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Echocardiographic study of the isovolumetric contraction time
ECHOCARDIOGRAPHIC STUDYOF THE ISOVOLUMETRICCONTRACTION TIME H. Lauboeck”
ABSTRACT The isovolumetric contraction time of the human heart, i.e. the time interval from the completion of the mitral valve closure to the beginning of the aortic valve opening was measured by means of echocardiography. The result of
INTRODUCTION
Strictly speaking, the ‘isovolumetric’ contraction of the left ventricle begins when the mitral valve bas closed and it ends when the aortic valve opens. It is only during this period that the volume of blood in the ventrical remains unchanged. Closure of the mitral valve is delayed for a certain time after the ventricular contraction has begun and the ventricular pressure is rising above the atrial pressure. This delay is an effect of the inertia of mitral blood flow as was recognized by Faber (1964). It was observed experimentally by Nolan et al. (1969), Laniado, Yellin et al. (1973), Bellhouse (1975) and Talukder, Reu1 et al. (1979) among others. Using dimensional analysis and data measured by Laniado (1973) on a dog’s heart, the present author (Lauboeck, 1980) computed the conditions of the human mitral valve’s closure and suggested that the delay should extend through an increasing fraction of the total cardiac cycle when the heart rate increases due to exercise. The aortic valve begins to open and ejection from the ventricle starts after the ventricular pressure exceeds the diastolic pressure in the aorta. The time interval during which the ventricular pressure rises from atria1 pressure to aortic pressure appears to be an almost constant fraction of the cardiac cycle, independent of the heart rate. Hence, as the heart rate increases, the isovolumetric contraction period should extend through a decreasing fraction of the total cardiac cycle and may even disappear at a certain elevated heart rate. When the heart rate surpasses this critical level, due to hard exercise, the aortic valve may possibly open before the mitral valve has completely closed. In order to check these predictions for the human heart, experimentally by a noninvasive method, we used echo-cardiography to observe simultaneously the motions of both the mitral and aortic valves of an untrained healthy person at rest and during exercise. The results of the study, which tend to confirm the predictions, are presented below. A Department of Anaesthesia and Intensive Hospita& Bergmannsheil, West Germany.
0141-5425/80/040281-04 0 1980 IPC Business Press
care, University
of Bochum
this investigotion verifies a theoretical prediction by the author, that the isovolumetric contraction time should decrease more than in proportion with the heart period when the heart rate increases due to exercise, and that it should even disappear at a sufficiently elevated heart rate.
paper using comparable published by Hirschfeld
experimental (1976).
methods
was
METHOD
During the experiments, the subject (the author) lay on his back. The R-wave peak of the ECG was used as a zero time reference and for measuring the instantaneous heart rate. Echocardiographic equipment supplied by Edwards Laboratories, Munich, was used. During the first tests only one device was available. The transmitter was applied to two positions on the chest successively to observe the motion of either valve. In later tests, two devices of the same type were employed to observe both valves simultaneously. The speed of the recording paper was 200 mm/s so that 1 mm of the record equals 5 ms, which seems to be the limit of resolution of this device. Measurements were taken at a low heart rate with the subject at rest and then at a faster rate, after exercise on a bicycle ergometer which could be used in the supine position. The exercise had to be interrupted to obta.in suffïciently quiet conditions at the chest surface to provide reproducible records on the echocardiograph. Hence the measurements at elevated heart rate were not taken in a steady state with constant heart rate, but in a state of decreasing heart rate during recovery after interruption of exercise.
RESULTS
Typical echocardiographic records of early systole are shown in Figures 1 to 4. Figures 1 and 2 were taken simultaneously with the subject at rest, heart rate (HR) of 64 beats/min and a cardiac cycle time (T) of 0.94 s. Figures 3 and 4 were taken simultaneously after exercise with HR = 138 beatslmin and T = 0.34 sec. Figures 1 and 3 show the position and motion of the mitral valve. The traces of both the anterior and posterior cusps may be distinguished during diastole and it can be seen that the cus s approach each other when the valve closes. A Pter-
$02.00 J. Biomed.
