o s s of d e t a i l around the o r i g i n and vagueness concerning the temporal r e l a t i o n s h i p between p a r t s of the vectorcardiogram and c e r t a i n elements i n the e l e c t r o c a r d i o g r a m which are c l i n i c a l l y important. Another way to d i s p l a y e l e c t r o c a r d i o g r a p h i c data i s to r e c o r d the p o l a r c o o r d i n a t e s of the heart v e c t o r on a time s c a l e . Such r e c o r d i n g s are known as polarcardiograms (Figure 1.2). 5 Despite a continued i n t e r e s t i n t r i g o n o m e t r i c computers f o r t h i s use* the only p o l a r c a r d i o g r a p h t h a t has performed s u c c e s s f u l l y under c l i n i c a l c o n d i t i o n s has been the one developed i n t h i s l a b o r a t o r y . However, the development and c l i n i c a l t r i a l of t h i s device have suggested s e v e r a l p o s s i b i l i t i e s f o r improvement. These are as f o l l o w s J (1) Increase i n input r e s i s t a n c e to reduce the e f f e c t s of s k i n r e s i s t a n c e and thus s i m p l i f y the technique of e l e c t r o d e a p p l i c a t i o n , (2) Improvement i n b a s e - l i n e clamping to compensate a u t o m a t i c a l l y f o r v a r i a t i o n s i n heart r a t e * and automatic s e l e c t i o n of clamp t r i g g e r i n g s i g n a l . 5 (3) Simultaneous r e c o r d i n g of s p h e r i c a l polarcardiograms u s i n g three d i f f e r e n t choices of p o l a r a x i s . (4) Removal of indeterminate angle outputs a s s o c i a t e d w i t h small magnitudes by a t h r e s h o l d c o n t r o l c i r c u i t . (5) Obtaining magnitude and d i r e c t i o n outputs when the heart v e c t o r i s p a r a l l e l to the p o l a r a x i s . This t h e s i s d e s c r i b e s the design and c o n s t r u c t i o n of an improved p o l a r c a r d i o g r a p h embodying the above f e a t u r e s . The use of t r a n s i s t o r s and p r i n t e d c i r c u i t s together w i t h improvements i n design makespossible a c o n s i d e r a b l e r e d u c t i o n i n p h y s i c a l s i z e as w e l l as an improvement i n r e a l i a b i l i t y and ease of s e r v i c i n g . 6 2. PRINCIPLE OF THE COMPUTER The b a s i c o p e r a t i n g p r i n c i p l e of t h i s p o l a r c a r d i o g r a p h i c computer i s s i m i l a r to t h a t used i n other v e r s i o n s of the 5 9 10 instrument. ' ' Two v o l t a g e s p r o p o r t i o n a l to the orthogonal components of a v e c t o r i n two dimensions are m u l t i p l i e d by corresponding quadrature s i n u s o i d s of u n i t amplitude and the outputs are summed. The angle t>f the v e c t o r can be found by comparing the phase of the waveform vector- w i t h that of one of of the quadrature c a r r i e r s i g n a l s , while the envelope of the waveform i s p r o p o r t i o n a l to the magnitude of the v e c t o r . Two such t r i g o n o m e t r i c computers can be combined to give the angle and magnitude of a v e c t o r i n three dimensions. A simple v e r s i o n of a two—dimensional t r i g o n o m e t r i c computer i s shown i n Fi g u r e 2.1. The orthogonal s et of 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 coordinates x and y are r e l a t e d to the p o l a r coordinates r and 0 as fol l o w s ? x = r.cos0 (2.1) y = r.sin0 (2.2) r =-\| x 2 + y 2 (2.3) 0 = t a n ^ y / x (2.4) The plane p o l a r coordinates r and 0 can be obtained i n the f o l l o w i n g manner. The input s i g n a l s x and y are m u l t i -p l i e d by quadrature s i n u s o i d s v^ and v 2 > g i v i n g v^x = r.cos0. 'Siniot (2.5) 7 1 y r X v^ = sinwQt M u l t i p l y xv n Sum y M u l t i p l y yv-v l o r v 2 1 Phase Comparatoi 0 xv^ + y v 2 = r.sin(a>t + 0) Magnitude Detector v 2 = cost) = R.sin(wt + ©) (2.14) 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 and © are obtained from the summed m u l t i p l i e r outputs as b e f o r e . The instrument to be d e s c r i b e d here i s made up of two two-dimensional t r i g o n o m e t r i c computers of the type above, except t h a t square waves are s u b s t i t u t e d f o r the s i n u s o i d s (see Chapter 5 ) . The coordinates ( r , 0) of t h e ^ p r o j e c t i o n of the heart v e c t o r i n the x-y plane are giv e n by the f r o n t a l computer. The remaining two p o l a r coordinates (R, ©) are provided by the p o l a r computer. II Standard e l e c t r o c a r d i o g r a p h i c l e a d systems do not o r d i n a r i l y give x, y, and z d i r e c t l y . However, l i n e a r com-b i n a t i o n s of the v o l t a g e s obtainable from the p a t i e n t can be used to d e r i v e x, y, and z by means of r e s i s t i v e summing networks. Because the f l u c t u a t i o n s i n the p o t e n t i a l d i f f e r e n c e s being observed are of the order of one m i l l i v o l t , and because there may i n a d d i t i o n be a l a r g e dc b i a s due to e l e c t r o d e p o l a r i z a t i o n , i t w i l l be necessary to amplify the s i g n a l s and to e l i m i n a t e the dc component before analogue computation i s done. The f o l l o w i n g chapter w i l l d e s c r i b e the a m p l i f i e r s and r e s i s t i v e networks used. 12 3. AMPLIFIER AND LEAD-SYSTEM NETWORKS A c i r c u i t which w i l l d e r i v e and amplify analogue 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 coordinates