The fourth sound of Korotkoff in pregnancy: a myth1

European Journal of Obstetrics & Gynecology and Reproductive Biology 76 (1998) 53–59

The fourth sound of Korotkoff in pregnancy: a myth 1 a, a a b Arie Franx *, Inge M. Evers , Karlijn A.M.I. van der Pant , Joris A.M. van der Post , Hein W. Bruinse a , Gerard H.A. Visser a a

Department of Obstetrics and Gynaecology, F05.829, University Hospital Utrecht, P.O. Box 85500, 3508 GA Utrecht, The Netherlands b Department of Obstetrics and Gynaecology, Academic Medical Centre, Amsterdam, The Netherlands Received 20 June 1997; received in revised form 23 July 1997; accepted 28 July 1997

Abstract Objective: To determine the detection rate and the reproducibility of the first (K1), the fourth (K4) and the fifth (K5) phases of the Korotkoff sounds in pregnant women. Study design: In 77 pregnant women receiving antenatal care in a tertiary referral centre, two observers took 231 simultaneous blood pressure measurements with a shared mercury sphygmomanometer and a multi-aural stethoscope. Detection rates, percentages of observer agreement within 5 mmHg and k values were calculated for K1, K4 and K5. Results: Both observers were able to detect K1, K4 and K5 in 98, 24 and 98% of all 231 measurements, respectively. In 46% of measurements, and in 23% of women, neither observer was able to detect K4. The observers agreed within 5 mmHg in 98 (k 50.99), 69 (k 50.42), and 96% (k 50.99) of measurements for K1, K4 and K5, respectively. Conclusion: K4 cannot be detected and reproduced accurately in a significant proportion of pregnant women, and therefore should be abandoned as diastolic endpoint in pregnancy.  1998 Elsevier Science Ireland Ltd. Keywords: Fourth sound of Korotkoff; Blood pressure measurement; Normotensives; Hypertensives

1. Introduction Measurement of blood pressure is considered to be a cornerstone of antenatal care. Definitions, diagnosis and clinical management of hypertensive disorders of pregnancy are primarily based on the level of diastolic blood pressure [1–3]. Up to now, the standard method of indirect blood pressure determination is auscultatory mercury sphygmomanometry. This technique relies on the auscultation of sounds heard over the brachial artery distal to a deflating cuff. The sounds bear the name of the Russian vascular surgeon Nicolai Sergeivich Korotkoff (Fig. 1), who presented the auscultatory method of blood pressure measurement on November 8, 1905, at a scientific seminar of the Imperial Military-Medical Academy in Saint Peters*Corresponding author. Tel.: 131 30 2506426; fax: 131 30 2541900. Condensation: The fourth sound of Korotkoff could not be detected and reproduced accurately in a substantial proportion of 77 normotensive and hypertensive pregnant women. 1

burg [4]. A report of the presentation, containing barely 200 words, and of the more lengthy discussion between Korotkoff and his audience, was published in the Academy’s Bulletin in 1905 (Fig. 2) [5]. Although one of the most cited in the entire medical literature, this original paper is extremely difficult to locate and therefore probably studied by only few of the numerous authors referring to it. The paper is not indexed in Index Medicus and the commonly used English translated name of the journal (Bulletin of the Imperial Military Medical Academy) is not used by the few libraries holding it. The National Library of Medicine in Bethesda, Maryland, and The New York Public Library each possess the original issues of the Academy’s Bulletin containing the Korotkoff paper [6], and use the transliterated journal name and article title, based on the originals in Cyrillic [5]. English translations of the text of Korotkoff’s presentation were published by Lewis [7], Ruskin [8], Geddes et al. [9], and Segall [10]. Remarkably, medical historians have neglected Korotkoff for decades until many details of his life and career

0301-2115 / 98 / $19.00  1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0301-2115( 97 )00156-5

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A. Franx et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 76 (1998) 53 – 59

Fig. 1. Nicolai Sergeivich Korotkoff (1874–1920), the discoveror of the auscultatory method for measuring arterial blood pressure.

