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The response of the surface electrocardiogram to inspiration
M e d i c a l H y p o t h e s e s 1 7 : 251-263, 1085
THE RESPONSE OF THE SURFACE ELECTROCARDIOGRAM TO
INSPIRATION
J.N. Amoore, Department of Biomedical Engineering, UCT Medical School, Observatory, Cape. 7925, South Africa. ABSTRACT The waveshape of the electrocardiogram (ECG), as is well known, This effect was varies with respiration. electrocardiography noted from the early days of clinical (1) and has generally been ascribed to changes in the posi~ft~;,~~ the heart. Although it has mostly been regarded as it is generated by a process and may contain , This paper presents two hypoinformation on the process. theses: firstly that the change of the ECG with a heldtransient inspiration can be separated into a step and a component and secondly that the transient component reflects the time course of changes of the right and left ventricular end-diastolic volumes during the maneuver. INTRODUCTION electrocardiogram (ECG) The shape of the surface waveform varies with respiration. which has This effect, largely been regarded as unwanted "noise" has been observed from the early days of electrocardiography. Einthoven et al (1) studied it systematically and ascribed it mainly to the change of position of the heart in the chest cavity, Subsequently the heart vector to explain it. and used recordings of the ECG have, sought. with a few exceptions, to minimize the respiratory modulation, either by choice Iof lead or by recording the ECG during quiet breathing or held expiration. 251
respia few authors have suggested that the However ratory modulation of the waveform may contain clinically that useful It has been pointed out information (3-5). noise is generated by a process and thus contains informa“One Or to put it another way: tion on the process (2). man’s noise is another man’s signal”. The functions of intimately cardiovascular and respiratory ‘systems are the connected and a specific respiratory maneuvre such as a held-inspiration may be viewed as a natural stimulus to the cardiovascular system, Respiratory maneuvres such as the Valsalva have been The response to the used to t e s t c a r d i a c f u n c t i o n (6,7). Valsalva has been assessed on the basis of peripheral ECG Does the arterial flow changes. heart rate and response contain any information? If so why? What informasuch tion is contained in the response to other maneuvres as a held-inspiration? This paper discusses the hypothesis that the respiraof the waveshape contains information on tory modulation cardio-respiratory function. In particular it is sugges- inspiration that the change of waveform with a held ted has b o t h “ s t e p ” a n d “ t r a n s i e n t ” c o m p o n e n t s ( F i g u r e 1) and separated. and that components can be identified these It is suggested that the transient may reflect an initial volume end-diastolic increase in right venticular the (RvEDv) with inspiration followed by a delayed increase in This end-diastolic volume (LVEDV). the left ventricular response would right ventricular change with either dysfunction or increased pulmonary vascular impedance.
In p r e s e n t i n g t h i s h y p o t h e s i s i t i s f i r s t n e c e s s a r y t o This the effect of inspiration on the circulation. review will be followed by a discussion of some of the factors description that effect the ECG and conclude with a brief of preliminary experimental and theoretical work. INSPIRATION AND T H E CIRCULATION been The effect of inspiration on the circulation has studied by several authors (8 - 14). Some of the effects intrathoracic are summarised in Figure 2. The decrease in pressure increases the venous right heart return to the and thus increases the volume of the right ventricle (RV) and its stroke volume (9 - 14). A decrease in LVEDV has left the been d e s c r i b e d (10,26) a n d t h e s t r o k e v o l u m e o f ventricle (LV) decreases (10, 11, 13).
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AHeart Rate
ECG and Heart Rate response to a held-inspiration.
Seperation of EGG response to inspiration into a step On the left is the beatand a transient component. by-beat plots of the S amplitude and ratio of the S to lead. The step R amplitude of a bipolar chest response is superimposed on the plot and used to determine the transient response shown on the right.
Several factors may be involved in the initial response of the LV. The pulmonary venous capacitance increases and this may relatively reduce the blood flow to the left heart and thus the LV filling. The decrease in the intrathoracic pressure may increase the afterload of the LV (13). And the enlarged RV may reduce the compliance of the LV (23) and hence its end-diastolic volume (EDV).
253
If the breath is held at end-inspiration then the flow, increased volume of blood ejected from the (RV) will after an appropriate transit delay to allow for passage into the left heart and through the pulmonary circulation, increase its volume. Changes in the pulmonary vascular These changes of impedance may chnage the transit time. the ventricular EDVs may be reflected in the ECG. A relationship between ventricular volumes and the ECG has been discussed by many authors (16 - 19) and has mainly been ascribed to the Brody effect (16).
