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Assessment of aortic regurgitation by means of pulsed Doppler ultrasound
Ultrasound in Med. & Biol., Vol.8, No. I, pp. I-5, 1982
0301-5629/82/010001-05503.00/0 Pergamon Press Ltd.
Printed in Great Britain.
ASSESSMENT OF AORTIC REGURGITATION BY MEANS OF PULSED DOPPLER ULTRASOUND K JELL HATTELAND and BJARNE K. H. SEMB Department of Thoracic and Cardiovascular Surgery, The National Hospital of Norway, Oslo, Norway (First received 28 July 1980; and in final form 24 March 1981)
Abstract--A comparison of aortic regurgitation ratios measured by pulsed Doppler ultrasound techniques and electromagnetic flowmetry was performed. The ultrasonic measurements were made preoperatively in the aortic arch, and the electromagnetic measurements preoperatively on the ascending aorta. Through mathematical correction for aortic arch flow characteristics, preoperative ultrasonic Doppler measurements in this area demonstrated a fairly close relationship to the aortic valve regurgitation volume determined by electromagnetic flowmetry on the ascending aorta intraoperatively. Kew words: Aortic insufficiency, Valve regurgitation, Doppler, Ultrasound.
INTRODUCTION
Establishing measuring procedures for the assessment of aortic regurgitation by means of noninvasive pulsed Doppler techniques would appear to be of considerable importance, because such measurements are easy to perform without discomfort to the patient. However, considerable difficulties have been encountered by various investigators when attempting to quantify aortic regurgitation by Doppler techniques in the clinical situation (Boughner, 1975; Brubakk et aL, 1977; Ward et al., 1977). The main purpose of the present investigation was to more closely define the feasibility of using Doppler ultrasound techniques in the clinical diagnosis of aortic valve insufficiency and to suggest methods for numerical quantification of the degree of transvalvular regurgitation. The most reasonable method of quantifying the regurgitated volume appears to be the percentage-wise leakage across the valve, establishing the fractional part of the stroke volume (cm 2) leaking through the valve into the left ventricle during diastole. If the stroke volume is denoted Vs and the regurgitated volume Vd, the regurgitation ratio can be expressed as Vd r = Vs"
(1)
Ideally Vd and Vs should be measured in the immediate vicinity of the valve orifices. This can hardly be achieved in the clinical situa-
tion. In the present study the ultrasonic measurements, therefore, were made in the aortic arch, where correction for bloodloss to the brain, upper extremities and the coronaries has to be made. Equation (1) therefore was modified to r=
V d m - Vdo V s m + Vso
(2)
where V d m is the measured diastolic regurgitati'on in the aortic arch; Vdo is the diastolic dissipated volume of the cerebral- and coronary circulation and upper extremities; V s m is the measured stroke volume in the aortic arch; and Vso is the ejected volume to the brain and upper extremities during systole. As a control parameter electromagnetic measurements of regurgitation were made in the ascending aorta at the time of operation. Because of the elasticity of the ascending aorta electromagnetic flow measurements might underestimate the regurgitation ratio of the aortic valve. This is so because due to the increasing pressure during systole the aorta will partially store the stroke volume, releasing the same volume during diastole at the time of pressure decrease. Thus, electromagnetic measurements on the ascending aorta might, therefore, suggest too small regurgitated volumes across the valve. In the present investigation no attempt was made to establish the elastic capacity of the ascending aorta between the aortic valve and the position of the electromagnetic probe, although particular attention was given to a jux-
K. HATTERLAND and B. K. H. SEMB
tavalvular positioning of the electromagnetic probe generally at a distance of five centimeters from the valve. THE DOPPLER MEASUREMENTS
A newly developed Doppler instrument, Unidop (Hatteland and Eriksen, 1980) was used for the noninvasive determination of the mean blood velocity in the aortic arch. The instrument was operated in the 1.5 MHz, pulsed mode, and a Doppler probe sufficiently large to cover the central part of the aortic lumen was used (diameter, 15 ram). Pulsed operation was preferred to the continuous mode for several reasons. Most important was perhaps that the pulsed Doppler mode enabled depth discrimination, with the possibility of eliminating disturbances from vessels close to the measuring point. Pulsed operation also utilized the whole area of the probe crystals for alternating transmittance and reception. This produced a more uniform illumination of the vessel which was of particular importance if the mean velocity over the area was to be computed. The pulsed operation gave an increased signal to total noise ratio with regard to electronic noise (white noise) generated