An Explanation of Asymmetric UpperExtremity Blood Pressures in Supravalvular

Aortic Stenosis

The Coanda Effect

By JAMES W. FRENCH, M.D., AND WARREN G. GUNTHEROTH, M.D.

SUMMARYThe Coanda effect, the tendency of a jet stream to adhere to a wall, was investigated

as an explanation of the unequal pressures in the upper extremities in patients withsupravalvular aortic stenosis (SVAS). Of 56 patients with SVAS reviewed, 48 had un-

equal blood pressures in the upper extremities. The average difference was 18 mm Hgsystolic. 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 thestenotic orifice, preventing any sustained high-velocity stream. However, the smooth,annular narrowing of SVAS creates a "step" between the orifice and the ascendingaortic wall which enhances the natural affinity of a jet for a boundary wall andconserves the kinetic energy of the jet stream. In most patients with SVAS, thehigh-velocity stream is along the right aortic wall, causing disproportionately high pres-

sure in the right arm.

Additional Indexing Words:Annular stenosis Jet stream

S UPRAVALVULAR aortic stenosis (SVAS)is one of several lesions which are

included in the congenital aortic stenosisgroup. Unequal systolic blood pressure in theupper extremities, which has been frequentlyreported with supravalvular stenosis,2-10 is animportant diagnostic sign because it has onlyrarely been reported in other congenitalcardiovascular lesions, except coarctation orinterruption of the transverse aortic arch.'1

From the Division of Pediatric Cardiology, Depart-ment of Pediatrics, University of Washington Schoolof Medicine, Seattle, Washington.

Supported by Training Grant TIHE-5281, andResearch Grant HE 07158 from the U. S. PublicHealth Service.

Presented in part at the 42nd Scientific Sessions,American Heart Association, Dallas, Texas, November1969. (Abstr.1)Received January 29, 1970; revision accepted for

publication April 22, 1970.

Circulation, Volume XLII, July 1970

Kinetic energy

We believe that aspects of fluid control theory,specifically the Coanda effect, offer a logicalexplanation of this phenomenon.The Coanda effect,'2-14 the tendency of a jet

stream to adhere to a boundary wall, was firstnoted in 1910 by Henri Coanda"5 andprobably represents a special case of the morefamiliar Bemoulli principle. As a jet exitsfrom a nozzle, it progressively broadens byentraining the surrounding fluid, the peakvelocity is proportionately diminished, and thekinetic energy of the jet is dissipated down-stream. An area of low pressure is produced atthe margins of the jet, and a counterflow iscreated to equalize the pressures (fig. LA). Ifa random disturbance causes the jet todeviate, inequalities will develop in thecounterflow, and the stream may "attach"' toone of the boundary walls. The course of thestream is then maintained by a combination of

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FRENCH, GUNTHEROTH

a low pressure area adjacent to the boundarywall and the countercurrent flow from theopposite side of the jet. A similar deviation isproduced if the space or chamber around thenozzle is not symmetrical. The simplestexample of this is shown in figure lB. Onewall of the chamber has been moved closer tothe nozzle exit. It can be shown that the jetwill consistently attach to this near wall,12even following interruptions in the jet such asdiastole. This tendency of the jet stream toreestablish a specific pattern is termed "reset"or '"memory."'4 Other variations in the dimen-sions and the configuration of the chamberwill produce consistent changes in the courseof the jet stream. One important modificationis the introduction of a "shoulder" or "step" inthe wall close to the nozzle. Experimentalwork has shown that this particular configura-tion enhances the Coanda effect if the step isnot too abrupt.13 If the step is too abrupt, thejet will not follow the boundary wall, and thepeak energy of the jet will be dissipated in an

expanding volume downstream. The reasonfor the separation is the large angle ofreflection necessary to reach the boundarywall.'2, 14 This is termed an "anti-Coandaconfiguration."By introducing a splitter or bifurcation

downstream (figs. 1A and B), it is possible todemonstrate the kinetic energy of the jetstream as differential pressures or flows.12 14The bifurcation must be at least two nozzlewidths distant from the nozzle (2:1 ratio) toestablish the Coanda effect.To investigate the frequency and signifi-

cance of the unequal pressures, we havereviewed the data in six of our cases of SVAS,pressure and dimension data from 50 casespresented in the literature, and compared theresults with the data from 20 of our patientswith valvular aortic stenosis (VAS). The VASgroup was chosen as a control because of thesimilarities between the two lesions; thus, ifthere is a significantly greater pressure differ-ential in the supravalvular group, it should be

Splitter

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A.Iw=-l

-.