INSPIRATION
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Pulmonary venous capacitance t
I Right Atria1 and RV Fillingt
Heart Rate
Lv Afterload t
t
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Pulmonary Blood Volume 7 I Delayed Rise in left atria1 Filling and LV Fillingt -_3 Heart Rate 1 1 LV volume
Fig 2.
t
Change of blood flow with inspiration
Flow chart of factors causing an initial increase in RVEDV and delayed increase in LVEDV with inspiration.
have been The heart rate changes with respiration With a held-inspiratory studied by several authors. the heart rate first increases and then decreases maneuver before settling down to a level different from the preHeart rate changes effect the inspiratory level (20). diastolic filling time and thus the ventricular EDVs (21). Clearly the response of the circulatory system to inspiration is complex. For the purposes of this study it aspects important to determine what changes occur in those of cardiovascular function which are reflected in the surface ECG. 254
RESBTRATION AND THE ECG F a c t o r s w h i c h i n f l u e n c e t h e ECG
T h e electrical a c t i v i t y o f t h e h e a r t c e l l s s e t s up an field which spreads through the inhomogeneously electrical Conductive thorax setting up an electrical potential The surface electrical distribution over the body surface. potential depends on the electrical activity of the heart and the “ c o n d u c t i v e p a t h ” (th.rt i s t h e v o l u m e c o n d u c t o r o f the between the source potential and thoracic the body) surface. T h i s c a n b e e x p r e s s e d as: ECG =
/Electrical
Activity
o f tieart/ * / T r a n s f e r Function
such includes The the heart electrical activity of factors as the shape and amplitude of the action potential, the and the pathway of depolarisation and repolarisation thickness or m a s s o f depolarising m u s c l e . The transfer elecfunction includes the the geometrical position of trically active heart with respect to the viewing site (as expressed by the solid angle concept) and the effect of the bounded, non-homogeneous, v o l u m e c o n d u c t o r . Transfer function to which factors may influence the ECG response inspiration include position of the heart (11, c o n d u c t i v i ty of the lung (24, 25) and ventricular volumes (3). S t u d i e s o f E C G c h a n g e s w i t h r e s p i r a t i o n (1,3, 2 8 - 3 6 ) . the Einthoven used the heart axis to describe et al changes with respiration and demonstrated an inferior shift of Studies of the t h e a x i s w i t h i n s p i r a t i o n (1). variation of the three-dimensional spatial vector (28,331 a n d b o d y s u r f a c e p o t e n t i a l m a p s (31,35) h a v e confirmed the inferior shift.
ECG
Most o f the studies of respiratory ECG changes have compared the ECG in inspiration to that in expiration or have however, quiet mid-respiration. Almasi and Schmitt requiring his t h e s u b j e c t t o v o l u n t a r i l y synchronise by followed the dynamic respiratory rhythm to his heart rate, changes during regular breathing (28). By averaging the response over s e v e r a l r e s p i r a t o r y c y c l e s t h e y w e r e a b l e t o show quite clearly the respiratory shifts in magnitude and The transient response of direction of the cardiac vector. the ECG waveform to inspiration not however has been studied in detail.
255
Why the ECG uaveform changes with resoiration. are to a lesser or “Most r e s p i r a t o r y movements . . . greater extent as diaphragmatic, and, the diaphragm the heart rhythmically assumes a high and a low position, must also rhythmically be displaced within the thorax” (1). has respiration with The change of waveform ECG largely been ascribed to changes in position of the heart. also it has been suggested that other factors are However suggested that the i n v o l v e d (1,3,29,32,34,35). Lamb clinical more offer changes “are more complicated and information than such a would be supposed from simple change of include: theory” These other factors (3). change v o l u m e s o f t h e l e f t a n d r i g h t v e n t r i c l e s (3,29,32); of electrical conductivity of the thorax as the lungs fill with varying a i r (1,24,25); change of chest dimensions heart; position of the electrodes with respect to the the and change of shape of the heart with respiration. the In order to understand why respiration the relative influences factors will need to be determined.
ECG changes with these of various
TRANSIENT EC6 RESPONSE TO A HELD-INSPIRATION A simple initial experiment was performed to determine held-inspiration the transient response of the ECG to a in normal subjects. The subjects were supine and were their to hold instructed to and then breath deeply in breath for about 10 to 15 end- i n s p i r a t i o n , seconds at chest ECG was recorded from either a set of unipolar The leads or a single bipolar chest lead. T h e t r a n s i e n t c h a n g e s c a n b e analysed b y m e a s u r i n g t h e heart rate them and the QRS amplitudes and plotting A typic:? beat. functions either of time or of heart response showing the ratio of the S to R amplitudes and the Figure heart rate as a function of heart beat is shown in 1. The change in QRS amplitude appears to consist of a how t h e Note transient response and a step response. change in the heart pattern to rate follows a similar waveform change. The hypothesis is that the step response is due to the change in position of the heart, that is the inferior shift, while transient the transient response is due to changes of the right and left ventricular end-diastolic
256
It thus becomes necessary to volumes with inspiration. determine a method of seperating the two components. As a first attempt the step response was considered to have the time course of the respiration. The inspiratory trace was volume that is the in fact the integral of the air flow, change. This was used to fit a step response between the held-inspiration pre-inspiration resting and the level level as shown. The transient was then determined by subtracting the experimental result from the step response.
