- Email: [email protected]
Methods and physical characteristics of the kinetocardiographic and apexcardiographic systems for recording low-frequency precordial motion
Experimental and laboratory
Methods
and
kinetocardiographic for recording
physical
reports
characteristics
and low-frequency
apexcardiographic precordial
of
the systems motion
William H. Bancrojt, Jr., M.S.* E. E. Eddleman, Jr., M.D.** Birmingham, Ala.
S
ince more emphasis is being placed on the use of kinetocardiography and apexcardiography as possible diagnostic aids,1-4 a careful determination of the physical characteristics of the two systems which are most frequently employed appears to be useful. The following study involves a strictly mechanical determination of the physical characteristics of the given units, using a vibration table as the displacement source for measuring frequency and phase angle response. Methods A specialized vibration table was developed to produce accurately calibrated displacements varying in amplitude from .002 to .05 inch. Frequencies could be varied from 0 to 100 cycles per second. The table consists of a lever coupled to an eccentric shaft. All moving parts have precision ball bearings and shafts. A variable speed motor drives the eccentric shaft and is coupled to the shaft with &‘ith From
neoprene belts. The frequency is determined by an electronic counter accurate to f 0.1 cycle per second. Amplitude of the displacements was determined l)y a measuring microscope accurate to % .OOOl inch. A photoelectric displacement transducer? was first tested on the table and found to be linear over the full range of frequencies tested within the limits of accuracy of the measuring devices used. The output of the photoelectric transducer was recorded using the D.C. channels of an oscilloscopic recorder.1 Amplitudes of output were measured with an accuracy to two significant figures at frequencies varying from .2 to 50 cycles per second. The amplitudes did not vary using this number of significant figures. Hereafter, the photoelectric transducer was used as a standard for measurements of displacement. The kinetocardiographic pickup includes a three-section bellows§ connected to a pressure transducer-l/ by a 20-cm. length of
the technical assistance of Larry N. Larkin. Electronics Technician. Veterans Administration Hospital. the Medical Service, Veterans Administration Hospital, and Department of Medicine, Medical College oi Alabama, Birmingham, .4la. Aided by United States Public Health Service Grants No. HE O-5080, HE O-6353. and HE O-9423. Received for publication July 8, 1966. *Physicist, Medical Research. Veterans Administration Hospital; Instructor in Physics, Medical College of Alabama. **Associate Chief of Staff for Research, Veterans Administration Hospital; Professor of Medicine, Medical College of Alabama. Wchworzer Instrument Company. Framingham. Mass. fElectronicsfor Medicine DR-8. PMade by Kelvin & Hughes America Corporation, Annapolis. Md. I~statham PS-A.
756
Fig. 1. Diagram of the kinetocardiographic setup used in recording low-frequency movements. The bellows in the center of the photograph is connected by Tygon tubing to the PSA Statham transducer, mounted on the crossbar. Thus, the probe on the other end of the bellows can be placed perpendicular to any point on the chest wall to record movements at that position. Shown is the two-flange bellows which is perfectly satisfactory; however, at the present time this laboratory .is using the threeflange unit.
x-inch Tygon tubing (Fig. l).5-7 The bellows has a spring constant of 80 pounds per inch, with a natural frequency of 220 cycles per second. The bellows is mounted from a fixed point above the chest ~~11 (iron crossbar), which allows the recording of al)solute displacement movements of the chest wall at any point desired. The average force applied to the chest \vall is 2 pounds; however, this pressure and rigidity of the bellows apparently does not in itself alter the movements of the chest wall, since identical traces can be obtained with the photocell. This will be discussed subsequently. The probe is applied usually in the intercostal spaces. This is done because there is less discomfort to the patient than recording directly on the ribs, although records from adjacent positions are almost identical in contour. Amplitude response of the system \vas measured as that described for the photocell. Phase shift was determined by comparing the simultaneously recorded outputs of the kinetocardiogram and photo-
electric transducers. At higher frequencies, accuracy of this measurement was +lO degrees. Linearity of the system was tested h\r measuring the amplitude response at varying displacements. To determine the effect of length of tubing and type of tubing, the amplitude response was determined using several different lengths of Tygon tubing, gum rubber, and neoprene tubing. The apexcardiographic pickup is a funnel-type pressure pickup connected by a !$inch I.D., .I$-inch wall-thickness gun1 rubber tubing to a piezoelectric microphone.8 The funnel is 2 inches in diameter, 1 inch to the closed apex, with the outlet to the microphone situated approximately x inch above the open end of the bell. The outlet tube is !i inch in diameter. Clinically, the funnel is mounted upon the chest \vall so that relative motions between the central portion and the rim are recorded. This is the standard apparatus and procedure for recording the apexcardiogram. Since the apexcardiographic pickup measures the change in pressure of the air in the final microphone chamber as a result of differential motion, the response characteristics of this system are more difficult to obtain. To approximate the chest and to generate differential motion, a double sheet of .Ol-inch elastic rubber was stretched across the end of a plastic funnel. The volume of the funnel was approximately 300 C.C. The pressure in the system could he c-hanged in a sine wave fashion I)y connecting the funnel to a I,ellows mounted on the vibration talAe. The amplitude and phase shift response of the membrane was determined by placing the photoelectric transducer on the center of the rubber diaphragm and ascertaining its characteristics. The apexcardiographic transducer was then centered on the diaand measurements were made. phragm, ‘The pressure in the system was monitored strain-gauge transducer l)V a Statham (1’231)). A\ correction factor for the frevariation of the diaphragm was quenc! made 1)). dividing the displacement amplitude of the diaphragm determined by the photocell output at 1 cycle per second by its amplitude over the range of frequencies studied. The corrected or true response of the npexmrdiographic transducer is then
