Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533528 | P a g eAuscultatory and Oscillometric methods of Blood pressuremeasurement: a SurveyKapse C.D.*, Patil B.R***(Department of Instrumentation, Watumull Institute of Electronics Engg. and Computer Technology, Worli,Mumbai (India).** (Department of Electrical Engineering, Lokmanya Tilak college of Enginnring, Koparkhairne, Navi Mumbai(India)Abstract:Accurate measurement and display ofarterial blood pressure is essential formanagement of cardiovascular diseases. Thoughintra-arterial catheter system is considered to begold standard of arterial blood pressuremeasurement, its use is however limited tomeasuring during surgery due to its invasivenature, In view of these problems, investigatorshave been developing non-invasive methods.Some approaches are the skin flush, palpatory,Korotkoff (auscultatory), oscillometric, andultrasound methods. Of these, the methods ofKorotkoff and oscillometry are in most commonuse and are reviewed here.Keywords: Auscultatory Method, Blood Pressure,Kortkooff Method, Ocillometric method, SpotMeasurement of Blood Pressure.I. Introduction„There are two types of methods for arterialpressure measurement; those that periodicallysample also may call as spot measurement and thosethat continuously record the pulse waveform(continuous monitoring). The sampling methodstypically provide systolic and diastolic pressure andsometimes mean pressure. These values arecollected over different heart beats during the courseof one minute. The continuous recording methodsprovide beat-to-beat measurements and often, theentire waveform. Some continuous methods onlyprovide pulse pressure waveform and timinginformation‟ . Automated oscillometric bloodpressure devices are increasingly being used inoffice blood pressure measurement, as well as forhome and ambulatory monitoring. When they areused in the office, the readings are typically lowerthan readings taken by a physician or nurse. Thepotential advantages of automated measurement inthe office are the elimination of observer error,minimizing the white coat effect [2, 3], andincreasing the number of readings. The maindisadvantages are the error inherent in theoscillometric method and the fact that epidemiologicdata are mostly based on auscultated blood pressuremeasures.For spot measurement of BP occlusive cuff methodsare mainly used. „The vascular unloading principleis fundamental to all occlusive cuff-based methodsof determining arterial blood pressure. It isperformed by applying an external compressionpressure or force to a limb such that it is transmittedto the underlying vessels. It is usually assumed thatthe external pressure and the tissue pressure (stress)are in equilibrium. The underlying vessels are thensubjected to altered transmural pressure (internalminus external pressure) by varying the externalpressure. It is further assumed that the tensionwithin the wall of the vessel is zero when transmuralpressure is zero. Various techniques have beendeveloped that attempt to detect vascular unloading.These generally rely on the fact that once a vessel isunloaded, further external pressure will cause it tocollapse. Most methods that employ the occlusivearm cuff rely on this principle and differ in themeans of detecting whether the artery is open orclosed‟ .II. Measurement of Blood Pressure:Historical Review„Although simple palpation of the pulsewas carried out by the early Egyptians, actualmeasurements of the pressure in parts of thecirculation really started in the middle of theeighteenth century with the experiments of StephenHales‟. He inserted a small brass pipe into leftcrural artery of horse; to this pipe glass tube wasconnected. The pumping action of the heartgenerated a pressure force, causing the blood levelto rise in the glass tube .The accurate study of blood pressurestarted with the introduction of mercury manometerby Poiseuille in 1828. He connected the manometerto a cannula filled with potassium carbonate whichacted as an anticoagulant and the cannula wasinserted directly into an artery in the experimentalanimal. Arteries as small as 2 mm in diameter werecannulated and Poiseuille was able to demonstratethat arterial pressure was maintained in the smallerarteries. He also proved that the blood flow throughthe mesenteric capillary bed did not depend onvenous pressure changes, but varied directly witharterial pressure.
Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533529 | P a g eBased on Poiseuille‟s innovations, Carl Ludwigdeveloped kymograph in 1847. He used the cannulaand mercury manometer same as that was used inPoiseuille‟s equipment, but a float with a writingpen attached was buoyed up by the open mercurycolumn and the pen arranged to write on arevolving, smoked drum. This was the first attemptto record the blood pressure.First non-invasive method was introducedin 1855. Vierordt postulated that an indirect,noninvasive technique might be used, by measuringthe counter pressure which would be necessary tocause the pulsation in an artery to cease. In order tosupport this theory, Vierordt attempted to measurethe pressure which was needed to cause obliterationof the radial pulse, by a weight attached to the leverof a sphygmograph. „He did not, however, meetwith very much success, due largely to thecumbersome design of his apparatus. Hissphygmograph was considerably improved byEtienne Jules Marey in 1860. Marey appliedVierordts principle of applying counter pressure toovercome the arterial pressure, but, in his apparatusthe arm was enclosed in a glass chamber filled withwater, which was connected both to asphygmograph and to a kymograph which recordedthe arterial pulsations in the arm. The chamber wasalso supplied with a moveable reservoir of water sothat the pressure in it could be varied, and with amanometer. The determination of the blood pressurewas done by first noting the pressure given by themercury manometer at which the greatest peak topeak distance of the sphygmographic tracingsoccurred, and then gradually increasing the pressureby raising the reservoir. The pressure at which nomore movement of the sphygmograph took placewas recorded as the systolic pressure. AlthoughMareys device was a masterpiece of ingenuity, itwas far too complicated for most doctors to useroutinely‟ .„In 1896, Riva-Rocci reported the methodupon which present-day technique is based. In histechnique a rubber bag, surrounded by a cuff ofsome inexpansible material, was wrapped round thearm and was inflated with air by means of anattached rubber bulb. The pressure in the cuff wasregistered by the usual mercury manometer, and wasincreased until the radial pulse could no longer bepalpated. When the pressure was slowly released themercury level in the manometer fell, and the readingat which the pulse reappeared was taken as thesystolic blood pressure. There was, however, onemain defect in Riva-Roccis method; he used anarrow cuff only 5 cm wide. This caused an acuteangle to form between the upper and lower edges ofthe cuff and the skin, which resulted in local areas ofhigh pressure building up and rendering the readingmildly inaccurate. This error was realized andcorrected by von Recklinghausen in 1901, whoreplaced the narrow armband with a wider one (12cm)‟.In 1905, N C Korotkoff, a Russian army physician,reported that by placing a stethoscope over thebrachial artery at the cubital fossa, distal to theRiva-Rocci cuff, tapping sounds could be heard asthe cuff was deflated, caused by blood flowing backinto the artery. This was the start of auscultatorymethod of blood pressure measurement.„Kortkoff‟s important contribution tomedicine was the devising of an accurate and easymethod of determining the blood pressure. Histechnique has stood the test of time as it has beenused for more than a century with practically nochanges made to it‟. Kortkoff laid the foundationfrom which many investigators worked on [6-9].The pneumatic sleeve or cuff, also referredto as a tourniquet, consisted usually of a rubberbladder woven inside a fabric. It enabled indirect,noninvasive arterial blood pressure measurement.Till today, the cuff has been the single mostimportant component of noninvasive blood pressuremeasurement devices. The cuff is usually attachedaround the arm, wrist or a finger. Pressuremeasurements can be made by using a mercury oraneroid manometer. These are now being replacedwith silicon-based pressure sensors inside automaticmeasurement devices, based usually on theauscultatory or oscillometric method. These devicesmay replace conventional mercury and aneroidmanometers in future .III. Spot Measurement of Blood PressureAuscultatory Method: In 1905, N CKorotkoff, a Russian army physician, reported thatby placing a stethoscope over the brachial artery atthe cubital fossa, distal to the Riva-Rocci cuff,tapping sounds could be heard as the cuff wasdeflated, caused by blood flowing back into theartery.Korotkoff sounds were corroborated by theBritish researchers MacWilliam et al. in 1914 and the American, Warfield in 1912 , who usedintra-arterial pressure measured from a dog as areference. In 1932, von Bonsdorff validatedKorotkoff‟s auscultatory method on humans usingintra-arterial blood pressure as a reference .Later, the characteristic sounds heard during cuffdeflation were divided into five phases on the basisof their intensity. First to publish were Goodmanand Howell (1911), followed by Grodel and Miller(1943), Korns (1926) as well as Rappaport, Luisada(1944) and O‟Brien et al.  in 1979.The method, as employed today, utilizes astethoscope placed distal to an arm cuff over thebrachial artery at the antecubital fossa. The cuff isinflated to about 30 mm Hg above systolic pressureand then allowed to deflate at a rate of 2 to 3 mmHg/s. With falling cuff pressure, sounds begin andslowly change their characteristics. The initial
Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533530 | P a g e“tapping” sounds are referred to as Phase IKorotkoff sound and denote systolic pressure. Thesounds increase in loudness during Phase II. Themaximum intensity occurs in Phase III, where thetapping sound may be followed by a murmur due toturbulence. Finally, Phase IV Korotkoff sound isidentified as muffled sound, and Phase V is thecomplete disappearance of sound. Phase IV isgenerally taken to indicate diastolic arterial pressure.However, Phase V has also been suggested to be amore accurate indication of diastolic pressure.Pressures are recorded to the nearest 2 mm Hg.When all sounds have disappeared the cuff shouldbe deflated rapidly and completely before repeatingthe measurement to prevent venous congestion ofthe arm.„At an initial examination blood pressureneeds to be measured in both arms. If the differencebetween arms is more than 10 mm Hg for eithersystolic or diastolic pressure, the arm with thehigher pressure is used for future measurements.Ideally, records of blood pressure measurementshould show the systolic pressure, the diastolicpressure, the endpoint used, the limb used andwhether right or left, the position of the patient, andthe presence of any arrhythmias or unusualcircumstances such as anxiety or confinement tobed‟ [11, 12]. The Phase III sound can be used todetermine mean arterial blood pressure, asdemonstrated by Davis and Geddes . Figure 1shows mercury sphygmomanometer, placement ofcuff and stethoscope.Measurements based on the auscultatory method aredifficult to automate, because the frequencyspectrum of the different phases of Korotkoffsounds is closely related to blood pressure. When apatient‟s blood pressure is high, also the recordedfrequency spectrum is higher than normal anddecreases as a function of blood pressure. Withhypotensive patients and infants, on the other hand,the highest spectrum components can be as low as 8Hz, which is below the human hearing bandwidth.Figure 1: (a) Mercury Sphygmomanometer; (b) Placement of cuff and stethoscopeNormotensive subjects, in turn, require a bandwidthof 20 Hz to 300 Hz for a sufficient reproduction ofKorotkoff sounds, although most of the energy ofthe signal spectrum is below 100 Hz. Sincetechnology improvements have enabled efficientsignal processing and calculation, a number ofpapers have been published on the classification ofKorotkoff sounds. Cozby and Adhami , forexample, discovered the sub-audible, low frequencypart of Korotkoff sounds and concluded that energyin the 1-10 Hz bandwidth of the total energy risesfrom 60% to 90%, when cuff pressure decreasesfrom above the systolic to a level below it. Thisfeature can be used as a thresholding algorithm fordetermining systolic blood pressure. Regueiro-Gomez and Pallas-Areny  were able to use thespectral energy dispersion ratio to determinesystolic, diastolic and mean blood pressure withhigh precision.In ambulatory measurements, when the patient isable to move moderately, noise may becomedominant, thereby spoiling the measurement. Thismay be avoided by using two identical microphonesunder the cuff, one located on the upper side, theother on the distal side. Ambient noise reaches bothmicrophones at the same time, but the bloodpressure pulse propagating through the brachialartery arrives after a time delay. This phenomenoncan be used for noise cancellation as described bySebald et al. .Allen et al.  used a Matlab based short-term time-frequency analysis to obtain spectralinformation of Korotkoff sounds. Their results showthat phase III has the largest overall amplitude andhigh frequency energy. In contrast, phases IV and Vhave the lowest amplitude and frequencycomponents. Statistically significant transitions wereobserved between the different phases; the transitionfrom phase I to II was characterized by increase inhigh frequency and sound duration, the transitionfrom phase II to III by a significant decrease insound duration, the transition from phase III to IVby decrease in maximum amplitude, highestfrequency and relative high frequency energy, andthe transition from phase IV to V by decrease in themaximum amplitude and high frequency energy.(a) (b)
Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533531 | P a g eThey concluded that the method was able to detectthe five phases also identified by an expertcardiologist, verifying that the method can be usedin automatic blood pressure measurements.Oscillometric Method: The oscillometric methodwas first introduced by Marey in 1876. Erlanger(1904) further improved by attaching a Riva-Roccicuff around the upper arm. Pressure oscillationswere recorded on a rotating drum. Later Pachon(1909) used dual-dial gauges, one for presentingoscillation amplitude and the other for showing cuffpressure. In those days, it was thought thatmaximum oscillation amplitude indicated diastolicblood pressure.Marey (1885) placed the arm within acompression chamber and observed that thechamber pressure fluctuated with the pulse. He alsonoted that the amplitude of pulsation varied withchamber pressure. Marey believed that themaximum pulsations or the onset of pulsations wereassociated with equality of blood pressure andchamber pressure. At that time, he was not certainwhat level of arterial pressure the maximumpulsations corresponded with . It has beentheoretically shown that the variation in cuffpressure pulsation is primarily due to the brachialartery buckling mechanics .Today, oscillometry is performed using astandard arm cuff together with an in-line pressuresensor. Due to the requirement of a sensor,oscillometry is generally not performed manually,but, rather, with an automatic instrument. Therecorded cuff pressure is high-pass-filtered above 1Hz to observe the pulsatile oscillations as the cuffslowly deflates. It has been established that themaximum oscillations actually correspond with cuffpressure equal to mean arterial pressure, confirmingMarey‟s early idea. Systolic pressure is located atthe point where the oscillations, are a fixedpercentage of the maximum oscillations .The majority of non-invasive automated bloodpressure measuring devices currently available, usethe oscillometric method based on empiricallyderived algorithms, generally patent protected,which calculate systolic and diastolic BP. Diastolicand systolic blood pressures can be determinedusing special fractions of the maximum oscillationamplitude, also known as characteristic ratios. Thereare no definite correct values for the systolic anddiastolic characteristic ratios; rather differentmanufactures use different values. Theoretical andexperimental work has suggested the followingvalues for characteristic ratios;(a) Systolic from 0.46 to 0.64 and diastolic from0.59 to 0.80 (theoretical work by Ursino andCristalli in 1996)(b) Systolic 0.593 and diastolic 0.717 (theoreticalwork by Drzewiecki et al. in 1994)(c) Systolic from 0.45 to 0.57 and diastolic from0.69 to 0.89 (experimental work by Geddes etal. in 1982)(d) Systolic (mean and SD) equal to 0.49 (0.11) anddiastolic equal to 0.72 (0.12) (experimentalwork by Amoore et al. in 2007)The oscillometric determination of MAP ismore accurate than systolic and diastolic pressures.Drzewiecki et al. in 1994 employed amodel of oscillometry to evaluate the derivative ofthe oscillation amplitude curve with respect to cuffpressure. When this derivative is plotted against cuffpressure, it was found that it reaches a maximumpositive value. This occurred when cuff pressureequals diastolic pressure. Additionally, theminimum negative value was found to occur atsystolic pressure. The advantage of this approach isthat the empirically based systolic and diastolicratios are not necessary. This method is called asderivative oscillometry .Traditionally, the arterial pulsations inoscillometric devices are picked up from theoccluding cuff by means of a manometer. However,in some implications a photoelectric detectiondirectly from the tissue (PPG) is also used. Othermethods than pneumatic pulse sensing seem to havebecome more popular in the wrist BP devices .IV. Discussion and Conclusion:The oscillometric method is increasinglyused in blood pressure measurement. Due to thesimplicity and reliability of this method, theoscillometric principle is employed in the majorityof present-day automatic and semiautomatic non-invasive blood pressure monitors . Automateddevices may also offer the opportunity to avoidexpensive and repetitive training of health careprofessionals in auscultation, which is necessary toreduce observer errors. Their use still requirescareful patient evaluation for caffeine or nicotineuse, selection of the correct cuff size, and properpatient positioning if accurate blood pressures are tobe obtained. Devices are now available that can takea series of sequential readings and automaticallyaverage them.Automated devices provide timed printoutsof BP, remove many of the sources of errorassociated with the conventional auscultatorytechnique, and thereby improve the overall accuracyof measurement, provided, that they themselves areaccurate. The accuracy and reliability of thesedevices may be questionable; these automateddevices should be validated against standards. Thereare two published standards for the evaluation ofautomatic BP measuring devices, the AmericanAssociation for the Advancement of MedicalInstrumentation standard, and the morecomprehensive protocol of British Hypertension
Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533532 | P a g eSociety. These protocols compare an automated BPmeasurement device against the traditionalauscultatory technique of BP measurement innormotensive and hypertensive subjects with a widerange of BP in varying age groups. On the basis ofthese results, the protocols recommend that onlythose devices that achieve a high grade of accuracyfor both systolic and diastolic BP should berecommended for clinical use .References: Bronzino Joseph D., Editor (2000), “TheBiomedical Engineering Hand Book”,Second Edition, CRC Press LLC, chapterno 71. Alcala F. V., Peralta J. L., Sanchez E. M.,Montoro A. E., Dominguez A. C., andChozas J. M. L. (2004), “AmbulatoryBlood Pressure Monitoring to Study WhiteCoat Effect in Patients with HypertensionFollowed in Primary Care,” Hypertension ,Rev Esp Cardiol , vol. 57, no. 7, pp. 652-660. Pickering T. G., Hall J. E., Appel L. J.,Falkner B. E., Graves J., Hill M. N., JonesD. W., Kurtz T., Sheps S. G. and RoccellaE. R. (2005), “Recommendations for BloodPressure Measurement in Humans andExperimental Animals: Part 1: BloodPressure Measurement in Humans: AStatement for Professionals from theSubcommittee of Professional and PublicEducation of the American HeartAssociation Council on High BloodPressure Research”, Circulation, vol. 111,pp. 697-716. Drzewiecki G., Bansal V., Hood E. K. R.,and Apple H. (1993), “Mechanics of theOcclusive Arm Cuff and Its Application asa Volume Sensor”, IEEE Transactions OnBiomedical Engineering, vol. 40, no.7, pp.704-708. Booth Jeremy (1977), “A Short History ofBlood Pressure Measurement”, Proc. RoyalSociety of Medicine, vol. 70, pp. 793-799. Mac WILLIAM J. A., and Melvin S. P.(1914), “Systolic and Diastolic BloodPressure Estimation, with SpecialReference to the Auditory Method”, BritishMedical Journal, vol. March 1914, pp.693-697. Warfield L. M., (1912), “Studies inAuscultatory Blood-Pressure Phenomena”,Arch. Inter. Med., vol. X(3), pp. 258-267. James Bordley-III, Connor C. A. R.,Hamilton W. F., Kerr W. J. and Wiggers C.J. (1951), “Recommendations for HumanBlood Pressure Determinations bySphygmomanometers”, Circulation, vol.IV, pp. 503-509. OBrien E. T. and OAulley K. (1979),“ABC of Blood Pressure Measurement-Reconciling the Controversies: a commenton the literature”, British Medical Journal,vol. 2, pp. 1201-1202. Tholl U., Forstner K. and Analauf M.(2004), “Measuring Blood Pressure:Pitfalls and Recommendations”, NephrolDial Transplant, vol. 19. pp 766-770. OBrien E. T. and OAulley K. (1979),“ABC of Blood Pressure Measurement-Technique”, British Medical Journal, vol.2, pp. 982-984. Beevers G., Lip G. Y. H., OBrien E.(2006), “ABC of Hypertension BloodPressure Measurement: Part-IIConventional Sphygmo-manometry:Technique of Auscultatory Blood PressureMeasurement”, BMJ, vol. 322, pp. 1043-1047. Devis G. J. and Geddes L. A. (1990),”Auscultatory Mean Blood Pressure”,Journal of Clinical Monitoring, vol. 6, pp.261-265. Blank S. G., West J. E., Muller F. B., CodyR. J., Harshfield G. A., Pecker M. S.,Laragh J. H. and Pickering T. G. (1988),“Wideband External Pulse RecordingDuring Cuff Deflation: A New Techniquefor Evaluation of The Arterial PressurePulse and Measurement of BloodPressure”, Circulation, vol.77, pp. 1297-1305. Cozby R. C. and Adhami R. R. (1993),“Low-Frequency Korotkoff SignalAnalysis and Application”, IEEETransactions on Biomedical Engineering,vol. 40, no. 10, pp. 1067-1070. Regueiro A.-Gomez and Pallas R.-Areny(1996), “A New Indicator for Non-invasiveArterial Blood Pressure Measurement”,18th Annual International Conference ofthe IEEE Engineering in Medicine andBiology Society, Amsterdam, pp. 117-118. Sebald D. J., Bahr D. E., Kahn A. R.(2002), “Narrowband Auscultatory BloodPressure Measurement”, IEEE
Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications(IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 2, March -April 2013, pp.528-533533 | P a g eTransactions on Biomedical Engineering,vol. 49, no. 9, pp. 1038-1044. Allen J., Gehrke T., OSullivan J. J., KingS. T. and Murray A. (2004),“Characterization of the Korotkoff Soundsusing Joint Time-Frequency Analysis”,Physiological Measurement, vol. 25, no. 1,pp. 107. Raamat R., Talts J., Jagomägi K. andKivastik J. (2010), “Comparison ofOscillometric Pulse Amplitude EnvelopesRecorded from the Locally CompressedRadial Arteries”, Medical Engineering andPhysics, vol. 32, pp. 1124-1130. OBrien E., Beevers G., Lip G. Y. H.(2001), “ABC of Hypertension BloodPressure Measurement, Part IV—Automated Sphygmomanometry: SelfBlood Pressure Measurement”, BMJ, vol.322, pp. 1167-1170.