x, y, and z to the l e v e l of t e n v o l t s needed by the m u l t i p l i e r s must meet the f o l l o w i n g nine requirementsi (1) The c i r c u i t should c o n t a i n a r e s i s t i v e network which w i l l transform v o l t a g e s a v a i l a b l e at the p a t i e n t i n t o a s e t of 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 coordinates 11 12 x, y» and z. * Although i t i s p o s s i b l e to use a set of p a t i e n t leads to d e r i v e these v o l t a g e s d i r e c t l y , t h i s r a i s e s d i f f i c u l t i e s because i t r e q u i r e s e l e c t r o d e p o s i t i o n s which are not easy to l o c a t e or are i n c o n v e n i e n t . I t i s more s a t i s f a c t o r y to place e l e c t r o d e s at e a s i l y l o c a t e d p o s i t i o n s on the body (e.g. l e f t l e g , r i g h t arm, centre of chest, etc.) and to d e r i v e the analogue s i g n a l s x, y* and z by l i n e a r combination of the e l e c t r o d e v o l t a g e s . The f u n c t i o n of the lead-system networks i s to c a r r y out t h i s t r a n s f o r m a t i o n . (2) The c i r c u i t must have high input r e s i s t a n c e i n order that the e f f e c t of p a t i e n t s k i n r e s i s t a n c e be s m a l l . Because the p a t i e n t s k i n r e s i s t a n c e i s sometimes as h i g h as 50 kilohms, the input r e s i s t a n c e should be s e v e r a l megohms. (3) Because t r a n s i s t o r s are to be used, i t i s neces-sary t h a t the f i r s t stage of a m p l i f i c a t i o n i n t h i s c i r c u i t be f e d from a l o w — r e s i s t a n c e source so t h a t the noise l e v e l w i l l be low. 13 (4) The average input s i g n a l i s of the order of one m i l l i v o l t , thus r e q u i r i n g an o v e r a l l v o l t a g e a m p l i f i c a t i o n of ten thousand. (5) The inputs to a l l a m p l i f i e r stages should be d i f f e r e n t i a l to give high in—phase r e j e c t i o n i n order t h a t the c i r c u i t be r e l a t i v e l y i n s e n s i t i v e to 60-cycle pick-up and to power-supply v a r i a t i o n s . (6) The c i r c u i t should remove the la r g e dc b i a s normally present i n the l o w — l e v e l s i g n a l s so th a t t h i s b i a s w i l l not tend to b l o c k the a m p l i f i e r s . (7) The output t e r m i n a l s of the c i r c u i t should have an average dc l e v e l c l o s e to zero v o l t s to s u i t the requirements of the m u l t i p l i e r s to be used, (8) The m u l t i p l i e r s a l s o r e q u i r e t h a t the output c i r c u i t have a low i n t e r n a l r e s i s t a n c e . (9) The c i r c u i t should be capable of r e - e s t a b l i s h i n g the zero l e v e l or b a s e - l i n e of the analogue output s i g n a l s once du r i n g each heart c y c l e . The c i r c u i t shown i n Figu r e 3 . 1 was designed to meet the above s p e c i f i c a t i o n s when us i n g as many as ei g h t p a t i e n t e l e c t r o d e s , i n c l u d i n g a ground e l e c t r o d e . I t can be seen from t h i s diagram that by i n s e r t i n g the r e s i s t i v e networks before the p r e a m p l i f i e r s , f o u r a m p l i f i e r s could have been e l i m i n a t e d , but t h i s was not f e a s i b l e because of the c o n f l i c t i n g c o n d i t i o n s imposed by requirements ( 2 ) and ( 3 ) . That i s , i f the r e s i s t i v e networks had been designed to give a hig h input r e s i s t a n c e , then the source r e s i s t a n c e as seen by the f i r s t stage of R R. s 1 r e s i s t i v e m a t r i x g i v i n g C a r t e s i a n c o o r d i n a t x', y', and x y -< s 1' R. 2 EF r e l a y - A / s / V -r e l a y clamp advance c i r c u i t tq^ m u l t i p l i e r s aiitomatic t r i g g e r s e l e c t o r F i g u r e 3.1 A m p l i f y i n g and clamping c i r c u i t 15 a m p l i f i c a t i o n would have been v e r y h i g h and would have given r i s e to a high noise l e v e l . The seven input a m p l i f i e r s , as w e l l as the three second-stage a m p l i f i e r s shown, are of the d i f f e r e n t i a l c o n f i g u r a t i o n 13 d e s c r i b e d by H i l b i b e r (Figures A . l and A.2). The input r e s i s t a n c e of an a m p l i f i e r i s of the order of two megohms and the v o l t a g e a m p l i f i c a t i o n i s equal to 100. Two a l t e r n a t i v e r e s i s t i v e networks are used here (Figure A.3), one f o r the Frank l e a d system,'''1 r e q u i r i n g seven 12 p a t i e n t e l e c t r o d e s , and the other f o r the RAFE system, r e q u i r i n g only f o u r . These networks are designed i n such a way that the i n t e r n a l r e s i s t a n c e seen at any output t e r m i n a l i s 100 kilohms (the o r i g i n a l Frank Network has been modified to achieve t h i s ) . The input r e s i s t a n c e of these networks i s approximately two to three times t h i s value.. The dc b i a s i s removed from the l o w — l e v e l s i g n a l s by RC c o u p l i n g between the f i r s t two stages of a m p l i f i c a t i o n , g i v i n g a lower h a l f power-frequency of approximately 0.08 c y c l e s per second. Compound emitter f o l l o w e r s i n c o n j u n c t i o n with zener diodes (Figure A.2) are used to give the r e q u i r e d l o w - r e s i s t a n c e output and zero average dc p o t e n t i a l a t the output t e r m i n a l s . The requirement t h a t the c i r c u i t r e - e s t a b l i s h the b a s e - l i n e of the analogue output s i g n a l s once duri n g each heart c y c l e i s f u l f i l l e d by using r e l a y s to g i v e gated feedback once du r i n g each c y c l e . This feedback arrangement i s d e s c r i b e d i n d e t a i l i n the f o l l o w i n g chapter. 