JACC Vol. 20, No.5
November I, 1992;1143-8
1143
Relation Between Doppler Color Flow Variables and Invasively
Determined Jet Variables in Patients With Aortic Regurgitation
SHARON
c. REIMOLD, MD, JAMES D. THOMAS, MD, FACC,* RICHARD T. LEE, MD, FACC
Bosloll, Massachusetts
Objecti~·es. The purpose of this study was to test the hypothesis
that im'ash'ely derh'ed jet l'ariables including regurgitant orifice
area and momentum determine the characteristics of Doppler
color flow jets in patients with aortic regurgitation.
Background. In l'itro studies ha\'e demonstrated that the
l'elocity distribution of a regurgitant jet is best characterized by
the momentum of the jet, which incorporates orifice area and
\"elocity of flow through the orifice.
Methods. Peak jet momentum, peak flow rate and regurgitant
orifice area were determined with intraaortic Doppler catheter
and cardiac catheterization techniques in 22 patients with chronic
aortic regurgitation. These inl'asiwly derived l'ariables were
compared with apical and parasternal long·axis Doppler color
echocardiographic \'ariables obtained in the catheterization labo·
ratory.
Results. Jet momentum increased significantly with the angio·
graphic grade of regurgitation. The apical color jet area of aortic
Noninvasive quantitation of valvular regurgitation is frequently performed with Doppler color flow mapping techniques (I). Typically this evaluation is based on color jet
variables such as jet width, length or area in one or more
imaging planes (2,3). Color jet area and width have been
found to correlate with angiography, another semiquantitative method, but these variables may be affected by such
factors as orifice shape, jet eccentricity, left ventricular
chamber constraints and imaging techniques (4-7). The
color appearance of regurgitant jets depends on the distribution of velocities within the jet and, in theory, analysis of the
velocity distribution could be used to derive regurgitant
flow. To date, however, clinical use of the velocity distribution within regurgitant jets has not been successful because
From the Noninvasive Cardiac Laboratory, Cardiovascular Division,
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, and the 'Cardiac Ultrasound Laboratory, Massachusetts General
Hospital, Boston. Dr. Reimold is a recipient of a 1991-1992 American College
of Cardiology/Merck Fellowship Award. Dr. Thomas is supported in part by
the Bayer Fund for Cardiovascular Research, New York, New York. Dr. Lee
is a recipient of Physician Scientist Award HL-OI835 from the National Heart,
Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland.
Manuscript received January 30, 1992; revised manuscript received May
13, 1992, accepted May 19, 1992.
Addres5 for correspondence: Richard T. Lee, MD, Cardiovascular Division, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts 02115.
101992 by the American College of Cardiology
regurgitation increased linearly with jet momentum and regurgitant orifice area in vim, but the correlations were only moderately good (r = 0.63 and 0.65, respectively). Color jet length also
increased linearly with jet momentum and with regurgitant orifice
area. There was only a trend for Doppler color jet width to
increase with all invash'ely derh'ed jet \'ariables.
Conclusions. Whereas jet area by Doppler color flow imaging
is directly related to both orifice area and jet momentum in vh'o,
Doppler color variables measured in planes normal to the orifice
do not correlate well enough with either jet momentum or
regurgitant orifice area to predict jet flow \'ariables in patients
with aortic regurgitation. It is likely that the important influence
of adjacent boundaries will limit the use of the wlocity distribution of aortic regurgitant jets for determining the se\'erity of
disease.
(J Am Coil CardioI1992;20:1l43-8)
of technical limitations of contemporary echocardiographic
imaging equipment.
Fluid dynamics principles predict that the' velocity distribution of a jet entering a receiving chamber should be best
characterized by the momentum of the jet, a term that
incorporates orifice area and velocity of flow through the
orifice (8-10). Principles of fluid mechanics state that linear
momentum is conserved in the absence of external forces.
Thus, jet momentum determined at a plane perpendicular to
the jet axis is the same as the momentum at the orifice (II).
Thomas et al. (12) demonstrated that momentum was the jet
variable that best predicted the Doppler color flow area in an
in vitro Doppler color flow model studying axisymmetric
jets. The in vivo relation between invasive jet variables such
as momentum and Doppler color flow variables has not been
assessed in part because methods of determining jet momentum have not been readily available.