758
Anncrqf’t
and Eddlemtrn
the product of the correction factor and the amplitude of the transducer output at each frequency. This procedure corrects for the variation in the frequency response of the diaphragm in order to ascertain only the frequency characteristics of the apexcardiograph. The phase shift correction was performed by a direct algebraic addition of the phase shift of the diaphragm and phase shift of the apexcardiographic transducer. The system in no way approximates the chest wall characteristics but offers a means by which the apexcardiographic transducer, funnel, and tubing can he tested as a unit, and not just the piezoelectric transducer. To study the possibility of variation in technique as used clinically, as well as inherent instrumentation error, kinetocardiograms and apexcardiograms were taken sequentially in 2 normal subjects on 9 different days. The kinetocardiograms were recorded by a technician, whereas the apexcardiograms \vere taken with care by a physician. Results Frequency response (Figs. kinetocardiographic system
2 clnd 3). The has an obvious
resonance at 80 cycles per second (Fig. 2 ). This system displays a smooth response curve ~2 db from D.C. to 28 cycles per second. The apexcardiographic system (Fig. 3) is f 1 db from 0.1 to 20 cycles per second, with a rapid rise above 22 cycles per second and a resonance at 25, as well as somewhere above 80 cycles per second. The response curve has another small resonance peak at 1.5 cycles per second, causing deviations from a smooth curve. Phtse shift (Figs. 2 and .3). The kinetocardiograph% system showed a surprising lack of phase shift. Within the limits of accuracy of the measuring procedure the kinetocardiogram showed zero phase shift in the range .2 to 40 cycles per second. The apexcardiographic system ranges from 65 degrees lead at .2 cycles per second, as well as a 138 degrees lead at 22 cycles per second. Linearity. Fig. 4 shows the linearit\, of the kinetocardiographic system at 1 cycle per second, using a 40-cm. Tygon tube connecting the bellows and transducer. The ordinate is the output, in millivolts, of the pressure transducer. The abscissa is the displacement of the vibration table producing the output. The output is linear
Fig. 2. The frequency response at phase characteristics of the kinetocardiographic system measured in decibles and degrees. Note that the kinetocardiographic system is linear within 2 decibels to about 20 cycles per second. However, there is a slow gradual rise reaching a resonance at approximately 80 cycles per second. No phase shift occurs until 30 cycles per second. One peculiar aspect of this system is the fact that the shift in phase is not 90 degrees at point of resonance; however, it should be noted that this is not a simple electrical system, bllt a complex system involving both electrical, air, and mechanical transmission, and that, therefore, the 9O-degree phase shift at point of resonance does not necessarily, occur.
Cycles/Sac. Fig. 3. The frequency response and phase characteristics of the apexcardiographic system as determined by the apparatus described. The cycles per second are given in the lower portion of the figure. Sote that the apexcnrdiogram is essentially linear in response from one-tenth cycle per second to approximately 20; however, there is a sharp rise in frequency response at approximately 20 cycles per second. The main resonance peak was apparentI> above 80 cycles per second. The phase characteristics are considerably abnormal and are distorted both in the lower frequency range and in the upper frequency range. There is approximately 60 degrees of phase shift at one-tenth cycle per second and more than 130 degrees of phase shift at approximately 20 cycles per second. This indicates that the use of the apexcardiographic system is not reliable in terms of phase characteristics.
LINEARITY
OF
KCG
PICKUP
Iwo-400 800 4 t E
-300 600-
h : z
400.
2
- 100
200 -
0
,002
,006
,004
Displacement
Fig. 1. The response of the kinetocardiographic pickup over various rardiographic apparatus is linear both at 1 and 1.5 cycles per second.
at all frequencies. It was found to be impractical to test the linearity of the apexcardiographic system with the apparatus as described. E$ect of tubing on response. Fig. 5 displays the change in frequent>response of the kinetocardiographic systems with a change in the length of the tubing connect-
.ooe
,010
in Inches
changes
in amplitude.
Note
that
the killeto-
ing the bellows and transducer. The shorter the tubing and the more rigid the tubing, the Ijetter is the frequency response. Discussion The kinetocardiographic apparatus used in recording precordial displacement movements involves the suspension of a linear
7 60
Huncroft
trnd Eddlcm(Ln
FREQUENCY _____-__
RESPONSE
OF KCG
PICKUP
I Db
1
2
3
4
5
6
7
(1980
Frequency
20
(cylsec
Fig. 5. The frequency response curve for the kinetocardiographic tubing to connect the bellows to the Statham PSA transducer. short&t Tygon tubing (arrow labeled Y ant.).