16 . 4 . BASE-LINE CLAMPING 4.1 General D e s c r i p t i o n In the t r a n s f o r m a t i o n from C a r t e s i a n to p o l a r coordinates shown i n F i g u r e 1.1, i t i s important to d e f i n e the o r i g i n of the system. Although the waveforms i n C a r t e s i a n coordinates are only a f f e c t e d i n average value by the p o s i t i o n of the o r i g i n , i t i s apparent t h a t the e q u i v a l e n t p o l a r coordinates are much more dependent upon the p o s i t i o n of the o r i g i n . The most n a t u r a l choice f o r the o r i g i n i s t h a t which l e t s x = y = z = 0 d u r i n g the r e s t i n g i n t e r v a l of the heart c y c l e (Figure 4.1), when the e l e c t r i c a l a c t i v i t y of the heart i s assumed to be z e r o . Because of the use of BC-coupled a m p l i f i e r s , the average value of x, y,, and z at the output of the a m p l i f i e r s i s not zero r e l a t i v e to the r e s t i n g l e v e l . Hence, i t i s necessary to r e s t o r e the b a s e — l i n e r e g u l a r l y by b a s e - l i n e clamping dur i n g each heart beat. In the o r i g i n a l p o l a r c a r d i o g r a p h , the b a s e - l i n e was r e - e s t a b l i s h e d by connecting together the input g r i d s of an RC-coupled a m p l i f i e r during the r e s t i n g i n t e r v a l of each c y c l e , (Figure 4.2)*'' The time constant of the c o u p l i n g c i r c u i t , (R + R.)C , was made la r g e i n order to h o l d the b i a s e s t a b l i s h e d . In the clamp system used i n t h i s instrument, the base-l i n e i s maintained by using gated feedback to r e s e t the output to zero during the clamp i n t e r v a l and to e s t a b l i s h a b i a s v o l t a g e on C„ which tends to be maintained u n t i l the next clamp one heart c y c l e -clamp de l a y time—s» clamp d u r a t i o n r e s t i n g i n t e r v a i r clamp advance" time R T a clamp d u r a t i o n zero l e v e l F i g u r e 4*1 T y p i c a l e l e c t r o c a r d i o g r a p h i c waveform Figure 4.2 Glamp system used i n the previous p o l a r -cardiograph i n t e r v a l (Figure 4*3). The elements R., B , R„, C , and C„ X S X C I i n t h i s c i r c u i t are so p r o p o r t i o n e d that the t r a n s i e n t v o l t a g on the a m p l i f i e r input t e r m i n a l s due to the b i a s e s t a b l i s h e d on decays with a long time constant and w i t h zero i n i t i a l slope when the r e l a y s open. In the previous instrument, the r e l a y s were t r i g g e r e d i n the f o l l o w i n g manner. The QRS p o r t i o n of one of the s i x waveforms x, -x, y, -y, z, and - z , was s e l e c t e d by the operator and used to t r i g g e r a delay c i r c u i t which i n t u r n actuated the r e l a y s a f t e r an a d j u s t a b l e i n t e r v a l , the clamp delay time T^ i n Figure 4,1• This system d i d not prove e n t i r s a t i s f a c t o r y because of the frequency w i t h which the operator 19 A + V w li-ft C s c R C ^—-AAA/ l(-R. R. A A A / R f \ A 0 R f / AAA/—' F i g u r e 4.3 Clamp system used i n t h i s p o l a r c a r d i o g r a p h had t o r e a d j u s t the c o n t r o l s . The p e r i o d of the h e a r t c y c l e can change over a r e l a t i v e l y s h o r t i n t e r v a l of t i m e , and the o p e r a t o r had to r e a d j u s t the clamp d e l a y , not o n l y from p a t i e n t t o p a t i e n t , but d u r i n g the course o f a r e c o r d i n g . The clamp t r i g g e r system t o be d e s c r i b e d here i s d e s i g n e d t o l e s s e n , and i n most cases t o e l i m i n a t e , the adjustments r e q u i r e d because of these v a r i a t i o n s . The p r i n c i p a l e f f e c t on h e a r t waveforms due t o a change i n h e a r t r a t e i s i n the d u r a t i o n of the r e s t i n g i n t e r v a l ( F i g u r e 4.1). T h i s f a c t has been used i n the d e s i g n of the p r e s e n t system, so t h a t clamping tends to occur a t a p r e s e t t i m e , T , i n advance of the i n s t a n t when the QRS complex has i t s g r e a t e s t r a t e of change, r a t h e r than at a p r e s e t time a f t e r t h i s i n s t a n t as i n the previous instrument. This i s done by a n t i c i p a t i n g the occurrence of the next t r i g g e r p u l s e , on the b a s i s of the known value of the preceding p e r i o d , and clamping at the p r e s e t time before t h a t p u l s e . Although i t i s expected that t h i s new system of clamp t r i g g e r i n g w i l l be a c o n s i d e r a b l e convenience i n the m a j o r i t y of cases, unforeseen d i f f i c u l t i e s may a r i s e i n o c c a s i o n a l cases w i t h complicated c a r d i a c rhythms. For t h i s reason, the o r i g i n a l system of clamp t r i g g e r i n g i s a v a i l a b l e to the operator as an a l t e r n a t i v e . 