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Circulatory model Block diagram of the circulatory and abdominal cavities. thoracic
257
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MODEL STUDY OF THE TRANSIENT RESPONSE OF THE CIRCULATION TO INSPIRATION A circulatory model (38) was used to study the time course of ventricular volume changes with inspiration. Inspiration was modelled by varying the intrathoracic and abdominal pressures (PITH and PAB). The circulation is modelled using 27 compliant chambers interconnected with The major veins to the right heart elements. resistive are modelled as collapsible vessels. Figure 3 shows a simplified block diagram of the model. When PITH and PAB are varied from their resting and 5 mmHg levels of - 2 mmHg and 1 mmHg to - 10 mmHg respectively (Figure 4) the venous return to the right increase in the heart increases and causes a transient RVEDV, followed about 4 seconds later by an increase in the This is the same order of magnitude of the LVEDV. follows transit times measured in man and (15), qualitatively the same time course of change of RVEDV and LVEDV which, given the link between ECG and heart volume
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change in RVEDV and LVEDV with a Change of intrathoracic pressure and abdominal pressure, Results Note the rapid rise in RVEDV of a model experiment. followed by the delayed rise in LVEDV. 258
(16) c o u l d c a u s e t h e t r a n s i e n t c h a n g e i n s u r f a c e E C G w i t h inspiration seen in Figures 1. In the presence of right ventricular dysfunction or increased pulmonary vascular impedance it can be expected that the response will be different. DISCUSSION Several factors are probably involved in the change of This paper has sugges the ECG waveform with respiration. held the change of waveform which occurs with a that ted ,ind a inspiration can be seperated into a step response transient response. The step response is caused primarily by the change in the heart position with respect to the fixed electrodes on body surface and also due to the change in &he conductivity The air. the chest as the lungs inflate and fill with of position significantly during of the heart does not vary the held inspiration (37).
A major cause of the transient changes is believed to the changes in ventricular volumes which accompany resbe piration. The link between ECG and ventricular volume is (16-19). complex and has been studied by several authors The mechanism behind this relationship is beyond the scope of this paper. The similar form of the transient changes in ECG waveform i n h e a r t r a t e s u g g e s t s t h a t t h e y may b e a t and least partly due to a common cause. It has been shown response that the heart rate exhibits a biphasic transient to inspiration (20) and that an increase in right atria1 left volume increases the heart rate while an increase in atria1 volume decreases the heart rate (30). Thus the i n i t i a l i n c r e a s e i n r i g h t h e a r t v o l u m e w i t h i n s p i r a t i o n may increase the heart rate via reflex action and also change delayed The ECG waveform due to the enlarged RVEDV. the increase in the left atria1 volume may cause the later decreased heart rate and the delayed increase in LVEDV may cause an opposite change in the ECG waveform to that of the earlier enlarged RVEDV. A simplified model study of the time course of the has inspiration of the ventricular volumes with changes been presented. It shows that on the basis of pressure changes alone transient changes in the relative volumes of the ventricles occur, To make it more realistic it will rate, need to heart be extended to include changes in pulmonary vascular impedance and effect of the each v e n t r i c u l a r v o l u m e o n t h e c o m p l i a n c e o f t h e o t h e r (22,23). 259
T h e s u r f a c e E C G is at any one time u n d e r t h e i n f l u e n c e of several factors and it is often very difficult to sepaIt is effects. rate and distinguish their individual central to this paper that the various factors which conto the change of the waveform with inspiration can tribute be separated into two groups, one responsible for the step In order to transient. response, other for the the d i s t i n g u i s h t h e t w o efEects a s i m p l e c o n s t r u c t i o n w a s u s e d . this and as This is approximation first obviously a construction is vital to the development of this theory an need to be will improved, construction more rigorous designed. It n e e d s t o b e b a s e d o n t h e c h a n g e o f p o s i t i o n of the heart in the chest.
CONCLUSION The response of the surface ECG to a held-inspiration the that has been suggested descrioed. has been It response can be separated into a step and a transient component. mechanisms responsible for these two Possible components have been discussed. It is suggested that the ventricular response will vary in the presence of right dysfunction and/or increased pulmonary vascular impedance,
ACKNOWLEDGEMENTS African South Financial support obtained from the Medical Research Council and the University of Cape Town Staff Research Fund is gratefully acknowledged.
REFERENCES 1.
Einthoven W, Fahr G, de Waart A. On the direction and the manifest size of the variations of potential in human heart and on the influence of the position of the electrocardiogram. heart on the the form of Translated by Hoff HE, Am Heart J Sekelj P. 40:163,1950
2.
Gupta MS. Applications the IEEE 63:996,1975.
3.
The effects of respiration on the electroLamb LE. cardiogram in relation to differences in right and left Am Heart J 54:342,1957. ventricular stroke volume.
of
260
electrical
noise.
Proc o f
4.
Stamatoiu I, Guiloni H, Gabersek V. Study of the respiratory frequency during sleep in relation to the amplitude of the R wave of the Electroenceph ECG. Clin Neurophys 29:100,1970.
5.
Ferrer MI. Respiratory maneuvres in electrocardiographic diagnosis (editorial). Chest 73:445,1978
6.
Malmberg R, Albrecht G, Baltazaar A, Buckingham WB, Levine H, Cugell DW. The Valsalva maneuvre as a test of cardiac function in patients with pulmonary disease. Am Rev Respir Dis 89:64,1964
7.
Zema MJ, Masters AP, Margouleff D. Dyspnea: The Heart or the Lungs? Differentiation at bedside by use of the simple Valsalva maneuvre. Chest 85:59,1984.
8.
Goldblatt A, Harrison DC, Glick G, Braunwald E. Studies on cardiac dimension in intact unanesthetized man II. Effects of respiration. Circ Res 13:448,1963.
9.
Wexler L, Bergel DH, Gabe IT, Makin GS, Mills CJ. Velocity of blood flow in normal human venae cavae. Circ Res 23:349,1968
10.