displacement device from a fixed point above the chest wall. Because of the position of the mount, these movements represent absolute displacement movements of the precordium. This technique does not record tangential chest wall motion but only those movements perpendicular to the chest wall. The name “kinetocardiography” has been applied rather than “apexwhich refers to recording cardiography,” the relative movements of the apex with the pickup mounted on the chest wall. In addition, with the kinetocardiographic technique, recordings can be made at many positions over the anterior chest wall, not just at the apex. Thus, it has been believed that a separate term, “kinetocardiography,” is justified. Since the photocell pickup was linear over a wide range of frequencies in the present study, it is obvious that it is the more ideal transducer for sensing low-frequency precordial movements than is either the bellows or the apexcardiographic transducer. I-lowever, because of the limitations in the travel of the probe (x-inch is the one used), it becomes a most difficult pickup to position clinically. Thus, the bellows has continued to be used in this laboratory, since its frequency response is adequate for the types of motion being recorded. It is easily applied by a technician, and the records are reproducible from day to day without a physician being involved in the procedure. Aithough the bellows system has a res-
30
40 so 60 m
130
1
Note
system using various that the best response
lengths and is obtained
types of with the
onance at 80 cycles per second, this is sufficiently high with respect to the frequencies which are being recorded not to add a significant distortion to the records, and is essentially free from phase shift. In addition, the records obtained with the photocell and bellows are almost identical (Fig. 6). The rigidity of the bellows and presswe upplied to the chest wall does not alter the movements, since the photocell records kinetocardiograms which are identical when taken from the same point on the precordium. The apexcardiogram, on the other hand, does not have a smooth linear response curve, although the response from 1 to 20 cycles per second appears to be satisfactory (Fig. 3). Even more important is the phase shift encountered, which is appreciable at certain frequencies and could distort physiologic time relationships. A recent study indicates that the physiologic time relationships of the apexcardiogram are distorted.g The phase shifts encountered possibly account for these findings. Reproducibility of the two techniques is not a part of this study. However, it should be mentioned that the kinetocardiographic traces are highly reproducible from day to day in the same subject, even when taken by a technician. Fig. 7 presents 4 out of 9 kinetocardiograms taken on consecutive days. On the other hand, reproducibility of the apexcardiogram depends upon the skill of the physician taking
l~olume humbcr
73 6
Kinetocardiogrnphic
nnd npeuclvdiogrclphic
sq’sfcrtzs
761
Fig. 6. Kinetocardiographicrecords obtained with the two types of transducers: ic$, with the bellows transducer as described; right, with a photoelectric cell in which the spring constant is considerably less than that with the bellows. In addition, the photocell record, as pointed out, has a linear frequency; response over the ranges tested (O-80 cycles per second). Note that the traces are essentially identical, indicntmg that the kinetocardiographic records as obtained with the bellows system faithfully reproduce the mo~ments of the chest wall, and that the rise in frequency response of the kinetocardiographic: apparatus in the high-frequency range insignificantly 1’. PC., Jr., ~tntl lkwrison, ‘1‘. R., The affects the contour of the kinetocardiographic records. (From Eddlcman, Kinetocardiogram in Patients with Ischemic Heart Disease, Progress ill Cnrdiov.ts;cul;n l)keascs o(3):189-211, November, 1963, by permission of the publisher.)
Pig. 7. Four of ten kinetocardiographic curves obtained from a normal individual. These curres were recorded by. a technician at daily intervals from the region of the apes of the heart. The most extreme variatious on the curves were selected for presentation. QRS: The onset of the QRS complex. CU: The onset of the carotid uf>stroke. CIN: The end of ejection as determined from the carotid incisuml notch. Note that there is some variation from day to day; howev-er, the main contours of the cur\-es are identical.
762
Rnncrqft
mm? Eddlemcrn
Fig. 8. A-D, Four extreme variations in the apexcardiogram from the same individual. ‘l‘he sensitivity of the apparatus was maintained constant and records were obtained over a IO-day period. In contrast to the kinetocardiogram, a physician recorded these in an attempt to obtain similar records from day to day. QRS: The onset of the QRS complex. CC: The onset of ejection as determined from the carotid upstroke. CIN: The end of ejection as determined from the carotid inc-isural notch. Kate that there is considerable variation in the part just before the QRS, as well as in the mid-sq-stolic and filling portions of the curves. D does represent an extreme variation, and is considerably different from the other records. It is obvious that this would not be considered to be a suitable apexcardiogram; however, it does point out the marked variation that can occur by slightly different positioning of the transducer front day to da>
the record. Nevertheless, Fig. 8 does present some of the variations encountered when a physician records consecutive daily records on a normal subject. The examples are extreme and the trace in Fig. 8,D would not be accepted as a usable record, but the figure does illustrate possible variations which are minimal with the kinetocardiographic technique. There are other important aspects in recording low-frequency displacement movements besides the type of transducer. The type of mount of the transducer is particularly significant. The apexcardiographic transducer is mounted on the chest wall and records only differential motion between the enclosed portion of the chest and the rim. This can result in records which may be difficult to interpret. For example, if the rim moves outward and there is a comparable movement of the apex for the central portion within the rim, no movement will he recorded, since no relative motion between the center and the rim has occurred. Fig. 9 illustrates several
theoretical situations which might occur. A defect may exist in any system which is mounted on the chest wall. On the other hand, a kinetocardiograph is mounted from a fixed point above the patient, so that only absolute movements of the point on the chest mall where the probe is placed is sensed. In addition, it should be pointed out that kinefocnrdiographic curves more closely resemble the movements detected by palpation ut the bedside, since the physician is feeling the chest wall from a fixed point above the patient. The position of the patient during the recording procedure offers another facet of the problem. The apexcardiograms are recorded with the patient turned obliquely on the left side. It is difficult to achieve the proper position in different patients, as well as in the same patient from day to day. This may account for some variations noted in Fig. 8. On the other hand, the kinetocardiographic system, used the recumbent position, which eliminates this difficulty. Apexcardiography offers an additional
Kinetocnrdiogrtrphic
No Movement
Resulting IK
Movemeni
Fig. Y. A theoretical consideration of the problems encountered with the apexcardiographic system. The diagram represents three possible theoretical situations which might occur to make the movements of the chest wall difficult to interpret with the apexcardiographic technique. The probe represents the movable central portion of the chest wall within the rim of the funnel. In the top diagram, the center portion within the funnel may rno1.e a considerable degree outward (upward); whereas. if the funnel portion which rests upon the chest wall moves inward, the resultant motion is altered in amplitude response. In the center diagram, if both the probe and the rim move the same degree, no response will be recorded. In the lower tigure, if the rim moves more in the opposite direction than does the central portion, a paradoxical response will occur. (From Eddleman, E. E., Jr., and Harrison, T. R., The Kinetocardiogratn in Patients with Ischemic Heart Disease, Progress in Cardiovascular Diseases 6(3):189-211, November, 1963, by permission of the publisher.)
