An Explanation of Asymmetric Upper Extremity Blood Pressures in

An Explanation of Asymmetric Upper
Extremity Blood Pressures in Supravalvular
Aortic Stenosis
The Coanda Effect
By JAMES W. FRENCH, M.D.,
AND
WARREN G. GUNTHEROTH, M.D.
SUMMARY
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The Coanda effect, the tendency of a jet stream to adhere to a wall, was investigated
explanation of the unequal pressures in the upper extremities in patients with
supravalvular aortic stenosis (SVAS). Of 56 patients with SVAS reviewed, 48 had unequal blood pressures in the upper extremities. The average difference was 18 mm Hg
systolic. Although 11 of the 20 patients in the control group (valvular aortic stenosis)
had some blood pressure asymmetry, the average difference was 3.5 mm Hg systolic.
In valvular aortic stenosis, the velocity of the jet is quickly dissipated beyond the
stenotic orifice, preventing any sustained high-velocity stream. However, the smooth,
annular narrowing of SVAS creates a "step" between the orifice and the ascending
aortic wall which enhances the natural affinity of a jet for a boundary wall and
conserves the kinetic energy of the jet stream. In most patients with SVAS, the
high-velocity stream is along the right aortic wall, causing disproportionately high pressure in the right arm.
as an
Additional Indexing Words:
Annular stenosis
Jet stream
Kinetic energy
We believe that aspects of fluid control theory,
specifically the Coanda effect, offer a logical
explanation of this phenomenon.
The Coanda effect,'2-14 the tendency of a jet
stream to adhere to a boundary wall, was first
noted in 1910 by Henri Coanda"5 and
probably represents a special case of the more
familiar Bemoulli principle. As a jet exits
from a nozzle, it progressively broadens by
entraining the surrounding fluid, the peak
velocity is proportionately diminished, and the
kinetic energy of the jet is dissipated downstream. An area of low pressure is produced at
the margins of the jet, and a counterflow is
created to equalize the pressures (fig. LA). If
a random disturbance causes the jet to
deviate, inequalities will develop in the
counterflow, and the stream may "attach"' to
one of the boundary walls. The course of the
stream is then maintained by a combination of
S UPRAVALVULAR aortic stenosis (SVAS)
is one of several lesions which are
included in the congenital aortic stenosis
group. Unequal systolic blood pressure in the
upper extremities, which has been frequently
reported with supravalvular stenosis,2-10 is an
important diagnostic sign because it has only
rarely been reported in other congenital
cardiovascular lesions, except coarctation or
interruption of the transverse aortic arch.'1
From the Division of Pediatric Cardiology, Department of Pediatrics, University of Washington School
of Medicine, Seattle, Washington.
Supported by Training Grant TIHE-5281, and
Research Grant HE 07158 from the U. S. Public
Health Service.
Presented in part at the 42nd Scientific Sessions,
American Heart Association, Dallas, Texas, November
1969. (Abstr.1)
Received January 29, 1970; revision accepted for
publication April 22, 1970.
Circulation, Volume XLII, July 1970
31
FRENCH, GUNTHEROTH
32
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a low pressure area adjacent to the boundary
wall and the countercurrent flow from the
opposite side of the jet. A similar deviation is
produced if the space or chamber around the
nozzle is not symmetrical. The simplest
example of this is shown in figure lB. One
wall of the chamber has been moved closer to
the nozzle exit. It can be shown that the jet
will consistently attach to this near wall,12
even following interruptions in the jet such as
diastole. This tendency of the jet stream to
reestablish a specific pattern is termed "reset"
or '"memory."'4 Other variations in the dimensions and the configuration of the chamber
will produce consistent changes in the course
of the jet stream. One important modification
is the introduction of a "shoulder" or "step" in
the wall close to the nozzle. Experimental
work has shown that this particular configuration enhances the Coanda effect if the step is
not too abrupt.13 If the step is too abrupt, the
jet will not follow the boundary wall, and the
peak energy of the jet will be dissipated in an
expanding volume downstream. The reason
for the separation is the large angle of
reflection necessary to reach the boundary
wall.'2, 14 This is termed an "anti-Coanda
configuration."
