The Significance of the IntermediateKorotkoff Sounds

By SiMoN RODBARD, M.D., PH.D.

Except for those sounds that mark the systolic and diastolic blood pressure levels, the murmurs

(luring sphygmomanometry are generally ignored. Our studies suggest that the intensity andduration of these murmurs provide an appraisal of the blood flow into the part beyond the cuffunder certain conditions.

T HE sounds heard at the brachial arterydistal to the point of compression by thesphygmomanometer cuff have been clas-

sified into several phases. As the cuff pressurefalls from high levels, the onset of a snappingsound characterizes the level of the systolicpressure. With further reduction of the pressurein the cuff the sound changes through an as-sortment of murmurs and rumbles until finallyit becomes muffled and then disappears entirely.The diastolic pressure has been variously desig-nated as related to the sudden marked changein tone as the cuff pressure continues to fall orto the complete disappearance of the brachialsounds.1 Since the sounds intermediate betweenthe systolic and diastolic levels have not beenequated with any specific physiologic event orclinical determinant, they are ordinarily ig-nored during the blood pressure determination.Our studies on flow through collapsible

vessels2 suggested that the Korotkoff soundsmay depend on the occurrence of flow in thearteries under the cuff, with the productionof a fluttering of the vessel walls. If this provedtrue, attention to the intensity and duration ofthe intermediate sounds would provide anindex of blood flow to the extremity beyondthe cuff. To test this hypothesis we undertookstudies on patients and on artificial circulationmodels.

From the Cardiovascular Department, lMedicalResearch Institute, Michael Reese Hospital, Chicago,Ill.

Aided by grants from the National Heart Institute(H-690 C) and the Michael Reese Research Founda-tion.

CLINICAL SURVEYPreliminary studies were carried out on 75

volunteers and patients on the wards of theMichael Reese Hospital. The essential experi-ment was carried out as follows: A blood pres-sure cuff was placed over the upper arm and astethoscope bell was placed over the brachialartery at the antebrachium. The blood pressurewas then taken according to the standardtechnics and criteria of the American HeartAssociation.1 Records were made not only ofthe systolic and diastolic levels but, when theywere clearly heard, of the time of appearanceof the intermediate rumble and of the suddenchange in tone auguring the diastolic level.The intermediate rumble usually became

audible at a level 5 to 10 mm. Hg below theonset of the snapping systolic sound. It oftenbecame intensified as the cuff pressure de-creased and occasionally split into a doublesound. The rumble then waned and changedsuddenly to a soft blowing sound, heralding thediastolic level. At a level only 5 to 15 mm. Hgbelow this level the sound usually disappearedentirely.The loudness and intensity of the rumble

was notable in all male subjects tested. Insome patients the intermediate sounds couldbe heard only with difficulty. They were oftenabsent or barely discernible especially in non-gravid women. They were easily heard inwomen in the last trimester of pregnancy.

These data lend themselves to the interpre-tation that the intensity of the intermediateKorotkoff sounds was related in some way tothe volume of blood flow to the distal portionof the extremity. In men with good muscular

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SIMON RODBARD

development of the forearm, the blood flowsupplied to this part is greater than in womenwith lesser muscular development. In pregnantwomen, generalized vasodilatation is the rule,the extremities apparently sharing in the in-creased cardiac output.3 To test this interpre-tation, experiments were designed to inducean increased or decreased flow through the armdistal to the cuff.

Effect of Reactive Hyperemia and Tourniquetupon ArteriophonogramsIn 15 subjects the Korotkoff sounds were

recorded by means of a Cambridge phono-cardiographic apparatus. The intensity and

-- l

A simple procedure was used to inducereactive hyperemia. The pressure inathe sphyg-momanometer cuff was raised above thesystolic pressure (250 mm. Hg) in order to ob-struct the blood flow beyond the cuff. Thepatient was then directed to open and closethe fist of the affected arm 50 times in about35 seconds. The cuff pressure was then allowedto fall as in the usual blood pressure determina-tion. This procedure had no effect on the sys-tolic and diastolic pressures, 'but the inter-mediate rumble was markedly intensified andprolonged in all instances (fig. 1, E).