problem in technique, and that is the positioning of the funnel. It usually requires a physician and repeated exploration of the apical area before a suitable impulse is obtained. This can 1~ seen in Fig. 8,D, in which slight differences in positioning result in marked changes in the contour. This, too, may be a factor which influences the reproducibility, although this should be minimized with the increasing skill of the physician. IHowever, the record finally decided upon is highly urbifmry and varies considerably in contour and amplitude with slight shifts in position and pressure. The size of the funnel also affects the apexcardiogram and is not standardized from one laborator\, to another. Fig. 10 illustrates the vnria;ion in contour obtained 11~ varying the size
clnd (lpescclrdiogrcrphic
systems
763
of the funnel. The apexcardiographic technique is limited in still another facet. Onl!, records of the apex impulse can be made lvith any regularity. Thus, records from the other areas of the precordium which may provide a great deal of clinical information are often onlitted.[“-I? For example, right ventricular almormalities are best detected in the parasternal areas, and bulges due to mvocardial infarctions, in the l-2 and Ytr po$tions.‘RJi There is little douljt that the physical system of the kinetocardiographic technique appears to IX superior to that of the apexcardiographic. This is not to dispute the fact that the apexcardiogram may clinicall! be of value. It should he mentioned that the beIlo\vs is not critical in the accurate recording of displacement precordial movements, in that any reasonable linear displacement transducer mounted from ;L
&
6.5 cm.
+
9.5cm.
&
Ilcm
Fig. IO. The changes in the contour of the apexcardiogram which can occur as a result of variations in the diameter of the fulmel used for recording the traces. The top record is a kinetocardiographic trace for comparison. Q: Onset of the QRS complex. Cl;: Onset of ejection as determined from the carotid upstroke. CZN: End of ejection as determined from the carotid incisural notch. Note that, as the size of the funnel is changed from 2.5 cm. to 11 cm. in diameter, a marked l.ariation in the contour of the records occ‘urs. This points out the necessit? of using a funnel of standard-size diameter m recording the apexcardiographic records.
764
Bnncroft
Am. Heart 1. Jnne, 1967
and Eddlemtrn
fixed point above the chest wall records identical to those described.
yields 5.
Summary
1. The physical systems of the kinetocardiographic and apexcardiographic techniques are presented. 2. The kinetocardiographic system is linear in the low-frequency ranges D.C.-20 cycles per second ; however, there is a resonance at 80 cycles per second. The apexcardiographic system is linear from .l to 20 cycles per second; however, the rise in response in the upper frequency range is distorted by several resonances. 3. No significant phase shift occurs in the kinetocardiographic system, but the apexcardiographic system has considerable phase shift from .1 to 2 cycles per second and in the higher frequency ranges. 4. A discussion of the comparison hetween the t\vo systems is presented. We wish Germagian, Administration preparation
to express our appreciation to Mr. Harr>Medical Illustration Dilrision, Veterans Hospital, Birmingham, Ala., for of the illustrations.
REFERENCES Eddleman, E. E., Jr., Holt, J. H., and Bancroft, if::. H., Jr.: Computer analysis of the kinetocardiogram from patients with atrial septal defects, AX HEART J. 71:435, 1966. 2. Schweizer, W., Bertrab, R. V., and Reist, Ph.: Kinetocardiography in coronary artery disease, Brit. Heart J. 27:263, 1965. 3. Beilin, L., and Mounsey, I’.: The left ventricular impulse in hypertensive heart disease, Brit. Heart J. 24:409, 1962. 4. Benchimol, A., and Dimond, E. G.: The apexcardiogram in normal older subjects and in
6.
7.
8.
9.
10.
11.
patients with arteriosclerotic heart disease. Effect of exercise on the “A” wave, AM. HEART J. 65:789, 1963. Eddleman, E. E., Jr., Willis, K., Reeves, T. J., and Harrison, T. R.: The kinetocardiogram. I. Method of recording precordial movements, Circulation 8:269, 1953. Eddleman, E. E., Jr.: Cardiovascular dyinmlica--Technics for indirect measurements. Clinical cardiopulmonary physiology, New York, 1960, Grune & Stratton, Inc., p. 158. EddIemail, E. E., Jr.: The kinetocardiogram---I’ltra low-frequency precordial movements, in Cardiology: An encyclopedia of the cardiovascular system, Vol. 2, Chapter 3, pp. 63 (Supp.)-70-X (Supp.), New York, 1962, >IcGraw-Hill Book Cornnan\, Inc. Benchimol, A., and Dimand, E. G.: The normal and abnormal apexcardiogram-Its physiologic variation and its relation to intracardiac events, Am. J. Cardiol. 12:368, 1963. Tavel, M. E., Campbell, R. W., Feigenbaum, H., and Steinmetz, E. F.: The apex cardiogram and its relationship to haemodynamic events within the left heart, Brit. Heart J. 27:829, 1965. EddIemali, E. E., Jr.: Kinetocardiographic changes in ischemic heart disease, Circulation 32:650, 1965. Tucker, \V. T., Knowles, J. L., and Eddleman, E. E.. Ir.: Mitral insufficiencv: Cardiac mechanics as studied with the kinetocardiogram and ballistocardiogram, Circulation 12:278, 1955. EddIeman, E. E., Jr., Yoe, R. H., Tucker, \V. T., Knowles, J. L., and Willis, K.: The dynamics of ventricular contraction and relaxation in patients with mitral stenosis as studied by the kinetocardiogram and ballistocardiogram, Circulation 11:774, 1955. Dnviei J. C., Langley, J. O., Dodson, 1%‘. H., and Eddleman. E. E.. It-.: Clinical and kinetocnrdiographic studies’01 paradoxical precordial motion;, .&. HEART J. 63:775, 1962. Sub, S. K., and Eddleman, E. E., Jr.: Kinetorardiographic findings of myocardial infarction, Circulation 19:5.31, 1959. ”
12.
