Over the last few decades, technological progress has led physicians to reconsider the possibility of measuring blood pressure at the wrist level, thanks to the introduction of electronic and more or less complex computer-operated devices. One example comprises a sophisticated and expensive device for continuous noninvasive blood pressure monitoring (Colin BP-508 monitor; Colin Co, Komaki City, Japan) , which is aimed at providing beat by beat quantitative assessment of the radial pulse through an applanation tonometer periodically calibrated by upper arm automated oscillometric blood pressure measurements. This system is now frequently used in cardiovascular physiology laboratories, but it is obviously not suitable in daily clinical routines because of its high cost. In clinical practice, the use of smaller and cheaper devices, sometimes only slightly bigger than a sports watch, has been proposed in recent years by manufacturers for home self-BPM, based on oscillometric automated wrist blood pressure readings. The dream of having a watch-like device that might improve the art of ‘feeling the pulse’ (Fig. 5) and might thus measure blood pressure at the wrist site in a simple and inexpensive fashion thus seemed to have become a reality.
Self-BPM at home is now regarded as a useful procedure to complement office blood pressure readings in the management of hypertensive patients, and also offers advantages in clinical trials on antihypertensive therapy. In fact, self-BPM values are more reproducible, are not affected by the ‘white-coat effect’ and therefore are more likely to be representative of the average daily pressure than clinic blood pressure values . Self-BPM has also been shown (although only by a few studies until now) to be more closely related to hypertension target organ damage and cardiovascular morbidity and mortality than clinic blood pressure [11,12]. Furthermore, self-BPM is of particular interest in assessing the effectiveness and the time distribution of the blood pressure effects of antihypertensive therapy, both in the routine follow-up of hypertensive patients and in drug studies [11,12]. This technique has also the advantage of stimulating patients to become more actively involved in the management of their own blood pressure problem, thus having the potential to improve patient compliance with the prescribed therapeutic regimen. and to provide a more cost-effective management of hypertensive subjects .
Manual blood pressure measurement at the upper arm level, using a mercury or, if frequently checked and calibrated, an aneroid sphygmomanometer, was in the past generally regarded as the standard method for home blood pressure monitoring. However, thanks to their easier and more practical application, electronic devices based on the oscillometric blood pressure measurement technique applied at the upper arm, wrist or finger site have now become very popular. Their diffusion has indeed shown a constant increase over the last 10–15 years, as testified by their current high rate of sale, which in Germany has reached the remarkable figure of 1.2 million for all home blood pressure monitoring devices sold annually .
In spite of their increasing popularity, however, the first electronic blood pressure monitoring devices undergoing independent validation testing all failed to satisfy the criteria of established protocols , such as those proposed by the British Hypertension Society (BHS)  and by the American Association for the Advancement of Medical Instrumentation (AAMI) . On the other hand, due to continuous progress in technology, some more recent electronic devices for self-BPM, based on automated arm cuff inflation, have been found to be acceptably accurate according to the above criteria [16–18]. In contrast, all finger devices proposed for home blood pressure monitoring have been proved inaccurate . Besides possible technical failures, this seems to depend on a number of other factors, such as (i) the physiological differences between pulse waveforms at the digital and the brachial artery levels (responsible for a narrower and higher systolic peak in the digital artery because of wave reflection effects); (ii) the effects of vasomotor activity changes in the extremities; and (iii) the impact of changes in the hydrostatic height pressure difference between the instrumented hand and the heart, whenever the hand is not carefully held at the heart level at the time of each blood pressure measurement . Because of all these problems, the clinical use of automated finger blood pressure measuring devices is definitely not recommended at present .
Over the very last few years, electronic devices which measure blood pressure from the wrist have become a very popular approach to self-BPM at home, with their sale comprising approximately 50% of all electronic devices for self-BPM sold annually in Germany . In fact, wrist devices have gained as much as 30% of the market share for all automated blood pressure measuring devices worldwide . Interestingly, more than 90% of patients performing self-BPM seem to prefer wrist rather than arm devices , the popularity of the former (in particular among elderly subjects) probably depending on their small size and light weight and by the fact that their use is found quite easy and convenient, as the cuff can be more easily wrapped around the wrist than around the arm, and because they allow blood pressure measurements to be obtained without undressing. Moreover, some patients also prefer wrist devices because they experience much less discomfort when a cuff is automatically inflated around the wrist rather than around the upper arm. These devices have the potential advantage of being more suitable than arm devices in obese subjects with extremely large or with cone-shape upper arms, although, to the best of our knowledge, the accuracy of wrist devices in obese patients has not been specifically tested according to international protocols.