Observations were also made on the Korot-koff sounds during obstruction to flow through

FIG. 1. Phonoarteriograms obtained on a normal subject. Record C (control) shows the soundsrecorded in a resting subject while the cuff pressure was permitted to fall rapidly as noted in thecalibrations given in millimeters of mercury at the bottom of the figure. Time is in 0.04 second.

Record E (exercise) was obtained after the sphygmomanometer cuff pressure had been raised andkept at 250 mm. Hg for 35 seconds, with the fist being opened and closed 50 times in this time period.Note the increased intensity and duration of the Korotkoff sounds in this reactive hyperemic period,compared with the control.

Record T (tourniquet) was obtained when a tourniquet was in place immediately distal to themicrophonic pickup. Note the marked diminution in intensity and duration of the Korotkoff soundsin this period of reduced flow, compared with the control. (Discussed in text.)

duration of the sounds were recorded as thecuff pressure fell from above systolic to lessthan diastolic (fig. 1, C). These records madeit possible to analyze the sounds objectivelyafter maneuvers affecting blood flow to ex-tremities. *

* The aural interpretation of intensity of a soundis due to a combination of amplitude of vibration,duration and frequency spectrum. This is particularlytrue in sounds of short duration as may occur in theKorotkoff or heart sounds. Graphic recording withstandard phonocardiographic equipment provides ameasure of the duration of the sound but does notalways give an entirely adequate representation ofthe frequency-time spectrum or of the subjectiveinterpretation of "intensity."

the arm. For this purpose, a tourniquet cuffwas placed immediately distal to the stetho-scope bell. This tourniquet cuff was then in-flated to 250 mm. Hg. Blood pressure deter-minations were then made as usual. Thetourniquet procedure had no effect on thesystolic and diastolic pressures, but in allinstances the intensity and duration of theKorotkoff sounds were markedly diminished(fig. 1, T).

MODEL EXPERIMENTS

Further studies were undertaken on a modelutilizing a segment of soft-walled Penrosetubing as an "artery" (fig. 2). The "artery"

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SIGNIFICANCE OF INTERMEDIATE KOROTKOFF SOUNDS

was enclosed in a glass chamber so that itcould be partially compressed by applying airpressure by means of a sphygmomanometerbulb. The cuff pressure was measured with amanometer attached to a side arm of the glasschamber. The arterial pressure was providedby maintaining a column of water at a fixedlevel above the artery.The pressure in the cuff was then raised

above the level of the supply reservoir. A smallbut definite volume of water flowed through

reservoir. When the flow was increased, ascould be done by providing a higher "arterial"pressure, the intensity of the sound was alsoincreased. When flow was stopped the sound

CUFF PRESSURECM H20140 p O

120

100

80

60

40

20

0

01i 56

1444239

,37

22

0

00

a. m m m

14

20 30 40 50 60 70

FIG. 2. Diagram of model employed. Flow takesplace under a driving head, A, through a rigid tubeto the "arterial" segment, B, and then out throughthe rigid portion, C. Cylinder D encloses the segmentABC. E are rubber stoppers inserted into each end ofcylinder, D, with holes permitting tubes A and Cto pass through. F is a syringe bulb used to increasepressure in the glass cylinder chamber, the pressure

being indicated in manometer G. (Discussed in text.)

the "artery," the amount depending on thelevel of the cuff pressure (fig. 3).The cuff pressure was then permitted to fall

steadily. When the cuff pressure was exactlyequal to the lateral pressure at the inlet tubeto the elastic segment, the walls of the "artery"began to vibrate, producing an audible murmurand a palpable thrill. Observation of the seg-ment by stroboscope or high speed cinematog-raphy revealed a regular fluttering of thewall at rates varying from 20 to 100 per second.The production of sound was absolutely

dependent on the occurrence of flow throughthe artery (fig. 4). The intensity of the soundwas associated with the height of the supply