Engng.
1980,
Vol.
2, October
281
Echocordiogroph:
H. louboeck 2
I
0
25
50
t/ms
6
Figure 1 Mitral valve closure at HR 64/min 1. R-wave peak, 2. mitral valve closure time, 3. Electrocardiogram, 4. anterior leaflet, 5. posterior leaflet, 6. single trace of closed valve.
Aortic valve opening at HR 64/min 1. R-wave peak, 2. aortic valve opening time, 3. Electrocardiogram, 4. anterior leaflet, 5. poste5. single trace of closed valve, 6. posterior wal1 of aorta.
Figure 3
Figure 4
282
Mitral valve closure at HR 138/min
J. Biomed.
Engng.
1980,
Vol.
2, October
Figure 2
Aortic valve opening at HR 138/min
Echocardiograph:
H. lauboeck
Figure 6 summarizes
all the relevant data. Two categories of experimental data are represented by special symbols: times measured at both valves during the same heart beat simultaneously and those measured at a single valve. As can be seen, simultaneous measurements of both valves are necessary to measure the isovolumetric time interval as exactly as possible.
The time after the R-wave peak of the mitral value closure is seen to vary only slightly with heart rate. This means that the mitral valve closing delay extends through an increasing fraction of the total cardiac cycle when the heart rate increases, as predicted. As the heart rate increases, the time measured from the R-wave peak to the aortic valve opening, decreases approximately in proportion to the total heart period duration. The interval between the two valve movements, i.e. the measured duration of the isovolumetric contraction in the strict sense, decreases with increasing heart rate and disappears at approximately 140 beats/min. Also shown in Figure 6 are two curves, each of which is drawn through two theoretical points. These points (at HR = 68 heats/ min and HR = 172 beats/min) are taken from the earlier paper (Lauboeck, 1980). They show the calculated time after the R-wave peak, when either the mitral valve closes or when the ventricular
Figure 5 Fig. 3 and 4 shown simultaneously 1. both R-wave peaks, 2. aortic valve opening and mitral valve closure time, 3. anterior wal1 of aorta, 4. anterior leaflet of mitral valve, 5. single trace of aortic cusps, 6. posterior leaflet of mitral valve, 7. single trace o,f closed mitral valve.
wards a single trace of the closed valve can be seen. The time of closure of the mitral leaflets as indicated in Figure I is 9.5 mm = 47 ms after the R-peak and in Figure 3 it is 3.5 mm = 17.5 ms after the R-peak. Figure 2 and 4 show the position and motion of the aortic valve. The single trace of the closed valve splits suddenly into two faintly visible traces when the cusps open. In Figure 2 the opening occurs at 13 mm = 65 ms after the R-peak and in Figure 4 at 3.5 mm = 17.5 ms after the R-peak. Al1 the events displayed in Figure 1 and 2 (and 3 and 4 respectively) are registered simultaneously during the same heart beat. So mitral valve closure and aortic valve opening give the complete echocardiographic valve motion during the first heart sound. Figure 5 is a montage of Figures 3 and 4 printed on the same time frame so that the time relations between the opening and closing movements of both valves can be compared in one picture. The evaluation of the records is not always easy. In many records, important details of the tracing are missing. For the same reason, the simultaneous registration of both valves was possible in only a few cases.
% of cordiac cycle 2
4
6
8
10
i
J 0
50
100 Heart
rote
Lbeots
150 /min
200
)
Figure 6 Isovolumetric time period in theory (mitral valve closure =V, aortic valve opening =V) compared with echocardiographic measurements of both valves nonsimultaneous (mitral valve closure = 0, aortic aalve opening = 0) and simultaneous (mitral valve closure = A, aortic valve opening = a). Shaded area = mean range of aortic valve opening Ces, and mitral valve closure time (a), The hyperbolas show the percent paction of heart period. In relation to this fraction aortic valve opening times remain constant in theory or even decrease in experiment while mitral valve closure time increases with increasing heart rate during exercise.