Effects of phasic respiration Waugh RA. Brenner JI, in a ventricular dimension and performance left on 57:122,1978. Circ normal population.
11.
Robotham JL, Lixfield W, Holland L, MacGregor D, Bryan Effects of respiration on cardiac Robson J. AC, J Appl Physiol: R.E.E.P. 44:703,1978. performance.
12.
A model of the effects of Mintzner W. Robotham JL, on left ventricular performance. J APP~ respiration Physiol: R.E.E.P. 46:411,1979.
13.
Summer WR, Permutt S, Sagawa K, Shoukas AA, BombergerEffects of spontaneous respiration on canine Barnea B. Circ Res 45:719,1979. left ventricular function.
14.
Determinants of pulmonary arterial flow Pinsky MR. variation during respiration. J Appl Physiol: R.E.E.P. 56:1237,1984
15.
Pulmonary Higgins CB. Bhargava V, Slutsky RA, circulation time: comparison of mean, median, peak and onset (appearance) values using indocyanine green a I d Am Heart J radionuclide techniques. first-transit 106:41,1983
261
16.
Brody DA. A theoretical analysis of intracavitary mass influence on the heart-lead relationship. blood Circ Res 4:731,1956
17.
Angelakos ET, Gokham N. Influence of venous inflow volume on the magnitude of QRS potentials in vivo. Cardiologia 42:337,1963
18.
Salu Y, Marcus ML. simulation of the Computer precordial QRS complex: Effects of simulated changes in ventricular wall thickness and volume. Am Heart J 92:758,1976
19.
Talbot S, Kilpatrick D, Jonathan A, Raphael MJ. QRS voltage of the electrocardiogram and Frank vectorcardiogram in relation to ventricular volume. Br Heart J 39:1109,1977
20.
Clynes M. Respiratory control of heart rate: derived simulation. from analog computer Trans Med Electronics 7:2,1960
21.
Van der Werff TJ. Interdependence of left ventricular 73:683, Chest volume and heart rate. end-diastolic 1978
22.
Ventricular Santamore WP. Bove AA, Prog Cardiovasc Dis 23:365,1981
23.
Weber KT, Janicki JS, Hunter WC, Shroff S, Pearlmon ES, The contractile behaviour of the Fishman AP. the coupling to its functional heart and circulation. Prog Cardiovasc Dis 24:375,1982.
24.
Geselowitz DB, Schmitt OH. in Biological Engineering. New York. 1969
25.
Rudy Y, Wood R, Plonsey R, Liebman J. The effect of high lung conductivity on electrocardiographic potentials. Results from human subjects undergoing bronchopulmonary lavage. Circ 65:440,1982
26.
Jardin F, Farcot JC, Prost JF, Ozier Y, Gueret P, Bourdarias JP. Electrocardiographic evaluation of ventricles during continuous positive airway pressure breathing. J Appl Physiol: R.E.E.P. 56:619,1984
262
Laws IRE
interpendence.
Electrocardiography. ~333 (HP Schwan ed) McGraw-Hill
27.
Brooks WCC, Lange C. Interaction of myogenic neurogenic mechanisms that control heart rate. National Acad Sci USA. ?4:1761,1977
and Proc
28.
Almasi JJ, Schmitt OH. Basic technology of voluntary cardiorespiratory synchronization in electrocardiology IEEE Trans Biomed Eng 21:264,1974
29.
Amoore JN. Changes in the QRS complex of electrocardiogram during sleep and exercise. Thesis, University of Pretoria. 1979.
I_ h e 41SC
30.
Flaherty JT, Blumenschein SD, Alexander AW, Gentzler Gallie TM, Boineau JP, Influence of Spach MS. RD, respiration on recording cardiac potentials. Am .J Cardiol 20:21,1967
31.
Raviele A, Riggs T, Garcia E, Hirschfeld S, Liebman J. Respiratory variation in Frank vectorcardiography and J Electrocardiol echocardiography in children. 14:73,1981
32.
Respiratory variability Ruttkay-Nedecky I, Cagan S. Reinfarction. of vectorcardiograms in myocardial view of Czechoslovsk Medicine 3:156,1974
33.
Effects of respiration and heart Ruttkay-Nedecky I. p120 in The position on the cardiac electric field. (CV Nelson, theoretical basis of electrocardiology. DB Geselowitz, eds), Clarendon Press, Oxford. 1976
34.
Respiratory Simonson E, Nakagawa K, Schmitt OH. reccrded change of the spatial vectorcardiogram Am Heart J 54:919,1957 with different lead systems.
35.
Sutherland DJ, McPherson DD, Spencer CA, Armstrong CS, Effects of posture and Horacek BM, Montague TJ. electrocardiogram. body surface respiration Am J Cardiol 5;:595,1983
36.
The effect of Mimbs JW, de Mello V, Roberts R. Am Heart respiration on normal and abnormal Q waves. J 94:579,1977
37.
Effect of Bogren HG, Lantz BMT, Miller RR, Mason DT. determined by respiration on cardiac motion 18:609,1977 cineangiography. Acta Radiology.
38.
Computer simulation studies Snyder MF, Rideout VC. the venous circulation. IEEE Trans Biomed Eng 16:325,1969.
