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  1. 1. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533 Auscultatory and Oscillometric methods of Blood pressure measurement: a Survey Kapse 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 of For spot measurement of BP occlusive cuff methodsarterial blood pressure is essential for are mainly used. „The vascular unloading principlemanagement of cardiovascular diseases. Though is fundamental to all occlusive cuff-based methodsintra-arterial catheter system is considered to be of determining arterial blood pressure. It isgold standard of arterial blood pressure performed by applying an external compressionmeasurement, its use is however limited to pressure or force to a limb such that it is transmittedmeasuring during surgery due to its invasive to the underlying vessels. It is usually assumed thatnature, In view of these problems, investigators the external pressure and the tissue pressure (stress)have been developing non-invasive methods. are in equilibrium. The underlying vessels are thenSome approaches are the skin flush, palpatory, subjected to altered transmural pressure (internalKorotkoff (auscultatory), oscillometric, and minus external pressure) by varying the externalultrasound methods. Of these, the methods of pressure. It is further assumed that the tensionKorotkoff and oscillometry are in most common within the wall of the vessel is zero when transmuraluse and are reviewed here. pressure is zero. Various techniques have been developed that attempt to detect vascular unloading.Keywords: Auscultatory Method, Blood Pressure, These generally rely on the fact that once a vessel isKortkooff Method, Ocillometric method, Spot unloaded, further external pressure will cause it toMeasurement of Blood Pressure. collapse. Most methods that employ the occlusive arm cuff rely on this principle and differ in theI. Introduction means of detecting whether the artery is open or „There are two types of methods for arterial closed‟ [4].pressure measurement; those that periodicallysample also may call as spot measurement and those II. Measurement of Blood Pressure:that continuously record the pulse waveform Historical Review(continuous monitoring). The sampling methods „Although simple palpation of the pulsetypically provide systolic and diastolic pressure and was carried out by the early Egyptians, actualsometimes mean pressure. These values are measurements of the pressure in parts of thecollected over different heart beats during the course circulation really started in the middle of theof one minute. The continuous recording methods eighteenth century with the experiments of Stephenprovide beat-to-beat measurements and often, the Hales‟[5]. He inserted a small brass pipe into leftentire waveform. Some continuous methods only crural artery of horse; to this pipe glass tube wasprovide pulse pressure waveform and timing connected. The pumping action of the heartinformation‟ [1]. Automated oscillometric blood generated a pressure force, causing the blood levelpressure devices are increasingly being used in to rise in the glass tube [5].office blood pressure measurement, as well as for The accurate study of blood pressurehome and ambulatory monitoring. When they are started with the introduction of mercury manometerused in the office, the readings are typically lower by Poiseuille in 1828. He connected the manometerthan readings taken by a physician or nurse. The to a cannula filled with potassium carbonate whichpotential advantages of automated measurement in acted as an anticoagulant and the cannula wasthe office are the elimination of observer error, inserted directly into an artery in the experimentalminimizing the white coat effect [2, 3], and animal. Arteries as small as 2 mm in diameter wereincreasing the number of readings. The main cannulated and Poiseuille was able to demonstratedisadvantages are the error inherent in the that arterial pressure was maintained in the smalleroscillometric method and the fact that epidemiologic arteries. He also proved that the blood flow throughdata are mostly based on auscultated blood pressure the mesenteric capillary bed did not depend onmeasures. venous pressure changes, but varied directly with arterial pressure. 528 | P a g e