were recovered by Segall [10–13], and completed by other authors [4,14]. From these biographies it appears that Korotkoff, who as a military surgeon treated wounded soldiers in the Russian–Japanese War (1904–1905), discovered the vascular sounds by listening to arteries of traumatized limbs, in order to estimate the potential of collaterals. The sounds were named after Korotkoff, although they had been described as early as 1901 by Theodore Caldwell Janeway, a physician from New York [15]. The true merit of Korotkoff is that he was the first to relate these sounds to systolic and diastolic blood pressure. He described the sequence of sounds audible during deflation of the cuff as follows: appearance of the first short tones, followed by systolic compression murmurs, passing again into tones and, finally, disappearance of all

sounds [5]. It was Ettinger who in 1907 delineated these sounds as phases 1, 2, 3 and 5, respectively, and, moreover, added a phase 4: the transition of clear tones into more soft and dull tones (‘muffling’), prior to their moment of disappearance [16]. Thus, from a historical point of view, the term ‘Korotkoff phase 4’ is a misnomer. Korotkoff designated the first sound audible during cuff deflation (Korotkoff phase 1, abbreviated as K1) as the identification point for systolic pressure and the last audible sound (K5) for diastolic pressure. Although K5 is generally accepted as the identification point for diastolic pressure in non-pregnant subjects, confusion and uncertainty remain whether K5 or the point of muffling (K4) should be used during pregnancy. The only argument in favour of K4 was launched by MacGillivray and col-

A. Franx et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 76 (1998) 53 – 59

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Fig. 2. The front page (above) of the issue of the Bulletin of the Imperial Military-Medical Academy in Saint Petersburg containing the report of Korotkoff’s presentation of the auscultatory method for blood pressure measurement (overleaf). The text spoken by Korotkoff on November 8, 1905, at a scientific seminar of the Academy is reproduced from the last line of the left column to the thirty-sixth line of the right column, and followed by almost two pages of discussion between Korotkoff and his impressed audience.

leagues in their classical paper on a blood pressure survey in 226 primigravid women [17]. Without presenting the supporting data, these authors stated that in many women the Korotkoff sounds do not disappear but persist until

very low or zero pressure is reached in the cuff because of the hyperkinetic state of pregnancy. Later studies however suggested that this phenomenon is rare in pregnant women [18,19].

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Fig. 2. (continued)

A. Franx et al. / European Journal of Obstetrics & Gynecology and Reproductive Biology 76 (1998) 53 – 59

We have determined the detection rates and reproducibility of K1, K4 and K5 in a group of normotensive and hypertensive pregnant women [20].

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one and neither of the observers were able to record K1, K4 and K5. The percentage of agreement between the observers within 5 mmHg and k values were calculated for K1, K4 and K5, where detected by both observers [23].

2. Materials and methods We re-analyzed data obtained in a validation procedure of an ambulatory blood pressure monitor in pregnancy. The procedure followed the guidelines set out by the British Hypertension Society [21]. Two observers were trained to measure blood pressure by means of the British Hypertension Society video [22], and subsequently assessed for accuracy against an expert [21]. The participating subjects were 77 pregnant women receiving antenatal care in the University Hospital Utrecht, a tertiary referral center in Utrecht, The Netherlands. Fifty-seven women were normotensive and 20 were hypertensive (K5$90 mmHg) at the time of the study. Of the hypertensive women, two had chronic hypertension, 12 gestational hypertension and six proteinuric preeclampsia. Four women were on antihypertensive medication. Thirty women were nulliparous and 47 were parous. Mean (SD) age was 31 (5) years. Mean (SD) gestational age was 29 (8) weeks. Four women were in the first trimester of pregnancy, 24 in the second and 49 in the third. Arm circumferences ranged from 22 to 37 cm. Blood pressure was measured with the woman in the sitting position after 5 min of rest. A large adult cuff was applied over the right upper arm and connected to both the ambulatory blood pressure measuring device and a calibrated standard mercury sphygmomanometer by a Y-connector. Cuff inflation was by the ambulatory device. During deflation at 2 mmHg / s both observers simultaneously auscultated K1, K4 and K5 with a multi-aural stethoscope. Pressures were read at the nearest 2 mmHg on the mercury sphygmomanometer. Three consecutive measurements were made in each woman to yield a total of 231 paired measurements. The observers were blinded for each other’s results and unaware of the pressures measured by the ambulatory device. We calculated the percentages of readings when both,

3. Results The observed ranges for K1, K4 and K5 were 98–182, 64–126 and 50–120 mmHg, respectively. Table 1 summarizes the detection rates and agreement for all three Korotkoff sounds. K1 and K5 were detected by both observers in 98% of all 231 paired measurements. In two women K5 was not recorded by one of the observers in one of the three measurements. In two other women K5 was recorded by neither observer in one of the three measurements. This was due to uncertainty about the exact point of disappearance of the vascular sounds without persistence of sounds to zero cuff pressure. When both observers were able to record the respective sound, agreement within 5 mmHg was 98% (k 50.99) for K1 and 96% (k 50.99) for K5. By contrast, K4 was detected by both observers in only 55 (24%) of 231 measurements. The observers agreed within 5 mmHg in only 38 (69%) of these 55 measurements (k 50.42). In 106 (46%) of all 231 measurements and in 18 (23%) of all 77 women none of the observers was able to detect K4. In only seven (9%) of all 77 women both observers heard K4 in all three measurements.