by the Doppler instrument, due to stronger low-pass filtration in the pulsed mode. Also pulsed Doppler tends to pick up a lower level of noise generated by micro-gaseous bubbles in the ultrasonic gel and disturbing Doppler frequencies from slowly moving tissues. This is due to the fact that a continuous Doppler picks up signals from every moving target lying in the ultrasonic field along the probe axis. Signals from moving tissues (vessel walls) often are of high amplitudes compared to Doppler spectrum, these components will cause an underestimation of the mean velocity. However, pulsed operation excluded the possibility of measuring high velocities (for Unidop above 1.5m/sec). For this reason only pure aortic insufficiency was studied since a concomitant valve stenosis easily could cause jets or turbulences of higher velocities than 1.5 m/sec. When knowing the shape of the mean velocity, the volumetric translocation during a given time interval of t(sec) could be calculated from V(cm3) = fo' A(cm2)Vmea"(cm/sec)dt
(3)
where A(cm 2) is the area of the vessel, and
Vmean(Cm/sec) is the mean velocity across the area A. According to equation 3, 2 could be modified denoting As as the mean effective systolic area of the aortic arch, and Ad a s the mean effective diastolic area of the aortic arch
Ad r= As
f f
diast
v mean d t - Vdo (4)
syst
v mean dt + Vso
In this manner, equation 2 was modified to an expression involving measurements of velocity rather than flow as done with an electromagnetic flowmeter. However, certain precautions had to be taken. As indicated, two different "effective areas" of the systole and diastole were used. The term, effective area, as used in equation 4, denoted the value which multiplied with the measured velocity gave the true volumetric flow. When the velocity vector was perpendicular to the crossectional area and the Doppler beam (probe axis) was parallel to the velocity vector, the effective area corresponded to the crossectional area. In the aortic arch, however, this relationship will inevitably be influenced by variations of the flow pattern due to the curved course of the vessel and to deviation of flow through vessel branches. Figure 4 shows a typical measuring situation of the aortic arch, denoting a: angle between velocity vector and normal vector of the crossectional area A,/3: angle between velocity vector and probe axis. Since the Doppler instrument only reflects velocity components parallel to the probe axis, and volumetric flow is crossectionai area A times velocity component normal to the surface, the flow is given by COS ot
Q = A " V.. cos/3 =At
V~
where Vm is the mean velocity measured by the Doppler instrument. In order to establish a more appropriate expression for the quantification of aortic regurgitation, equation 4 was modified to compensate for measuring errors due to limitations in the pulsed Doppler instrument as well as errors caused by unknown factors like cerebral and upper extremity flow during systole (Vso) and diastole (Vdo). In the present study, the measuring errors related to the
Assessment of aortic regurgitationby means of pulsed Doppler ultrasound Doppler instrumentation was affected by several variables. Thus, the degree of uniform illumination of the aorta would influence the accuracy of the mean velocity tracings. Also, the electronic design of vital parts of the Doppler instrument, as for instance,the highpass (HP) filter circuits would affect the signal/noise ratio and the concept of the mean velocity estimator might alter the overall accuracy. Hence, switchable HPfilters set too low, will underestimate the mean velocity, not discriminating signals from slowly moving tissues in the listening area of the instrument. HP-filters set too high, will overestimate the mean velocity compared to the blood velocities, due to removal of the lower Doppler spectrum components, generated from the blood itself and from slowly moving tissues. These considerations were taken into account in the technology of the Doppler instrument used. When assuming that the flow of the aortic arch was greatly turbulent, with all frequencies of the same amplitude, an overestimation of the mean velocity of half the band width of the HP-filter was made. As these errors were greater at smaller mean velocity values, they were of particular significance during measurements throughout diastole. Assuming that these errors were fairly constant, it was possible to incorporate the adjustment of the unknown V,~o. If Vsa was incorporated as a fraction (C+ 1) of the stroke volume, no major change of the denominator value in equation 4 was essential. These assumptions led to a favorable expression of regurgitation ratios where
Ad r.~.m
f
diast
v mean dt
cas /-jsyst v mean dt Vdo cAs
f
syst
v mean dt
or
r - ~ I a r u l - If
where ru~ is the measured regurgitation from velocity wave forms; Ia is the index for area variation of the aortic arch; and Ir is the flow index for bloodloss to the brain, coronaries and upper extremities.