As in the case of finger devices, one of the major disadvantages of wrist devices is that the wrist must be held at heart level during a blood pressure measurement, and it must be kept at that level at the time of each subsequent measurement. If this is not done, substantial systematic errors may occur due to the influence of the arm–heart hydrostatic pressure difference . Another problem is the possible errors introduced by flexion or extension of the wrist during measurement, which may lead to different degrees of compression of radial and ulnar arteries by the inflated cuff (see below). Therefore, because of these drawbacks and due to the limited data provided from properly conducted validation studies (the majority of which have yielded negative results), most authorities still recommend that devices measuring blood pressure at the arm level should be preferred to wrist devices .
In spite of these discouraging recommendations, which are in agreement with the latest Guidelines for Hypertension management issued by the World Health Organization/International Society of Hypertension and by the American Joint National Committee [21,22], whether wrist self-BPM devices should or should not be used is still a matter of debate in the scientific community, and even more so in clinical practice, due to the complex intertwining of the advantages and disadvantages that characterize their use. The need for further investigation in this field was also recently emphasized during the Eighth Consensus Conference on Blood Pressure Monitoring held in Sendai (Japan) in October 2001. The conclusion reached by an ad-hoc Task Force, including members of the Working Group on Blood Pressure Monitoring of the European Society of Hypertension, was that there is urgent need to reassess the possibility of using self-BPM devices on the background not only of their inherent limitations (see above), but also of their potential usefulness in specific populations, as well as regarding recent progress in technology (Proceedings of the Sendai Conference on Blood Pressure Monitoring, Blood Press Monit 2002; in press).
These conclusions, and in particular the need for caution in proposing wrist blood pressure devices in routine clinical practice, appear to be even more appropriate after critically considering the results of the study by Kikuya et al. .
Interest and limitations of the paper by Kikuya et al.
In their paper, Kikuya et al.  compare the values obtained by two wrist and two arm devices for self-BPM with those obtained through auscultatory readings. Although this study has the merit of including a fairly large number of subjects, an important criticism of these data is that none of the established validation protocols (BHS or AAMI) has been used. Therefore, it is difficult to precisely evaluate the accuracy of the tested devices based on the available standards, and to compare the present findings with previous reports. The validation procedure used in the study by Kikuya et al. showed that blood pressure values provided by wrist devices differ from auscultation by more than 10 mmHg in systolic and/or more than 5 mmHg in diastolic blood pressure in approximately 30 and 50% of the measurements, respectively. Although all the requirements of the AAMI validation protocol were not fulfilled in the present study, if we were to apply the AAMI validation criterion as a post-hoc procedure (according to which the average difference between tested and reference method should be ≤5 mmHg with a SD ≤ 8 mmHg) to the total of the data provided by each device , both wrist devices and one of the arm devices would be rejected as inaccurate. The large variation in the results observed for the same device when comparing data obtained by different clinical centres participating in the study is also of some concern, as there are differences in systolic/diastolic blood pressure measurement accuracy of 11.5/12.6 mmHg between Centres 6 and 12 for wrist device 1, and of 11.2/9.4 mmHg between Centres 6 and 7 for wrist device 2. These between-centre differences can hardly be explained simply on the basis of device inaccuracy. Patient characteristics do not seem to play a role either as there were no specific differences between centres in terms of the age of the participants or their blood pressure level. Thus, the between-centre differences in the reported findings should most likely be attributed to technical problems with observer performance in some centres. Training of observers to a very high standard is of critical importance in validation studies, as emphasized by the BHS protocol which has paid special attention to this methodological aspect . Between-centre differences with respect to ensuring proper positioning of the wrist compared to heart level at the time of blood pressure measurement may also have contributed to these data . Finally, because the between-centre differences in the reported results were larger for wrist than for arm devices, other problems specifically affecting the wrist measurement technique are likely to have contributed to the reported findings. Additional factors resulting from the use of a non-established validation procedure may have further affected the results. First, subjects with a rather narrow range of pressures (fewer than 10% of patients with diastolic blood pressure > 100 mmHg and systolic blood pressure > 180 mmHg) were included, which may have affected proper validation in favour of the devices because the accuracy of automated blood pressure measuring devices has been shown to deteriorate with increasing levels of blood pressure . Second, in the present study, the devices under investigation were not subjected to field use before validation, while the BHS protocol takes this aspect into consideration because the reliability of automated devices may also depend on whether they have or have not been exposed to an in-use assessment phase prior to the validation phase . Third, in this study, device validation was carried out by comparing automated and auscultatory measurements using a cross-over method. Using this method for measurement comparison, instead of sequential same arm measurements as proposed in the BHS protocol, might also have introduced some bias in the validation procedure .