263
M.H. ,D
of
THE RESPONSE OF THE SURFACE ELECTROCARDIOGRAM TO
INSPIRATION
J.N. Amoore, Department of Biomedical Engineering, UCT Medical School, Observatory, Cape. 7925, South Africa. ABSTRACT The waveshape of the electrocardiogram (ECG), as is well known, This effect was varies with respiration. electrocardiography noted from the early days of clinical (1) and has generally been ascribed to changes in the posi~ft~;,~~ the heart. Although it has mostly been regarded as it is generated by a process and may contain , This paper presents two hypoinformation on the process. theses: firstly that the change of the ECG with a heldtransient inspiration can be separated into a step and a component and secondly that the transient component reflects the time course of changes of the right and left ventricular end-diastolic volumes during the maneuver. INTRODUCTION electrocardiogram (ECG) The shape of the surface waveform varies with respiration. which has This effect, largely been regarded as unwanted "noise" has been observed from the early days of electrocardiography. Einthoven et al (1) studied it systematically and ascribed it mainly to the change of position of the heart in the chest cavity, Subsequently the heart vector to explain it. and used recordings of the ECG have, sought. with a few exceptions, to minimize the respiratory modulation, either by choice Iof lead or by recording the ECG during quiet breathing or held expiration. 251
respia few authors have suggested that the However ratory modulation of the waveform may contain clinically that useful It has been pointed out information (3-5). noise is generated by a process and thus contains informa“One Or to put it another way: tion on the process (2). man’s noise is another man’s signal”. The functions of intimately cardiovascular and respiratory ‘systems are the connected and a specific respiratory maneuvre such as a held-inspiration may be viewed as a natural stimulus to the cardiovascular system, Respiratory maneuvres such as the Valsalva have been The response to the used to t e s t c a r d i a c f u n c t i o n (6,7). Valsalva has been assessed on the basis of peripheral ECG Does the arterial flow changes. heart rate and response contain any information? If so why? What informasuch tion is contained in the response to other maneuvres as a held-inspiration? This paper discusses the hypothesis that the respiraof the waveshape contains information on tory modulation cardio-respiratory function. In particular it is sugges- inspiration that the change of waveform with a held ted has b o t h “ s t e p ” a n d “ t r a n s i e n t ” c o m p o n e n t s ( F i g u r e 1) and separated. and that components can be identified these It is suggested that the transient may reflect an initial volume end-diastolic increase in right venticular the (RvEDv) with inspiration followed by a delayed increase in This end-diastolic volume (LVEDV). the left ventricular response would right ventricular change with either dysfunction or increased pulmonary vascular impedance.
In p r e s e n t i n g t h i s h y p o t h e s i s i t i s f i r s t n e c e s s a r y t o This the effect of inspiration on the circulation. review will be followed by a discussion of some of the factors description that effect the ECG and conclude with a brief of preliminary experimental and theoretical work. INSPIRATION AND T H E CIRCULATION been The effect of inspiration on the circulation has studied by several authors (8 - 14). Some of the effects intrathoracic are summarised in Figure 2. The decrease in pressure increases the venous right heart return to the and thus increases the volume of the right ventricle (RV) and its stroke volume (9 - 14). A decrease in LVEDV has left the been d e s c r i b e d (10,26) a n d t h e s t r o k e v o l u m e o f ventricle (LV) decreases (10, 11, 13).
252
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.
.
.
.
.
.
.
.
“2 eelIt
.,.
.1
15
lnspwatfon
Insptrahon
Fig 1.
.
AHeart Rate
ECG and Heart Rate response to a held-inspiration.
Seperation of EGG response to inspiration into a step On the left is the beatand a transient component. by-beat plots of the S amplitude and ratio of the S to lead. The step R amplitude of a bipolar chest response is superimposed on the plot and used to determine the transient response shown on the right.
Several factors may be involved in the initial response of the LV. The pulmonary venous capacitance increases and this may relatively reduce the blood flow to the left heart and thus the LV filling. The decrease in the intrathoracic pressure may increase the afterload of the LV (13). And the enlarged RV may reduce the compliance of the LV (23) and hence its end-diastolic volume (EDV).
253
If the breath is held at end-inspiration then the flow, increased volume of blood ejected from the (RV) will after an appropriate transit delay to allow for passage into the left heart and through the pulmonary circulation, increase its volume. Changes in the pulmonary vascular These changes of impedance may chnage the transit time. the ventricular EDVs may be reflected in the ECG. A relationship between ventricular volumes and the ECG has been discussed by many authors (16 - 19) and has mainly been ascribed to the Brody effect (16).