J. Biomed.
Engng.
1980,
Vol.
2, October
283
Echocardiogroph:
H. louboeck
pressure equals 55 and 65 Torr respectively, which is taken here to indicate the moment of opening of the aortic valve. The-theoretical curves intersect at a heart rate of 140 beats/min. DISCUSSION
Besides the experimental and theoretical times of the valve motions as a function of heart rate, Figure 6 also contains for the purpose of comparison some hyperbolas representing constant fractions of the cardiac cycle. There is some scatter of the experimental data which requires explanation. However, the mean values of the measured times - here indicated roughly by two shaded strips for both valves respectively - correlate reasonably wel1 with the theoretical curves. Thus the theoretical statement of the author (Lauboeck, 1980) is experimentally confrmed: the duration of the isovolumetric contraction occupies a decreasing fraction of the cardiac cycle when the heart rate increases during exercise. Within the resolution of the equipment used, the measured isovolumetric contraction phase disappears at about the same heart rate as predicted. ,The experimental times of the mitral valve closure after the R-wave peak tend to be smaller than those predicted by the theory. This may be due to a smaller stroke volume of the present subject as compared with those investigated by Roskamm et al. (1972,1977) on which the theoretical data of Lauboeck (1980) are based. An analogous discrepanty concerning the opening of the aortic valve may also be due to rather low diastolic pressure in the aorta of the subject of this investigation. Some of the scatter of the measured times of valve motions at higher heart rates could perhaps be explained by the interruption of the exercise which was necessary to take the echocardiogram. If the peripheral resistance is increased when the heart is $ll beating fast, there should be a higher diastolic pressure in the aorta and accordingly, the aortic valve should open later. It should be noted that divergences from the mean values of the data points measured simultaneously tend to occur in the same direction and with the same magnitude for
284
J. Biomed.
Engng.
1980,
Vol.
2, October
both valves, so that the isovolumetric contraction time diverges only slightly from the mean in these cases. The delay of the mitral valve closure permits the inflow of blood into the ventricle to continue even after the ventricular contraction has begun and the pressure is rising. A certain amount of blood (- 10% of the stroke volume) stil1 enters the ventricle and increases its volume. This fact may bear consequente for the Starling mechanism: while the contractile elements are already contracting the elastic elements are stil1 being stretched more than during isovolumetric contraction. ACKNOWLEDGEMENT
The author thanks Dr. Kümmell, Intemal Medicine, Gemeinschaftskrankenhaus Herdecke, Germany, for his help in echocardiography and Dr. Kraemer, Max Planck Institute, for his advice in fluid dynamics. REFERENCES Bellhouse and Bellhouse (1975) Congress about the mitral valve. Paris 1975 Bubenheimer, P. and Roskamm, H. (1977) ‘Echokardiographie zur Beurteihmg der Arbeitswerte des linken Ventrikels mit dynamicher körperlicher Belastung.’ Sportarzt und Sportmedizin, 28,352-354 Faber, J J. (1964) ‘Origin and conduction of the mitral sound in the heart’. Chirc. Res, 14,426 Hirschfeld, St. (1976) ‘The isovolumic contraction time of the left ventricle. An echographic study’. Circulution 54, 751-756 Laniado, S., Yellin, E.L. et al. (1973) ‘Temporal relations of the first heart sound to closure of the mitral valve’. Circulation 47, 1006-1014 Lauboeck, H. (1980) ‘The conditions of mitral valve closure’. closure’. Vortrag EUROMECH 118, Zuoz 1979 J. Biomed. Engn. 2 (2), 93-96 Nolan, S.P. et al. (1969) ‘The influence of atrial contraction and mitral valve mechanics on ventricuIar filling’. Amer. Heart J. 77, 784 Roskamm, H. (1972) ‘Die Ko ntrakilitatsreserve des gesunden linken Ventrikels’. 2. Kreislaufforshung 61, 673-689 Talukder, N., Reul, H. and Mueller, E.-W. (1979) ‘Fluid mechanics of the natural mitral valve’. Euromech 118, Zuoz, Schweiz
ABSTRACT The isovolumetric contraction time of the human heart, i.e. the time interval from the completion of the mitral valve closure to the beginning of the aortic valve opening was measured by means of echocardiography. The result of