  2. 2. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533Based on Poiseuille‟s innovations, Carl Ludwig replaced the narrow armband with a wider one (12developed kymograph in 1847. He used the cannula cm)‟[5].and mercury manometer same as that was used in In 1905, N C Korotkoff, a Russian army physician,Poiseuille‟s equipment, but a float with a writing reported that by placing a stethoscope over thepen attached was buoyed up by the open mercury brachial artery at the cubital fossa, distal to thecolumn and the pen arranged to write on a Riva-Rocci cuff, tapping sounds could be heard asrevolving, smoked drum. This was the first attempt the cuff was deflated, caused by blood flowing backto record the blood pressure. into the artery. This was the start of auscultatory First non-invasive method was introduced method of blood pressure 1855. Vierordt postulated that an indirect, „Kortkoff‟s important contribution tononinvasive technique might be used, by measuring medicine was the devising of an accurate and easythe counter pressure which would be necessary to method of determining the blood pressure. Hiscause the pulsation in an artery to cease. In order to technique has stood the test of time as it has beensupport this theory, Vierordt attempted to measure used for more than a century with practically nothe pressure which was needed to cause obliteration changes made to it‟. Kortkoff laid the foundationof the radial pulse, by a weight attached to the lever from which many investigators worked on [6-9].of a sphygmograph. „He did not, however, meet The pneumatic sleeve or cuff, also referredwith very much success, due largely to the to as a tourniquet, consisted usually of a rubbercumbersome design of his apparatus. His bladder woven inside a fabric. It enabled indirect,sphygmograph was considerably improved by noninvasive arterial blood pressure measurement.Etienne Jules Marey in 1860. Marey applied Till today, the cuff has been the single mostVierordts principle of applying counter pressure to important component of noninvasive blood pressureovercome the arterial pressure, but, in his apparatus measurement devices. The cuff is usually attachedthe arm was enclosed in a glass chamber filled with around the arm, wrist or a finger. Pressurewater, which was connected both to a measurements can be made by using a mercury orsphygmograph and to a kymograph which recorded aneroid manometer. These are now being replacedthe arterial pulsations in the arm. The chamber was with silicon-based pressure sensors inside automaticalso supplied with a moveable reservoir of water so measurement devices, based usually on thethat the pressure in it could be varied, and with a auscultatory or oscillometric method. These devicesmanometer. The determination of the blood pressure may replace conventional mercury and aneroidwas done by first noting the pressure given by the manometers in future [10].mercury manometer at which the greatest peak topeak distance of the sphygmographic tracings III. Spot Measurement of Blood Pressureoccurred, and then gradually increasing the pressure Auscultatory Method: In 1905, N Cby raising the reservoir. The pressure at which no Korotkoff, a Russian army physician, reported thatmore movement of the sphygmograph took place by placing a stethoscope over the brachial artery atwas recorded as the systolic pressure. Although the cubital fossa, distal to the Riva-Rocci cuff,Mareys device was a masterpiece of ingenuity, it tapping sounds could be heard as the cuff waswas far too complicated for most doctors to use deflated, caused by blood flowing back into theroutinely‟ [5]. artery. „In 1896, Riva-Rocci reported the method Korotkoff sounds were corroborated by theupon which present-day technique is based. In his British researchers MacWilliam et al. in 1914 [6]technique a rubber bag, surrounded by a cuff of and the American, Warfield in 1912 [7], who usedsome inexpansible material, was wrapped round the intra-arterial pressure measured from a dog as aarm and was inflated with air by means of an reference. In 1932, von Bonsdorff validatedattached rubber bulb. The pressure in the cuff was Korotkoff‟s auscultatory method on humans usingregistered by the usual mercury manometer, and was intra-arterial blood pressure as a reference [8].increased until the radial pulse could no longer be Later, the characteristic sounds heard during cuffpalpated. When the pressure was slowly released the deflation were divided into five phases on the basismercury level in the manometer fell, and the reading of their intensity. First to publish were Goodmanat which the pulse reappeared was taken as the and Howell (1911), followed by Grodel and Millersystolic blood pressure. There was, however, one (1943), Korns (1926) as well as Rappaport, Luisadamain defect in Riva-Roccis method; he used a (1944) and O‟Brien et al. [11] in 1979.narrow cuff only 5 cm wide. This caused an acute The method, as employed today, utilizes aangle to form between the upper and lower edges of stethoscope placed distal to an arm cuff over thethe cuff and the skin, which resulted in local areas of brachial artery at the antecubital fossa. The cuff ishigh pressure building up and rendering the reading inflated to about 30 mm Hg above systolic pressuremildly inaccurate. This error was realized and and then allowed to deflate at a rate of 2 to 3 mmcorrected by von Recklinghausen in 1901, who Hg/s. With falling cuff pressure, sounds begin and slowly change their characteristics. The initial 529 | P a g e
