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Korotkoff Sounds

Observations on Pressure-Pulse ChangesUnderlying Their Formation

By MORTON E. TAVEL, M.D., JAMES FARIs, M.D., WILLiAM K. NASSER, M.D.,

HARVEY FEIGENBAUM, M.D., AND CHARLES FIsCH, M.D.

SUMMARYWe have studied Korotkoff sounds in 10 subjects by recording pressures and sounds

simultaneously through a brachial arterial needle at locations both beyond and beneaththe inflatable cuff. The Korotkoff sounds coincided with a small dip and ensuing steeprise in pressure immediately beyond the distal edge of the cuff. Sound intensity parallelednot only the rate and the acceleration of this steep ascent, but also the total pressurethrough which it was maintained. Pressures beneath the midportion of the cuff showeda more pronounced sharp initial negative dip, usually followed by a rapid reversal andsteep rise, and the sounds were also recorded here in association with these rapid pressurechanges. This study supports the hypothesis that the initial Korotkoff sound is producedby rapid changes of pressure both beneath and distal to the compressing cuff, sufficientin rate to impart sonic vibrations to the vessel wall and surrounding tissues. We haveattempted to explain how these rapid pressure changes are produced.

Additional Indexing Words:Intravascular soundsSphygmomanometry

S INCE Korotkoff introduced the ausculta-tory method for indirect sphygmomano-

metry in 1905,1 many theories have beenpromulgated to explain the genesis of thesounds produced. There remains, however,no generally accepted explanation of themechanism of origin of these sounds.Erlanger,2 in 1916, proposed the water-ham-mer theory, which relates the sounds to thevibrations produced when blood enters thecompressed artery with a velocity far in ex-cess of normal velocity, striking the bloodin the uncompressed artery. In later studies,Erlanger3 and Bramwell,4 working in Erlan-

From the Department of Medicine, Indiana Uni-versity School of Medicine and the Krannert In-stitute of Cardiology, Marion County General Hosptal,Indianapolis, Indiana.

Supported in part by the Herman C. KrannertFund, U. S. Public Health Service Grants HE-6308,HTS-5363, HE-5749, and the Indiana Heart As-sociation.

Circulation, Volume XXXIX, April 1969

Indirect deternination of blood pressure

ger's laboratory, proposed that the rapid vibra-tions, or positive and negative "pre-anacroticwaves" that appear in front of the main up-stroke of the brachial pulse, cause interferencein the course of transmission and that this isan important factor in producing the Korotkoffsounds.

Other theories5 have centered about flow-induced vibrations. These have implicatedturbulent jets, turbulent wakes, cavitation,systolic impact with stenotic flow and pro-todiastolic recoil, resonation of the arm asthe pulse enters, and phenomena attributedto the Bernoulli effect.Rappaport and Luisada6 proposed the idea

that these sounds are produced not only bythe greatly increased blood velocity at thetime of beginning ejection as it passesthrough the partially collapsed artery, butalso by the rapid distention of the arteryand surrounding tissue due to the sharpprimary pulse oscillation. More recently, the

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findings of McCutcheon and Rushmer5 havetended to support this latter concept. Amajor obstacle to this theory, however, is pro-vided by the finding of Lange and asso-

ciates' that sounds recorded from the sur-face of the skin at the distal edge of thecuff preceded the arterial pressure rise inthis area. They concluded that "Korotkoffsounds are related to periods of unsteadyflow and that these periods occur as theresult of rapid changes from one velocityprofile to another. The energy which is re-leased manifests itself as sound."

In the various previous studies addressedto this problem, there is a notable lack ofconcern with simultaneous intravascularsound and pressure recordings in the twoareas of major importance, namely the por-tions of the vessel both beyond and beneaththe occluding cuff. In this study, therefore,we have sought, by the use of such record-ings, information about how and where theKorotkoff sound is produced.

MethodsWe have studied 10 subjects who underwent

cardiac catheterization for diagnostic evaluation(table 1). A needle was inserted into the bra-chial arteiy in the antecubital fossa (18-gaugeJelco intra-arterial needle with plastic shaft, or18-gauge Cournand needle). A standard in-flatable sphygmomanometer cuff (14 cm wide)was used. Experiments were performed withthe tip of the Jelco plastic shaft beneath themidportion of the cuff and also with the cuffpositioned above the needle tip, so that theneedle tip lay immediately beyond the distaledge of the cuff. One study was performed witha cuff 7 cm wide so that the needle tip couldalso be positioned just proximal to the upperedge of the cuff.