INTRODUCTION
Strictly speaking, the ‘isovolumetric’ contraction of the left ventricle begins when the mitral valve bas closed and it ends when the aortic valve opens. It is only during this period that the volume of blood in the ventrical remains unchanged. Closure of the mitral valve is delayed for a certain time after the ventricular contraction has begun and the ventricular pressure is rising above the atrial pressure. This delay is an effect of the inertia of mitral blood flow as was recognized by Faber (1964). It was observed experimentally by Nolan et al. (1969), Laniado, Yellin et al. (1973), Bellhouse (1975) and Talukder, Reu1 et al. (1979) among others. Using dimensional analysis and data measured by Laniado (1973) on a dog’s heart, the present author (Lauboeck, 1980) computed the conditions of the human mitral valve’s closure and suggested that the delay should extend through an increasing fraction of the total cardiac cycle when the heart rate increases due to exercise. The aortic valve begins to open and ejection from the ventricle starts after the ventricular pressure exceeds the diastolic pressure in the aorta. The time interval during which the ventricular pressure rises from atria1 pressure to aortic pressure appears to be an almost constant fraction of the cardiac cycle, independent of the heart rate. Hence, as the heart rate increases, the isovolumetric contraction period should extend through a decreasing fraction of the total cardiac cycle and may even disappear at a certain elevated heart rate. When the heart rate surpasses this critical level, due to hard exercise, the aortic valve may possibly open before the mitral valve has completely closed. In order to check these predictions for the human heart, experimentally by a noninvasive method, we used echo-cardiography to observe simultaneously the motions of both the mitral and aortic valves of an untrained healthy person at rest and during exercise. The results of the study, which tend to confirm the predictions, are presented below. A Department of Anaesthesia and Intensive Hospita& Bergmannsheil, West Germany.
0141-5425/80/040281-04 0 1980 IPC Business Press
care, University
of Bochum
this investigotion verifies a theoretical prediction by the author, that the isovolumetric contraction time should decrease more than in proportion with the heart period when the heart rate increases due to exercise, and that it should even disappear at a sufficiently elevated heart rate.
paper using comparable published by Hirschfeld
experimental (1976).
methods
was
METHOD
During the experiments, the subject (the author) lay on his back. The R-wave peak of the ECG was used as a zero time reference and for measuring the instantaneous heart rate. Echocardiographic equipment supplied by Edwards Laboratories, Munich, was used. During the first tests only one device was available. The transmitter was applied to two positions on the chest successively to observe the motion of either valve. In later tests, two devices of the same type were employed to observe both valves simultaneously. The speed of the recording paper was 200 mm/s so that 1 mm of the record equals 5 ms, which seems to be the limit of resolution of this device. Measurements were taken at a low heart rate with the subject at rest and then at a faster rate, after exercise on a bicycle ergometer which could be used in the supine position. The exercise had to be interrupted to obta.in suffïciently quiet conditions at the chest surface to provide reproducible records on the echocardiograph. Hence the measurements at elevated heart rate were not taken in a steady state with constant heart rate, but in a state of decreasing heart rate during recovery after interruption of exercise.
RESULTS
Typical echocardiographic records of early systole are shown in Figures 1 to 4. Figures 1 and 2 were taken simultaneously with the subject at rest, heart rate (HR) of 64 beats/min and a cardiac cycle time (T) of 0.94 s. Figures 3 and 4 were taken simultaneously after exercise with HR = 138 beatslmin and T = 0.34 sec. Figures 1 and 3 show the position and motion of the mitral valve. The traces of both the anterior and posterior cusps may be distinguished during diastole and it can be seen that the cus s approach each other when the valve closes. A Pter-
$02.00 J. Biomed.
Engng.