3
CLINICAL MEASUREMENTS
In order to establish the feasibility of measuring aortic regurgitation by means of ultrasonic Doppler instruments, a comparison of invasive electromagnetic flow patterns and noninvasive ultrasonic velocity patterns was performed. None of the patients had aortic stenosis, ensuring that the velocities of the aorta were below the upper limit for pulsed Doppler measurements. The patients were placed in a supine position and the Doppler probe was positioned in the suprasternal notch. Both the depth setting and direction of ultrasonic beam were carefully adjusted to maximum deflection of the mean velocity estimator. This indicated a measuring volume of the Doppler where the vessel wall was parallel to the probe axis, ensuring maximum signal amplitude from the blood and minimum signal amplitude from wall motion. In this position, shifting of the high pass filter caused only a slight change of the peak mean of the velocity during systole. The ultrasonic measurements were made preoperatively. The electromagnetic measurements were performed during the initial part of the operation prior to handling of the heart. The measurements were performed in eight patients. A typical velocity pattern for small and large degrees of aortic valve regurgitation as measured by Doppler techniques is demonstrated in (Fig. la, b). The interpretation of these Doppler tracings requires some fundamental understanding of the measuring procedure and the flow/pressure relationship in the aorta. In the presence of minor regurgitation a fiat waveform of the mean velocity is common during diastole, due to the moderate pressure drop during this part of the cardiac cycle. In the presence of higher regurgitation volumes, larger pressure fluctuations occur producing a more triangular form of the diastolic velocity curve. In early s y s t o l e and diastole the Doppler measurements are considerably affected both by rigid wall motion and movements of the total aorta. Wall motion tends to reduce the mean velocity towards zero because of the addition of lower frequency components with high amplitude to the Doppler spectrum. In Fig. l(a), a wall motion artifact has been indicated during early systole and aortic movements are depicted during early diastole. The actual areas used for calculation of the regurgitation ratios were also indicated. The corresponding findings in the presence of
K. HATTELANDand B. K. H. SEMB ULTRASONIC
Fig. l(a). Expected velocity profile when a small degree of aortic regurgitation exists. Notice aortic wall artifact in early systole, below ascending interrupted line.
ELECTROMAGNETIC # I
Fig. l(b). Expected velocity profile for a more pronounced degree of aortic regurgitation with a more triangular velocity profile during diastole.
Fig. 2(a). Examples of ultrasonic and electromagnetic printouts for a small regurgitation volume. Regurgitation ratio: r ~0.25.
larger regurgitation ratios were depicted in Fig. l(b). Figure 2(a) demonstrates a comparison between a typical ultrasonic and electromagnetic flow pattern in mild aortic insufficiency whereas, Fig. 2(b) shows a similar comparison in a patient with a more pronounced degree of valve regurgitation. Regurgitation ratios were determined from the relationship between calculated areas during systole and diastole. Figure 3 demonstrates the relationship between the regurgitation ratio rul and the corresponding electromagnetic regurgitation re,, when plotted vs each other. Regression analysis of the values for elasticity and flow index gave Ia ~ 1 . I / t ~ +0.05.
ULTRASONIC
'1
~ELECT~O_I~AGN ET I C
CONCLUSION
Although ultrasonic and electromagnetic measurements of aortic regurgitation were not performed simultaneously, the results from these determinations reflected a close relationship of aortic valve insufficiency in the individual patients. Through simple mathematical correction for flow distribution in the aortic arch, a near linear relationship
Fig. 2(b). Examples of measurements made with a higher regurgitation ratio, r ~- 0.35.