Intravascular pressure events were recordedby connecting a Statham strain-gauge pressuretransducer (P23Db) directly to the hub of theintra-arterial needle without any interveningplastic tubing. The incoming electrical signalswere recorded with a multichannel Electronicsfor Medicine recorder (model DR-8) at a paperspeed of 100 mm/sec.

Intravascular sounds were simultaneously re-corded by the method described by Luisadaand Lui.8 This entails differentiation of thepressure waves and subsequent filtration througha band-pass filter which was set at 40 to 2,000cps (filter slope of 6 db [decibels] per octave


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KOROTKOFF SOUNDS

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Changes in the various measures at various cuff pres-sures in case 2 (needle tip placed beyond the distaledge of the cuff). Units of sound amplitude are ar-bitrary and based upon maximum height of wave de-flection.

beyond cut-off limits). The response of thissystem,9 although not linear, has been shownto be capable of recording frequencies up to430 cps before a significant loss of amplituderesults. Korotkoff sounds were easily recordedwith this apparatus, owing to the fact that theylie chiefly in the range of 40 to 300 cps.5 10-12The lack of linearity of the transducer precludedattempts to compare sound intensity among dif-ferent patients, but we were able to obtain arough estimate of changes of sound intensityin the same patient (fig. 1). There was a 5-msec delay of wave conduction through thissystem, and this was ascertained by the follow-ing experiment: The intra-arterial needle tipOrculation, Volume XXXIX, April 1969

was submerged in a water-filled beaker, and acontact microphone was applied to the externalsurface of this container. Sound was producedby tapping sharply on the container at a pointmidway between the needle tip and micro-phone, and two simultaneous sound recordswere made and compared at a paper speed of200 mm/sec.

Sounds were recorded with a crystal micro-phone (Electronics for Medicine) from the sur-face of the skin at the lower edge of the cuff.These sounds were filtered with a band-passfilter set at 40 to 2,000 cps.The rate of change of the arterial pressure

(dp/dt) was continuously determined with anRC differentiating circuit (Electronics for Med-icine), having a 0.00044 sec time constant.The differentiating circuit was calibrated byimposing a signal of constant and known slopefrom an integrating amplifier and measuringthe resulting response of the differentiator. Thesecond derivative (dp/dt2) was estimated bymeasuring the time elapsing from the lowestpoint of the pressure front (usually the nadir ofa small dip) to the point at which the peakfirst derivative was reached. This time was thendivided into the previously determined firstderivative (dp/dt) from the same wave com-plex. The time intervals were measured withthe aid of a hand lens and were accurate with-in -+- 1 msec.The basic experimental method was as fol-

lows: With the intra-arterial needle in place,the sphygmomanometer cuff was inflated to alevel exceeding the patient's systolic blood pres-sure. The cuff was then gradually deflated, therecording begun, and with each successive 10mm Hg drop in pressure, a mark was placed onthe recording strip. An aneroid manometer wasused and standardized with a mercury mano-meter.

ResultsNeedle Tip Placed Immediately Beyondthe Lower Edge of the Cuff

When the cuff is inflated to pressures ex-ceeding systolic pressure, the intravascularpressure at this point falls for several sec-onds and reaches a plateau of approximate-ly 30 to 70 mm Hg.As the cuff pressure falls slowly below

systolic pressure levels, one begins to seesudden pressure changes at the point justdistal to the lower edge of the cuff (fig. 2).The initial disturbance is a small quick pres-sure dip lasting from 2 to 10 msec, followedby a sudden rise. From figures 3 and 4, one

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(A to C) Continuous recording in case 2 as the cuff pressure falls gradually from 140 to 0. Intra-vascular sounds and pressures are recorded through a needle tip placed just beyond the loweredge of the cuff, and external sounds are recorded with the microphone placed on the skinoverlying the needle tip.

can see that the onset of the intravascularKorotkoff sounds coincide exactly with thisearly dip, but that the sounds' maximumamplitude coincides with the steep rise im-mediately thereafter. Moreover, the relativesound amplitude varies according to cuff-pressure levels, reaching maximum levelsmidway between systolic and diastolic pres-

sures. Changes of sound amplitude bore a

close relationship to the changes of maxi-mum rates of rise (dp/dt) of each accom-

panying steep wave front (fig. 1). As thecuff pressure falls well below the systoliclevels, but still remains above diastolic pres-

sure, the wave form following the steep ris-ing portion becomes larger and slower and