F\

A

-High velocity jet stream

-Lowpressure Nozarea

Figure 1A jet stream flowing into a bounded chamber causes entrainment of fluid by the jet, genera-

tion of low pressures at the jet margins, and a counterflow (represented by arrows) of chamberfluid. (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 "at-tachment" of the jet stream, with conservation of its kinetic energy and direction of thestream into the right branch.

Circulation, Volume XLII, July 1970

pressurearea

B

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COANDA EFFECT

0 0

00

0000

0000

0

8

0

00

0 0

0 00

0

0 00000

0

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0 000

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L>R R>L-o

SVAS

00 000 0

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0 0

0 0

L>R R>LVAS

Figure 2

Differences in systolic blood pressures in upper ex-

tremities. Each dot represents one patient (total num-

ber of cases, 76). SVAS =supravalvular aortic ste-nosis group; VAS = control group with valvular aorticstenosis; R > L = systolic pressure in right arm ex-

ceeds that in left arm. L > R = systolic pressure inleft arm exceeds that in right arm.

due to the specific configuration of thesupravalvular lesion.

MethodsThe blood pressures in patients with supra-

valvular or valvular stenosis seen in the Universityof Washington Hospital were obtained with a

standard sphygmomanometer cuff by auscultation.The proper-sized cuff was judged to be 20% widerthan the diameter of the extremity where the cuffwas applied.16 All patients were examined eitherin the Pediatric Cardiology Clinic or as in-patients on the Pediatric Cardiology Service atUniversity Hospital. Cases were accepted fromliterature if blood pressures in both upperextremities were recorded in the report.3-10, 17-25Angiocardiographic films were reviewed forstep configuration (gradual transition betweenthe stenotic annulus and the poststenotic wall)and to determine the ratio of the chamber length(from the level of stenosis to the orifice of theinnominate artery) to the stenotic orifice.

Results (Table 1; Fig. 2)Of the 56 patients with SVAS under review,

48 or 86% had unequal systolic blood pressuresin the upper extremities. The average differ-ence 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 rightarm in 40 or 83% of the patients with adifference in pressures. In the control group of20 patients with valvular aortic stenosis, 11 or55% had a systolic pressure differential in theupper extremities, but the difference for allvalvular 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 infive or 45% of patients with differentialpressures. The average differences in systolicpressure between the two arms in SVAS, 18mm Hg, is significantly greater (P < 0.01) thanthe average difference in systolic pressures inVAS, 3.5 mm Hg. In all cases reviewed, theratio of chamber length to stenotic diameterexceeded the minimum 2:1 ratio necessaryfor the Coanda effect to be established.

Table 1

Data on Upper Extremity Systolic Blood Pressures in SVAS and VAS

SVAS VAS

Total no. of cases 56 20No. with unequal pressures 48 (86%7) 11 (55%o)

Right greater than left 40 5Left greater than right 8 6

Average difference (all cases) inblood pressures (mm Hg) 18 (=i=3.1)* 3.5 (-0.20)*

Range of difference (mm Hg) 0-60 0-10

*Standard error of mean.Circulation, Volume XLII, July 1970

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FRENCH, GUNTHEROTH

DiscussionTwo principal explanations have been pro-

posed for the differential pressures in theupper extremities. A selective stenosis at theorigin of arch vessels has been suggested as acause of the unilaterally diminished pres-sure.4, 8, 20, 26, 27 However, recent reviews ofpathologic specimens by Peterson and associ-ates28 and radiologic material by Kupic andAbrams22 have suggested that the incidence ofsignificant selective aortic arch vessel stenosisis in the range of only 15 to 20%. Based on theradiologic report, selective stenoses of eitherthe left common carotid or left subelavianvessels are more common, although only 22 ofthe 121 cases reviewed had any significantstenosis of arch vessels. While it is probablethat selective arch vessel stenosis is significantin some cases, the frequency is too low toexplain the rather high incidence of differen-tial pressures in patients with SVAS.We support the alternate theory that the