Assessment of aortic regurgitation by means of pulsed Doppler ultrasound
.7
rein .6 .5 .4 .3 .2 .1
.I
.2
.3
./,
.5
.{5
.7
rut
Fig. 3. Comparison between he ultrasonic regurgitation ratio r.~ and its electromagnetic equivalent rein.
~
~
~D.[r06° ~
t I area:A
Fig. 4. Geometrical configuration for the ultrasonic measurement of blood velocity in the aortic arch.
was derived between the Doppler regurgitation ratio measured in the aortic arch and the electromagnetic regurgitation ratio measured in the ascending aorta. Certain difficulties were, however, encountered in the performance of the Doppler measuring procedure and also in the interpretation of the mean velocity tracings. Thus, it was surprising to find that the area index Ia of these measurements was given a value greater than one, indicating a larger effective area of the aortic arch during diastole than during systole. Judged by our present findings it appears likely to assume that ultrasonic detection and quantification of aortic valve regurgitation is possible for clinical purposes. However, further investigation has to be performed to
substantiate our preliminary findings with particular reference to the ultrasonic Doppler measurement procedure and the interpretation of the mean velocity tracings.
REFERENCES Boughner, D. R. (1975) Assessment of aortic insufficiency by transcutaneous Doppler ultrasound. Circulation $2, 874--879. Brubakk, A. O., Angelsen, B. A. J. and Hatle, L. (1977) Diagnosis of valvular heart disease using transcutaneous Doppler ultrasound. Cardiovasc. Res. II, 461-469. Hatteland, K. and Eriksen, M. (1981) A heterodyne ultrasound blood velocity meter. Med. & Biol. Engng & Comput. 19, 91-96. Ward, J. M., Baker, D. W., Rubenstein, S. A. and Johnson, S. L. (1977) Detection of aortic insufficiency by pulsed Doppler echocardiography. J. Clin. Ultrasound. 5, 5-10.
0301-5629/82/010001-05503.00/0 Pergamon Press Ltd.
Printed in Great Britain.
ASSESSMENT OF AORTIC REGURGITATION BY MEANS OF PULSED DOPPLER ULTRASOUND K JELL HATTELAND and BJARNE K. H. SEMB Department of Thoracic and Cardiovascular Surgery, The National Hospital of Norway, Oslo, Norway (First received 28 July 1980; and in final form 24 March 1981)
Abstract--A comparison of aortic regurgitation ratios measured by pulsed Doppler ultrasound techniques and electromagnetic flowmetry was performed. The ultrasonic measurements were made preoperatively in the aortic arch, and the electromagnetic measurements preoperatively on the ascending aorta. Through mathematical correction for aortic arch flow characteristics, preoperative ultrasonic Doppler measurements in this area demonstrated a fairly close relationship to the aortic valve regurgitation volume determined by electromagnetic flowmetry on the ascending aorta intraoperatively. Kew words: Aortic insufficiency, Valve regurgitation, Doppler, Ultrasound.