4.2 The Automatic T r i g g e r S e l e c t o r The c i r c u i t shown i n F i g u r e 4.4 i s used to i d e n t i f y the occurrence of the g r e a t e s t slope of the three component waveforms. This i s done on the b a s i s of the g r e a t e s t p o s i t i v e slope of the s i x waveformsf x* ~x, y, -y, z, and - z . These s i g n a l s are d i f f e r e n t i a t e d and f e d i n t o a m p l i f i e r s b i a s e d beyond c u t o f f . The s i x output pulses c o n s i s t i n g of n e g a t i v e -going spikes r e l a t i v e to the c o l l e c t o r supply v o l t a g e (12 v o l t s ) , d r i v e an OR-gate through e m i t t e r f o l l o w e r s . The output of the OR—gate i s shunted w i t h a l a r g e c a p a c i t o r ( 2 m i c r o f a r a d s ) , and the maximum volt a g e appearing across the c a p a c i t o r w i l l be equal to that of the l a r g e s t s p i k e , which c o i n c i d e s with the g r e a t e s t slope of the QRS complex. The c a p a c i t o r w i l l discharge through the shunt r e s i s t o r * R^, between QRS complexes. I f the minimum d i f f e r e n c e between the maximum spike and the next l a r g e s t i s g r e a t e r than the decay i n c a p a c i t o r v o l t a g e d u r i n g one c y c l e , then the charging c u r r e n t f o r each c y c l e w i l l be only —z d/dt b i a s e d amp* •—m EF EF +12 v o l t s to clamp advance c i r c u i t F i g u r e 4.4 Automatic t r i g g e r s e l e c t o r to 22 th a t produced by the l a r g e s t s p i k e . The c a p a c i t o r v o l t a g e i s a p p l i e d to an emitter f o l l o w e r and the " d i s c o n t i n u i t i e s " i n t h i s s i g n a l are used to t r i g g e r the clamp advance c i r c u i t . 4.3 The Clamp Advance C i r c u i t The assumption t h a t adjacent heart c y c l e s tend to be of equal d u r a t i o n i s used i n the design of the " p r e d i c t o r " . By g e n e r a t i n g a v o l t a g e p r o p o r t i o n a l to the d u r a t i o n of a heart p e r i o d and comparing i t w i t h a ramp vo l t a g e i n i t i a t e d at the s t a r t of the subsequent c y c l e , one can a n t i c i p a t e the i n s t a n t of occurrence of the next t r i g g e r p u l s e . The clamp advance i n t e r v a l can be set by adding a v a r i a b l e b i a s to the ramp before comparison. Coincidence of the two v o l t a g e l e v e l s then a c t i v a t e s a monostable c i r c u i t which c l o s e s the clamp r e l a y s f o r 30 m i l l i s e c o n d s . F i g u r e 4.5 i s a b l o c k diagram of the system and F i g u r e 4.6 i s a diagram of the system waveforms* The pulse sequence shown i n Fig u r e 4.6a i s obtained from the output of the automatic t r i g g e r s e l e c t o r * and i s used to t r i g g e r f o u r monostable f l i p - f l o p s whose outputs (Figure 4.6b, 4.6c, 4.6dj and 4*6e) c o n t r o l the s i x gates shown i n F i g u r e A.9. As soon as the 0.15-second monostable c i r c u i t r e t u r n s to i t s s t a b l e s t a t e ^ gates numbers one and s i x open, and c a p a c i t o r s C-^ and C^ (Figure 4.5) begin to charge* and continue to do so u n t i l the next t r i g g e r pulse a r r i v e s * The c a p a c i t o r s are f e d from c o n s t a n t - c u r r e n t sources and the v o l t a g e s appearing across them t h e r e f o r e increase l i n e a r l y w i t h time as shown i n F i g u r e s 4.6f and 4«6h, reaching f i n a l v a l u e s which are p r o p o r t i o n a l to the a Mono . • - Mono • Mono • 50 ras b 50 ms c 50 ms from auto t r i g g e r s e l e c t o r Notes L e t t e r s a-j r e f e r to waveforms i n Fi g u r e 4»6. Mono . 150 ms Current Gen. —. Gate #1 C l —^ Gate #2 +12v EF g U 2 Gate #4 +12v B i a s EF c Gate C o n t r o l *— °3 #5 +12v F i g u r e 4.5 Clamp advance c i r c u i t to +12v -12v F i g u r e 4.6 Waveforms generated i n the clamp advance c i r c u i t 25 p e r i o d of the heart c y c l e . Gates two, f o u r , and f i v e r e s e t the c a p a c i t o r s d u r i n g a p p r o p r i a t e i n t e r v a l s i n the cycle-. When gate number three opens* charge i s t r a n s f e r r e d to the i n i t i a l l y - u n c h a r g e d c a p a c i t o r which then has a v o l t a g e one—half t h a t reached on This v o l t a g e (Figure 4.6g) i s compared with the ramp f u n c t i o n on c a p a c i t o r C^ i n the succeeding c y c l e . A d i f f e r e n t i a l a m p l i f i e r i s used f o r t h i s comparison. The ramp f u n c t i o n appearing on C^ (Figure 4.6h) i s b i a s e d i n order to give the d e s i r e d clamp advance i n t e r v a l T (Figure 4 . 6 i ) . 1 26 5. THE TWO-DIMENSIONAL COMPUTER 5.1 D e s c r i p t i o n The a c t u a l two-dimensional t r i g o n o m e t r i c computers (Fig u r e s 5.1 and A.6) are somewhat d i f f e r e n t from t h a t d e s c r i b e d i n Chapter 2. The quadrature s i n u s o i d s are r e p l a c e d by quadrature square-waves, t h a t i s , square-waves whose f u n -damental components are i n quadrature, and a low-pass f i l t e r i s i n s e r t e d between the adder and the d e t e c t i o n u n i t s . The low—pass f i l t e r i s designed to pass only the fundamental component of the square-waves and to give a 90° p h a s e - s h i f t at c a r r i e r frequency fQ. This p h a s e - s h i f t i s chosen r a t h e r than some a r b i t r a r y value i n order that the phase re f e r e n c e can be made to l i e on one of the axes, e.g., the p o s i t i v e x-axis i n the f r o n t a l computer. 