A method of estimating the regurgitant orifice area using
catheterization laboratory and echocardiographic techniques
was recently described (13). From the estimates of orifice
area and velocity of regurgitant blood flow, jet momentum
and flow rate may be calculated. The purpose of this study
was to test the hypothesis that invasively derived jet variables including regurgitant orifice area and momentum determine Doppler color echocardiographic variables in patients
with aortic regurgitation.
0735-10971921$5.00
1144
REIMOLD ET AL.
DOPPLER COLOR FLOW VARIABLES IN AORTIC REGURGITATION
Methods
Theoretic background. In aortic regurgitation, blood
flows from the aorta into the left ventricle through an orifice
of effective area A with velocity Y. The flow rate (Q) through
the area A is given as Q = A·Y. The regurgitant jet velocity
is a function of radial and axial distance from the orifice with
the Doppler transducer aligned parallel to the jet axis; the
appearance of a given jet on Doppler color flow imaging
results from this velocity distribution.
Mass, energy and momentum are transferred from the jet
into the receiving chamber (left ventricular outflow tract in
patients with aortic regurgitation). These entities are conserved and characterize the behavior of the jet. Momentum
may be defined as the product of velocity and mass flux,
which is represented as the amount of blood passing through
an area per unit of time. A change in momentum must equal
a change in forces applied to the jet. At the orifice, the axial
component of momentum (M) is defined as the product of
flow rate and axial velocity (M = Q. V). The total momentum
flow across a transverse plane orthogonal to the jet axis is
constant throughout the full jet; this is the conservation of
momentum.
Momentum may be expressed in several ways at the level
of the jet origin where plug flow is present. By combining the
continuity equation (Q = A·Y) with the basic definition for
momentum (M = Q.y):
Thus, if orifice area and the velocity of blood flow through
the orifice are known, jet momentum may be calculated.
Catheterization protocol. Patients were asked to enroll in
this study if they were undergoing cardiac catheterization to
define the severity of aortic regurgitation. Thus, all 22
patients (14 men, 8 women) underwent right and left heart
catheterization and aortography. Informed consent was obtained before the procedure in accordance with guidelines
established by the Brigham and Women's Hospital Committee for the Protection of Human Subjects From Research
Risks. A detailed description of the catheterization protocol
and calculations of the regurgitant orifice area in 20 of the
patients have been published previously (13). The angiographic grades and regurgitant orifice areas obtained from
the catheterization protocol of these patients are used in this
study for comparative purposes (13). Angiographic grading
of aortic regurgitation was performed by an angiographer
who was unaware of the Doppler echocardiographic results
(14).
Retrograde diastolic aortic flow velocities were determined with a Doppler catheter (Millar) positioned 2 cm
above the aortic valve and steadied with a guiding catheterl
wire system (13). A flexible guide wire passed through the
Doppler catheter was positioned in the left ventricular apex
to align the Doppler catheter in the ascending aorta with the
direction of regurgitant flow in the aorta. The Doppler
catheter, calibrated in an in vitro flow system, was con-
JACC Vol. 20. No.5
November 1. 1992:1143-8
nected to a photographic multichannel oscillographic recorder (Electronics for Medicine model YRI6) to display
velocity waveforms. Left ventricular pressure and central
aortic pressure tracings were obtained on the same oscillographic recorder from 7F fluid-filled catheters (13,15).
Echocardiographic protocol. Two-dimensional and Doppler echocardiograms were obtained in the catheterization
laboratory with the patient positioned in the left lateral
decubitus or supine position. All studies were performed on
a Hewlett-Packard 77020 AC/AR phased-array ultrasonographic imaging device using a 2.5-MHz transducer. Imaging
continuous wave Doppler sampling of aortic regurgitation
was recorded from the apical five-chamber or second right
intercostal space windows. The continuous wave Doppler
velocity-time integral was corrected for angle errors of> 25°
by dividing the integral by the cosine of the angle of
incidence (1 of22 patients). Doppler color flow mapping was
performed from the parasternal long-axis and apical two- and
five-chamber views. Gain settings and other imaging variables were adjusted to optimize color images and remained
constant throughout each individual study. The same Doppler color variance flow map was used for each patient.