INTRODUCTION
Establishing measuring procedures for the assessment of aortic regurgitation by means of noninvasive pulsed Doppler techniques would appear to be of considerable importance, because such measurements are easy to perform without discomfort to the patient. However, considerable difficulties have been encountered by various investigators when attempting to quantify aortic regurgitation by Doppler techniques in the clinical situation (Boughner, 1975; Brubakk et aL, 1977; Ward et al., 1977). The main purpose of the present investigation was to more closely define the feasibility of using Doppler ultrasound techniques in the clinical diagnosis of aortic valve insufficiency and to suggest methods for numerical quantification of the degree of transvalvular regurgitation. The most reasonable method of quantifying the regurgitated volume appears to be the percentage-wise leakage across the valve, establishing the fractional part of the stroke volume (cm 2) leaking through the valve into the left ventricle during diastole. If the stroke volume is denoted Vs and the regurgitated volume Vd, the regurgitation ratio can be expressed as Vd r = Vs"
(1)
Ideally Vd and Vs should be measured in the immediate vicinity of the valve orifices. This can hardly be achieved in the clinical situa-
tion. In the present study the ultrasonic measurements, therefore, were made in the aortic arch, where correction for bloodloss to the brain, upper extremities and the coronaries has to be made. Equation (1) therefore was modified to r=
V d m - Vdo V s m + Vso
(2)
where V d m is the measured diastolic regurgitati'on in the aortic arch; Vdo is the diastolic dissipated volume of the cerebral- and coronary circulation and upper extremities; V s m is the measured stroke volume in the aortic arch; and Vso is the ejected volume to the brain and upper extremities during systole. As a control parameter electromagnetic measurements of regurgitation were made in the ascending aorta at the time of operation. Because of the elasticity of the ascending aorta electromagnetic flow measurements might underestimate the regurgitation ratio of the aortic valve. This is so because due to the increasing pressure during systole the aorta will partially store the stroke volume, releasing the same volume during diastole at the time of pressure decrease. Thus, electromagnetic measurements on the ascending aorta might, therefore, suggest too small regurgitated volumes across the valve. In the present investigation no attempt was made to establish the elastic capacity of the ascending aorta between the aortic valve and the position of the electromagnetic probe, although particular attention was given to a jux-
K. HATTERLAND and B. K. H. SEMB
tavalvular positioning of the electromagnetic probe generally at a distance of five centimeters from the valve. THE DOPPLER MEASUREMENTS
A newly developed Doppler instrument, Unidop (Hatteland and Eriksen, 1980) was used for the noninvasive determination of the mean blood velocity in the aortic arch. The instrument was operated in the 1.5 MHz, pulsed mode, and a Doppler probe sufficiently large to cover the central part of the aortic lumen was used (diameter, 15 ram). Pulsed operation was preferred to the continuous mode for several reasons. Most important was perhaps that the pulsed Doppler mode enabled depth discrimination, with the possibility of eliminating disturbances from vessels close to the measuring point. Pulsed operation also utilized the whole area of the probe crystals for alternating transmittance and reception. This produced a more uniform illumination of the vessel which was of particular importance if the mean velocity over the area was to be computed. The pulsed operation gave an increased signal to total noise ratio with regard to electronic noise (white noise) generated by the Doppler instrument, due to stronger low-pass filtration in the pulsed mode. Also pulsed Doppler tends to pick up a lower level of noise generated by micro-gaseous bubbles in the ultrasonic gel and disturbing Doppler frequencies from slowly moving tissues. This is due to the fact that a continuous Doppler picks up signals from every moving target lying in the ultrasonic field along the probe axis. Signals from moving tissues (vessel walls) often are of high amplitudes compared to Doppler spectrum, these components will cause an underestimation of the mean velocity. However, pulsed operation excluded the possibility of measuring high velocities (for Unidop above 1.5m/sec). For this reason only pure aortic insufficiency was studied since a concomitant valve stenosis easily could cause jets or turbulences of higher velocities than 1.5 m/sec. When knowing the shape of the mean velocity, the volumetric translocation during a given time interval of t(sec) could be calculated from V(cm3) = fo' A(cm2)Vmea"(cm/sec)dt
(3)
where A(cm 2) is the area of the vessel, and
Vmean(Cm/sec) is the mean velocity across the area A. According to equation 3, 2 could be modified denoting As as the mean effective systolic area of the aortic arch, and Ad a s the mean effective diastolic area of the aortic arch
Ad r= As
f f
diast
v mean d t - Vdo (4)
syst
v mean dt + Vso