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KOROTKOFF SOUNDS

140-

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Figure 3Magnified portion from figure 2 (the locations 1 and2 are denoted in figure 2 by the numbered arrows).In the complex at the right the brachial pressureshows a small rise preceding the initial dip.

begins to resemble the normal arterial pulse.The small pressure dip described above

preceded the rapid pressure rise in most ofthe beats. Occasionally, we were able toidentify an extremely small, slow rise pre-ceding the small initial dip (fig. 3). As cuff-pressures fell to near diastolic levels, thedip disappeared, the wave appeared to showa squared contour at the onset of its rise,the maximum rate of rise fell, and the soundsbecame softer and lower in frequency (fig.2, beats 2 to 4 of line C). This point wasbelieved to correspond to subjective "muf-fling" of the sounds. Shortly thereafter, asthe pressure in the cuff was further reduced,the sounds disappeared, and the waveadopted a normal-appearing rounded slowrise.During sound production, the height

through which the accompanying steep pres-sure front was sustained could be measuredin most waves from the nadir of the early dipto the point at which the wave form changedabruptly from a rapidly to a slowly ascendingslope. The height of the steep wave front,so determined, paralleled closely the peakrate of pressure rise (dp/dt) of this wavefront, and, therefore, also varied with thesound intensity changes (fig. 1).Circulation, Volume XXXIX, April 1969

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(A) All pressures and sounds are recorded just beyonddistal edge of cuff, showing all phenomena beginningsimultaneously. (B) With the brachial pressure andintravascular sounds recorded from beneath the cuff,these events are seen to precede the external soundsrecorded just beyond the distal edge of the cuff.

From figure 1, one can also see that thesound derivative (dp/ dt2 ) of the pulse as-cent varies in the same direction as themaximum slope, or first derivative, of thiswave, thus also paralleling closely the in-tensity of the Korotkoff sounds.The sounds recorded through a micro-

phone placed on the surface of the skinover the needle tip begin simultaneously

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Figure 5Maximum rate of rise of brachial pressure (dp/dt)without compression plotted against the maximumrate of pressure rise at the time of loudest Korotkoffsound for each of the 10 cases (r = 0.6614, P < 0.02).

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with those recorded internally, when allow-ance is made for the small delay throughthe later circuit (figs. 3 and 4).The maximal rate of rise (dp/dt) of the

parent pulse wave (the wave which is propa-gated from the aortic root to reach the upperedge of the cuff) appears to influence the max-imal rate of rise of the steep pressure ascentappearing below the cuff during the loudestKorotkoff sound. The scatter plot in figure 5shows a slight but significant correlation (r =0.6614) P < 0.02) between these two measures.

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This suggests that more rapidly ascending pulsewaves, upon reaching the occluding cuff,are more apt to produce a steeper wavefront emerging from below the cuff at thetime of inscription of the loudest Korotkoffsounds.

Needle Tip Placed Beneath the CuffWhen the cuff was positioned in such a

way that the needle tip lay beneath the mid-portion of the cuff (7 cm above the loweredge) in three patients, the recorded pres-sure pulses and sounds were modified in a

150

Brach. Pressure

Figure 6With the needle tip lyinzg beneath the middle of the 7-cm compressing cuff, the pressure withinthe cuff is allowed to fall slowly. Each intravascular sound accompanies a sharp niegative anda sharp positive deflection of the brachial pulse. Several beats give rise to two separate Korot-koff sounzds, attributable to the bifid pulse of idiopathic hypertrophic subaortic stenosis (case 8).

