Journal of Cardiology (2010) 56, 97—110

available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/jjcc

Original article

Spiral systolic blood ﬂow in the ascending aorta andaortic arch analyzed by echo-dynamography
Motonao Tanaka (MD, FJCC) a,∗, Tsuguya Sakamoto (MD, FJCC) b,
Shigeo Sugawara (MD, FJCC) a, Hiroyuki Nakajima (RMS) a,
Takeyoshi Kameyama (MD) a, Yoshiaki Katahira (MD) a,
Shigeo Ohtsuki (PhD) c, Hiroshi Kanai (PhD) da

Cardiovascular Center, Tohoku Welfare Pension Hospital, Fukumuro 1-12-1, Miyagino-ku, Sendai, 983-0005, Japan
Hanzohmon Hospital, Kojimachi 1-14, Chiyoda-ku, Tokyo 102-0083, Japanc
Institute of Medical Ultrasound Technology, Yokoyama 2-12-15, Sagamihara252-0242, Japand
Department of Electrical Engineering, Tohoku University, Aramaki-Aoba6-6-05, Aoba-ku, Sendai 980-8579, Japanb

Received 9 February 2010; accepted 8 March 2010
Available online 13 May 2010

KEYWORDS
Flow structure;
Twisted spiral ﬂow;
Vorticity;
Changing
acceleration of theﬂow direction;
Velocity vector
distribution;
Ascending aorta;
Echo-dynamography

Summary Using echo-dynamography, systolic blood ﬂow structure in the ascending aorta andaortic arch was investigated in 10 healthy volunteers. The blood ﬂow structure was analyzed
based on the two-dimensional (2D) and 1D velocity vector distributions, changing accelerationof ﬂow direction (CAFD), vorticity distribution, and Doppler pressure distribution. To justify
the results obtained in humans, in vitro experiments were done using straight and curved tube
models of 20 mm diameter.
The distribution of the CAFD showed a spiral staircase pattern along the ﬂow axis line. In
addition, the changes in the velocity proﬁle in the short-axis direction, 2D distribution of thevorticity, and velocity vector distribution on the aortic cross-section plane, all conﬁrmed thepresence of systolic twisted spiral ﬂow rotating clockwise toward the peripheral part of theascending aorta.
The rotation cycle of this spiral ﬂow correlated inversely with the maximum velocity of theaortic ﬂow, so that this cycle was shorter in early systole and longer in late systole. The modelexperiments showed similar results.
The spiral ﬂow seemed to be produced by several factors: (i) anterior shift of the directionof ejected blood ﬂow due to the anterior displacement of the projection of the aorta; (ii)accelerated high pressure ﬂow ejected antero-upward; (iii) inertia resistance at the peripheral
boundary of the sinus of Valsalva; and (iv) reﬂection caused by the concave spherical structureof the inner surface of the basal part of the aorta.

∗ Corresponding author. Tel.: +81 22 719 5161; fax: +81 22 719 5166.

E-mail address: m.tanaka@jata-miyagi.org (M. Tanaka).
0914-5087/$ — see front matter © 2010 Japanese College of Cardiology. Published by Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.jjcc.2010.03.008

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M. Tanaka et al.
Because the main spiral ﬂow axis line nearly coincided with the center line of the aorta, it isconcluded that the occurrence of the spiral ﬂow plays an important role in maintaining the bloodﬂow direction passing through the cylindrical curved aortic arch and thus in keeping the mosteffective ejection as well as in dispersing the shear stress in the aortic wall.
© 2010 Japanese College of Cardiology. Published by Elsevier Ireland Ltd. All rights reserved.

Introduction
The structure of the accelerated blood ﬂow accompanying
high pressure in the ascending aorta during the very shortejection period seems to be complicated because of the speciﬁc truncal anatomy of the aorta and the cylindrical curved
structure of the inner surface of the aortic arch.
Accordingly, the blood ﬂow structure and the ﬂow
dynamics have been of interest in both clinical [1,2] andexperimental [3—5] ﬁelds including computer simulation[6,7]. However, the ﬂow structure in the aorta in a humanbeing [8] has not been deﬁnitely clariﬁed because of the lackof a suitable technique for measuring the ﬂow structure.
Recently, magnetic resonance imaging (MRI) [9] and thecolor Doppler method [10] have been proposed to measure
the aortic ﬂow. The former disclosed the helical ﬂow [9],but the spatial resolution (ca 8—10 mm) is not enough foraccurate measurement. The ultrasonic method has difﬁcultyin obtaining the velocity as the vector.
In the present study, echo-dynamography [9—12] wasutilized to investigate the ﬂow structure in the ascending aorta and aortic arch and to disclose the speciﬁccharacteristics.