5.2 The M u l t i p l i e r s Each m u l t i p l i e r used i n t h i s device c o n s i s t s of two synchronous gates c o n t r o l l e d by square-waves of c a r r i e r frequency f ^ . Each gate i s made up of a set of complementary t r a n s i s t o r s connected i n the c o n f i g u r a t i o n shown i n Fi g u r e 5.2. The gates are a l t e r n a t e l y opened and c l o s e d by a p p l y i n g the c a r r i e r v o l t a g e s to the bases of the t r a n s i s t o r s . In the open s t a t e , the emitter—base j u n c t i o n s of the t r a n s i s t o r s are forward-biased p u t t i n g the t r a n s i s t o r s i n t o s a t u r a t i o n so that the gate has a very low forward r e s i s t a n c e , of the order of one ohm. The gates are c l o s e d by r e v e r s e - b i a s i n g the e m i t t e r -base j u n c t i o n s . By a p p l y i n g a d i f f e r e n t i a l input s i g n a l , r v i = sinttt + M u l t i p l y M u l t i p l y v l x Sum Low-pass f i l t e r 5 Kc v 'x C l i p p e r F l i p - f l o p Low-pass f i l t e r (galvo.) r.cos(wt + 0) R e c t i f i e i — ^ Low—pass f i l t e r (galvo.) r 0 v 2 = COSfi)t + . . . • F i g u r e 5.1 Block diagram of the two-dimensional t r i g o n o m e t r i c computer as constructed to 28 A A A / B F i g u r e 5*2 C i r c u i t diagram of a m u l t i p l i e r s u p p r e s s e d — c a r r i e r modulation i s achieved. 5»3 The C a r r i e r Generator As i n the previous p o l a r c a r d i o g r a p h , ^ a c a r r i e r frequency of fo u r k i l o c y c l e s per second has been adapted. The gate-type m u l t i p l i e r s mentioned above r e q u i r e four square-waves of the type shown i n Fig u r e 5.3, which can be obtained as f o l l o w s . S i x t e e n — k i l o c y c l e c l o c k - p u l s e s are d e r i v e d from a s i x t e e n - k i l o c y c l e a s t a b l e f l i p - f l o p by d i f f e r e n t i a t i n g and c l i p p i n g one of i t s outputs. This pulse sequence i s used to t r i g g e r a b i s t a b l e f l i p - f l o p (B^ i n Figu r e 5.4) which giv e s two e i g h t - k i l o c y c l e square-waves 180° out of phase and of equal on-off d u r a t i o n . When these two square-waves are d i f f e r e n t i a t e d and c l i p p e d , two e i g h t -29 g 0 12-sincot + . .« (by d e f i n i t i o n ) +12 0__ -12 - s i n t t t + . • +12 0_ -12 coswt + ••• +12 0— -12 ~COS(0t + . F i g u r e 5.3 C a r r i e r generator output waveforms k i l o c y c l e pulse sequences 180 out of phase are obtained. By u s i n g these two pulse sequences to t r i g g e r the remaining two b i s t a b l e f l i p - f l o p s (B2 and B^ i n F i g u r e 5.4), there are a v a i l a b l e at t h e i r outputs f o u r f o u r - k i l o c y c l e square-waves of equal on-off d u r a t i o n and d i f f e r i n g i n phase from one another by nx90° (n = 1, 2, 3 ) . Notes L e t t e r s a-f r e f e r to F i g u r e 5.5. L e t t e r s g-j r e f e r to F i g u r e 5.3. A s t a b l e > B i n a r y 16 Kc B l a Delay Sum Scnmitt t r i g g e r 7 e Gate f B i n a r y B 3 • EF Amp< EF sincat + EF Amp. EF - s i n a t + i costtt + EF Amp. EF — - 3 * -co scot + F i g u r e 5.4 4-kc c a r r i e r generator 3.1 I f we say t h a t one of the square-wave outputs of has a fundamental component equal to sinw^t. then the other square-wave generated by t h a t b i s t a b l e u n i t w i l l have a fundamental component of -sinw^t. The two remaining f o u r -k i l o c y c l e square—waves generated by w i l l have fundamental components equal to cosw^t and —cosw^t. In order to e s t a b l i s h a f i x e d phase sequence f o r the f o u r outputs, independent of the i n i t i a l s t a t e s of the b i s t a b l e u n i t s , the pulse t r a i n used to t r i g g e r B^ i s gated. A g a t i n g pulse i s obtained by f i r s t adding two of the outputs, c l i p p i n g o f f the negative p o r t i o n , and d e l a y i n g the r e s u l t a n t wave-form by X seconds (Figure 5*5)* The delay c i r c u i t c o n s i s t s of an RC i n t e g r a t o r and a Schmitt t r i g g e r (Figure A .7). The g a t i n g c i r c u i t works as f o l l o w s . I f the four output waveforms have the proper sequence, a g a t i n g pulse (Figure 5.5e) i s generated* However, i f the d e s i r e d sequence does not appear, a g a t i n g pulse i s not generated, thus b l o c k i n g one of the pulses t r i g g e r i n g B j^ which causes i t s output to s h i f t by 180° and r e t u r n to i t s proper sequence. Fi g u r e A.7 i s a complete c i r c u i t diagram of the c a r r i e r generator* A potentiometer i s used i n the a s t a b l e f l i p - f l o p i n order to a d j u s t the c l o c k frequency. The e m i t t e r - f o l l o w e r c o n f i g u r a t i o n used i n the output c i r c u i t s was d i c t a t e d by the magnitude of the output s i g n a l s (+ 12 v o l t s ) and the need f o r low output r e s i s t a n c e , 5*4 The Low-pass F i l t e r The f o u r - k i l o c y c l e fundamental component i s e x t r a c t e d from the summed m u l t i p l i e r outputs by a low-pass f i l t e r 32 pulse sequence d e r i v e d from co scot + -sincot + ..» sum of waveforms b and c g a t i n g pulse pulse sequence a r r i v i n g at B^ Fig u r e 5»5 Waveforms used to ensure c o r r e c t phasing of c a r r i e r generator outputs 33 Figure 5*6 Low-pass f i l t e r designed using the i n s e r t i o n — l o s s technique (Figure 5.6). I t produces 90° phase—shift at four k i l o c y c l e s and 270° phase-shift at twelve k i l o c y c l e s . The phase—shift at twelve k i l o c y c l e s was set at some m u l t i p l e of 90° i n order to avoid a r e s u l t a n t phase-s h i f t due to the r e s i d u a l third—harmonic component of the f i l t e r e d waveforms. Second—harmonic components are absent because the waveforms are the sum of square-waves.. The i n s e r t i o n l o s s at four k i l o c y c l e s and at dc was made equal to zero. The f i l t e r c h a r a c t e r i s t i c s are shown i n Figure 5*7. 