Circulation, Volume XXXIX, Apri 1969

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KOROTKOFF SOUNDS

130 ClU'if r~es 120 IPs'iolllPil!!ioIl Figr 711

Figure 7Repeat tracing of case 8 (see fig. 6) with the compressing cug moved proximally to allow theneedle tip to lie beyond the distal edge of the cuf. In this position, the sounds appear louderthan those recorded at the same sensitivity beneath the cuff, and the initial negative pressuredips are smaller.

characteristic fashion. The resting intravas-cular pressure between heart beats was ap-proximately that present within the interiorof the cuff. As the cuff-pressure fell to sys-tolic levels, each beat resulted in a prom-inent sharp negative deflection (which wasoften the major deflection) followed by asudden rise (fig. 6). Korotoff sounds wererecorded in this location and correspondedin time to both the dip and subsequent rise.Similar to the situation described above forthe pressures at the lower cuff edge, wecould occasionally identify a diminutive slowrise preceding the sharp initial dip. Through-out the major range of cuff pressures asso-ciated with Korotkoff sounds, the early dipwas present and more pronounced than itscounterpart recorded beyond the distal edgeof the cuff (figs. 6 and 7). As the cuffreached diastolic levels, the initial dip dis-appeared in much the same fashion as thatdescribed for the pulse wave beyond thedistal edge of the cuff. These pressure trac-ings resemble closely the volumetric changesrecorded in the vessel beneath the com-pressing chamber in the classic study ofErlanger.3

In one case where intravascular soundswere recorded with the same sensitivityfrom both beneath and beyond the cuff(figs. 6 and 7), both the sounds and firstderivative of the pressure rise were less inamplitude in the position beneath the mid-portion of the cuff. When the 14-cm cuffCirculation, Volume XXXIX, April 1969

was adjusted so that the tip of the needlelay under more distal portions, or when theentire distance underlying the 7-cm cuff wasexplored, numerous resulting tracings re-sembled those produced midway beneaththese cuffs.The location of earliest sound production

was ascertained in the following fashion:With both the external microphone andneedle tip at the distal edge of the 14-cmcuff, Korotkoff sounds were recorded. Thenthe cuff and external microphone weremoved down in such a way that the needletip lay beneath the midportion of the cuff (7cm above distal edge), and the externalmicrophone continued to lie at the distaledge of the cuff. Figure 4 shows soundsrecorded from both positions at cuff pres-sures of 80 mm Hg. From this one can seethat the internal sounds begin concomitant-ly with the external sounds when the needletip is beyond the cuff, but with the needlebeneath the cuff, the sounds recorded fromthis point clearly precede the external soundsrecorded just beyond the cuff. This indicatesthat the sounds appear earlier beneath thecuff than at points beyond the distal edge.

Needle Tip at the Proximal Edge of the Cuff

In the one experiment performed with thenarrow cuff, the tip of the intra-arterialneedle was positioned at the proximal edgeof the cuff. At this position, no Korotkoffsounds were recorded at any time.

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DiscussionOur study shows clearly that the Korot-

koff sounds appear both beneath and be-yond the cuff and coincide exactly withrapid and abrupt changes of pressure atthese locations. The sounds appear more in-tense, however, beyond the cuff. The rela-tive intensity of the resulting sound appearsto be inextricably associated with both therate of pressure rise (dp/dt) and also withhow quickly this maximum rate of rise isattained (dp/ dt2). Sound intensity is alsorelated to the amplitude of the steep pres-sure front regularly accompanying thesesounds. This abruptly rising pressure frontrequired as little as 2 to 4 msec to rise fromits minimum to its maximum height, mean-ing that such pressure changes are capableof inducing sound vibrations as rapid as250 to 300 cps. This finding coincides withthat of previous workers,10-12 which placesthe major frequency spectrum of these soundsbetween 20 and 300 cps. The steep wave frontmight be likened to a sharp "tap"5 on the tis-sues, during which the arterial wall and sur-rounding structures are set into vibration, last-ing until the pronounced damping effect ofthe soft tissues quickly eliminates them. Thisinitial transient, upon which the clinician reliesprimarily for blood pressure determina-tions,13 is not related to the amount of bloodflowing through the narrowed segment, butmay be related to rapid acceleration ofblood. A supervening, more prolonged "com-pression murmur" is sometimes heard and isrelated to turbulence (or eddy formation)of the high-velocity jet through the con-stricted segment.5 The appearance of soundsfirst beneath the occluding cuff coincidentwith an early dip in pressure provides evi-dence against the water-hammer theory ofsound production.The pressure phenomena noted in our

study might best be explained in the follow-ing manner: When the occluding cuff is in-flated to levels above systolic levels, one is,in effect, separating the arterial tree intotwo noncommunicating components-a por-