Subjects and methods
Subjects
Ten presumably healthy adult volunteers aged from 20 to 50
years were the subjects of this study.

Methods
Analysis of the human blood ﬂow structure in the left
ventricle and aorta: in vivo study
Acquisition of the ﬂow velocity data by ultrasound. Commercially available ultrasonic equipment (model 6500, Aloka
Co., Tokyo, Japan) was used. The ultrasonic frequency
was 3 MHz, and supine or left lateral decubitus position
was selected. Two-dimensional (2D) echocardiograms wererecorded whenever 2D sector scan with transthoracic apicalor parasternal approach was required. The most advantageous long axis was selected to analyze blood ﬂow in theventricle, and the longitudinal section to the ascending
aorta including the anterior part of the aortic arch was also
selected.
After the 2D Doppler velocity data were recorded, all
the data were transferred to a personal computer throughmagneto-optical disk memory. The Doppler ﬂow velocity
data were processed off-line by using software for echodynamography [11].
Detection of blood ﬂow velocity vector and its representation. The orthogonal velocity component to the ultrasonicbeam direction was deduced from the Doppler velocity data

by using the ﬂow function theory [11,13] of ﬂuid mechanics[14]. Then, the 2D distribution of ﬂow velocity vector in various points was calculated from the 2 velocity components,
the one that was in the beam direction and the other, in theorthogonal direction.
The magnitude of the velocity vector was shown by thelength of a yellow line and the standard length of the vector
as a reference (20 cm/s etc.) at the left upper corner ofthe screen. The direction of the vector was indicated by the
inclination of a yellow line with a red mark at the tip.
The blood ﬂow velocity vector overlapped with 2D
echocardiogram was depicted by the following 5 display
manners.
(i) 2D distribution of the vector overlapped with 2D
echocardiogram (Fig. 1, left),(ii) 1D distribution of the vector overlapped with 2D
echocardiogram to display (a) and (b); i.e.
(a) velocity vector on the central axis line of the aorta
displayed perpendicularly to the center line of theaorta (Fig. 2, right),(b) the vector on the central axis line along this line
(Fig. 2, left).
(iii) 2D distribution of the velocity vector on the short-axis
cross-section plane (Fig. 1, right)(iv) velocity proﬁle in the short-axis direction of the aorta(Fig. 3)
Measurement of the vorticity and its representation. To
observe the various eddy components involved in theejected blood ﬂow, the vorticity (ω) [14] was calculated
from the rotation of the ﬂow velocity vector in many
places on the scanning plane and overlapped with 2D
echocardiogram by color (Fig. 6, left). The positive vorticity was shown by warm color and the negative one by cold
color.
Measurement of the 2D distribution of the changing acceleration of ﬂow direction. The information regarding theeffect of the shape and structure of the aortic pathway to
instantaneously changing blood ﬂow direction was obtained
quantitatively to estimate the ﬂow structure and ﬂow
dynamics. The product of the vorticity (ω) and the velocity vector (v), which is deﬁned as ‘‘changing acceleration of
ﬂow direction (CAFD) (v · ω)’’ was calculated [15].
From the 2D distribution of this acceleration and the 1D
distribution in the central line of the aorta, characteristicsof the ﬂow structure in the aorta were analyzed. The magnitude of the acceleration vector was indicated by the lengthof a blue line, and the direction was shown by the inclinationof the vector having a red mark at the tip.
Measurement of the Doppler pressure distribution. To
deduce the dynamic pressure from the distribution of theﬂow velocity data, the Navier—Stokes’ equation of motion
was applied for processing the Doppler velocity data, andSpiral systolic blood ﬂow in the ascending aorta and aortic arch