INSPIRATION
L::l”:~
Pulmonary venous capacitance t
I Right Atria1 and RV Fillingt
Heart Rate
Lv Afterload t
t
I
Pulmonary Blood Volume 7 I Delayed Rise in left atria1 Filling and LV Fillingt -_3 Heart Rate 1 1 LV volume
Fig 2.
t
Change of blood flow with inspiration
Flow chart of factors causing an initial increase in RVEDV and delayed increase in LVEDV with inspiration.
have been The heart rate changes with respiration With a held-inspiratory studied by several authors. the heart rate first increases and then decreases maneuver before settling down to a level different from the preHeart rate changes effect the inspiratory level (20). diastolic filling time and thus the ventricular EDVs (21). Clearly the response of the circulatory system to inspiration is complex. For the purposes of this study it aspects important to determine what changes occur in those of cardiovascular function which are reflected in the surface ECG. 254
RESBTRATION AND THE ECG F a c t o r s w h i c h i n f l u e n c e t h e ECG
T h e electrical a c t i v i t y o f t h e h e a r t c e l l s s e t s up an field which spreads through the inhomogeneously electrical Conductive thorax setting up an electrical potential The surface electrical distribution over the body surface. potential depends on the electrical activity of the heart and the “ c o n d u c t i v e p a t h ” (th.rt i s t h e v o l u m e c o n d u c t o r o f the between the source potential and thoracic the body) surface. T h i s c a n b e e x p r e s s e d as: ECG =
/Electrical
Activity
o f tieart/ * / T r a n s f e r Function
such includes The the heart electrical activity of factors as the shape and amplitude of the action potential, the and the pathway of depolarisation and repolarisation thickness or m a s s o f depolarising m u s c l e . The transfer elecfunction includes the the geometrical position of trically active heart with respect to the viewing site (as expressed by the solid angle concept) and the effect of the bounded, non-homogeneous, v o l u m e c o n d u c t o r . Transfer function to which factors may influence the ECG response inspiration include position of the heart (11, c o n d u c t i v i ty of the lung (24, 25) and ventricular volumes (3). S t u d i e s o f E C G c h a n g e s w i t h r e s p i r a t i o n (1,3, 2 8 - 3 6 ) . the Einthoven used the heart axis to describe et al changes with respiration and demonstrated an inferior shift of Studies of the t h e a x i s w i t h i n s p i r a t i o n (1). variation of the three-dimensional spatial vector (28,331 a n d b o d y s u r f a c e p o t e n t i a l m a p s (31,35) h a v e confirmed the inferior shift.
ECG
Most o f the studies of respiratory ECG changes have compared the ECG in inspiration to that in expiration or have however, quiet mid-respiration. Almasi and Schmitt requiring his t h e s u b j e c t t o v o l u n t a r i l y synchronise by followed the dynamic respiratory rhythm to his heart rate, changes during regular breathing (28). By averaging the response over s e v e r a l r e s p i r a t o r y c y c l e s t h e y w e r e a b l e t o show quite clearly the respiratory shifts in magnitude and The transient response of direction of the cardiac vector. the ECG waveform to inspiration not however has been studied in detail.
255
Why the ECG uaveform changes with resoiration. are to a lesser or “Most r e s p i r a t o r y movements . . . greater extent as diaphragmatic, and, the diaphragm the heart rhythmically assumes a high and a low position, must also rhythmically be displaced within the thorax” (1). has respiration with The change of waveform ECG largely been ascribed to changes in position of the heart. also it has been suggested that other factors are However suggested that the i n v o l v e d (1,3,29,32,34,35). Lamb clinical more offer changes “are more complicated and information than such a would be supposed from simple change of include: theory” These other factors (3). change v o l u m e s o f t h e l e f t a n d r i g h t v e n t r i c l e s (3,29,32); of electrical conductivity of the thorax as the lungs fill with varying a i r (1,24,25); change of chest dimensions heart; position of the electrodes with respect to the the and change of shape of the heart with respiration. the In order to understand why respiration the relative influences factors will need to be determined.
ECG changes with these of various
TRANSIENT EC6 RESPONSE TO A HELD-INSPIRATION A simple initial experiment was performed to determine held-inspiration the transient response of the ECG to a in normal subjects. The subjects were supine and were their to hold instructed to and then breath deeply in breath for about 10 to 15 end- i n s p i r a t i o n , seconds at chest ECG was recorded from either a set of unipolar The leads or a single bipolar chest lead. T h e t r a n s i e n t c h a n g e s c a n b e analysed b y m e a s u r i n g t h e heart rate them and the QRS amplitudes and plotting A typic:? beat. functions either of time or of heart response showing the ratio of the S to R amplitudes and the Figure heart rate as a function of heart beat is shown in 1. The change in QRS amplitude appears to consist of a how t h e Note transient response and a step response. change in the heart pattern to rate follows a similar waveform change. The hypothesis is that the step response is due to the change in position of the heart, that is the inferior shift, while transient the transient response is due to changes of the right and left ventricular end-diastolic
256
It thus becomes necessary to volumes with inspiration. determine a method of seperating the two components. As a first attempt the step response was considered to have the time course of the respiration. The inspiratory trace was volume that is the in fact the integral of the air flow, change. This was used to fit a step response between the held-inspiration pre-inspiration resting and the level level as shown. The transient was then determined by subtracting the experimental result from the step response.