Notwithstanding these problems two important observations made by Kikuya et al. should be emphasized, as they contribute to making their study quite different compared to most of the available validation studies on wrist monitors, and suggest new perspectives in the assessment of the accuracy of wrist blood pressure measuring devices . First, these authors clearly showed that changing the wrist angle between hand and forearm (i.e. shifting from palmar-flexion to dorsal-flexion (extension) of the hand and vice-versa) is accompanied by significant changes in measured systolic and diastolic wrist blood pressure. Second, also as a function of the hand–forearm angle of flexion, inflation of the wrist cuff above systolic blood pressure levels in some cases failed to completely occlude the radial and/or the ulnar artery, as shown by the persisting presence in this condition of a finger pulse, assessed through finger plethysmography. This phenomenon was particularly common during flexion of the wrist, occurring in six out of 29 subjects included in the study. It should be noted that measurements performed in these conditions were not considered as erroneous by the devices, and always gave higher systolic blood pressure values compared to the simultaneous auscultatory readings . These novel observations are methodologically important, because a complete artery occlusion is an essential prerequisite for accurate measurement of blood pressure according to the classical ‘arterial occlusion technique’ introduced by von Bash, Potain and Riva Rocci, even when performed by the oscillometric approach. Moreover, the dependence of wrist blood pressure measurements on the wrist–forearm angle as well as on the wrist-heart hydrostatic height difference also emphasizes the need for very careful training of patients before the proper use of wrist blood pressure monitors might be guaranteed. Although these conclusions may not be necessarily valid for all wrist devices, the findings by Kikuya et al. should focus greater attention on these issues, which were largely neglected in previous validation papers.
Validation of wrist blood pressure measuring devices has indeed been performed by a number of other studies in the last few years, either using established validation protocols [12,23–26] or by means of non-established validation procedures [27–30]. While, in some of these studies, an acceptable correspondence was reported between wrist blood pressure measurements and the reference blood pressure measuring technique, most of them came to the conclusion that wrist devices fail to meet the required validation criteria. Taken together, in addition to the results and the methodological problems raised in the study by Kikuya et al., these conflicting data support the view that the available evidence is not enough to allow a final conclusion to be reached on the actual accuracy and suitability of wrist devices in hypertension management. Given the widespread use of wrist blood pressure monitors, which makes solving this issue considerably important from a clinical perspective, there is thus an urgent need for additional validation studies to be carefully carried out according to established protocols.
In spite of the time-honoured interest in wrist blood pressure measurement, the above observations strongly emphasize the need for great caution when dealing with wrist blood pressure measuring devices, and in agreement with recent Hypertension Management Guidelines, they support the view their general use in clinical practice should not at present be recommended.
In particular, this cautious approach is based on the following: (i) the evidence that blood pressure measuring devices based on arm-cuff inflation provide more reliable measurements in most cases, and that in virtually all the outcome studies that demonstrated the higher risk associated with elevated blood pressure and the benefits of antihypertensive treatment, arm-cuff and not wrist-cuff devices were used; (ii) the conflicting data provided by available validation studies on wrist blood pressure monitors, (iii) the methodological problems that have affected most of these studies, allowing them to fulfil the requirements of established validation protocol only in a minority of cases; and (iv) the additional technical difficulties associated with the wrist approach, related to wrist anatomy, which have emerged from the study by Kikuya et al. .