99

Figure 1 Left: Two-dimensional (2D) mapping of ﬂow velocity vector on the longitudinal section plane of the ascending aorta
during systole in a healthy adult. The timing is shown on the ECG by a yellow line and the magnitude of the vector is indicated by
the length of the yellow line. The direction is displayed by the inclination of yellow lines with a red mark at the tip. Reference ofthe vector is shown by the yellow bar at the left upper corner of the ﬁgure. AO, aorta; LA, left atrium; ES, early systolic phase; MS,
mid-systolic phase; LS, late systolic phase. Right: 2D mapping of the velocity vector on the cross-section of the ascending aorta.
The section plane set in the short-axis direction corresponding to the white line (S) shown in Fig. 1 ES. Clockwise rotation of thevector observed. Thick arrow (ES, right) indicates the ﬂow direction. R, reversal ﬂow appeared in late systole. (For interpretationof the references to color in this ﬁgure legend, the reader is referred to the web version of the article.)

the theory of Helmholtz was applied to transfer fromthe velocity information as a vector value to the pressure information as a scalar value [16,17]. The latter wasdemonstrated by color overlapped with 2D echocardiogram.

Positive component of the pressure was displayed with warm
color and negative one by cold color.
Detailed pressure distribution was estimated by the 1D
display of a red line graph (Fig. 6, right).

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M. Tanaka et al.

Figure 2 Left: One-dimensional (1D) display of the ﬂow velocity vector along the longitudinal axis line of the ascending aorta.
Twisted pattern of the velocity vector is demonstrated along the axis line. Right: 1D distribution of the magnitude of the velocity
vector along the ﬂow direction on the longitudinal axis line of the ascending aorta. The magnitude of the vector is shown perpendicular to this axis by the yellow bar. The maximum velocity abruptly decreases to about 50% due to the inertia resistance at the
distal margin of the sinus of Valsalva in ES (white arrow). AO, aorta; LA, left atrium; ES, early systolic phase; MS, mid-systolic phase;LS, late systolic phase. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web versionof the article.)‘‘In vitro’’ experiment
As the ﬂow model, an optically and acoustically transparent
vinyl tube of 20 mm internal diameter and 2 mm in thickness
was used. The models were 2 types, one, a straight tube of
1 m in length, the other, a curved tube with 70 mm in its
radius of curvature (Fig. 9). These tubes were set in suchconditions that the central axis line of the tube was horizontal to avoid a pressure difference between the inlet andoutlet of the tube, and were ﬁxed by immersing in ca 3%transparent agar solution.
For optical and acoustic observations of the ﬂow structure, a minute particle of ion exchange resin (Amberlite,Spiral systolic blood ﬂow in the ascending aorta and aortic arch

101

Figure 3 Left: Flow velocity proﬁles in the short-axis direction at the subvalvular outﬂow tract area. Right: Flow velocity proﬁles
at the area near the peripheral edge of the sinus of Valsalva. Reference of the vector shows at the left upper corner of the ﬁgure.
LA, left atrium; LV, left ventricle; AO, aorta; ES, early systolic phase; MS, mid-systolic phase; LS, late systolic phase.

Rohm and Haas, Philadelphia, PA, USA) of about 10—15 ␮mmixed in 20—30% glycerine solution were used, the densityof which was adjusted to the viscosity of blood. The speedof the ﬂow was about 1—1.5 m/s, which was nearly identicalto the velocity of blood ﬂow in a normal subject.
To measure the ﬂow velocity by the ultrasonic Doppler
method, the sector scanning plane was horizontal to thelongitudinal section plane which includes the central ﬂow
axis line of the model. The ﬂow velocity was obtained by
the color Doppler method. At the same time, ﬂat light of
2 mm in thickness was shed to the ﬂow horizontally as in thecase of the ultrasonic scanning plane, and high frame rate

photographs were recorded perpendicularly to the ﬂat lightplane, so as to analyze the ﬂow structure optically.

Results
In vivo study
2D distribution of the blood ﬂow velocity vector in theascending aorta
Initially, the direction of the blood ﬂow velocity vector inearly systole (ES) was antero-upward in the outﬂow tract
area (1 in Fig. 1), whereas it was postero-downward in the

102basal area of the aorta (2 in Fig. 1), and then antero-upwardagain in the ascending aorta (3 in Fig. 1), resulting in a zigzag
pattern. About 100 ms later (in mid-systole, MS), this zigzag
pattern was nearly constant while it gradually subsided inlate systole (LS).

M. Tanaka et al.
2D distribution of the velocity vector on the obliquecross-section plane (ca 45◦ ) of the ascending aorta (whiteline S in Fig. 1, left) disclosed that the direction of this vector inclined right obliquely in the area near the anterior walland further left near the posterior wall (Fig. 1, right).