Calculations. The diameter of the ascending aorta 2 cm
above the aortic valve was determined from the parasternal
long-axis view in early diastole at the end of the T wave, and
was measured with leading edge techniques from twodimensional images (16). Calculation of the regurgitant orifice area was based on the continuity equation (II). Thus,
Regurgitant orifice area = (VTI Dc · CSA aorta)NTl cw ,
where YTI Dc (cm) is the diastolic velocity-time integral
recorded from the Doppler catheter and digitized on an
offline analysis system, CSA aorta (cm 2) is the crosssectional area of the aorta measured 2 cm above the aortic
valve and YTI cw (cm) is the diastolic velocity-time integral
of flow through the aortic valve determined from digitizing
the continuous wave Doppler signal of aortic regurgitation.
The peak jet flow rate was calculated as
Peak jet flow rate
=
CSA aorta' Peak velocityDc.
where Peak velocitYDc (cm/s) was determined from the
diastolic aortic Doppler catheter signal. The peak jet momentum (cm 4/s2) was determined as
Peak jet momentum
= Regurgitant orifice area' (Peak velocitYcw)2,
where Peak velocitycw is the peak velocity of flow (cm/s)
determined from the continuous wave Doppler tracing.
The left ventricular outflow tract diameter was measured
beneath the aortic valve from the parasternal long-axis
window with leading edge techniques (16). Each study was
viewed frame by frame to identify abnormal diastolic color
flow in the left ventricular outflow tract originating from the
level of the aortic valve. Jets were identified early in diastole. Doppler color jet variables of jet area and length were
1145
REI MOLD ET AL.
DOPPLER COLOR FLOW VARIABLES IN AORTIC REGURGITATION
20 r-----------------------~
o
...'-" 15
E
u
......,
C
II
:t
....II
10
"o
L.
'0
(J
5
o
~
__ ____
~
o
50
determined from these apical views by digitizing three images on an offline analysis system (GTI Freeland Medical
Division). Color jet length was measured from the level of
the aortic valve to the maximal depth the color disturbance
extended into the left ventricle along a line. The Doppler
color jet width and left ventricular outflow tract diameter
were measured from the parasternal long-axis view in early
diastole. The largest of three measurements for each variable
was recorded, as previously described by Perry et al. (2).
Statistics. Relations between invasive jet variables (regurgitant orifice area, jet flow rate and jet momentum) and
Doppler jet variables (color jet area, color jet width and color
jet length) were determined by using linear regression analysis. A p value < 0.05 was considered statistically significant. The relation between jet momentum and grade of
regurgitation was determined by using Kendall rank order
testing; tau (correlation coefficient) and the p value are given
where this method was used. The Fisher Z transformation
was used to compare correlation coefficients.
__
~~
__
200
2
Momentum (em /sec • X 10
~
250
-3
)
Figure 2. Jet momentum (cm4/s2) versus color jet area (cm2) for 22
patients with aortic regurgitation. Jet momentum increased linearly
with momentum: Color jet area (cm2) = 3.7 . 10- 5 s2/cm2 . Momentum
(cm4/s2) + 3.9 cm2 (r = 0.63; p = 0.002). The regression line (solid)
and 95% confidence intervals (dotted lines) are shown.
Similar to results obtained in in vitro Doppler color flow
mapping studies (12), the abnormal apical color jet area of
aortic regurgitation increased linearly with peak jet momentum in vivo,(r = 0.63, p = 0.(02) (Fig. 2):
Color jet area (cm2)
3.7 x 10-5 s2/cm2. Momentum (cm4/s2)
=
+ 3.9 cm2•
The color jet area was also significantly related to the
regurgitant orifice area (r = 0.65, p = 0.011) (Fig. 3):
Figure 3. Regurgitant orifice area (cm2) versus color jet area (cm2) for
22 patients with aortic regurgitation. Regurgitant orifice area increased
linearly with color jet area: Color jet area (cm2) = 6.6 . regurgitant
orifice area (cm2) + 3.7 cm2 (r = 0.65; p = 0.011). The regression line
(solid) and 95% confidence intervals (dotted lines) are shown.