FIG. 3. Flow through the elastic segment illus-trated in figure 2. Flow is maintained by a drivinghead arranged to provide a lateral pressure of 120cm. H20 at the inflow to the "artery." Vertical axisrepresents cuff pressure (sphygmomanometer) incentimeters of water. Horizontal axis gives flow inmilliliters per second. The numbers on the curve

represent the fundamental frequency of flutter of the"artery" at different degrees of compression indi-cated by the vertical axis. This value was obtainedwith the use of the stroboscope. When cuff pressureis higher than driving (arterial) pressure, a smallflow occurs, but no murmur is produced (flutterfrequency equals zero). When cuff pressure fallsbelow lateral pressure, flow continues to increase, butat a different slope, and the murmur is heard withfundamental frequencies indicated by the numbersalongside the curve. At a critical lower cuff pressurethe murmur suddenly ceases. Below the critical value,cuff pressure has little effect on flow. (Discussed intext.)

also stopped. The frequency of flutter, andthe fundamental pitch of the sound, were

dependent on the cuff pressure, that is, uponthe degree of compression of the elastic seg-ment. As the cuff pressureriwasylpermitted to

0 10F LOWCC/SEC

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SIMON RODBARD

fall, a critical level was reached, usually about20 cm. H20, below which the murmur andthrill ceased abruptly.

DIscUSSIONWhen the auscultatory method of blood

pressure determination was first described byKorotkoff,4 many attempts were made toexplain the mechanism of the sounds. Theseexplanations have included attributing thesounds to the passage of the blood pressurewave, causing the opening of the compressedartery and producing a slapping tone,4 towater-hammer pulses,5 to vibrations producedby a change in the form of the compressedvessels,6 to conversion of the compressed areaof the arm into a resonating mass,7 and to

together, and the degree of constriction in-creases. The velocity of the stream through theconstricted area increases further, the lateralpressure is reduced still more and the process ofconstriction becomes more marked. This con-tinues until the vessel is almost entirely closed.At this point, velocity drops toward zero andall the energy of the column becomes availableas lateral pressure. The walls of the constrictedportion are then momentarily blown apart.Then the process of increased velocity with itsprogressive constriction begins again and thecycle is repeated. These flutterings of the wallsare suggested as the mechanism of productionof murmurs and palpable thrill. When the cuffpressure is above arterial pressure, a slightflow takes place but no flutter is produced.

_-- A~~~~lo-_ Heiw01i

FIG. 4. Phonogram obtained in model experiment. The horizontal white bars show two periodsduring which water was permitted to flow through the elastic segment of the apparatus describedin figure 2. Flow was obstructed in the intermittent periods. Time is in 0.04 second. Sound is notedin the upper tracing shortly after flow begins and disappears shortly after flow ceases. (Discussedin text.)

waves reflected from the point of occlusion.8Other factors have been implicated in theproduction of the sounds heard in sphygmoma-nometry, including turbulence, impact andrecoil.'Our present results suggest that the flutter

mechanism with the production of murmursand thrills is derived from the operation of thelaw of conservation of energy. In brief, thislaw states that the energy of a volume of fluidmay be considered to be the sum of the energyexpressed as lateral pressure, plus the kineticenergy of movement. As applied to the arteryunder the cuff, the following events take place:The artery is partially constricted by thepressure in the cuff. As blood flows through thestenotic portion, its velocity must increase.The increase in velocity results in a reductionin lateral pressure energy at the constrictedsite. In consequence, the lateral pressure atthis point falls, the walls tend to move closer

When cuff pressure has fallen to levels at whichno stenosis is produced, flutter is again absentsince there is no site of high velocity flow.

In the case of sphygmomanometry the flut-tering is probably produced at the site of partialconstriction of the artery underneath the cuff.The flow through the arterial segment underthe cuff, when arterial pressure is greater thancuff pressure, is presumed to throw the wallsinto flutter producing the Korotkoff sounds.The experiments with the model suggest thatthe greatest flutter activity occurs at the distalend of the artery under the cuff. This mayaccount for the fact that the sounds are loudestat this point.The present study suggests that the dura-

tion and intensity of the Korotkoff sounds are

related to flow through a segment of collapsiblevessel. Reduction of flow produced by place-ment of a tourniquet beyond the point ofauscultation results in a diminution or even

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SIGNIFICANCE OF INTERMEDIATE KOROTKOFF SOUNDS

elimination of the sounds. An increase in thevolume of flow brought about by the produc-tion of a reactive hyperemia causes anintensification and prolongation of the mur-murs. Similar effects can be illustrated re-peatedly in the model. The intensity and dura-tion of the Korotkoff sounds, therefore, maybe considered to provide a rough, but perhapsuseful, appreciation of the volume flow throughthe arteries under the cuff. This volume bloodflow depends, of course, on the resistance toflow through the vascular bed of the extremity,provided arterial pressure is constant.