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Circulatory model Block diagram of the circulatory and abdominal cavities. thoracic
257
model
showing
the
MODEL STUDY OF THE TRANSIENT RESPONSE OF THE CIRCULATION TO INSPIRATION A circulatory model (38) was used to study the time course of ventricular volume changes with inspiration. Inspiration was modelled by varying the intrathoracic and abdominal pressures (PITH and PAB). The circulation is modelled using 27 compliant chambers interconnected with The major veins to the right heart elements. resistive are modelled as collapsible vessels. Figure 3 shows a simplified block diagram of the model. When PITH and PAB are varied from their resting and 5 mmHg levels of - 2 mmHg and 1 mmHg to - 10 mmHg respectively (Figure 4) the venous return to the right increase in the heart increases and causes a transient RVEDV, followed about 4 seconds later by an increase in the This is the same order of magnitude of the LVEDV. follows transit times measured in man and (15), qualitatively the same time course of change of RVEDV and LVEDV which, given the link between ECG and heart volume
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change in RVEDV and LVEDV with a Change of intrathoracic pressure and abdominal pressure, Results Note the rapid rise in RVEDV of a model experiment. followed by the delayed rise in LVEDV. 258
(16) c o u l d c a u s e t h e t r a n s i e n t c h a n g e i n s u r f a c e E C G w i t h inspiration seen in Figures 1. In the presence of right ventricular dysfunction or increased pulmonary vascular impedance it can be expected that the response will be different. DISCUSSION Several factors are probably involved in the change of This paper has sugges the ECG waveform with respiration. held the change of waveform which occurs with a that ted ,ind a inspiration can be seperated into a step response transient response. The step response is caused primarily by the change in the heart position with respect to the fixed electrodes on body surface and also due to the change in &he conductivity The air. the chest as the lungs inflate and fill with of position significantly during of the heart does not vary the held inspiration (37).
A major cause of the transient changes is believed to the changes in ventricular volumes which accompany resbe piration. The link between ECG and ventricular volume is (16-19). complex and has been studied by several authors The mechanism behind this relationship is beyond the scope of this paper. The similar form of the transient changes in ECG waveform i n h e a r t r a t e s u g g e s t s t h a t t h e y may b e a t and least partly due to a common cause. It has been shown response that the heart rate exhibits a biphasic transient to inspiration (20) and that an increase in right atria1 left volume increases the heart rate while an increase in atria1 volume decreases the heart rate (30). Thus the i n i t i a l i n c r e a s e i n r i g h t h e a r t v o l u m e w i t h i n s p i r a t i o n may increase the heart rate via reflex action and also change delayed The ECG waveform due to the enlarged RVEDV. the increase in the left atria1 volume may cause the later decreased heart rate and the delayed increase in LVEDV may cause an opposite change in the ECG waveform to that of the earlier enlarged RVEDV. A simplified model study of the time course of the has inspiration of the ventricular volumes with changes been presented. It shows that on the basis of pressure changes alone transient changes in the relative volumes of the ventricles occur, To make it more realistic it will rate, need to heart be extended to include changes in pulmonary vascular impedance and effect of the each v e n t r i c u l a r v o l u m e o n t h e c o m p l i a n c e o f t h e o t h e r (22,23). 259
T h e s u r f a c e E C G is at any one time u n d e r t h e i n f l u e n c e of several factors and it is often very difficult to sepaIt is effects. rate and distinguish their individual central to this paper that the various factors which conto the change of the waveform with inspiration can tribute be separated into two groups, one responsible for the step In order to transient. response, other for the the d i s t i n g u i s h t h e t w o efEects a s i m p l e c o n s t r u c t i o n w a s u s e d . this and as This is approximation first obviously a construction is vital to the development of this theory an need to be will improved, construction more rigorous designed. It n e e d s t o b e b a s e d o n t h e c h a n g e o f p o s i t i o n of the heart in the chest.
CONCLUSION The response of the surface ECG to a held-inspiration the that has been suggested descrioed. has been It response can be separated into a step and a transient component. mechanisms responsible for these two Possible components have been discussed. It is suggested that the ventricular response will vary in the presence of right dysfunction and/or increased pulmonary vascular impedance,
ACKNOWLEDGEMENTS African South Financial support obtained from the Medical Research Council and the University of Cape Town Staff Research Fund is gratefully acknowledged.
REFERENCES 1.
Einthoven W, Fahr G, de Waart A. On the direction and the manifest size of the variations of potential in human heart and on the influence of the position of the electrocardiogram. heart on the the form of Translated by Hoff HE, Am Heart J Sekelj P. 40:163,1950
2.
Gupta MS. Applications the IEEE 63:996,1975.
3.
The effects of respiration on the electroLamb LE. cardiogram in relation to differences in right and left Am Heart J 54:342,1957. ventricular stroke volume.
of
260
electrical
noise.
Proc o f
4.
Stamatoiu I, Guiloni H, Gabersek V. Study of the respiratory frequency during sleep in relation to the amplitude of the R wave of the Electroenceph ECG. Clin Neurophys 29:100,1970.
5.
Ferrer MI. Respiratory maneuvres in electrocardiographic diagnosis (editorial). Chest 73:445,1978
6.
Malmberg R, Albrecht G, Baltazaar A, Buckingham WB, Levine H, Cugell DW. The Valsalva maneuvre as a test of cardiac function in patients with pulmonary disease. Am Rev Respir Dis 89:64,1964
7.
Zema MJ, Masters AP, Margouleff D. Dyspnea: The Heart or the Lungs? Differentiation at bedside by use of the simple Valsalva maneuvre. Chest 85:59,1984.
8.
Goldblatt A, Harrison DC, Glick G, Braunwald E. Studies on cardiac dimension in intact unanesthetized man II. Effects of respiration. Circ Res 13:448,1963.
9.
Wexler L, Bergel DH, Gabe IT, Makin GS, Mills CJ. Velocity of blood flow in normal human venae cavae. Circ Res 23:349,1968
10.