In this manner, equation 2 was modified to an expression involving measurements of velocity rather than flow as done with an electromagnetic flowmeter. However, certain precautions had to be taken. As indicated, two different "effective areas" of the systole and diastole were used. The term, effective area, as used in equation 4, denoted the value which multiplied with the measured velocity gave the true volumetric flow. When the velocity vector was perpendicular to the crossectional area and the Doppler beam (probe axis) was parallel to the velocity vector, the effective area corresponded to the crossectional area. In the aortic arch, however, this relationship will inevitably be influenced by variations of the flow pattern due to the curved course of the vessel and to deviation of flow through vessel branches. Figure 4 shows a typical measuring situation of the aortic arch, denoting a: angle between velocity vector and normal vector of the crossectional area A,/3: angle between velocity vector and probe axis. Since the Doppler instrument only reflects velocity components parallel to the probe axis, and volumetric flow is crossectionai area A times velocity component normal to the surface, the flow is given by COS ot
Q = A " V.. cos/3 =At
V~
where Vm is the mean velocity measured by the Doppler instrument. In order to establish a more appropriate expression for the quantification of aortic regurgitation, equation 4 was modified to compensate for measuring errors due to limitations in the pulsed Doppler instrument as well as errors caused by unknown factors like cerebral and upper extremity flow during systole (Vso) and diastole (Vdo). In the present study, the measuring errors related to the
Assessment of aortic regurgitationby means of pulsed Doppler ultrasound Doppler instrumentation was affected by several variables. Thus, the degree of uniform illumination of the aorta would influence the accuracy of the mean velocity tracings. Also, the electronic design of vital parts of the Doppler instrument, as for instance,the highpass (HP) filter circuits would affect the signal/noise ratio and the concept of the mean velocity estimator might alter the overall accuracy. Hence, switchable HPfilters set too low, will underestimate the mean velocity, not discriminating signals from slowly moving tissues in the listening area of the instrument. HP-filters set too high, will overestimate the mean velocity compared to the blood velocities, due to removal of the lower Doppler spectrum components, generated from the blood itself and from slowly moving tissues. These considerations were taken into account in the technology of the Doppler instrument used. When assuming that the flow of the aortic arch was greatly turbulent, with all frequencies of the same amplitude, an overestimation of the mean velocity of half the band width of the HP-filter was made. As these errors were greater at smaller mean velocity values, they were of particular significance during measurements throughout diastole. Assuming that these errors were fairly constant, it was possible to incorporate the adjustment of the unknown V,~o. If Vsa was incorporated as a fraction (C+ 1) of the stroke volume, no major change of the denominator value in equation 4 was essential. These assumptions led to a favorable expression of regurgitation ratios where
Ad r.~.m
f
diast
v mean dt
cas /-jsyst v mean dt Vdo cAs
f
syst
v mean dt
or
r - ~ I a r u l - If
where ru~ is the measured regurgitation from velocity wave forms; Ia is the index for area variation of the aortic arch; and Ir is the flow index for bloodloss to the brain, coronaries and upper extremities.
3
CLINICAL MEASUREMENTS
In order to establish the feasibility of measuring aortic regurgitation by means of ultrasonic Doppler instruments, a comparison of invasive electromagnetic flow patterns and noninvasive ultrasonic velocity patterns was performed. None of the patients had aortic stenosis, ensuring that the velocities of the aorta were below the upper limit for pulsed Doppler measurements. The patients were placed in a supine position and the Doppler probe was positioned in the suprasternal notch. Both the depth setting and direction of ultrasonic beam were carefully adjusted to maximum deflection of the mean velocity estimator. This indicated a measuring volume of the Doppler where the vessel wall was parallel to the probe axis, ensuring maximum signal amplitude from the blood and minimum signal amplitude from wall motion. In this position, shifting of the high pass filter caused only a slight change of the peak mean of the velocity during systole. The ultrasonic measurements were made preoperatively. The electromagnetic measurements were performed during the initial part of the operation prior to handling of the heart. The measurements were performed in eight patients. A typical velocity pattern for small and large degrees of aortic valve regurgitation as measured by Doppler techniques is demonstrated in (Fig. la, b). The interpretation of these Doppler tracings requires some fundamental understanding of the measuring procedure and the flow/pressure relationship in the aorta. In the presence of minor regurgitation a fiat waveform of the mean velocity is common during diastole, due to the moderate pressure drop during this part of the cardiac cycle. In the presence of higher regurgitation volumes, larger pressure fluctuations occur producing a more triangular form of the diastolic velocity curve. In early s y s t o l e and diastole the Doppler measurements are considerably affected both by rigid wall motion and movements of the total aorta. Wall motion tends to reduce the mean velocity towards zero because of the addition of lower frequency components with high amplitude to the Doppler spectrum. In Fig. l(a), a wall motion artifact has been indicated during early systole and aortic movements are depicted during early diastole. The actual areas used for calculation of the regurgitation ratios were also indicated. The corresponding findings in the presence of
K. HATTELANDand B. K. H. SEMB ULTRASONIC
Fig. l(a). Expected velocity profile when a small degree of aortic regurgitation exists. Notice aortic wall artifact in early systole, below ascending interrupted line.