cause of the differential pressures is a highvelocity jet streaming into the origin of aspecific arch vessel. In 1963, Lurie andMandelbaum,29 working with a canine model,and more recently Goldstein and Epstein,30with an aortic arch model, have confirmedthat the kinetic energy developed in a jetstream under simulated pathologic conditions(that is, with SVAS) is sufficient to cause theclinically observed difference in pressures. Ithas been suggested that the differential wasthe result of the alignment of the ascendingaorta and the orifice of the right innominateartery. However, this would not explainpatients with higher pressures on the left side.In addition, patients with VAS without SVAShave high velocity jets, but rarely unequalpressures. The high incidence of differentialpressures in SVAS logically suggests a uniquemechanism controlling the course of thestream between the stenotic area and the archvessel bifurcation.The major difference between the valvular

and supravalvular lesions occurs in the im-mediate poststenotic area. In valvular aorticstenosis, the initial step between the valveorifice and the ascending aortiic wall is large

and abrupt (fig. 3A). This is made even moreextreme by the commonly associated postste-notic dilatation. Consequently, the jet streamdoes not attacb to the aortic wall. By contrast,the annular hourglass narrowing of thesupravalvular lesion creates an optimal step orshoulder transition between the stenotic areaand the wall of the ascending aorta (figs. 3Band 4). The limiting effect of the boundarywall on one surface and the confining effect ofthe counterflow on the opposite surface tendto stabilize the jet and retard its naturaltendency to broaden and disperse. With theaortic wall as a boundary, a positivelydirected, sustained jet stream is produced.Although the higher pressures are usuallyrecorded in the right arm, the Coanda effectwould apply equally well to patients who havehigher pressures in the left arm. This is logicalif the aorta is considered in its threedimensions (fig. 4). The jet stream couldeasily flow up the posterior wall of the aorta,bypassing the right innominate artery and en-tering the left common carotid or the left

A B

Figure 3Diagrammatic representations. (A) Valvular aorticstenosis with mild poststenotic dilatation. Note abrupttransition between stenotic valve and ascending aorticwall. (B) Supravalvular aortic stenosis. Note gradualtransition (step) between annular stenosis and ascend-ing aortic wall.

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COANDA EFFECT

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 theaortic wall.

In summary, we have proposed an explana-tion for the difference in systolic bloodpressures in the upper extremities seen inSVAS. We have emphasized that althoughboth valvular and supravalvular aortic stenosisproduce jet streams, the unique step configu-ration of the supravalvular aortic stenosis andthe Coanda principle provide an explanationfor the unequal carotid and brachial arterysystolic pressures commonly seen in thepatients with supravalvular lesions.

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effect: An explanation of asymmetric bloodpressures in supravalvular aortic stenosis.(Abstr) Circulation 40: (suppl III): 111-84,1969

2. WoouEY CF, HOsIER DM, MECKSTROTH CV, ETAL: Supravalvular aortic stenosis: An emergingclinical entity. (Abstr) Circulation 28: 827,1963

Circulaion, Volume XLII, July 1970

3. EISENBERG R, YOUNG D, JACOBSON B, ET AL:Familial supravalvular aortic stenosis. Amer JDis Child 108: 341, 1964

4. LOC;AN WFWE, JONES EW, WALKER E, ET AL:Familial supravalvular aortic stenosis. BritHeart J 27: 547, 1965

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11. SISSM;sAN NJ: Anomalies of the aortic archcomplex. In Heart Disease in Infants, Childrenand Adolescents, edited by AJ Moss, FHAdams. Baltimore, Williams & Wilkins Co.,1968, p 418

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17. GARCIA RE, FRIEDMAN WF, KABACK MM, ETAL: Idiopathic hypercalcemia and supravalvu-lar aortic stenosis: Documentation of a newsyndrome. New Eng J Med 271: 117, 1964

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25. NAJAF H, DYE WS, JULIAN OC: Successful onestage correction of both supravalvular aorticstenosis and typical coarctation of aorta in onepatient. J Thorac Cardiovasc Surg 48: 644,1964

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JAMES W. FRENCH and WARREN G. GUNTHEROTHSupravalvular Aortic Stenosis: The Coanda Effect

An Explanation of Asymmetric Upper Extremity Blood Pressures in

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1970 American Heart Association, Inc. All rights reserved.

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