1.
13.
14.
Methods
and
kinetocardiographic for recording
physical
reports
characteristics
and low-frequency
apexcardiographic precordial
of
the systems motion
William H. Bancrojt, Jr., M.S.* E. E. Eddleman, Jr., M.D.** Birmingham, Ala.
S
ince more emphasis is being placed on the use of kinetocardiography and apexcardiography as possible diagnostic aids,1-4 a careful determination of the physical characteristics of the two systems which are most frequently employed appears to be useful. The following study involves a strictly mechanical determination of the physical characteristics of the given units, using a vibration table as the displacement source for measuring frequency and phase angle response. Methods A specialized vibration table was developed to produce accurately calibrated displacements varying in amplitude from .002 to .05 inch. Frequencies could be varied from 0 to 100 cycles per second. The table consists of a lever coupled to an eccentric shaft. All moving parts have precision ball bearings and shafts. A variable speed motor drives the eccentric shaft and is coupled to the shaft with &‘ith From
neoprene belts. The frequency is determined by an electronic counter accurate to f 0.1 cycle per second. Amplitude of the displacements was determined l)y a measuring microscope accurate to % .OOOl inch. A photoelectric displacement transducer? was first tested on the table and found to be linear over the full range of frequencies tested within the limits of accuracy of the measuring devices used. The output of the photoelectric transducer was recorded using the D.C. channels of an oscilloscopic recorder.1 Amplitudes of output were measured with an accuracy to two significant figures at frequencies varying from .2 to 50 cycles per second. The amplitudes did not vary using this number of significant figures. Hereafter, the photoelectric transducer was used as a standard for measurements of displacement. The kinetocardiographic pickup includes a three-section bellows§ connected to a pressure transducer-l/ by a 20-cm. length of
the technical assistance of Larry N. Larkin. Electronics Technician. Veterans Administration Hospital. the Medical Service, Veterans Administration Hospital, and Department of Medicine, Medical College oi Alabama, Birmingham, .4la. Aided by United States Public Health Service Grants No. HE O-5080, HE O-6353. and HE O-9423. Received for publication July 8, 1966. *Physicist, Medical Research. Veterans Administration Hospital; Instructor in Physics, Medical College of Alabama. **Associate Chief of Staff for Research, Veterans Administration Hospital; Professor of Medicine, Medical College of Alabama. Wchworzer Instrument Company. Framingham. Mass. fElectronicsfor Medicine DR-8. PMade by Kelvin & Hughes America Corporation, Annapolis. Md. I~statham PS-A.
756
Fig. 1. Diagram of the kinetocardiographic setup used in recording low-frequency movements. The bellows in the center of the photograph is connected by Tygon tubing to the PSA Statham transducer, mounted on the crossbar. Thus, the probe on the other end of the bellows can be placed perpendicular to any point on the chest wall to record movements at that position. Shown is the two-flange bellows which is perfectly satisfactory; however, at the present time this laboratory .is using the threeflange unit.
x-inch Tygon tubing (Fig. l).5-7 The bellows has a spring constant of 80 pounds per inch, with a natural frequency of 220 cycles per second. The bellows is mounted from a fixed point above the chest ~~11 (iron crossbar), which allows the recording of al)solute displacement movements of the chest wall at any point desired. The average force applied to the chest \vall is 2 pounds; however, this pressure and rigidity of the bellows apparently does not in itself alter the movements of the chest wall, since identical traces can be obtained with the photocell. This will be discussed subsequently. The probe is applied usually in the intercostal spaces. This is done because there is less discomfort to the patient than recording directly on the ribs, although records from adjacent positions are almost identical in contour. Amplitude response of the system \vas measured as that described for the photocell. Phase shift was determined by comparing the simultaneously recorded outputs of the kinetocardiogram and photo-
electric transducers. At higher frequencies, accuracy of this measurement was +lO degrees. Linearity of the system was tested h\r measuring the amplitude response at varying displacements. To determine the effect of length of tubing and type of tubing, the amplitude response was determined using several different lengths of Tygon tubing, gum rubber, and neoprene tubing. The apexcardiographic pickup is a funnel-type pressure pickup connected by a !$inch I.D., .I$-inch wall-thickness gun1 rubber tubing to a piezoelectric microphone.8 The funnel is 2 inches in diameter, 1 inch to the closed apex, with the outlet to the microphone situated approximately x inch above the open end of the bell. The outlet tube is !i inch in diameter. Clinically, the funnel is mounted upon the chest \vall so that relative motions between the central portion and the rim are recorded. This is the standard apparatus and procedure for recording the apexcardiogram. Since the apexcardiographic pickup measures the change in pressure of the air in the final microphone chamber as a result of differential motion, the response characteristics of this system are more difficult to obtain. To approximate the chest and to generate differential motion, a double sheet of .Ol-inch elastic rubber was stretched across the end of a plastic funnel. The volume of the funnel was approximately 300 C.C. The pressure in the system could he c-hanged in a sine wave fashion I)y connecting the funnel to a I,ellows mounted on the vibration talAe. The amplitude and phase shift response of the membrane was determined by placing the photoelectric transducer on the center of the rubber diaphragm and ascertaining its characteristics. The apexcardiographic transducer was then centered on the diaand measurements were made. phragm, ‘The pressure in the system was monitored strain-gauge transducer l)V a Statham (1’231)). A\ correction factor for the frevariation of the diaphragm was quenc! made 1)). dividing the displacement amplitude of the diaphragm determined by the photocell output at 1 cycle per second by its amplitude over the range of frequencies studied. The corrected or true response of the npexmrdiographic transducer is then