5*5 Magnitude Detection A voltage p r o p o r t i o n a l to the magnitude,, r , of the heart vector i s obtained from the s i g n a l r.sin(wt + 0) (Figure 5.1) by r e c t i f y i n g and f i l t e r i n g * The f i l t e r i n g i s done by the recording galvonometers, and full-wave r e c t i f i -c a t i o n i s accomplished using a complementary t r a n s i s t o r c o n f i g u r -a t i o n (Figure A.7). The low s a t u r a t i o n - r e s i s t a n c e of the 34 ( k i l o c y c l e s per second) 315° 0 2 4 6 8 10 12 14 16 18 20 ( k i l o c y c l e s per second) Fig u r e 5*7 Low-pass f i l t e r response curves 35 t r a n s i s t o r s gives a l i n e a r r e c t i f i e r c h a r a c t e r i s t i c over a l a r g e v o l t a g e range. 0 pulses d e r i v e d from re f e r e n c e s i g n a l pulses d e r i v e d from c l i p p e r output v o l t a g e waveform between c o l l e c t o r s of phase comparator Fig u r e 5.8 Waveform of the phase comparator 5.6 Angle D e t e c t i o n (phase comparison) Angle d e t e c t i o n i s c a r r i e d out i n the f o l l o w i n g manner. The waveform r.sin(«ot + 0) (Figure 5.1) i s a m p l i f i e d and c l i p p e d i n s e v e r a l stages i n order to remove the modulation envelope. The r e s u l t i n g square-wave i s d i f f e r -e n t i a t e d and the negative pulses obtained are used to t r i g g e r one side of a s e t - r e s e t b i s t a b l e f l i p - f l o p . The other side of the f l i p - f l o p i s t r i g g e r e d from corresponding negative 36 pulses obtained from a square-wave of constant phase, i . e . , one of the c a r r i e r s i g n a l s * The average value of the v o l t a g e d i f f e r e n c e between the c o l l e c t o r s of the f l i p - f l o p i s d i r e c t l y 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 , 0, between the two pulse sequences t r i g g e r i n g i t (Figure 5.8). Averaging i s accomplished by the r e c o r d i n g galvonometers which have a c u t o f f frequency of 240 c y c l e s per second. 5.7 The C l i p p e r The c l i p p e r has three stages, each c o n s i s t i n g of an a m p l i f i e r , a b u f f e r a m p l i f i e r ( e m i t t e r - f o l l o w e r ) , and a c l i p p i n g c i r c u i t . The f i r s t stage has a g a i n of three and the remaining two stages each have gains of approximately t h i r t y . The t r a n s i s t o r arrangement shown i n Figure A.7 i s used f o r c l i p p i n g the outputs of the f i r s t two stages. A forward avalanche v o l t a g e of about 0.2 v o l t s across the emitter-base j u n c t i o n of the 2N404 t r a n s i s t o r g i v e s t h i s c i r c u i t a 0.4 v o l t peak-to-peak c l i p p e d output. The t h i r d c l i p p e r uses two o r d i n a r y diodes and a 6.2—volt zener diode to give a 7-volt peak-to-peak c l i p p e d output (Figure A.7). Delays due to t r a n s i s t o r s a t u r a t i o n are e l i m i n a t e d by having a l l three a m p l i f i e r s working i n the c l a s s - A r e g i o n . Each c l i p p e r u n i t has a dynamic range of about 100:1^ t h a t i s , the c l i p p e r w i l l produce a square-wave from magnitudes as low as one percent of maximum s i g n a l v a l u e . 37 5 . 8 The Threshold C i r c u i t In the s i g n a l r.sin(-i Sum Mult. F i l t e r 5 Kc F i l t e r 500 cps Rect, M u l t . v_, =^ costtt +. . 2 o z F i l t e r M u l t . 500 Kc Cllppe:: Rect. F l i p -f l o p J Sum T r F i l t e r 5 Kc C l i p p e r F l i p -f l o p r -5»-0 0 v, = sincot +.. 1 ° Fi g u r e 6.1 Block diagram of the three-dimensional p o l a r c a r d i o g r a p h 42 7. TEST RESULTS The l i n e a r i t y of the magnitude outputs of the two and three—dimensional computers was demonstrated by apply i n g t e s t s i g n a l s at 20 c y c l e s per second to t h e i r inputs and measuring the d e t e c t e d output s i g n a l s as d i s p l a y e d by a Honeywell Type 1508 V i s i c o r d e r . The input v o l t a g e s were measured by observing the peak—to-peak s i g n a l s as d i s p l a y e d on a CRT. The o v e r a l l angular response of these two computers was demonstrated by a p p l y i n g equal—amplitude sine and cosine s i g n a l s at 1 c y c l e per second to t h e i r i n p u t s . Since the v e c t o r l o c u s of such a set of s i g n a l s i s a c i r c l e whose centre i s at the o r i g i n , the angle output f o r the two-dimensional device should be a sawtooth waveform. Because the output of the f r o n t a l computer i s always a p o s i t i v e q u a n t i t y , the pol a r - a n g l e out-put of the three-dimensional computer should be a t r i a n g u l a r waveform. The o p e r a t i o n of the t h r e s h o l d c i r c u i t was demonstrated by j o i n i n g together the inputs of the two-dimensional computer and a p p l y i n g a s i n u s o i d of about 25% maximum amplitude at 1 cy c l e per second. Because the s i g n a l f e e d i n g both inputs i s the same, i t s angle output should be a square-wave f u n c t i o n which switches between + 4 5 ° and -135° while the magnitude out-put should be a r e c t i f i e d sine wave. By v a r y i n g the t h r e s h o l d l e v e l , the angle output was made to switch to the reference l e v e l of +180° f o r th a t p o r t i o n of the c y c l e f o r which the magnitude of the input s i g n a l was below the t h r e s h o l d l e v e l . 