tion proximal and a portion distal to thecuff. The arterial segment beneath the cuffis collapsed, but the distal segment, main-taining a significant, although lower, intravas-cular pressure, remains open. The persistenceof such pressure in the distal segmentprobably can be attributed to the factthat the venous outflow is also occluded,and venous pressure equilibrates with arte-rial pressure. A head of pressure may alsobe directed into this distal system from prox-imal arteries via vascular collaterals throughbone. When the pressure in the cuff fallsjust beneath systolic pressure levels, thelower portion of the arterial pulse wave,which lies below cuff pressure, fails to pene-trate the entire length of the vessel beneaththe cuff. In the process of being extinguished,however, this lower portion of the waveprobably opens a cone-shaped segment ofthe vessel beneath the proximal cuff, asshown by the studies of Erlanger.3 13 Thediminutive slow intravascular pressure riseoccasionally seen preceding the sharp initialdip probably reflects a small pressure risewithin the vessel beneath the cuff as thefoot of the pulse wave is extinguished andmight correspond to the formation of thiscone. During that phase, we have observedan increase of pressure within the pneumat-ic cuff, and this rise is probably transmittedto a distal vessel, accounting for a similarintravascular pressure rise at this level aswell. Only the summit of the pulse wavewhich is higher than cuff pressure succeedsin opening the entire length of the vesselunderlying the cuff. With this opening, theresuddenly appears an open conduit betweenthe high pressure in the vessel underlying thecuff and the relatively low pressure in thedistal vessel. As might be anticipated, the highpressure in the artery beneath the cuff thendrops precipitously in the direction of thelower pressure beyond.With this sharp drop in pressure, a new

lower pressure equilibrium is reached at thearterial junction formed at the distal edgeof the cuff. This favors a slightly lower pres-sure in the portion of the artery beyond the


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KOROTKOFF SOUNDS

distal edge of the cuff and probably accountsfor the early pressure dip at that level whenthe Korotkoff sound begins. Such a "pre-anacrotic" pressure dip in the distal vesselhas been noted previously.3 4 14 During theearly pressure dip in the vessel underlyingthe cuff, the pressure in the advancing proxi-mal wave continues to rise and thus createsa pressure differential between the higher por-tion of this proximal wave and the momentari-ly lower pressure beneath the cuff. Such apressure difference appears to supply thedriving force to create the ensuing rapid pres-sure rise both beneath and beyond the cuff.This steep pressure ascent is finally terminatedas one of two conditions is fulfilled: (1) Thepressure in the distal vessel (beneath and be-yond the cuff) rises to a point where it equalsthe higher instantaneous pressure in the prox-imal wave, at which time both waves equal-ize and continue to follow a pattern thatresembles the normal pulse wave. (2) Thepressure in the distal vessel rises rapidlyuntil the advancing pressure pulse penetrat-ing the cuff is disspiated and can no longermaintain the vessel underlying the cuff inan open position. This results in reclosureof the vessel underlying the cuff before thepressure beyond the cuff can equalize withthe pressure in the vessel beneath the cuff.The latter event is always seen when thecuff pressure is inflated to near systolic lev-els and probably accounts for the failure ofthe pulse beyond the cuff to ascend to sys-tolic pressure levels (figs. 2 and 7). Withrelatively high cuff pressure, the only por-tion of the pulse wave lying above cuff pres-sure is its rounded peak portion, a portionwhich is probably incapable of maintainingthe occluded segment in an open positionfor a prolonged period.When the cuff pressure falls to diastolic

and subdiastolic levels, the arterial segmentunderlying the cuff remains open through-out, proximal and distal pressures then re-main equal, and the factors mentionedabove are no longer operative in producingthe momentary pressure differences and theCirculation, Volume XXXIX, April 1969

rapid pressure changes responsible for soundproduction.Our findings are in sharp conflict with

those of Lange and co-workers,7 who foundthat (1) the Korotkoff sounds preceded thepressure rise in the arterial segment beyondthe cuff, (2) the rise in pressure beyondthe cuff was usually not preceded by a dip,and (3) the duration of the anacrotic pres-sure rise was on the order of 0.04 to 0.08sec, which was deemed too slow to accountfor a sound vibration of up to 200 cps. Be-cause of these observations, they discardedthe idea that sounds could be produced bysudden expansion of the vessel wall. Theirpressures, however, were recorded througha needle connected to an 80-cm length ofplastic tubing, and when their tracings arescrutinized, they appear damped. In thisstudy we found that even with direct cou-pling of the transducer to the needle, damp-ing would occur unless extreme care wasexercised to exclude all air bubbles and par-ticulate matter. Damping may also eliminatethe early dip preceding the rapid rise.