758
Anncrqf’t
and Eddlemtrn
the product of the correction factor and the amplitude of the transducer output at each frequency. This procedure corrects for the variation in the frequency response of the diaphragm in order to ascertain only the frequency characteristics of the apexcardiograph. The phase shift correction was performed by a direct algebraic addition of the phase shift of the diaphragm and phase shift of the apexcardiographic transducer. The system in no way approximates the chest wall characteristics but offers a means by which the apexcardiographic transducer, funnel, and tubing can he tested as a unit, and not just the piezoelectric transducer. To study the possibility of variation in technique as used clinically, as well as inherent instrumentation error, kinetocardiograms and apexcardiograms were taken sequentially in 2 normal subjects on 9 different days. The kinetocardiograms were recorded by a technician, whereas the apexcardiograms \vere taken with care by a physician. Results Frequency response (Figs. kinetocardiographic system
2 clnd 3). The has an obvious
resonance at 80 cycles per second (Fig. 2 ). This system displays a smooth response curve ~2 db from D.C. to 28 cycles per second. The apexcardiographic system (Fig. 3) is f 1 db from 0.1 to 20 cycles per second, with a rapid rise above 22 cycles per second and a resonance at 25, as well as somewhere above 80 cycles per second. The response curve has another small resonance peak at 1.5 cycles per second, causing deviations from a smooth curve. Phtse shift (Figs. 2 and .3). The kinetocardiograph% system showed a surprising lack of phase shift. Within the limits of accuracy of the measuring procedure the kinetocardiogram showed zero phase shift in the range .2 to 40 cycles per second. The apexcardiographic system ranges from 65 degrees lead at .2 cycles per second, as well as a 138 degrees lead at 22 cycles per second. Linearity. Fig. 4 shows the linearit\, of the kinetocardiographic system at 1 cycle per second, using a 40-cm. Tygon tube connecting the bellows and transducer. The ordinate is the output, in millivolts, of the pressure transducer. The abscissa is the displacement of the vibration table producing the output. The output is linear
Fig. 2. The frequency response at phase characteristics of the kinetocardiographic system measured in decibles and degrees. Note that the kinetocardiographic system is linear within 2 decibels to about 20 cycles per second. However, there is a slow gradual rise reaching a resonance at approximately 80 cycles per second. No phase shift occurs until 30 cycles per second. One peculiar aspect of this system is the fact that the shift in phase is not 90 degrees at point of resonance; however, it should be noted that this is not a simple electrical system, bllt a complex system involving both electrical, air, and mechanical transmission, and that, therefore, the 9O-degree phase shift at point of resonance does not necessarily, occur.
Cycles/Sac. Fig. 3. The frequency response and phase characteristics of the apexcardiographic system as determined by the apparatus described. The cycles per second are given in the lower portion of the figure. Sote that the apexcnrdiogram is essentially linear in response from one-tenth cycle per second to approximately 20; however, there is a sharp rise in frequency response at approximately 20 cycles per second. The main resonance peak was apparentI> above 80 cycles per second. The phase characteristics are considerably abnormal and are distorted both in the lower frequency range and in the upper frequency range. There is approximately 60 degrees of phase shift at one-tenth cycle per second and more than 130 degrees of phase shift at approximately 20 cycles per second. This indicates that the use of the apexcardiographic system is not reliable in terms of phase characteristics.
LINEARITY
OF
KCG
PICKUP
Iwo-400 800 4 t E
-300 600-
h : z
400.
2
- 100
200 -
0
,002
,006
,004
Displacement
Fig. 1. The response of the kinetocardiographic pickup over various rardiographic apparatus is linear both at 1 and 1.5 cycles per second.
at all frequencies. It was found to be impractical to test the linearity of the apexcardiographic system with the apparatus as described. E$ect of tubing on response. Fig. 5 displays the change in frequent>response of the kinetocardiographic systems with a change in the length of the tubing connect-
.ooe
,010
in Inches
changes
in amplitude.
Note
that
the killeto-
ing the bellows and transducer. The shorter the tubing and the more rigid the tubing, the Ijetter is the frequency response. Discussion The kinetocardiographic apparatus used in recording precordial displacement movements involves the suspension of a linear
7 60
Huncroft
trnd Eddlcm(Ln
FREQUENCY _____-__
RESPONSE
OF KCG
PICKUP
I Db
1
2
3
4
5
6
7
(1980
Frequency
20
(cylsec
Fig. 5. The frequency response curve for the kinetocardiographic tubing to connect the bellows to the Statham PSA transducer. short&t Tygon tubing (arrow labeled Y ant.).