  3. 3. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533“tapping” sounds are referred to as Phase I should show the systolic pressure, the diastolicKorotkoff sound and denote systolic pressure. The pressure, the endpoint used, the limb used andsounds increase in loudness during Phase II. The whether right or left, the position of the patient, andmaximum intensity occurs in Phase III, where the the presence of any arrhythmias or unusualtapping sound may be followed by a murmur due to circumstances such as anxiety or confinement toturbulence. Finally, Phase IV Korotkoff sound is bed‟ [11, 12]. The Phase III sound can be used toidentified as muffled sound, and Phase V is the determine mean arterial blood pressure, ascomplete disappearance of sound. Phase IV is demonstrated by Davis and Geddes [13]. Figure 1generally taken to indicate diastolic arterial pressure. shows mercury sphygmomanometer, placement ofHowever, Phase V has also been suggested to be a cuff and stethoscope.more accurate indication of diastolic pressure. Measurements based on the auscultatory method arePressures are recorded to the nearest 2 mm Hg. difficult to automate, because the frequencyWhen all sounds have disappeared the cuff should spectrum of the different phases of Korotkoffbe deflated rapidly and completely before repeating sounds is closely related to blood pressure. When athe measurement to prevent venous congestion of patient‟s blood pressure is high, also the recordedthe arm. frequency spectrum is higher than normal and „At an initial examination blood pressure decreases as a function of blood pressure. Withneeds to be measured in both arms. If the difference hypotensive patients and infants, on the other hand,between arms is more than 10 mm Hg for either the highest spectrum components can be as low as 8systolic or diastolic pressure, the arm with the Hz, which is below the human hearing bandwidthhigher pressure is used for future measurements. [14].Ideally, records of blood pressure measurement (a) (b) Figure 1: (a) Mercury Sphygmomanometer; (b) Placement of cuff and stethoscopeNormotensive subjects, in turn, require a bandwidth under the cuff, one located on the upper side, theof 20 Hz to 300 Hz for a sufficient reproduction of other on the distal side. Ambient noise reaches bothKorotkoff sounds, although most of the energy of microphones at the same time, but the bloodthe signal spectrum is below 100 Hz. Since pressure pulse propagating through the brachialtechnology improvements have enabled efficient artery arrives after a time delay. This phenomenonsignal processing and calculation, a number of can be used for noise cancellation as described bypapers have been published on the classification of Sebald et al. [17].Korotkoff sounds. Cozby and Adhami [15], for Allen et al. [18] used a Matlab based short-example, discovered the sub-audible, low frequency term time-frequency analysis to obtain spectralpart of Korotkoff sounds and concluded that energy information of Korotkoff sounds. Their results showin the 1-10 Hz bandwidth of the total energy rises that phase III has the largest overall amplitude andfrom 60% to 90%, when cuff pressure decreases high frequency energy. In contrast, phases IV and Vfrom above the systolic to a level below it. This have the lowest amplitude and frequencyfeature can be used as a thresholding algorithm for components. Statistically significant transitions weredetermining systolic blood pressure. Regueiro- observed between the different phases; the transitionGomez and Pallas-Areny [16] were able to use the from phase I to II was characterized by increase inspectral energy dispersion ratio to determine high frequency and sound duration, the transitionsystolic, diastolic and mean blood pressure with from phase II to III by a significant decrease inhigh precision. sound duration, the transition from phase III to IVIn ambulatory measurements, when the patient is by decrease in maximum amplitude, highestable to move moderately, noise may become frequency and relative high frequency energy, anddominant, thereby spoiling the measurement. This the transition from phase IV to V by decrease in themay be avoided by using two identical microphones maximum amplitude and high frequency energy. 530 | P a g e