4. Comment Korotkoff sounds are produced by vibration of the vessel wall and modulated by specific changes in the pattern and direction of blood flow waveforms in the partially occluded brachial artery segment [24–26]. In pregnant women, K4 is associated with a transformation of reverse flow subsequent to the systolic peak velocity into continuous forward or reverse flow between successive systolic peaks. K5 is associated with an increase in the diastolic component of the brachial artery waveform, but

Table 1 Detection of and agreement for the first (K1), the fourth (K4) and the fifth (K5) Korotkoff sounds by two observers performing 231 simultaneous blood pressure measurements in 77 pregnant women Korotkoff Sound

k value a

Number of readings(%) Agreement #5 mmHg a

Detection by:

K1 K4 K5 a

both observers

one observer

neither observer

226 (98%) 55 (24%) 227 (98%)

3 (1%) 70 (30%) 2 (1%)

2 (1%) 106 (46%) 2 (1%)

221 (98%) 38 (69%) 218 (96%)

0.99 0.42 0.99

Agreement between the two observers for blood pressure within 5 mmHg for those paired measurements where both observers were able to detect the sound.

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the distinction between K4 and K5 waveforms is often subtle [26]. Those recommending K4 as the appropriate diastolic identification point in pregnant women contend that, because of the hyperkinetic circulatory changes of gestation, Korotkoff sounds often persist until zero cuff pressure. Unfortunately, the two studies usually referred to in the debate of this matter omitted to present the percentage or number of women in which zero values for K5 were observed [17,27]. Nevertheless, authoritative committees have advocated K4 for pregnancy [1,28,29]. Recent studies, however, indicate that zero values for K5 are rare in pregnant women: K5 was measured at zero in none of 197 and 50 women [18,19], and in less than 0.5% of more than 100 000 measurements in 1194 women [30]. Whilst several authors have raised concern about the ability to detect K5 during pregnancy, few have given attention to the detectability of K4. In the present study both of the trained observers heard K4 in only a quarter of the simultaneous measurements. Where it was detected by both observers, agreement within 5 mmHg was not impressive (69%). In almost a quarter of the women K4 was not detected at all, and in only 9% of women it was detected by both observers on every occasion. By contrast, K5 was detected by both observers in all but four of 231 measurements and interobserver agreement for this diastolic identification point was excellent. Our results are nearly identical to those reported by Shennan and colleagues [31]. The first part of their study was also a re-analysis of data obtained in a validation study with the British Hypertension Society protocol, in 85 pregnant women. For two pairs of observers, detection rates and percentage agreement within 5 mmHg for K4 were similar to ours. K5 was detected in all instances and agreement for this sound was perfect. To confirm these initial results Shennan and colleagues additionally studied six pairs of trained observers in 80 pregnant and 80 non-pregnant women. Each pair recorded blood pressure in 16 pregnant and 16 non-pregnant women, taking seven measurements in each subject. Compared to the first part of the study, yet lower detection rates were found for K4. It was not heard in any of the seven measurements in 26%, and in all seven measurements in only 7% of the pregnant women. K4 was identified significantly less often in nonpregnant than in pregnant women. Agreement for K4 differed substantially between observer pairs. In another study by Blank and colleagues in 42 hypertensive and 16 normotensive pregnant women, one observer was able to detect K4 in 53% of the measurements and a second observer in 44%. K5 was detected by both observers in 98% of the measurements [32]. Findings by Shennan et al., Blank et al. and ourselves contrast with the far better K4 detection rates (81–96%) reported by Johenning et al. for three trained observers, simultaneously measuring blood pressure in 98 pregnant women [33]. In this study the K4 detection rates on average equalled those for K5 but