1980,
Vol.
2, October
281
Echocordiogroph:
H. louboeck 2
I
0
25
50
t/ms
6
Figure 1 Mitral valve closure at HR 64/min 1. R-wave peak, 2. mitral valve closure time, 3. Electrocardiogram, 4. anterior leaflet, 5. posterior leaflet, 6. single trace of closed valve.
Aortic valve opening at HR 64/min 1. R-wave peak, 2. aortic valve opening time, 3. Electrocardiogram, 4. anterior leaflet, 5. poste5. single trace of closed valve, 6. posterior wal1 of aorta.
Figure 3
Figure 4
282
Mitral valve closure at HR 138/min
J. Biomed.
Engng.
1980,
Vol.
2, October
Figure 2
Aortic valve opening at HR 138/min
Echocardiograph:
H. lauboeck
Figure 6 summarizes
all the relevant data. Two categories of experimental data are represented by special symbols: times measured at both valves during the same heart beat simultaneously and those measured at a single valve. As can be seen, simultaneous measurements of both valves are necessary to measure the isovolumetric time interval as exactly as possible.
The time after the R-wave peak of the mitral value closure is seen to vary only slightly with heart rate. This means that the mitral valve closing delay extends through an increasing fraction of the total cardiac cycle when the heart rate increases, as predicted. As the heart rate increases, the time measured from the R-wave peak to the aortic valve opening, decreases approximately in proportion to the total heart period duration. The interval between the two valve movements, i.e. the measured duration of the isovolumetric contraction in the strict sense, decreases with increasing heart rate and disappears at approximately 140 beats/min. Also shown in Figure 6 are two curves, each of which is drawn through two theoretical points. These points (at HR = 68 heats/ min and HR = 172 beats/min) are taken from the earlier paper (Lauboeck, 1980). They show the calculated time after the R-wave peak, when either the mitral valve closes or when the ventricular
Figure 5 Fig. 3 and 4 shown simultaneously 1. both R-wave peaks, 2. aortic valve opening and mitral valve closure time, 3. anterior wal1 of aorta, 4. anterior leaflet of mitral valve, 5. single trace of aortic cusps, 6. posterior leaflet of mitral valve, 7. single trace o,f closed mitral valve.
wards a single trace of the closed valve can be seen. The time of closure of the mitral leaflets as indicated in Figure I is 9.5 mm = 47 ms after the R-peak and in Figure 3 it is 3.5 mm = 17.5 ms after the R-peak. Figure 2 and 4 show the position and motion of the aortic valve. The single trace of the closed valve splits suddenly into two faintly visible traces when the cusps open. In Figure 2 the opening occurs at 13 mm = 65 ms after the R-peak and in Figure 4 at 3.5 mm = 17.5 ms after the R-peak. Al1 the events displayed in Figure 1 and 2 (and 3 and 4 respectively) are registered simultaneously during the same heart beat. So mitral valve closure and aortic valve opening give the complete echocardiographic valve motion during the first heart sound. Figure 5 is a montage of Figures 3 and 4 printed on the same time frame so that the time relations between the opening and closing movements of both valves can be compared in one picture. The evaluation of the records is not always easy. In many records, important details of the tracing are missing. For the same reason, the simultaneous registration of both valves was possible in only a few cases.
% of cordiac cycle 2
4
6
8
10
i
J 0
50
100 Heart
rote
Lbeots
150 /min
200
)
Figure 6 Isovolumetric time period in theory (mitral valve closure =V, aortic valve opening =V) compared with echocardiographic measurements of both valves nonsimultaneous (mitral valve closure = 0, aortic aalve opening = 0) and simultaneous (mitral valve closure = A, aortic valve opening = a). Shaded area = mean range of aortic valve opening Ces, and mitral valve closure time (a), The hyperbolas show the percent paction of heart period. In relation to this fraction aortic valve opening times remain constant in theory or even decrease in experiment while mitral valve closure time increases with increasing heart rate during exercise.
J. Biomed.
Engng.
1980,
Vol.