Figure 4 1D (right) and 2D (left) distribution of the changing acceleration of ﬂow direction (CAFD) in the ascending aorta. The
magnitude of the acceleration vector is indicated by the length of blue line and the direction of the vector is shown by the inclinationof the blue bar with the red tip. In the 2D distribution, semi-circular radial distribution of the vector originated from the aortic
inner wall is arranged alternately in the anterior or posterior wall of the aorta. The tip of the vector is ﬁgured as a wave patternin ES and MS, and as a linear pattern in LS (left). In the 1D distribution, the acceleration vector appeared perpendicularly fromthe center line of the aorta, and shows a radial pattern, which is demonstrated alternately in the anterior or posterior direction
from the center line. Assuming the 3D ﬂow, the CAFD distribution looks like a spiral staircase. LA, left atrium; AO, aorta; ES, earlysystolic phase; MS, mid-systolic phase; LS, late systolic phase. (For interpretation of the references to color in this ﬁgure legend,
the reader is referred to the web version of the article.)Spiral systolic blood ﬂow in the ascending aorta and aortic arch
This conﬁrmed the presence of the clockwise rotation ofblood ﬂow in the ascending aorta. In LS, reversal blood ﬂow
vectors separating from the main ﬂow were observed at thebasal part near the aortic wall (R in Fig. 1, LS).
The ﬂow velocity vector proﬁle on the long-axis line of
the aorta
The tip of the ﬂow velocity vector along the center line of
the ascending aorta alternatively shifted anteriorly or posteriorly. This means that the vector was twisted (Fig. 2, left).
As seen in the 1D distribution of the velocity vector proﬁlealong the longitudinal-axis line of the ascending aorta, theﬂow velocity was maximum at the basal part and decreased
abruptly about 50% at the distal margin in the sinus of
Valsalva in the ES (Fig. 2, right, white arrow). In MS andafterward, velocity gradient in the basal part gradually
decreased and was steady in LS (Fig. 2, right). This abrupt
decrement of the velocity indicated the presence of theinertia resistance from the blood in the peripheral aorticroute.

103
The ﬂow velocity vector proﬁle on the short-axis line of
the aorta
In the short-axis direction, analysis of the velocity proﬁlein the plane of aortic curvature beneath the aortic valve
disclosed a large ﬂow velocity vector in the outer layer in
ES, whereas it was small in the inner layer, so that a velocity
gradient developed between these 2 layers (Fig. 3, left, ES).
The inclination of the velocity gradient curve was smoothand the fast component was about twofold compared withthe slow one. In MS (nearly 100 ms later), this gradient was
reversed, and in LS (further delay of ca 100 ms), the velocity
proﬁle again showed the reverse, giving a sharp triangle pattern with the largest velocity vector at the central part of
the aorta. On the other hand, at the area near the boundaryof the distal margin of the sinus of Valsalva (about 20 mm
distant from the aortic oriﬁce), the largest vector appearedin the inner layer, whereas it was small in the outer layer of
the aortic arch (Fig. 3, right). In MS, (about 100 ms later),the largest vector appeared at the central part, and thelocation in the LS was at the center part of the aorta. In the

Figure 5 Upper two ﬁgures are 2D and 1D distribution of the changing acceleration of ﬂow direction (CAFD) in early systole. Rightgraph shows the acceleration vector distribution along the white line in the left ﬁgure, and an interval between two black bars on
the graph indicates the wave length of the wave pattern of the 2D distribution of the CAFD. Lower ﬁgure shows the correlation
between the wave length and the maximum ﬂow velocity in the pathway in vitro (blue) and in vivo (red). Negative correlation ispresented. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of thearticle.)104

M. Tanaka et al.

Figure 6 Left: 2D distribution of the vorticity in the left ventricle and aorta in ejection phase. Positive vorticity is shown by
the warm color and negative vorticity, cold one. The grade of the vorticity is estimated by the color bar in the right side of theﬁgure. The positive vorticity appears in the area near the antero-upper wall and the negative one, near the postero-lower wall of
the ascending aorta. The maximum vorticity appears alternately. This ﬁnding indicates that strong rotation occurs in the basal partof the aorta. (1) Initial rotation, (2) 2nd rotation, and (3) 3rd rotation. Right: 2D distribution of the Doppler pressure in the left
ventricle and aorta. Cold color area means a negative pressure and warm color area, a positive one. Reference point is set at theaortic valve ring. The negative pressure (about −3 mm Hg) areas appear in both the outﬂow tract area beneath the aortic valve andthe basal part of the ascending aorta in ES. Rapid pressure increase due to the inertia resistance occurs at the distal margin of thesinus of Valsalva (black and white arrows in ES). Thereafter, the pressure gradient becomes small with the time course (MS, LS). The
minimum Doppler pressure area appears along the center line of the ascending aorta and arch. LA, left atrium; LV, left ventricle;
AO, aorta; ES, early systolic phase; MS, mid-systolic phase; LS, late systolic phase.