differed substantially among observers. The percentage of women with a detectable K4 increased when two measurements were obtained instead of one. Hense et al. investigated distributions of K4 and K5 in 2195 non-pregnant subjects. Non-detection of K4 ranged from 10 to 79% between 13 highly trained observers [34]. So, results from the previous and the present studies are not unequivocal, but indicate that K4 cannot be reproduced as accurately by different observers as K5. Observer rather than patient characteristics seem to account for this. We speculate that K4 detection rates are biased by the observers’ belief or disbelief in the presence of the sound. The first part of the study by Shennan et al., and our own data, may be less biased by such observer prejudice, since determination of the K4 detection rate was not a primary goal. However, in the second part of their study, undertaken to confirm their hypothesis that K4 is difficult to identify, Shennan and colleagues found even lower rates of K4 detection than in the first part. By contrast, in Johenning and colleagues’ study, the one observer using K4 in daily practice was able to detect the sound more often than the other two observers. K5 has been shown to estimate true intra-arterial diastolic pressure in pregnant women more accurately than K4 [35,36]. Automated blood pressure measuring devices approximate K5 rather than K4 in pregnancy [37,38]. An additional issue raised by some is that most published epidemiological and treatment studies on hypertensive disorders of pregnancy have used K4 and a change to K5 would cause confusion in interpreting the results. Given its poor detectability and reproducibility, we are at a loss to see how K4 really can be used rigorously in research. Moreover, this argument to retain K4 was proven invalid by Zarifis et al., who surveyed the literature on hypertension in pregnancy between 1975 and 1994 [39]. Of 100 original papers containing data on the clinical measurement of blood pressure, 26 reported the use of K4 and 36 of K5, while 38 did not specify which diastolic identification point was used. Only one study has attempted to compare the prognostic value of K4 and K5 for the occurrence of hypertensive complications of pregnancy [30]. K5 showed a better association with proteinuria, intra-uterine growth retardation and hyperuricaemia than K4. Finally, authorities in both the United States and Britain recommend use of K5 in non-pregnant subjects [3,28]. The same health care personnel measure blood pressure in pregnant and non-pregnant patients. It would therefore seem less confusing to use the same sound for both. Although K4 is currently recommended in Britain [28], practitioners of a single obstetric unit were almost evenly split on the use of K4 or K5 [40]. In conclusion, K4 has not been described by Korotkoff and in a substantial number of pregnant women this sound can neither be detected nor reproduced accurately. The time has come for a definitive settlement on K5 as the only diastolic endpoint.

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Acknowledgements ¨ We thank Professor W.H. Birkenhager (Rotterdam, The Netherlands), Professor E. O’Brien (Dublin, Ireland) and Mr. Kim-Gau Ng (Kingston, Canada) for their help with our search for the original paper by Nicolai Sergeivich Korotkoff.

References [1] Davey DA, MacGillivray I. The classification and definition of the hypertensive disorders of pregnancy. Am J Obstet Gynecol 1988;158:892–8. [2] Redman CWG, Jefferies M. Revised definition of pre-eclampsia. Lancet 1988;i:809–12. [3] National High Blood Pressure Education Program Working Group Report on high blood pressure in pregnancy. Am J Obstet Gynecol 1990;163:1691–712. [4] Shevchenko YL, Tsitlik JE. 90th Anniversary of the development by Nikolai S. Korotkoff of the auscultatory method of measuring blood pressure. Circulation 1996;94:116–8. [5] Korotkoff NS. K’voprosu o metodakh’ izsledovaniya krovyanogo davleniya (iz’ kliniki Prof. S.P. Fedorov). Izvestiya Imperatorskoy Voenno-Meditsinskoy Akademii 1905;11:365–7. [English translation of this transliterated bibliographic description: Korotkoff NS. On the subject of methods of determining blood pressure (from the clinic of Prof. S.P. Fedorov). Bull Imperial Military-Med Acad 1905;11:365–7. [6] Ng KG. Papers by Korotkoff (1905) and Riva-Rocci (1896): Bibliographic descriptions and sources of originals and English translations. J Clin Eng 1995;20:185–6. [7] Lewis Jr. WH. The evolution of clinical sphygmomanometry. Bull NY Acad Med 1941;17:871–81. [8] Ruskin A. Classics in Arterial Hypertension. Springfield, IL: Charles C. Thomas 1956:126–30. [9] Geddes LA, Hoff HE, Badger AS. Introduction of the auscultatory method of measuring blood pressure—including a translation of Korotkoff’s original paper. Cardiovasc Res Center Bull 1966;5:57– 74. [10] Segall HN, Experiments for Determining the Efficiency of Arterial Collaterals by N.S. Korotkoff. Montreal: Mansfield Book Mart, 1980:245–50. [11] Segall HN. Dr NC Korotkoff. Discoverer of the auscultatory method for measuring arterial pressure. Ann Intern Med 1965;63:147–9. [12] Segall HN. How Korotkoff, the surgeon, discovered the auscultatory method of measuring arterial pressure. Ann Intern Med 1975;83:561–2. [13] Segall HN. NC Korotkoff—1874–1920—Pioneer vascular surgeon. Am Heart J 1976;91:816–8. [14] Laher M, O’Brien E. In search of Korotkoff. Br Med J 1982;285:1796–8. [15] Janeway TC. Some observations on the estimation of blood pressure in man, with especial reference to the value of the results obtained with the newer sphygmomanometers. NY Univ Bull Med Sci 1901;1:106–26. [16] Ettinger W. Auskultatorische Methode der Blutdruckbestimmung und ihr praktischer Wert. Wien Klin Wochenschr 1907;20:992–6. [17] MacGillivray I, Rose G, Rowe B. Blood pressure survey in pregnancy. Clin Sci 1969;37:395–407.