By introducing a splitter or bifurcation
downstream (figs. 1A and B), it is possible to
demonstrate the kinetic energy of the jet
stream as differential pressures or flows.12 14
The bifurcation must be at least two nozzle
widths distant from the nozzle (2:1 ratio) to
establish the Coanda effect.
To investigate the frequency and significance of the unequal pressures, we have
reviewed the data in six of our cases of SVAS,
pressure and dimension data from 50 cases
presented in the literature, and compared the
results with the data from 20 of our patients
with valvular aortic stenosis (VAS). The VAS
group was chosen as a control because of the
similarities between the two lesions; thus, if
there is a significantly greater pressure differential in the supravalvular group, it should be
Splitter
k&I
A.I
-High velocity jet stream
w=-l
-.
F\
Nozzle
-Low
pressure
area
pressure
area
Noz
B
A
Figure 1
A jet stream flowing into a bounded chamber causes entrainment of fluid by the jet, generation of low pressures at the jet margins, and a counterflow (represented by arrows) of chamber
fluid. (A) The jet kinetic energy is dissipated downstream, as the high-velocity stream broadens.
(B) Unequal counterfiow as a result of asymmetry of the chamber causes deviation and "attachment" of the jet stream, with conservation of its kinetic energy and direction of the
stream into the right branch.
Circulation, Volume XLII, July 1970
COANDA EFFECT
33
standard sphygmomanometer cuff by auscultation.
The proper-sized cuff was judged to be 20% wider
than the diameter of the extremity where the cuff
was applied.16 All patients were examined either
in the Pediatric Cardiology Clinic or as inpatients on the Pediatric Cardiology Service at
University Hospital. Cases were accepted from
literature if blood pressures in both upper
extremities were recorded in the report.3-10, 17-25
Angiocardiographic films were reviewed for
step configuration (gradual transition between
the stenotic annulus and the poststenotic wall)
and to determine the ratio of the chamber length
(from the level of stenosis to the orifice of the
innominate artery) to the stenotic orifice.
70rz
$ 60-
0
0
^ 50-
C
00
400000
to
'AI)
0000
Results (Table 1; Fig. 2)
0
8
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0
*. 20-
00
0
0
0
00
0
109
%,lo
oo
0
00000
00
0
0
00
0
0
0
000
0
L>R
0
0
0
0
L>R
R>L
-o
SVAS
R>L
VAS
Figure 2
Differences in systolic blood pressures in upper extremities. Each dot represents one patient (total number of cases, 76). SVAS =supravalvular aortic stenosis group; VAS = control group with valvular aortic
stenosis; R > L = systolic pressure in right arm exceeds that in left arm. L > R = systolic pressure in
left arm exceeds that in right arm.
due to the specific configuration of the
supravalvular lesion.
Methods
The blood pressures in patients with supravalvular or valvular stenosis seen in the University
of Washington Hospital were obtained with a
Of the 56 patients with SVAS under review,
48 or 86% had unequal systolic blood pressures
in the upper extremities. The average difference in all cases of SVAS was 18 mm Hg
(sE,+ 3.1). The range was 0 to 60 mm Hg.
Higher pressures were obtained in the right
arm in 40 or 83% of the patients with a
difference in pressures. In the control group of
20 patients with valvular aortic stenosis, 11 or
55% had a systolic pressure differential in the
upper extremities, but the difference for all
valvular cases was only 3.5 mm Hg
(SE, + 0.2). The range was 0 to 10 mm Hg.
Higher pressures were obtained on the right in
five or 45% of patients with differential
pressures. The average differences in systolic
pressure between the two arms in SVAS, 18
mm Hg, is significantly greater (P < 0.01) than
the average difference in systolic pressures in
VAS, 3.5 mm Hg. In all cases reviewed, the
ratio of chamber length to stenotic diameter
exceeded the minimum 2:1 ratio necessary
for the Coanda effect to be established.
Table 1
Data on Upper Extremity Systolic Blood Pressures in SVAS and VAS
VAS
SVAS
Total no. of cases
No. with unequal pressures
Right greater than left
Left greater than right
Average difference (all cases) in
blood pressures (mm Hg)
Range of difference (mm Hg)
*Standard error of
mean.