displacement device from a fixed point above the chest wall. Because of the position of the mount, these movements represent absolute displacement movements of the precordium. This technique does not record tangential chest wall motion but only those movements perpendicular to the chest wall. The name “kinetocardiography” has been applied rather than “apexwhich refers to recording cardiography,” the relative movements of the apex with the pickup mounted on the chest wall. In addition, with the kinetocardiographic technique, recordings can be made at many positions over the anterior chest wall, not just at the apex. Thus, it has been believed that a separate term, “kinetocardiography,” is justified. Since the photocell pickup was linear over a wide range of frequencies in the present study, it is obvious that it is the more ideal transducer for sensing low-frequency precordial movements than is either the bellows or the apexcardiographic transducer. I-lowever, because of the limitations in the travel of the probe (x-inch is the one used), it becomes a most difficult pickup to position clinically. Thus, the bellows has continued to be used in this laboratory, since its frequency response is adequate for the types of motion being recorded. It is easily applied by a technician, and the records are reproducible from day to day without a physician being involved in the procedure. Aithough the bellows system has a res-
30
40 so 60 m
130
1
Note
system using various that the best response
lengths and is obtained
types of with the
onance at 80 cycles per second, this is sufficiently high with respect to the frequencies which are being recorded not to add a significant distortion to the records, and is essentially free from phase shift. In addition, the records obtained with the photocell and bellows are almost identical (Fig. 6). The rigidity of the bellows and presswe upplied to the chest wall does not alter the movements, since the photocell records kinetocardiograms which are identical when taken from the same point on the precordium. The apexcardiogram, on the other hand, does not have a smooth linear response curve, although the response from 1 to 20 cycles per second appears to be satisfactory (Fig. 3). Even more important is the phase shift encountered, which is appreciable at certain frequencies and could distort physiologic time relationships. A recent study indicates that the physiologic time relationships of the apexcardiogram are distorted.g The phase shifts encountered possibly account for these findings. Reproducibility of the two techniques is not a part of this study. However, it should be mentioned that the kinetocardiographic traces are highly reproducible from day to day in the same subject, even when taken by a technician. Fig. 7 presents 4 out of 9 kinetocardiograms taken on consecutive days. On the other hand, reproducibility of the apexcardiogram depends upon the skill of the physician taking
l~olume humbcr
73 6
Kinetocardiogrnphic
nnd npeuclvdiogrclphic
sq’sfcrtzs
761
Fig. 6. Kinetocardiographicrecords obtained with the two types of transducers: ic$, with the bellows transducer as described; right, with a photoelectric cell in which the spring constant is considerably less than that with the bellows. In addition, the photocell record, as pointed out, has a linear frequency; response over the ranges tested (O-80 cycles per second). Note that the traces are essentially identical, indicntmg that the kinetocardiographic records as obtained with the bellows system faithfully reproduce the mo~ments of the chest wall, and that the rise in frequency response of the kinetocardiographic: apparatus in the high-frequency range insignificantly 1’. PC., Jr., ~tntl lkwrison, ‘1‘. R., The affects the contour of the kinetocardiographic records. (From Eddlcman, Kinetocardiogram in Patients with Ischemic Heart Disease, Progress ill Cnrdiov.ts;cul;n l)keascs o(3):189-211, November, 1963, by permission of the publisher.)
Pig. 7. Four of ten kinetocardiographic curves obtained from a normal individual. These curres were recorded by. a technician at daily intervals from the region of the apes of the heart. The most extreme variatious on the curves were selected for presentation. QRS: The onset of the QRS complex. CU: The onset of the carotid uf>stroke. CIN: The end of ejection as determined from the carotid incisuml notch. Note that there is some variation from day to day; howev-er, the main contours of the cur\-es are identical.
762
Rnncrqft
mm? Eddlemcrn
Fig. 8. A-D, Four extreme variations in the apexcardiogram from the same individual. ‘l‘he sensitivity of the apparatus was maintained constant and records were obtained over a IO-day period. In contrast to the kinetocardiogram, a physician recorded these in an attempt to obtain similar records from day to day. QRS: The onset of the QRS complex. CC: The onset of ejection as determined from the carotid upstroke. CIN: The end of ejection as determined from the carotid inc-isural notch. Kate that there is considerable variation in the part just before the QRS, as well as in the mid-sq-stolic and filling portions of the curves. D does represent an extreme variation, and is considerably different from the other records. It is obvious that this would not be considered to be a suitable apexcardiogram; however, it does point out the marked variation that can occur by slightly different positioning of the transducer front day to da>
the record. Nevertheless, Fig. 8 does present some of the variations encountered when a physician records consecutive daily records on a normal subject. The examples are extreme and the trace in Fig. 8,D would not be accepted as a usable record, but the figure does illustrate possible variations which are minimal with the kinetocardiographic technique. There are other important aspects in recording low-frequency displacement movements besides the type of transducer. The type of mount of the transducer is particularly significant. The apexcardiographic transducer is mounted on the chest wall and records only differential motion between the enclosed portion of the chest and the rim. This can result in records which may be difficult to interpret. For example, if the rim moves outward and there is a comparable movement of the apex for the central portion within the rim, no movement will he recorded, since no relative motion between the center and the rim has occurred. Fig. 9 illustrates several
theoretical situations which might occur. A defect may exist in any system which is mounted on the chest wall. On the other hand, a kinetocardiograph is mounted from a fixed point above the patient, so that only absolute movements of the point on the chest mall where the probe is placed is sensed. In addition, it should be pointed out that kinefocnrdiographic curves more closely resemble the movements detected by palpation ut the bedside, since the physician is feeling the chest wall from a fixed point above the patient. The position of the patient during the recording procedure offers another facet of the problem. The apexcardiograms are recorded with the patient turned obliquely on the left side. It is difficult to achieve the proper position in different patients, as well as in the same patient from day to day. This may account for some variations noted in Fig. 8. On the other hand, the kinetocardiographic system, used the recumbent position, which eliminates this difficulty. Apexcardiography offers an additional
Kinetocnrdiogrtrphic
No Movement
Resulting IK
Movemeni
Fig. Y. A theoretical consideration of the problems encountered with the apexcardiographic system. The diagram represents three possible theoretical situations which might occur to make the movements of the chest wall difficult to interpret with the apexcardiographic technique. The probe represents the movable central portion of the chest wall within the rim of the funnel. In the top diagram, the center portion within the funnel may rno1.e a considerable degree outward (upward); whereas. if the funnel portion which rests upon the chest wall moves inward, the resultant motion is altered in amplitude response. In the center diagram, if both the probe and the rim move the same degree, no response will be recorded. In the lower tigure, if the rim moves more in the opposite direction than does the central portion, a paradoxical response will occur. (From Eddleman, E. E., Jr., and Harrison, T. R., The Kinetocardiogratn in Patients with Ischemic Heart Disease, Progress in Cardiovascular Diseases 6(3):189-211, November, 1963, by permission of the publisher.)