  4. 4. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533They concluded that the method was able to detect (c) Systolic from 0.45 to 0.57 and diastolic fromthe five phases also identified by an expert 0.69 to 0.89 (experimental work by Geddes etcardiologist, verifying that the method can be used al. in 1982)in automatic blood pressure measurements. (d) Systolic (mean and SD) equal to 0.49 (0.11) andOscillometric Method: The oscillometric method diastolic equal to 0.72 (0.12) (experimentalwas first introduced by Marey in 1876. Erlanger work by Amoore et al. in 2007)(1904) further improved by attaching a Riva-Roccicuff around the upper arm. Pressure oscillations The oscillometric determination of MAP iswere recorded on a rotating drum. Later Pachon more accurate than systolic and diastolic pressures(1909) used dual-dial gauges, one for presenting [19].oscillation amplitude and the other for showing cuff Drzewiecki et al. in 1994 employed apressure. In those days, it was thought that model of oscillometry to evaluate the derivative ofmaximum oscillation amplitude indicated diastolic the oscillation amplitude curve with respect to cuffblood pressure. pressure. When this derivative is plotted against cuff Marey (1885) placed the arm within a pressure, it was found that it reaches a maximumcompression chamber and observed that the positive value. This occurred when cuff pressurechamber pressure fluctuated with the pulse. He also equals diastolic pressure. Additionally, thenoted that the amplitude of pulsation varied with minimum negative value was found to occur atchamber pressure. Marey believed that the systolic pressure. The advantage of this approach ismaximum pulsations or the onset of pulsations were that the empirically based systolic and diastolicassociated with equality of blood pressure and ratios are not necessary. This method is called aschamber pressure. At that time, he was not certain derivative oscillometry [1].what level of arterial pressure the maximum Traditionally, the arterial pulsations inpulsations corresponded with [1]. It has been oscillometric devices are picked up from thetheoretically shown that the variation in cuff occluding cuff by means of a manometer. However,pressure pulsation is primarily due to the brachial in some implications a photoelectric detectionartery buckling mechanics [4]. directly from the tissue (PPG) is also used. Other Today, oscillometry is performed using a methods than pneumatic pulse sensing seem to havestandard arm cuff together with an in-line pressure become more popular in the wrist BP devices [19].sensor. Due to the requirement of a sensor,oscillometry is generally not performed manually, IV. Discussion and Conclusion:but, rather, with an automatic instrument. The The oscillometric method is increasinglyrecorded cuff pressure is high-pass-filtered above 1 used in blood pressure measurement. Due to theHz to observe the pulsatile oscillations as the cuff simplicity and reliability of this method, theslowly deflates. It has been established that the oscillometric principle is employed in the majoritymaximum oscillations actually correspond with cuff of present-day automatic and semiautomatic non-pressure equal to mean arterial pressure, confirming invasive blood pressure monitors [19]. AutomatedMarey‟s early idea. Systolic pressure is located at devices may also offer the opportunity to avoidthe point where the oscillations, are a fixed expensive and repetitive training of health carepercentage of the maximum oscillations [1]. professionals in auscultation, which is necessary toThe majority of non-invasive automated blood reduce observer errors. Their use still requirespressure measuring devices currently available, use careful patient evaluation for caffeine or nicotinethe oscillometric method based on empirically use, selection of the correct cuff size, and properderived algorithms, generally patent protected, patient positioning if accurate blood pressures are towhich calculate systolic and diastolic BP. Diastolic be obtained. Devices are now available that can takeand systolic blood pressures can be determined a series of sequential readings and automaticallyusing special fractions of the maximum oscillation average them.amplitude, also known as characteristic ratios. There Automated devices provide timed printoutsare no definite correct values for the systolic and of BP, remove many of the sources of errordiastolic characteristic ratios; rather different associated with the conventional auscultatorymanufactures use different values. Theoretical and technique, and thereby improve the overall accuracyexperimental work has suggested the following of measurement, provided, that they themselves arevalues for characteristic ratios; accurate. The accuracy and reliability of these(a) Systolic from 0.46 to 0.64 and diastolic from devices may be questionable; these automated 0.59 to 0.80 (theoretical work by Ursino and devices should be validated against standards. There Cristalli in 1996) are two published standards for the evaluation of(b) Systolic 0.593 and diastolic 0.717 (theoretical automatic BP measuring devices, the American work by Drzewiecki et al. in 1994) Association for the Advancement of Medical Instrumentation standard, and the more comprehensive protocol of British Hypertension 531 | P a g e