Spiral systolic blood ﬂow in the ascending aorta and aortic archspace between the basal area of the outﬂow tract beneaththe aortic oriﬁce and the distal margin of the sinus of Valsalva, the reversed velocity gradient was observed at every
certain time interval from the onset of the ejection and at
every certain distance from the oriﬁce. The equilateral triangular or sharpened parabolic velocity proﬁle (Fig. 3, LS)seemed to be produced by the rolling friction in the rotating
ﬂow.

105
These results indicate that the strong rotation occurred inthis space, and the maximum velocity vector in the ascending aorta appeared at the central part during systolic phase,resulting in the rotation ﬂow in the ascending aorta.
2D distribution of the CAFD in the ascending aorta
A more detailed ﬁgure of the second parameter of thisrotation was evaluated by CAFD. In the ES and MS, 2D distri-Figure 7 Experimental results obtained by using the straight tube model. 1, 2D distribution of the ﬂow velocity vector; 2, 1D
distribution of the ﬂow velocity vector on the center line of the tube along the ﬂow axis; 3, Flow velocity proﬁle in the short-axis
direction; 4, 2D distribution of the CAFD; 5, 1D distribution of the CAFD on the center line of the tube along the ﬂow direction;
6, Flow velocity proﬁle in the long-axis direction. White arrow indicates the ﬂow direction. CAFD, changing acceleration of ﬂow
direction.

106
bution of CAFD on the longitudinal section plane of the aorta
demonstrated a fan of the radial pattern from the inner surface of the aortic wall (Fig. 4, left). Many radially arranged
vectors alternately appeared from the anterior or posteriorwall of the aorta. Thus, the line connecting the tips of theacceleration vector constituted a red snaky pattern in thecentral area of the aorta. As systole progressed (LS), theacceleration vector originated perpendicularly from the wall

M. Tanaka et al.
into the blood, therefore, the line connected with the tipsof the vector tended toward the linear pattern.
CAFD along the central-axis line of the aorta showed apattern of the radial vector distribution alternately toward
the opposite direction. The line connecting with the tips ofthe vector showed a wave pattern. Thus, it was disclosed
that, three-dimensionally, the spiral staircase acceleration
vector developed in the ascending aorta.

Figure 8 Results experimentally obtained by using the curved tube model. 1, 2D distribution of the ﬂow velocity vector; 2, 1D
distribution of the ﬂow velocity vector on the center line of the tube along the ﬂow axis; 3, Flow velocity proﬁle in the short-axis
direction; 4, 2D distribution of the CAFD; 5, 1D distribution of the CAFD on the center line of the tube along the ﬂow direction;
6, Flow velocity proﬁle in the long-axis direction of the tube model. White arrow indicates the ﬂow direction. CAFD, changing
acceleration of ﬂow direction.

Spiral systolic blood ﬂow in the ascending aorta and aortic arch
The magnitude of the CAFD in ES was large in the anterosuperior direction at the basal part of the ascending aorta
compared to that in the peripheral part. On the other hand,
the magnitude in the peripheral part became larger in MS
and LS, indicating the occurrence of large rotation of theblood ﬂow in the basal part of the aorta and progression to
the peripheral part of the aorta with time course.
The wave length of the wave pattern ﬁgured by the tipof the acceleration vector had an inverse correlation withthe maximum velocity in the aorta (Fig. 5), i.e. the higher
the velocity, the faster the rotation.
2D distribution of the vorticity of the blood ﬂow in theascending aorta
One parameter of this rotation was the vorticity of theejecting ﬂow. At the beginning of the ejection (Fig. 6,left), the maximum area of the positive vorticity (red area,
100—150/s) appeared at the anterior part of the outﬂow
tract beneath the aortic valve. On the other hand, the negative vorticity area (blue area, −100 to −150/s) appeared
posteriorly just above the aortic valve (2nd rotation (2)).
These positive (+) and negative (−) components of the vorticity alternately appeared toward the peripheral part andthe vorticity gradually decreased after MS, both indicating
the strong rotation produced at the part from the outﬂow
tract to the basal part of the aorta.
2D distribution of the Doppler pressure in the ascending
aorta
About −3 mm Hg negative pressure was shown in both theoutﬂow tract area beneath the valve ring and the basal area