ELECTROMAGNETIC # I
Fig. l(b). Expected velocity profile for a more pronounced degree of aortic regurgitation with a more triangular velocity profile during diastole.
Fig. 2(a). Examples of ultrasonic and electromagnetic printouts for a small regurgitation volume. Regurgitation ratio: r ~0.25.
larger regurgitation ratios were depicted in Fig. l(b). Figure 2(a) demonstrates a comparison between a typical ultrasonic and electromagnetic flow pattern in mild aortic insufficiency whereas, Fig. 2(b) shows a similar comparison in a patient with a more pronounced degree of valve regurgitation. Regurgitation ratios were determined from the relationship between calculated areas during systole and diastole. Figure 3 demonstrates the relationship between the regurgitation ratio rul and the corresponding electromagnetic regurgitation re,, when plotted vs each other. Regression analysis of the values for elasticity and flow index gave Ia ~ 1 . I / t ~ +0.05.
ULTRASONIC
'1
~ELECT~O_I~AGN ET I C
CONCLUSION
Although ultrasonic and electromagnetic measurements of aortic regurgitation were not performed simultaneously, the results from these determinations reflected a close relationship of aortic valve insufficiency in the individual patients. Through simple mathematical correction for flow distribution in the aortic arch, a near linear relationship
Fig. 2(b). Examples of measurements made with a higher regurgitation ratio, r ~- 0.35.
Assessment of aortic regurgitation by means of pulsed Doppler ultrasound
.7
rein .6 .5 .4 .3 .2 .1
.I
.2
.3
./,
.5
.{5
.7
rut
Fig. 3. Comparison between he ultrasonic regurgitation ratio r.~ and its electromagnetic equivalent rein.
~
~
~D.[r06° ~
t I area:A
Fig. 4. Geometrical configuration for the ultrasonic measurement of blood velocity in the aortic arch.
was derived between the Doppler regurgitation ratio measured in the aortic arch and the electromagnetic regurgitation ratio measured in the ascending aorta. Certain difficulties were, however, encountered in the performance of the Doppler measuring procedure and also in the interpretation of the mean velocity tracings. Thus, it was surprising to find that the area index Ia of these measurements was given a value greater than one, indicating a larger effective area of the aortic arch during diastole than during systole. Judged by our present findings it appears likely to assume that ultrasonic detection and quantification of aortic valve regurgitation is possible for clinical purposes. However, further investigation has to be performed to
substantiate our preliminary findings with particular reference to the ultrasonic Doppler measurement procedure and the interpretation of the mean velocity tracings.
REFERENCES Boughner, D. R. (1975) Assessment of aortic insufficiency by transcutaneous Doppler ultrasound. Circulation $2, 874--879. Brubakk, A. O., Angelsen, B. A. J. and Hatle, L. (1977) Diagnosis of valvular heart disease using transcutaneous Doppler ultrasound. Cardiovasc. Res. II, 461-469. Hatteland, K. and Eriksen, M. (1981) A heterodyne ultrasound blood velocity meter. Med. & Biol. Engng & Comput. 19, 91-96. Ward, J. M., Baker, D. W., Rubenstein, S. A. and Johnson, S. L. (1977) Detection of aortic insufficiency by pulsed Doppler echocardiography. J. Clin. Ultrasound. 5, 5-10.