Effects of phasic respiration Waugh RA. Brenner JI, in a ventricular dimension and performance left on 57:122,1978. Circ normal population.
11.
Robotham JL, Lixfield W, Holland L, MacGregor D, Bryan Effects of respiration on cardiac Robson J. AC, J Appl Physiol: R.E.E.P. 44:703,1978. performance.
12.
A model of the effects of Mintzner W. Robotham JL, on left ventricular performance. J APP~ respiration Physiol: R.E.E.P. 46:411,1979.
13.
Summer WR, Permutt S, Sagawa K, Shoukas AA, BombergerEffects of spontaneous respiration on canine Barnea B. Circ Res 45:719,1979. left ventricular function.
14.
Determinants of pulmonary arterial flow Pinsky MR. variation during respiration. J Appl Physiol: R.E.E.P. 56:1237,1984
15.
Pulmonary Higgins CB. Bhargava V, Slutsky RA, circulation time: comparison of mean, median, peak and onset (appearance) values using indocyanine green a I d Am Heart J radionuclide techniques. first-transit 106:41,1983
261
16.
Brody DA. A theoretical analysis of intracavitary mass influence on the heart-lead relationship. blood Circ Res 4:731,1956
17.
Angelakos ET, Gokham N. Influence of venous inflow volume on the magnitude of QRS potentials in vivo. Cardiologia 42:337,1963
18.
Salu Y, Marcus ML. simulation of the Computer precordial QRS complex: Effects of simulated changes in ventricular wall thickness and volume. Am Heart J 92:758,1976
19.
Talbot S, Kilpatrick D, Jonathan A, Raphael MJ. QRS voltage of the electrocardiogram and Frank vectorcardiogram in relation to ventricular volume. Br Heart J 39:1109,1977
20.
Clynes M. Respiratory control of heart rate: derived simulation. from analog computer Trans Med Electronics 7:2,1960
21.
Van der Werff TJ. Interdependence of left ventricular 73:683, Chest volume and heart rate. end-diastolic 1978
22.
Ventricular Santamore WP. Bove AA, Prog Cardiovasc Dis 23:365,1981
23.
Weber KT, Janicki JS, Hunter WC, Shroff S, Pearlmon ES, The contractile behaviour of the Fishman AP. the coupling to its functional heart and circulation. Prog Cardiovasc Dis 24:375,1982.
24.
Geselowitz DB, Schmitt OH. in Biological Engineering. New York. 1969
25.
Rudy Y, Wood R, Plonsey R, Liebman J. The effect of high lung conductivity on electrocardiographic potentials. Results from human subjects undergoing bronchopulmonary lavage. Circ 65:440,1982
26.
Jardin F, Farcot JC, Prost JF, Ozier Y, Gueret P, Bourdarias JP. Electrocardiographic evaluation of ventricles during continuous positive airway pressure breathing. J Appl Physiol: R.E.E.P. 56:619,1984
262
Laws IRE
interpendence.
Electrocardiography. ~333 (HP Schwan ed) McGraw-Hill
27.
Brooks WCC, Lange C. Interaction of myogenic neurogenic mechanisms that control heart rate. National Acad Sci USA. ?4:1761,1977
and Proc
28.
Almasi JJ, Schmitt OH. Basic technology of voluntary cardiorespiratory synchronization in electrocardiology IEEE Trans Biomed Eng 21:264,1974
29.
Amoore JN. Changes in the QRS complex of electrocardiogram during sleep and exercise. Thesis, University of Pretoria. 1979.
I_ h e 41SC
30.
Flaherty JT, Blumenschein SD, Alexander AW, Gentzler Gallie TM, Boineau JP, Influence of Spach MS. RD, respiration on recording cardiac potentials. Am .J Cardiol 20:21,1967
31.
Raviele A, Riggs T, Garcia E, Hirschfeld S, Liebman J. Respiratory variation in Frank vectorcardiography and J Electrocardiol echocardiography in children. 14:73,1981
32.
Respiratory variability Ruttkay-Nedecky I, Cagan S. Reinfarction. of vectorcardiograms in myocardial view of Czechoslovsk Medicine 3:156,1974
33.
Effects of respiration and heart Ruttkay-Nedecky I. p120 in The position on the cardiac electric field. (CV Nelson, theoretical basis of electrocardiology. DB Geselowitz, eds), Clarendon Press, Oxford. 1976
34.
Respiratory Simonson E, Nakagawa K, Schmitt OH. reccrded change of the spatial vectorcardiogram Am Heart J 54:919,1957 with different lead systems.
35.
Sutherland DJ, McPherson DD, Spencer CA, Armstrong CS, Effects of posture and Horacek BM, Montague TJ. electrocardiogram. body surface respiration Am J Cardiol 5;:595,1983
36.
The effect of Mimbs JW, de Mello V, Roberts R. Am Heart respiration on normal and abnormal Q waves. J 94:579,1977
37.
Effect of Bogren HG, Lantz BMT, Miller RR, Mason DT. determined by respiration on cardiac motion 18:609,1977 cineangiography. Acta Radiology.
38.
Computer simulation studies Snyder MF, Rideout VC. the venous circulation. IEEE Trans Biomed Eng 16:325,1969.
263
M.H. ,D
of