43 The t h r e s h o l d l e v e l i s i n d i c a t e d as a percentage of the maximum s i g n a l l e v e l (e.g., a t h r e s h o l d l e v e l of 3$ corresponds to an e q u i v a l e n t input s i g n a l of 0.45 v o l t s peak-to-peak). The r e s u l t s of the above t e s t s are shown i n F i g u r e s 7.1 to 7.5. F i g u r e 7.3 Recording of angle outputs of the two-dimensional computer f o r three d i f f e r e n t peak-to-peak i n p u t -s i g n a l l e v e l s , (a) 15 v o l t s , (b) 4 v o l t s , (c) 0.8 v o l t s 47 - 9 0 — 90 F i g u r e 7.4 Recording of p o l a r angle output of the t h r e e -dimensional computer f o r three d i f f e r e n t peak-to-peak i n p u t - s i g n a l l e v e l s , (a) 15 v o l t s , (b) 4 v o l t s , (c) 0.8 v o l t s F i g u r e 7.5 Recording of angle output of the two-dimensional computer showing t h r e s h o l d c i r c u i t i n o p e r a t i o n f o r four d i f f e r e n t t h r e s h o l d l e v e l s , (a) 10fo, (b) Tfo, (c) 3%, (d) 1.5% £ 00 49 8. CONCLUSIONS The design of a two-dimensional p o l a r c a r d i o g r a p h and the use of two such two-dimensional devices to r e a l i z e a t h r e e -dimensional p o l a r c a r d i o g r a p h has been d e s c r i b e d , together w i t h the c i r c u i t r y necessary to d e r i v e and amplify a set of 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 coordinates x, y, and z. Although the instrument has not y e t been t e s t e d c l i n i c a l l y , t e s t s performed on i t i n the l a b o r a t o r y i n d i c a t e t h a t i t i s w e l l w i t h i n the accuracy r e q u i r e d . Both the f r o n t a l and p o l a r magnitude outputs were shown to remain l i n e a r even f o r small input s i g n a l s . When t e s t e d with s i g n a l s of the order of 5$ of maximum input s i g n a l l e v e l , the f r o n t a l angle output maintained i t s c a l i b r a t i o n , while the p o l a r angle output s t a r t e d to show s l i g h t d i s t o r t i o n . The b a s e - l i n e clamping system, i n c l u d i n g the auto-matic t r i g g e r s e l e c t o r and the clamp advance c i r c u i t , was t e s t e d u s i n g a simulated heart waveform and found to f u n c t i o n s a t i s f a c t o r i l y . 50 APPENDIX The three-dimensional computer d e s c r i b e d i n t h i s t h e s i s has been subdivided i n t o ten d i f f e r e n t s e c t i o n s and assembled on p r i n t e d c i r c u i t boards. Each p r i n t e d c i r c u i t card i s s i x by nine inches i n s i z e and i s designed to plug i n t o a standard 22-pin Amphenol connector. The l e t t e r s i n the f o l l o w i n g c i r c u i t diagrams, F i g u r e s A.1-10, correspond to the t e r m i n a l l e t t e r i n g of the Amphenol connectors. A b r i e f d e s c r i p t i o n of each p r i n t e d c i r c u i t card (P.C.C.) type follows i P . C»C » ^1» The seven p r e a m p l i f i e r s d e s c r i b e d i n Chapter 3 and shown i n F i g u r e A . l are assembled on t h i s u n i t . The potentiometer R ^ i s f o r c e n t r i n g . The input t e r m i n a l marked Z i s common to a l l seven a m p l i f i e r s and i s used as a p a t i e n t ground. Each a m p l i f i e r i s decoupled from the +24 and -24 v o l t s u p p l i e s . P >C«C. j^ 2 » The three second-stage a m p l i f i e r s and the t h i r d - s t a g e e m i t t e r - f o l l o w e r outputs a s s o c i a t e d w i t h each are assembled i n t h i s u n i t . A d e s c r i p t i o n of these a m p l i f i e r s i s g i v e n i n Chapter 3 and the c i r c u i t diagram i s presented i n F i g u r e A.2. C e n t r i n g i s obtained by adjustment of R-^Q« A v a r -i a t i o n i n g a i n of about 20$ i s a v a i l a b l e by a d j u s t i n g R ^ g . ^20 '"'S u s e ( * ^° s e ^ ^ n e o u t p u t l e v e l to zero v o l t s . Each of the u n i t s shown i n Figure A.2 i s decoupled from the +24 and —24 v o l t power s u p p l i e s * 51 The Prank and RAFE lead—system networks d e s c r i b e d i n Chapter 3 and shown i n Fi g u r e A.3 are mounted on t h i s u n i t . P r e v i s i o n i s made i n the p r i n t e d c i r c u i t l a y o u t so th a t e m i t t e r - f o l l o w e r s may be i n s e r t e d at the inputs to the networks. A l l p r i n t e d c i r c u i t connections are made on one side of the u n i t while the reverse side i s kept i n t a c t so t h a t i t serves as a s h i e l d . P.C.C. #4. The c o u p l i n g c a p a c i t o r s and feedback c i r c u i t r y ( r e l a y s , e t c.) d e s c r i b e d i n Chapter 4 are mounted on t h i s c a r d . P.C.C* #5. The automatic t r i g g e r s e l e c t o r , the clamp delay c i r c u i t , and the r e l a y t r i g g e r c i r c u i t (Chapter 4) are assembled on t h i s p r i n t e d c i r c u i t c a r d . The c i r c u i t diagram f o r these u n i t s i s shown i n Fig u r e A.5. The clamp delay time i s set by adjustment of