References1. KOROTKOFF, N. C.: On the question of methods

of determining the blood pressure. Reportsof the Imperial Military Academy, St. Peters-burg, 11: 365,1905.

2. ERLANGER, J.: Studies in blood pressure estima-tion by indirect methods: II. Mechanism ofthe compression sounds of Korotkoff. AmerJ Physiol 40: 82, 1916.

3. ERLANGER, J.: Studies in blood pressure estima-tion by indirect methods: III. Movements inthe artery under compression during bloodpressure determinations. Amer J Physiol 55:85, 1921.

4. BRAMWELL, J. C.: Change in form of thepulse wave in the course of transmission.Heart 12: 23, 1925.

5. MCCUTCHEON, E. P., and RuSHMIER, R. F.:Korotkoff sounds: Experimental critique. Cir-culation Research 20: 149, 1967.

6. RAPPAPORT, M. B., and LUISADA, A. A.: Indirectsphygmomanometry. J Lab Clin Med 29:638, 1944.

7. LANGE, R. L., CARLISLE, R. P., and HECHT, H.H.: Observations on vascular sounds: "Pistol-shot" sound and the Korotkoff sound. Circula-tion 13: 873, 1956.

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8. LUISADA, A. A., and Lux, C. K.: Simple methodsfor recording intracardiac phonocardiogramsand electrocardiograms during left and rightheart catheterization. Amer Heart J 54: 531,1957.

9. FRY, D. L., NOBLE, F. WV., AND MALLOS, A. J.:Evaluation of modern pressure recording sys-tems. Circulation Research 5: 40, 1957.

10. GEDDES, L. A., SPENCER, W. A., and HOFF, H.E.: Graphic recording of the Korotkoff sounds.Amer Heart J 57: 361, 1959.

11. WALLACE, J. D., LEWIS, D. H., and KHALIL,S. A.: Korotkoff sounds in humans. J AccoustSoc Amer 33: 1178, 1961.

12. KORNS, M. H.: Nature and tiIne relations ofthe compression sounds of Korotkoff in man.Amer J Physiol 76: 246, 1926.

13. ERLANGER, J.: Studies in blood pressure estima-tions by indirect methods: I. Mechanism ofthe oscillatory criteria Amer J Physiol 39:401, 1916.

14. DRUBE, H. C., and ANSCHUTZ, F.: Vber dasAuftreten von Kubitalispulsen ohne Arteri-entonen bei der Blutdruckmessung nach Riva-Rocci/Karotkoff. Z Kreislaufforsch 43: 534,1954.

Viewpoints of a Biologist and a Chemist

This account illustrates the point that the biological outlook, in particular the realisa-tion that living organisms form a whole in which each component plays a useful part,was essential in clarifying the problem of the intermediary stages of biological oxidations.If there is a difference in the outlook of the biologist on the one hand, and that of thechemist and physicist on the other, it is the urge of the biologist to look upon everyproperty of living material as part of a complex system and to enquire into the functionalsignificance of this property. Time and again this has proved a most fruitful workinghypothesis-and it is no more than a working hypothesis. To do this effectively, he mustbe a widely trained "compleat" biologist. At the same time he must know a good deal ofthe basic sciences. Scientists who are reasonably compleat in biology and the variousbranches of the physical sciences are bound to become exceedingly rare with the increas-ing size of the subjects. So, in the future, the most effective research in biology is likelyto arise from the efforts of teams wvhich include compleat biologists, compleat chemists,compleat physicists and compleat mathematicians.-HANs ADOLF KREBS: The Biologist'sand the Chemist's Approach to Biochemical Problems. In Reflections on Biologic Re-search, edited by Giulio Gabbiani, St. Louis, Warren H. Green, Inc., 1967, p. 127.


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FEIGENBAUM and CHARLES FISCHMORTON E. TAVEL, JAMES FARIS, WILLIAM K. NASSER, HARVEY

FormationKorotkoff Sounds: Observations on Pressure-Pulse Changes Underlying Their

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1969 American Heart Association, Inc. All rights reserved.

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