107of the aorta in the ES (Fig. 6, right). An abrupt pressure
increase occurred at the peripheral margin of the sinus of
Valsalva (Fig. 6, right, white and black arrows). Following
MS, the pressure difference was restored and reached thelevel of 0.5—0.8 mm Hg, thus the pressure curve also showeda cyclic pattern.

In vitro study
Straight tube ﬂow model
2D distribution of the ﬂow velocity vector in the straighttube model showed a parallel pattern (Fig. 7-1). 1D distribution of the velocity vector on the center line along the ﬂow
direction (Fig. 7-2) and the velocity proﬁle in the short-axis
direction showed a lineal ﬂow character parallel to the tube
wall (Fig. 7-3 and -6).
2D distribution of the CAFD showed a laminar patternwith nearly the same magnitude of acceleration vector perpendicularly to the tube wall (Fig. 7-4). The rectangularcomponent of the acceleration described in the curved tube
was not observed in 1D distribution of the CAFD (Fig. 7-5).
Curved tube ﬂow model
As shown in Fig. 8, all of the information regarding the ﬂow
structure such as 2D and 1D distribution of the ﬂow velocity
vector along the longitudinal direction, ﬂow velocity proﬁle in the short-axis direction, 2D and 1D distribution of
the CAFD along the main ﬂow axis line, and the correlation
between ﬂow velocity and wave length of the wave pattern in 2D distribution, all showed nearly the same results
as those obtained in the clinical observation. Clockwise rota-

Figure 9 Flow visualization in the curved model at the 4 stages in pulsatile ﬂow. The effects of the curvature of the tube areshown and the centralized rotating ﬂow is also observed. White arrow indicates the ﬂow direction.

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M. Tanaka et al.

Figure 10 Schematic representation of the ﬂow structure in the ascending aorta and aortic arch in ES, MS, and LS. Blue radial
pattern indicates the changing acceleration of ﬂow direction. ES, High accelerated ﬂow due to the centrifugal force produced by
the eddy just behind the anterior mitral leaﬂet passes the LV outﬂow antero-upward and the momentum extends the curvature of
the aorta antero-upward and expands the basal part of the aorta. Thus the ﬂow shifted antero-upward. However, both the expansion
and extension are impeded by the rigidity of the surrounding tissues, and the ejected ﬂow is imposed a large inertia resistanceat the distal margin of the sinus of Valsalva. A part of the motion energy will be converted into the rotation energy. Thus, theejected ﬂow is reﬂected and turned over at the spherical concave inner surface of the antero-basal part of the aorta and the ﬂow
directs postero-downward, and the rotation begins. Then, the ﬂow reﬂected again and turned over at the convex inner surfaceof the postero-inferior part of the arch. Thus the twisted spiral ﬂow is produced. MS, The continuing rotation due to reﬂection
and turn-over at the convex inner surface of postero-inferior part of the arch goes up to antero-upward and the second rotation
occurs. Thereafter, the rotating ﬂow turns over at the concave inner surface of the antero-upper part of the aorta. LS, The rotation
continues and the twisted spiral ﬂow progressed to the peripheral part. In this phase, the deceleration appears and the reversal
ﬂow occurs along the inner surface of the basal part of the aorta, and the vortex is produced in the sinus of Valsalva. ES, earlysystolic phase; MS, mid-systolic phase; LS, late systolic phase.

Spiral systolic blood ﬂow in the ascending aorta and aortic archtion of the ejected ﬂow was also demonstrated in the curved
tube model.
Visualization of the ﬂow in curved tube model using ﬂatlight method
The ﬂow structure on the longitudinal cross-section examined using ﬂat light method (Fig. 9) disclosed that brightlines from the reﬂector in the ﬂow were longer along theunder layer of the curved tube compared to those along theupper layer in the early stage of ejection. The ﬂow velocity
is faster in the under layer compared to those in the upper
layer (Fig. 9, beginning stage).
During early and mid-stage, the length of the bright line
was longer at the central area compared to that adjacent to
the wall, where the line became shorter and decreased andﬁnally converged toward the main ﬂow axis line.
The main axis of the rotation ﬂow in the curved tube was
supposed to coincide with the center line of the tube. The
ﬂat-light method, which observed ﬂow structure from thelongitudinal cross-section, disclosed that the transit timeof reﬂector passing through the ﬂat light became long andthe length of the bright line also became long at the central area, but the reverse was true at the area adjacent to
the wall, conﬁrming the occurrence of rotation ﬂow duringejection.