  5. 5. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533Society. These protocols compare an automated BP [7] Warfield L. M., (1912), “Studies inmeasurement device against the traditional Auscultatory Blood-Pressure Phenomena”,auscultatory technique of BP measurement in Arch. Inter. Med., vol. X(3), pp. 258-267.normotensive and hypertensive subjects with a widerange of BP in varying age groups. On the basis of [8] James Bordley-III, Connor C. A. R.,these results, the protocols recommend that only Hamilton W. F., Kerr W. J. and Wiggers C.those devices that achieve a high grade of accuracy J. (1951), “Recommendations for Humanfor both systolic and diastolic BP should be Blood Pressure Determinations byrecommended for clinical use [20]. Sphygmomanometers”, Circulation, vol. IV, pp. 503-509.References: [1] Bronzino Joseph D., Editor (2000), “The [9] OBrien E. T. and OAulley K. (1979), Biomedical Engineering Hand Book”, “ABC of Blood Pressure Measurement- Second Edition, CRC Press LLC, chapter Reconciling the Controversies: a comment no 71. on the literature”, British Medical Journal, vol. 2, pp. 1201-1202. [2] Alcala F. V., Peralta J. L., Sanchez E. M., [10] Tholl U., Forstner K. and Analauf M. Montoro A. E., Dominguez A. C., and (2004), “Measuring Blood Pressure: Chozas J. M. L. (2004), “Ambulatory Pitfalls and Recommendations”, Nephrol Blood Pressure Monitoring to Study White Dial Transplant, vol. 19. pp 766-770. Coat Effect in Patients with Hypertension [11] OBrien E. T. and OAulley K. (1979), Followed in Primary Care,” Hypertension , “ABC of Blood Pressure Measurement- Rev Esp Cardiol , vol. 57, no. 7, pp. 652- Technique”, British Medical Journal, vol. 660. 2, pp. 982-984. [12] Beevers G., Lip G. Y. H., OBrien E. [3] Pickering T. G., Hall J. E., Appel L. J., (2006), “ABC of Hypertension Blood Falkner B. E., Graves J., Hill M. N., Jones Pressure Measurement: Part-II D. W., Kurtz T., Sheps S. G. and Roccella Conventional Sphygmo-manometry: E. R. (2005), “Recommendations for Blood Technique of Auscultatory Blood Pressure Pressure Measurement in Humans and Measurement”, BMJ, vol. 322, pp. 1043- Experimental Animals: Part 1: Blood 1047. Pressure Measurement in Humans: A Statement for Professionals from the [13] Devis G. J. and Geddes L. A. (1990),” Subcommittee of Professional and Public Auscultatory Mean Blood Pressure”, Education of the American Heart Journal of Clinical Monitoring, vol. 6, pp. Association Council on High Blood 261-265. Pressure Research”, Circulation, vol. 111, [14] Blank S. G., West J. E., Muller F. B., Cody pp. 697-716. R. J., Harshfield G. A., Pecker M. S., Laragh J. H. and Pickering T. G. (1988), [4] Drzewiecki G., Bansal V., Hood E. K. R., “Wideband External Pulse Recording and Apple H. (1993), “Mechanics of the During Cuff Deflation: A New Technique Occlusive Arm Cuff and Its Application as for Evaluation of The Arterial Pressure a Volume Sensor”, IEEE Transactions On Pulse and Measurement of Blood Biomedical Engineering, vol. 40, no.7, pp. Pressure”, Circulation, vol.77, pp. 1297- 704-708. 1305. [15] Cozby R. C. and Adhami R. R. (1993), [5] Booth Jeremy (1977), “A Short History of “Low-Frequency Korotkoff Signal Blood Pressure Measurement”, Proc. Royal Analysis and Application”, IEEE Society of Medicine, vol. 70, pp. 793-799. Transactions on Biomedical Engineering, vol. 40, no. 10, pp. 1067-1070. [6] Mac WILLIAM J. A., and Melvin S. P. [16] Regueiro A.-Gomez and Pallas R.-Areny (1914), “Systolic and Diastolic Blood (1996), “A New Indicator for Non-invasive Pressure Estimation, with Special Arterial Blood Pressure Measurement”, Reference to the Auditory Method”, British 18th Annual International Conference of Medical Journal, vol. March 1914, pp. the IEEE Engineering in Medicine and 693-697. Biology Society, Amsterdam, pp. 117-118. [17] Sebald D. J., Bahr D. E., Kahn A. R. (2002), “Narrowband Auscultatory Blood Pressure Measurement”, IEEE 532 | P a g e
  6. 6. Kapse C.D., Patil B.R / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 2, March -April 2013, pp.528-533 Transactions on Biomedical Engineering, vol. 49, no. 9, pp. 1038-1044.[18] Allen J., Gehrke T., OSullivan J. J., King S. T. and Murray A. (2004), “Characterization of the Korotkoff Sounds using Joint Time-Frequency Analysis”, Physiological Measurement, vol. 25, no. 1, pp. 107.[19] Raamat R., Talts J., Jagomägi K. and Kivastik J. (2010), “Comparison of Oscillometric Pulse Amplitude Envelopes Recorded from the Locally Compressed Radial Arteries”, Medical Engineering and Physics, vol. 32, pp. 1124-1130.[20] OBrien E., Beevers G., Lip G. Y. H. (2001), “ABC of Hypertension Blood Pressure Measurement, Part IV— Automated Sphygmomanometry: Self Blood Pressure Measurement”, BMJ, vol. 322, pp. 1167-1170. 533 | P a g e