20
Results
An estimate of peak jet momentum based on the supravalvular diastolic aortic flow and the velocity of retrograde
blood flow through the aortic valve was obtained from each
patient by using invasive catheterization and Doppler catheter techniques. Jet momentum increased with the angiographic grade of aortic regurgitation (tau = 0.647, p <
0.00(1) (Fig. I). The peakjet momentum of patients with 1+
aortic regurgitation was estimated to be 4 to 14 X 103 cm4/s 2
and of those with 2+ aortic regurgitation was 20 to 78 x
103 cm4/s2. More severe (3 +) regurgitation was associated
with a larger range of jet momentum (25 to 158 x 103 cm4/s2).
The jet momentum for the two patients with 4+ regurgitation
was estimated as 125 to 143 x 103 cm4/s 2.
~
150
4
Angiographic Grade
Figure 1. Relation between jet momentum and angiographic grade
of aortic regurgitation. Jet momentum increases significantly with
angiographic grade (p < 0.0001).
_ L_ _ _ _
100
r-------------------------,
o
o
.....
.,c
:t
....
"
~
8
8
10
.........0............0................0 ..
I)
.···0..··0
L.
...90'.
0
.........'0
6?. . . ..
5
o
. . . . . . . .;
O~6
__ ____
~
0.00
~
0.25
- L_ _ _ _
0.50
~
____
0.75
0
~
__
1.00
Regurgitant Orifice Area (em 2)
~
1.25
REIMOLD ET AL.
DOPPLER COLOR FLOW VARIABLES IN AORTIC REGURGITATION
1146
12
...... 10
....
C'
.,
....
...,.,
Another Doppler color variable, the width of the jet
beneath the aortic valve, is theoretically directly related to
the regurgitant orifice area. There was a trend for Doppler
color jet width to increase with jet momentum, regurgitant
orifice area and flow rate (r = 0.24, p = 0.29; r = 0.32, p =
0.14; r = 0.40, p = 0.07, respectively):
0
E
~
.c
0
B
&::
Color jet width (em) = 1.1· 10- 6 s2/em 3• Momentum (em4/s2)
-I
...
0
0
0
JACC Yol. 20. No.5
November 1.1992:1143-8
6
+ 0.55 em;
Color jet width (cm)
4-
= 0.28 cm - I
. Regurgitant orifice area (cm2)
Color jet width (cm)
50
100
150
200
4
Figure 4. Jet momentum (cm /s2) versus color jet length (cm) for 22
patients with aortic regurgitation. Jet momentum increased linearly
with color jet length: Color jet length (cm) = 1.36.10-5 s2/cm3•
Momentum (cm4/s2) + 3.6 cm (r = 0.49; p = 0.021). The regression
line (solid) and 95% confidence intervals (dotted lines) are shown.
= 6.6' Regurgitant orifice area (cmz)
+ 3.7 cm z•
The peak apical color area increased with the estimated peak
flow rate (r = 0.55, p = 0.(09):
Color jet area (cmz)
= 0.008 s/cm • Peak flow rate (cm3/s)
+ 3.93 emz•
Because the peak jet momentum is equal to the product of
regurgitant orifice area and the square of the peak velocity of
blood flow through the aortic valve, these results suggest
that the primary determinant of color jet area in patients with
aortic regurgitation is the orifice area. The reason for this
observation was that the range in regurgitant orifice area
(0.04 to 1.11 cm2) was proportionately much wider than the
observed range in peak velocity (257 to 546 crnls). Modeling
the relation between color jet area and momentum as a
nonlinear function did not improve the correlation between
these variables over the range of jet momentum in these
patients.
The distance the abnormal aortic diastolic flow disturbance extends into the left ventricle may be semiquantitated
by routine pulsed Doppler velocity mapping or by measurement of the Doppler color jet length. Color jet length
increased withjet momentum (Fig. 4) and regurgitant orifice
area (r = 0.49, p = 0.021; r = 0.49, p = 0.02, respectively):
Color jet length (em) = 1.36· 10-5 sZIcm3• Momentum (cm4/sz)
+ 3.6 cm;
Color jet length (em) = 2.5 (cm- I). Regurgitant orifice area (emz)
+ 3.4 em.