Circulation, Volume XLII, July 1970
56
48
40
8
(86%7)
18 (=i=3.1)*
0-60
20
11
5
6
(55%o)
3.5 (-0.20)*
0-10
34
FRENCH, GUNTHEROTH
Discussion
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Two principal explanations have been proposed for the differential pressures in the
upper extremities. A selective stenosis at the
origin of arch vessels has been suggested as a
cause of the unilaterally diminished pressure.4, 8, 20, 26, 27 However, recent reviews of
pathologic specimens by Peterson and associates28 and radiologic material by Kupic and
Abrams22 have suggested that the incidence of
significant selective aortic arch vessel stenosis
is in the range of only 15 to 20%. Based on the
radiologic report, selective stenoses of either
the left common carotid or left subelavian
vessels are more common, although only 22 of
the 121 cases reviewed had any significant
stenosis of arch vessels. While it is probable
that selective arch vessel stenosis is significant
in some cases, the frequency is too low to
explain the rather high incidence of differential pressures in patients with SVAS.
We support the alternate theory that the
cause of the differential pressures is a high
velocity jet streaming into the origin of a
specific arch vessel. In 1963, Lurie and
Mandelbaum,29 working with a canine model,
and more recently Goldstein and Epstein,30
with an aortic arch model, have confirmed
that the kinetic energy developed in a jet
stream under simulated pathologic conditions
(that is, with SVAS) is sufficient to cause the
clinically observed difference in pressures. It
has been suggested that the differential was
the result of the alignment of the ascending
aorta and the orifice of the right innominate
artery. However, this would not explain
patients with higher pressures on the left side.
In addition, patients with VAS without SVAS
have high velocity jets, but rarely unequal
pressures. The high incidence of differential
pressures in SVAS logically suggests a unique
mechanism controlling the course of the
stream between the stenotic area and the arch
vessel bifurcation.
The major difference between the valvular
and supravalvular lesions occurs in the immediate poststenotic area. In valvular aortic
stenosis, the initial step between the valve
orifice and the ascending aortiic wall is large
and abrupt (fig. 3A). This is made even more
extreme by the commonly associated poststenotic dilatation. Consequently, the jet stream
does not attacb to the aortic wall. By contrast,
the annular hourglass narrowing of the
supravalvular lesion creates an optimal step or
shoulder transition between the stenotic area
and the wall of the ascending aorta (figs. 3B
and 4). The limiting effect of the boundary
wall on one surface and the confining effect of
the counterflow on the opposite surface tend
to stabilize the jet and retard its natural
tendency to broaden and disperse. With the
aortic wall as a boundary, a positively
directed, sustained jet stream is produced.
Although the higher pressures are usually
recorded in the right arm, the Coanda effect
would apply equally well to patients who have
higher pressures in the left arm. This is logical
if the aorta is considered in its three
dimensions (fig. 4). The jet stream could
easily flow up the posterior wall of the aorta,
bypassing the right innominate artery and entering the left common carotid or the left
A
B
Figure 3
Diagrammatic representations. (A) Valvular aortic
stenosis with mild poststenotic dilatation. Note abrupt
transition between stenotic valve and ascending aortic
wall. (B) Supravalvular aortic stenosis. Note gradual
transition (step) between annular stenosis and ascending aortic wall.
Circulation. Volume XLII, July 1970
COANDA EFFECT
35
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Figure 4
Angiocardiographic study on patient with SVAS. SV =annular stenosis: AV=aortic valve.
Contrast material was injected into the left ventricle. The annular stenosis creates an optimal
"'step" between the aortic valve and the wall of the ascending aorta.
subclavian artery without separating from the
aortic wall.
In summary, we have proposed an explanation for the difference in systolic blood
pressures in the upper extremities seen in
SVAS. We have emphasized that although
both valvular and supravalvular aortic stenosis
produce jet streams, the unique step configuration of the supravalvular aortic stenosis and
the Coanda principle provide an explanation
for the unequal carotid and brachial artery
systolic pressures commonly seen in the
patients with supravalvular lesions.
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Circulaton, Volume XII, July 1970
An Explanation of Asymmetric Upper Extremity Blood Pressures in
Supravalvular Aortic Stenosis: The Coanda Effect
JAMES W. FRENCH and WARREN G. GUNTHEROTH
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Circulation. 1970;42:31-36
doi: 10.1161/01.CIR.42.1.31
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