Discussion
The results of the present study on the systolic blood
ﬂow structure in the ascending aorta and aortic arch are
schematically shown in Fig. 10.
The accelerated blood ﬂow in the cylindrical tube curved
like the aorta inevitably ensures secondary ﬂow due to viscosity, pressure gradient, centrifugal force, etc., and shows
the high velocity component in the outside bend and low
one in the inside bend and also the slowly rotating helicalstructure [2,6,7]. Peronneau et al. [5] demonstrated in dogs
that the blood ﬂow velocity distribution in the ascending
aorta was higher at the inner (under) part of the arch andlower in the outer (upper) part. Kilner et al. [9] reported theright-handed helical ﬂow in the ascending aorta in humansubjects. Our data conﬁrmed their results. In this respect,
the data obtained by computer simulation were quite different from the present study observed in the human being.
Our results further revealed the upward displacement of
the base of the aorta and distension of the arch as well as
the diameter change. Therefore, the ﬂow structure seemed
to be complex including its rotation. However, the characteristics of such a ﬂow structure have not been clariﬁed
yet.
Echo-dynamography enabled us to analyze 2D distribution of the velocity both in the longitudinal- and short-axis
directions, vorticity, CAFD, and the development of the
spiral twisted ﬂow was deﬁnitely demonstrated. At the
beginning of ejection, the high accelerated ejection ﬂow
forcefully displaced the basal part of the aorta anteroupward together with stretched curvature of the arch andexpansion of the aorta. Thus the ejected ﬂow shifted in
the antero-upward direction and collided with and was
reﬂected at the spherical concave inner surface of theantero-basal part of the aorta. A brisk clockwise rotation

109
ﬂow was observed in the basal part of the aorta including
the sinus of Valsalva, and the spiral twisted ﬂow appearedin the ascending aorta.
The occurrence of the spiral twisted ﬂow will have thefollowing three merits for: one, stabilizing the ﬂow direction for passing through the curved pathway because thecenter of rotation always coincided with the center line of
the aorta, two, maintaining the most effective ﬂow volume
by defeating the high inertia resistance because of the reversal correlation between the rotation rate and the maximum
speed of the ejected ﬂow, and three, dispersing the shear
stress in the aortic wall which occurred by passing throughthe high accelerated ﬂow. From the 2D distribution of thevorticity, it was considered that the rotating ﬂow at the basal
part of the aorta is produced by the momentum due to thehigh accelerated ejection ﬂow in the early stage of ejection
impeded by the rigidity of the surrounding aortic tissue. On
the other hand, the distal margin of the sinus of Valsalva
imposes a large inertia resistance from the peripheral aorticroute. A part of the motion energy for ejection, which was
equivalent to the velocity decrement and dynamic pressure
increment (Fig. 2, ES, white arrow; Fig. 6, ES, black arrow),
will be converted into rotation energy.
Though the tube experiment has no dilated part such as
the sinus of Valsalva, the results were nearly the same as
to the twisted spiral ﬂow in the human beings. There may
be a loose ﬁxation of the entrance of the tube, but thisexperiment also clearly demonstrated the importance of
the antero-upward displacement of the basal part together
with shifting the ﬂow direction antero-upward, the inertia
resistance, and the curvature of the inner surface of thecylindrical curve of the tube to cause the spiral twisted ﬂow.

Conclusion
Using echo-dynamography, the complicated systolic blood
ﬂow structure in the ascending aorta and arch was investigated.
During ejection, the twisted spiral ﬂow was produced in
the ascending aorta and arch, which started from the junction of the left ventricle and aorta and proceeded to theperipheral part. The cycle of the rotation inversely correlated with the maximum ﬂow velocity. It is concluded that
this twisted spiral ﬂow is important to settle the directionof the accelerated blood ﬂow under high pressure and is also
helpful to disperse the shear stress in the aortic wall. Thus
the blood was effectively ejected during the short period
through the curved aortic pathway.

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