problem in technique, and that is the positioning of the funnel. It usually requires a physician and repeated exploration of the apical area before a suitable impulse is obtained. This can 1~ seen in Fig. 8,D, in which slight differences in positioning result in marked changes in the contour. This, too, may be a factor which influences the reproducibility, although this should be minimized with the increasing skill of the physician. IHowever, the record finally decided upon is highly urbifmry and varies considerably in contour and amplitude with slight shifts in position and pressure. The size of the funnel also affects the apexcardiogram and is not standardized from one laborator\, to another. Fig. 10 illustrates the vnria;ion in contour obtained 11~ varying the size
clnd (lpescclrdiogrcrphic
systems
763
of the funnel. The apexcardiographic technique is limited in still another facet. Onl!, records of the apex impulse can be made lvith any regularity. Thus, records from the other areas of the precordium which may provide a great deal of clinical information are often onlitted.[“-I? For example, right ventricular almormalities are best detected in the parasternal areas, and bulges due to mvocardial infarctions, in the l-2 and Ytr po$tions.‘RJi There is little douljt that the physical system of the kinetocardiographic technique appears to IX superior to that of the apexcardiographic. This is not to dispute the fact that the apexcardiogram may clinicall! be of value. It should he mentioned that the beIlo\vs is not critical in the accurate recording of displacement precordial movements, in that any reasonable linear displacement transducer mounted from ;L
&
6.5 cm.
+
9.5cm.
&
Ilcm
Fig. IO. The changes in the contour of the apexcardiogram which can occur as a result of variations in the diameter of the fulmel used for recording the traces. The top record is a kinetocardiographic trace for comparison. Q: Onset of the QRS complex. Cl;: Onset of ejection as determined from the carotid upstroke. CZN: End of ejection as determined from the carotid incisural notch. Note that, as the size of the funnel is changed from 2.5 cm. to 11 cm. in diameter, a marked l.ariation in the contour of the records occ‘urs. This points out the necessit? of using a funnel of standard-size diameter m recording the apexcardiographic records.
764
Bnncroft
Am. Heart 1. Jnne, 1967
and Eddlemtrn
fixed point above the chest wall records identical to those described.
yields 5.
Summary
1. The physical systems of the kinetocardiographic and apexcardiographic techniques are presented. 2. The kinetocardiographic system is linear in the low-frequency ranges D.C.-20 cycles per second ; however, there is a resonance at 80 cycles per second. The apexcardiographic system is linear from .l to 20 cycles per second; however, the rise in response in the upper frequency range is distorted by several resonances. 3. No significant phase shift occurs in the kinetocardiographic system, but the apexcardiographic system has considerable phase shift from .1 to 2 cycles per second and in the higher frequency ranges. 4. A discussion of the comparison hetween the t\vo systems is presented. We wish Germagian, Administration preparation
to express our appreciation to Mr. Harr>Medical Illustration Dilrision, Veterans Hospital, Birmingham, Ala., for of the illustrations.
REFERENCES Eddleman, E. E., Jr., Holt, J. H., and Bancroft, if::. H., Jr.: Computer analysis of the kinetocardiogram from patients with atrial septal defects, AX HEART J. 71:435, 1966. 2. Schweizer, W., Bertrab, R. V., and Reist, Ph.: Kinetocardiography in coronary artery disease, Brit. Heart J. 27:263, 1965. 3. Beilin, L., and Mounsey, I’.: The left ventricular impulse in hypertensive heart disease, Brit. Heart J. 24:409, 1962. 4. Benchimol, A., and Dimond, E. G.: The apexcardiogram in normal older subjects and in
6.
7.
8.
9.
10.
11.
patients with arteriosclerotic heart disease. Effect of exercise on the “A” wave, AM. HEART J. 65:789, 1963. Eddleman, E. E., Jr., Willis, K., Reeves, T. J., and Harrison, T. R.: The kinetocardiogram. I. Method of recording precordial movements, Circulation 8:269, 1953. Eddleman, E. E., Jr.: Cardiovascular dyinmlica--Technics for indirect measurements. Clinical cardiopulmonary physiology, New York, 1960, Grune & Stratton, Inc., p. 158. EddIemail, E. E., Jr.: The kinetocardiogram---I’ltra low-frequency precordial movements, in Cardiology: An encyclopedia of the cardiovascular system, Vol. 2, Chapter 3, pp. 63 (Supp.)-70-X (Supp.), New York, 1962, >IcGraw-Hill Book Cornnan\, Inc. Benchimol, A., and Dimand, E. G.: The normal and abnormal apexcardiogram-Its physiologic variation and its relation to intracardiac events, Am. J. Cardiol. 12:368, 1963. Tavel, M. E., Campbell, R. W., Feigenbaum, H., and Steinmetz, E. F.: The apex cardiogram and its relationship to haemodynamic events within the left heart, Brit. Heart J. 27:829, 1965. EddIemali, E. E., Jr.: Kinetocardiographic changes in ischemic heart disease, Circulation 32:650, 1965. Tucker, \V. T., Knowles, J. L., and Eddleman, E. E.. Ir.: Mitral insufficiencv: Cardiac mechanics as studied with the kinetocardiogram and ballistocardiogram, Circulation 12:278, 1955. EddIeman, E. E., Jr., Yoe, R. H., Tucker, \V. T., Knowles, J. L., and Willis, K.: The dynamics of ventricular contraction and relaxation in patients with mitral stenosis as studied by the kinetocardiogram and ballistocardiogram, Circulation 11:774, 1955. Dnviei J. C., Langley, J. O., Dodson, 1%‘. H., and Eddleman. E. E.. It-.: Clinical and kinetocnrdiographic studies’01 paradoxical precordial motion;, .&. HEART J. 63:775, 1962. Sub, S. K., and Eddleman, E. E., Jr.: Kinetorardiographic findings of myocardial infarction, Circulation 19:5.31, 1959. ”
12.
1.
13.
14.