2, October
283
Echocardiogroph:
H. louboeck
pressure equals 55 and 65 Torr respectively, which is taken here to indicate the moment of opening of the aortic valve. The-theoretical curves intersect at a heart rate of 140 beats/min. DISCUSSION
Besides the experimental and theoretical times of the valve motions as a function of heart rate, Figure 6 also contains for the purpose of comparison some hyperbolas representing constant fractions of the cardiac cycle. There is some scatter of the experimental data which requires explanation. However, the mean values of the measured times - here indicated roughly by two shaded strips for both valves respectively - correlate reasonably wel1 with the theoretical curves. Thus the theoretical statement of the author (Lauboeck, 1980) is experimentally confrmed: the duration of the isovolumetric contraction occupies a decreasing fraction of the cardiac cycle when the heart rate increases during exercise. Within the resolution of the equipment used, the measured isovolumetric contraction phase disappears at about the same heart rate as predicted. ,The experimental times of the mitral valve closure after the R-wave peak tend to be smaller than those predicted by the theory. This may be due to a smaller stroke volume of the present subject as compared with those investigated by Roskamm et al. (1972,1977) on which the theoretical data of Lauboeck (1980) are based. An analogous discrepanty concerning the opening of the aortic valve may also be due to rather low diastolic pressure in the aorta of the subject of this investigation. Some of the scatter of the measured times of valve motions at higher heart rates could perhaps be explained by the interruption of the exercise which was necessary to take the echocardiogram. If the peripheral resistance is increased when the heart is $ll beating fast, there should be a higher diastolic pressure in the aorta and accordingly, the aortic valve should open later. It should be noted that divergences from the mean values of the data points measured simultaneously tend to occur in the same direction and with the same magnitude for
284
J. Biomed.
Engng.
1980,
Vol.
2, October
both valves, so that the isovolumetric contraction time diverges only slightly from the mean in these cases. The delay of the mitral valve closure permits the inflow of blood into the ventricle to continue even after the ventricular contraction has begun and the pressure is rising. A certain amount of blood (- 10% of the stroke volume) stil1 enters the ventricle and increases its volume. This fact may bear consequente for the Starling mechanism: while the contractile elements are already contracting the elastic elements are stil1 being stretched more than during isovolumetric contraction. ACKNOWLEDGEMENT
The author thanks Dr. Kümmell, Intemal Medicine, Gemeinschaftskrankenhaus Herdecke, Germany, for his help in echocardiography and Dr. Kraemer, Max Planck Institute, for his advice in fluid dynamics. REFERENCES Bellhouse and Bellhouse (1975) Congress about the mitral valve. Paris 1975 Bubenheimer, P. and Roskamm, H. (1977) ‘Echokardiographie zur Beurteihmg der Arbeitswerte des linken Ventrikels mit dynamicher körperlicher Belastung.’ Sportarzt und Sportmedizin, 28,352-354 Faber, J J. (1964) ‘Origin and conduction of the mitral sound in the heart’. Chirc. Res, 14,426 Hirschfeld, St. (1976) ‘The isovolumic contraction time of the left ventricle. An echographic study’. Circulution 54, 751-756 Laniado, S., Yellin, E.L. et al. (1973) ‘Temporal relations of the first heart sound to closure of the mitral valve’. Circulation 47, 1006-1014 Lauboeck, H. (1980) ‘The conditions of mitral valve closure’. closure’. Vortrag EUROMECH 118, Zuoz 1979 J. Biomed. Engn. 2 (2), 93-96 Nolan, S.P. et al. (1969) ‘The influence of atrial contraction and mitral valve mechanics on ventricuIar filling’. Amer. Heart J. 77, 784 Roskamm, H. (1972) ‘Die Ko ntrakilitatsreserve des gesunden linken Ventrikels’. 2. Kreislaufforshung 61, 673-689 Talukder, N., Reul, H. and Mueller, E.-W. (1979) ‘Fluid mechanics of the natural mitral valve’. Euromech 118, Zuoz, Schweiz