pot-entiometer R-^ C;* P.C.C. #6. The clamp advance c i r c u i t shown i n Figure A.6 and d e s c r i b e d i n Chapter 4 i s assembled on the p r i n t e d c i r c u i t c a rd. The slope of the ramp f u n c t i o n shown i n Figure 4.6h i s c o n t r o l l e d by R^-j* R^ Q i s used to adjust the clamp advance time; i t i s a c t u a l l y l o c a t e d on the c o n t r o l panel and connected to the card through t e r m i n a l s Pj R and S. P.C.C. #7. The complete c i r c u i t of the two-dimensional computer d e s c r i b e d i n Chapter 5 and shown i n F i g u r e A.7 i s assembled on t h i s u n i t . The inputs to the computer are e q u a l i z e d by adjustment of ^2.0* Potentiometers and R ^ c o n t r o l the amplitude of the magnitude and angle outputs r e s p e c t i v e l y . P.C.C. #8« The c i r c u i t r y f o r the c a r r i e r generator (Figure A.8) d e s c r i b e d i n Chapter 5 i s assembled on t h i s u n i t . Potentiometer R 2 i s adjusted to give the r e q u i r e d f o u r -k i l o c y c l e output frequency. P.C.C. # 9 » Three of the t h r e s h o l d u n i t s (Figure A.8) d e s c r i b e d i n Chapter 5 are assembled on one p r i n t e d c i r c u i t c ard. P.C.C. #10. This u n i t contains the c i r c u i t r y shown i n Fig u r e A.10 and d e s c r i b e d i n Chapter 6t necessary f o r o b t a i n i n g the t h i r d c o o r d i n a t e • Potentiometers R^g and R ^ are used f o r c e n t r i n g , while R9E. i s a g a i n adjustment. R13 100 A A — +24V A AMPLIFIER # 1 2 3 U 5 6 7 INPUT H J K L P N M OUTPUT R S T U V W X OA202 OA202 A/122. _2AV E Figure A-1Circuit Diagram for Preamplifiers U l OUTPUT+ -24 V 1N965A AMPLIFIER # 1 2 3 INPUT + K S W INPUT — J R V OUTPUT+ H P U OUTPUT — F N T R16 3-3K •OUTPUT— Figure A-2 Circuit Diagram for Second and Third Stage Amplifiers VJ1 RV A.137K R2A .225K — R3 A A316K R4 A A196K ® R6A A374K R8A A649K ® B — O R 9A A576K .RIOyv^ nOK lRiL\A2f8K Q R I S A ^ Vx + u V w X Y INPUT + — § 2 N 1 3 1 6 2N13161* Rig^Aioo + 2 4 V A 0-DENOTES PATIENT LEAD POSITION " + ] c i Q -DENOTES EMITTER FOLLOWER - J t y j f ALL RESISTORS 1 EMITTER FOLLOWER CIRCUIT OUTPUT .R31 >10K C2 Figure A3 Circuit Diagram for Frank and R A F E Lead Systems 56 INPUT 1- C1\.8uf OUTPUT 1 R1 500K C 3 RELAY1 2jjf INPUT 2-f C2)|8jjfJ RELAY 2 INPUT 3 INPUT 4 R2 500K •OUTPUT 2 — 12V« RELAY 1 S RELAY 2 1 TO OTHER RELAYS CONTROL IN 5lA/^l<|^NA04 + 12V- J I INPUT 1 INPUT 2 INPUT 3 INPUT OUTPUT 1 OUTPUT 2 CIRCUIT 1 W V A F M N CIRCUIT 2 U Z H J P R CIRCUIT 3 Y X K L S T Figure A-A Circuit Diagram of Coupling Network and Relays 57 Figure A-5 Circuit Diagram for Automatic Triggtr Selector Figure A-6 Circuit Diagram tar Clamp Advanea Circuit Figure A-7 Circuit Diagram for Two-dimensional Computer NO TRANSISTORS Q# 's 1 - 2 5 ore 2N404 ! s ' s 2 6 - 2 9 ore 2N1304's - 1 2 V cf-oi»fT1"5iT *7| 22K " * ! JX15 T O W R43 B3 > R 4 6 '470 . >470 C2O|^00P> 200Pfj,C21 R45'8-2K C3QX rU9>l [ 0 2 6 025 024 1027 H R63 47 - V > 12V » f C 1 3 +J250pf 250* j f R62 47 • A *— +12V + 12V K R61 47 •A^ 12V 2rC26 X 2 5 0 p f + * C 2 7 - J 2 5 0 p f R60 47 A / V — +12V Figure A-8 Circuit Diagram for A KC Carrier Generator 22K — 1 2 V LOCATED ON FRONT PANEL 10K 8-2K + 2 4 CIRCUIT # 1 2 3 INPUT 1 E L S INPUT 2 F M T INPUT 3 H N U INPUT k J P V OUTPUT 1 K R W ALL TRANSISTORS ARE 2N404 s Figure A-9 Circuit Diagram for Threshold Control ON 63 REFERENCES I. Einthoven, W., Fahr, G. and de Waart, A., "On the D i r e c t i o n and M a nifest S i z e of the V a r i a t i o n s of P o t e n t i a l i n the Human Heart and on the Influence of the P o s i t i o n of the Heart on the Form of the E l e c t r o -cardiogram", t r a n s l a t e d by Hoff, H.E. and S e k e l j , P., Anu Heart J . . 40;163, (1950). 2i C a n f i e l d , R., "On the E l e c t r i c a l F i e l d Surrounding Doublets and i t s S i g n i f i c a n c e from the Standpoint of Einthoven's Equations", Heart (New York, N.Y.), 14:102, (1927). 3. Frank, E., "The Elements of E l e c t r o c a r d i o g r a p h i c Theory", Trans. AIEE (Communications and E l e c t r o n i c s ) , p. 125, (May* 1,953). 4. G l a s s e t , 0.* "Medical P h y s i c s " . The Year Book P u b l i s h e r s Inc.* Chicago, 111., p* 241, ( i 9 6 0 ) . 5. Moore, A.D., Harding, P. and Dower, G.E., "The P o l a r -c a r d i o g r a p h . An Analogue Computer t h a t Provides S p h e r i c a l P o l a r Coordinates of the"Heart V e c t o r " , Am. Heart J , • 64:382-391, (September, 1962). 6« McFee, R., "A Trigonometric Computer with 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 " , Rev. Sc. -Instr., 21:1031, (1950). 7. Sayers, B.McA., "A S p a t i a l Magnitude E l e c t r o c a r d i o g r a p h " , Am. Heart J.« 49:336, (1955). 8. A b i l d s k o v , J.A., Hisey, B.L. and Ingerson, V.E., "The Magnitude and O r i e n t a t i o n of V e n t r i c u l a r E x c i t a -t i o n V e c t o r s i n the Normal Heart and F o l l o w i n g Myocardial I n f a r c t i o n " , Am. Heart J.-, 55:104, (1958). I 9* Park, W.K.R.* "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). 10. Poole, E.G., "A 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", 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, (1955) . I I . Frank, E,, "An Accurate* C l i n i c a l l y P r a c t i c a l System f o r S p a t i a l V e c t o r c a r d i o g r a p h " , C i r c u l a t i o n , 13:737, (1956) . 12. Dower, G.E., and Osborne, J