= 4.86· 104 stcm2• Peak flow rate (cm3/s)
250
2
3
Momentum (cm4/sec , X 10- )
Color jet area (cmz)
+ 0.51 em;
+ 0.46 cm.
The ratio of jet width to left ventricular outflow tract
diameter, which attempts to normalize the measurement of
jet width for body surface area, also did not significantly
correlate with any of the measured invasively derived jet
variables. The addition of the velocity data to the regurgitant
orifice area data did not significantly improve the correlation
with any of the color jet variables.
Discussion
Momentum and color jet area. Momentum is a function of
the orifice area and the velocity of flow through the orifice.
In vitro Doppler color flow studies have demonstrated that
momentum is the optimal variable for predicting color jet
area (12). The curvilinear nature of the relation between
these variables, however, limits the ability to predict jet
momentum from the displayed color jet area. Even in in vitro
systems, chamber constraints exist and may alter the appearance of Doppler color flow maps (5,6). The current in
vivo study demonstrates that both regurgitant orifice area
and jet momentum increase with color jet area. The linear
relation between color jet area and orifice area or momentum
derived in this study is not ideal and precludes accurate
prediction of either regurgitant orifice area, jet momentum or
peak flow rate from the observed Doppler color jet area in
vivo. Although our data can be modeled by using a curvilinear relation, a linear model fits the data equally well for the
range of jet momentum associated with aortic regurgitant
jets in patients.
Role of surrounding structures. The primary reason that
Doppler jet variables cannot reliably predict orifice flow
variables is probably related to adjacent boundary effects. In
the case of aortic regurgitation, the jet is bounded by the
interventricular septum and mitral valve. Fluid dynamics
principles suggest that the effect of the interaction between
aortic regurgitant jets and surrounding structures on the
Doppler color appearance of the jet may vary with the
location of impingement (distance from the aortic valve at
which the jet appears to impinge on adjacent structures) as
well as with left ventricular dimensions and chamber com-
lAce Vol. 20, No.5
November I, 1992:1143-8
REIMOLD ET AL.
DOPPLER COLOR FLOW VARIABLES IN AORTIC REGURGITATION
pliance (17). Left ventricular structure and chamber geometry may affect the displayed jet in two ways: 1) actual
transfer of momentum to the wall due to jet impingement
(which makes the jet smaller overall), and 2) jet distortion
due to adjacent walls (Coanda effect), which flattens the jet,
leading to a smaller than expected jet in some projections but
a much larger jet if imaged en face (18,19).
Determinants of jet length. The depth that a regurgitant
jet extends into the receiving chamber depends in part on the
pressure gradient (driving pressure) between the proximal
and receiving chambers (5,6). Color jet length was directly
related to orifice area in this investigation, suggesting that
the intrusion distance into the left ventricle is influenced by
the regurgitant orifice size. These results support earlier
theoretic predictions that jet length is a function of momentum (12), because momentum is proportional to the product
of regurgitant orifice area and driving pressure. In usual
clinical practice, the dominant determinant of jet length, like
color jet area, is the regurgitant orifice area because this
value may range 100-fold over pathologic conditions,
whereas peak driving pressure varies no more than 4-fold
over all but the most extreme hemodynamic conditions.
Nevertheless, it is critically important that blood pressure be
. recorded at the time of echocardiographic examination to
allow proper interpretation of all Doppler aortic regurgitant
variables (including color, pulsed and continuous wave
Doppler recordings in the aortic arch) in patients undergoing
serial examinations. The color jet length may also be influenced by adjacent boundaries within the left ventricle.
Limitations of the study. Prior studies (20) have suggested
that the ratio of the short-axis color jet area to the short-axis
aortic valve cross-sectional area is a reliable index of the
severity of aortic regurgitation. Short-axis color images were
not obtained from our patients because our primary goal was
to evaluate jets in planes normal to the orifice. Because some
of the jet width measurements were obtained from the apical
view in this study, our results may not be directly comparable with those of earlier studies using only the parasternal
window (2). If the short-axis color jet area is measured
nearly at the level of the aortic valve orifice (ideally at the
level of the vena contracta), it may predict the regurgitant
orifice area and be proportional to the severity of regurgitation (20). Close to the level of the aortic orifice, orifice shape
may have a major influence on the measurement of color jet
width in apical images (7,21). In patients with eccentric jets
or with nonuniform orifices, measurement of the color jet
width beneath the aortic valve from apical or parasternal
windows may provide an unreliable estimation of the clinical
severity of regurgitation. The lack of significant correlation
between jet width and momentum or regurgitant orifice area
in our study may be due to the influence of eccentricity,
nonuniform orifice shape, or lack of adequate lateral resolution on the measurement of jet width.