In other studies10 we have demonstratedthat a rough index of flow through peripheralarteries can be obtained by appropriate analy-ses of oscillometric pulsations. A combinationof the technic described in the present com-munication and that utilizing oscillometricpulsations may provide a simple clinical ap-praisal of flow through the vessels of theextremities, or, conversely. of the peripheralresistance provided by the vascular bed ofthe extremity. This may perhaps be achievedby noting simultaneously the intensity of themurmurs and the oscillations of the sphygmo-manometer mercury column or aneroid indi-cator.

SUMMARY

Conditions favoring blood flow (reactivehyperemia) through the arteries under thesphygmomanometer cuff increased the in-tensity and duration of the sounds heard dur-ing auscultatory measurement of the bloodpressure. Conditions reducing flow through thearteries under the cuff, as by the application ofa tourniquet distal to the stethoscope pickup,decreased the intensity and duration of thesesounds. The murmurs heard over the arteryare shown to be produced as a result of the dy-namic pressure-velocity relationships resultingfrom partial constriction of the vessels by the

cuff pressure. The intensity and duration ofthe Korotkoff sounds, therefore, can be usedto appraise the blood flow into an extremity.

SUMARIO ESPAROLExcepto por los sonidos que indican los nivie-

les de presion sistolica y diastolica, los ruidospresentes durante la esfigmomanometria songeneralmente ignorados. Nuestros estudios su-gieren que la intensidad y duracion de estosruidos proveen un estimado de la circulacionde sangre a la parte distal de la banda pneuma-tica bajo ciertas condiciones.

REFERENCES1BORDLEY, J., III, CONNOR, C. A. R., HAMILTON,

W. F., KERR, W. J., AND WIGGEIAS, C. J.:Recommendations for human blood pressuredeterminations by sphygmomanometers. Ci rcu-lation 4: 503, 1951.

2 RODBARD, S.: Hydrodynamics illustrated in anartificial circulation model (varicosities, aneu-rysms, coarctation, sphygmomanometry, cor-onary flow). J. Appl. Physiol. 5: 191, 1952.

ABRAMSON, D. I.: Vascular Responses in tle Ex-tremities of Man in Health and Disease. Chi-cago, University of Chicago Press, 1944.

KOROTKOFF, N. C.: On the question of methods ofdetermining the blood plessure. Reports of theImperial Military Medical Academy, St. Peters-berg 11: 365, 1905.

ERLANGER, J.: Studies in blood pressure estima-tion by indirect methods. II. The mechanismof the compression sounds of Korotkoff. Am. J.Physiol. 40: 82, 1916.

6MACWILLIAM, J. A., AND MELVIN, G. S.: Theestimation of diastolic blood pressure in man.Heart 5: 153, 1914.

7FLACK, M., HILL, L., AND MCQUEEN, J.: Themeasurement of the arterial pressure in man.Proc. Roy. Soc., London, s.B 88: 508, 1915.

8VON FREY: Quoted in reference 5.9EDWARDS, E. A., AND LEVINE, H. D.: IPeripheral

vascular murmurs. Mechanism of productionand diagnostic significance. Arch. Int. Med. 90:284, 1952.

'° RODBARD, S., AND JANNOTTA, F.: An analysis ofoscillometrie pulsations. Circulation 7: 922,1953.

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SIMON RODBARDThe Significance of the Intermediate Korotkoff Sounds

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1953 American Heart Association, Inc. All rights reserved.

is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation doi: 10.1161/01.CIR.8.4.600

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