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[18] Perry IJ, Stewart BA, Brockwell J et al. Recording diastolic blood pressure in pregnancy. Br Med J 1990;301:1198. [19] Brown MA, Withworth JA. Recording diastolic blood pressure in pregnancy. Br Med J 1991;303:120–1. [20] Franx A, van der Post JAM, van Montfrans GA, Bruinse HW, Visser GHA. The fourth sound of Korotkoff in pregnancy: a myth?. Lancet 1996;347:841. [21] O’Brien E, Petrie J, Littler W et al. The British Hypertension Society protocol for the evaluation of automated and semi-automated blood pressure measuring devices with special reference to ambulatory systems. J Hypertens 1990;8:607–19. [22] Jamieson M, Petrie J, O’Brien E, Padfield P, Littler WA, de Swiet M. Videotape Blood Pressure Measurement. London: BMJ Publishing Group, 1989. [23] Altman DG. Practical Statistics for Medical Research. London: Chapman & Hall, 1991:403–9. [24] Chungcharoen D. Genesis of Korotkoff sounds. Am J Physiol 1964;207:190–4. [25] Rodbard S. The significance of the intermediate Korotkoff sounds. Circulation 1953;8:600–4. [26] Quinn M. Korotkoff’s sounds in pregnancy. Ultrasound Obstet Gynecol 1995;6:58–61. [27] Whichman K, Ryden G, Whichman M. The influence of different positions and Korotkoff sounds on the blood pressure measurements in pregnancy. Acta Obstet Gynecol Scand Suppl 1984;118:25–8. [28] Petrie JC, O’Brien ET, Littler WA, de Swiet M. Recommendations on blood pressure measurement. Br Med J 1986;293:611–5. [29] World Health Organisation Study Group. The Hypertensive Disorders of Pregnancy. Geneva: World Health Organisation, 1987; WHO technical report series 758. ´ ´ JM, Villar J, Bergel E. The measurement of [30] Lopez MC, Belizan blood pressure during pregnancy: which Korotkoff phase should be used?. Am J Obstet Gynecol 1994;170:574–8. [31] Shennan A, Gupta M, Halligan A, Taylor DJ, de Swiet M. Lack of reproducibility in pregnancy of Korotkoff phase IV as measured by sphygmomanometry. Lancet 1996;347:139–42. [32] Blank SG, Helseth G, Pickering TG, West JE, August P. How should diastolic blood pressure be defined during pregnancy?. Hypertension 1994;24:234–40. [33] Johenning AR, Karrison TG, Barron WM. Interobserver variability in the measurement of diastolic blood pressure in pregnancy. Hypertens Pregnancy 1995;14:301–11. [34] Hense HW, Stieber J, Chambless L. Factors associated with measured differences between fourth and fifth phase diastolic blood pressure. Int J Epidemiol 1986;14:513–8. [35] Raftery EB, Ward AP. The indirect method of recording blood pressure. Cardiovasc Res 1968;2:210–8. [36] Brown MA, Reiter L, Smith B, Buddle ML, Morris R, Withworth JA. Measuring blood pressure in pregnant women: a comparison of direct and indirect methods. Am J Obstet Gynecol 1994;171:661–7. [37] Shennan AH, Kissane J, de Swiet M. Validation of the SpaceLabs 90207 ambulatory blood pressure monitor in pregnancy. Br J Obstet Gynaecol 1993;100:904–8. [38] Franx A, van der Post JAM, Elfering I et al. Validation of automated blood pressure recording in pregnancy. Br J Obstet Gynaecol 1994;101:66–9. [39] Zarifis J, Lip GYH, Blackman DJ, Churchill D, Beevers DG. Measurement of diastolic blood pressure in obstetrical research. Hypertens Pregnancy 1996;15:135–7. [40] Perry IJ, Wilkinson LS, Shinton RA, Beevers DA. Conflicting views on the measurement of blood pressure in pregnancy. Br J Obstet Gynaecol 1991;98:241–3.