Several potential limitations are inherent in both the
echocardiographic and the catheterization methods used in
this study. To calculate ascending aorta cross-sectional area,
1147
the aorta was assumed to be circular, an assumption that
may lead to small errors. Instrumentation factors may affect
Doppler color jet appearance by increasing the sensitivity to
low velocity signals (low pulse repetition frequency, high
ensemble length, low wall filter setting) or low amplitude
signals (high gain, low transducer frequency, high tissue
priority overwrite setting). Instrumentation was standardized throughout this study and should not have significantly
affected the results. General image quality and signal to
noise ratios of the backscattered ultrasound will also influence the appearance of the color jet. Because displayed jet
variables may vary throughout the cardiac cycle and from
beat to beat, an attempt was made to identify the maximaljet
dimensions from several cardiac cycles. Another potential
error relates to errors in measuring the velocity-time integral
or velocity of flow across the aortic valve by continuous
wave Doppler echocardiography. Such errors are unlikely to
have affected our results significantly because the correlation between velocity-time integrals derived from catheter
pressure recordings with the modified Bernoulli equation
and the Doppler echocardiography derived velocity-time
integrals was excellent (13).
Potential technical limitations in deriving invasive jet
variables are related to positioning of the Doppler catheter
and acquisition of velocity tracings. The Doppler catheter
was carefully positioned under the guidance of fluoroscopy
and catheter pressure tracings. At 2 cm above the aortic
valve, the recorded Doppler catheter velocity was assumed
to represent the mean velocity of retrograde blood flow
across the aorta (that is, the flow profile was relatively
blunt); this is a reasonable assumption in persons without
severe aortic dilation (aorta diameter <4.8 em.) (13). The
Millar velocimetry system uses a zero-crossing signal analysis method that may give inaccurate measurements in the
presence of turbulence. Measurement of the retrograde flow
velocity in the aorta with this technique may be complicated
by turbulence resulting from aortic stenosis. It is likely that
spectral analysis using real-time fast Fourier transform analysis would improve this technique. However, our measurements of regurgitant flow were quantitatively similar to those
obtained by Nichols et al. (22) using an electromagnetic flow
system.
Use o/the colltinuity equation to estimate the regurgitant
orifice area as described in this study assumes that all of the
regurgitant flow in the ascending aorta crosses the aortic
valve. In fact, the "retrograde volume" used in this technique includes both aortic valve regurgitant flow and diastolic coronary artery flow. Total coronary flow increases in
aortic regurgitation, but the flow pattern changes to a systolic predominance (23,24); these factors are unlikely to have
altered significantly our estimates of regurgitant orifice area.
Conclusions. The appearance of aortic regurgitant jets on
Doppler color flow imaging is primarily determined by three
factors: I) jet momentum, 2) instrumentation factors, and
3) receiving chamber geometry. For a completely free jet
with perfect imaging, the displayed jet area is a linear
1148
REIMOLD ET AL.
DOPPLER COLOR FLOW VARIABLES IN AORTIC REGURGITATION
function of the peak jet momentum, a variable that is a
function of regurgitant orifice area and peak jet velocity. The
displayed appearance of an aortic regurgitant jet may be
altered by instrumentation factors or affected by chamber
geometry.
Jet momentum increases with angiographic grade of regurgitation, suggesting that this variable is related to the
severity of regurgitation. Unfortunately, Doppler color flow
imaging variables measured in planes normal to the orifice do
not correlate well enough with either jet momentum or
regurgitant orifice area to allow confident estimation of any
invasive jet variable. Any technique, such as echocardiography or the signal void technique of magnetic resonance
imaging, that quantitates the severity of aortic regurgitation
on the basis of an abnormal velocity distribution within the
left ventricle may be influenced by boundary conditions (25).
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