In practice, this means that measurement of blood pressure at the upper arm level should still be regarded as the standard method in the diagnostic and therapeutic management of hypertensive patients, both in the doctor's office and at the patients’ home.
However, given the potential advantages of the wrist approach in specific populations, such as the obese or the elderly patients in whom arm-cuff devices are sometimes not applicable, the possibility of recommending wrist blood pressure monitoring by modern devices, at least in selected clinical conditions, needs to be further addressed. This should be performed through properly conducted validation studies carried out by expert groups, taking into account the methodological issues raised by Kikuya et al. .
1. Kikuya M, Chonan K, Imai Y, Goto E, Ishii M, on behalf of the Research Group. Accuracy and reliability of wrist-cuff devices for self-measurement of blood pressure: result from the Research Group to Assess the Validity of Automated Blood Pressure Measurement Devices in Japan. J Hypertens 2002; 20: 629–638.
2. Parati G, Mancia G. La misurazione della pressione arteriosa: dal laboratorio sperimentale alla pratica clinica. Il contributo di Scipione Riva Rocci
. Salerno: Momento Medico Ed; 2001. pp. 1–131.
3. Snellen HA. EJ Marey and cardiology
. Rotterdam: Kooyker Scientific Publications; 1980. pp. 128–129.
4. Vierordt K. Die Lehre vom Arterienpuls.
Braunshweig: F Vieweg; 1855.
5. Marey EJ. Physiologie médicale de la circulation du sang.
Paris: Adrien Delahye; 1863. pp. 176176.
6. Dudgeon RE. The sphygmograph.
London: Bailliere, Tindall & Cox; 1882.
7. von Bash S. Ueber die messung des blutdrucks am menschen. Z Klein Med 1880; 2: 79–96.
8. Potain PCE. Du sphygmomanometer et de la mesure de la pression artérielle chez l'homme. Arch Physiol Norm Pathol 1889; I: 556–569.
9. Riva Rocci S. Un nuovo sfigmomanometro. Gazz Med Torino
10. Sato T, Nishinaga M, Kawamoto A, Ozawa T, Takatsuji H. Accuracy of a continuous blood pressure monitor based on arterial tonometry. Hypertension 1993; 21: 866–874.
11. Asmar R, Zanchetti A. Guidelines for the use of self-blood pressure monitoring: a summary report of the First International Consensus Conference. Groupe Evaluation and Measure of the French Society of Hypertension. J Hypertens 2000; 18: 493–508.
12. Eckert S, Gleichmann S, Gleichmann U. Blood pressure self-measurement in upper arm and in wrist for treatment control of arterial hypertension compared to ABPM. Z Kardiol 1996; 85 (suppl 3) : 109–111.
13. O'Brien E, De Gaudemaris R, Bobrie G, Agapiti Rosei E, Vaisse B. Consensus conference on self-blood pressure measurement. Devices and validation. Blood Press Monit 2000; 5: 93–100.
14. O'Brien E, Petrie J, Littler W, de Swiet M, Padfield PL, Altman DG. et al
. An outline of the revised British Hypertension Society protocol for the evaluation of blood pressure measuring devices. J Hypertens 1993; 11: 677–679.
15. American National Standard. Electronic or automated sphygmomanometers
. Arlington, VA: Association for the Advancement of Medical Instrumentation; 1993.
16. O'Brien E, Mee F, Atkins N, Thomas M. Evaluation of three devices for self-measurement of blood pressure according to the revised British Hypertension Society Protocol: the Omron HEM-705CP, Philips HP5332, and Nissei DS-175. Blood Press Monit 1996; 1: 55–61.
17. Sesler JM, Munroe WP, McKenney JM. Clinical evaluation of a finger oscillometric blood pressure device. Ann Pharmacother 1991; 25: 1310–1314.
18. O'Brien E, Waeber B, Parati G, Myers MG. Blood pressure measuring devices: recommendations of the European Society of Hypertension. BMJ 2001; 322: 531–536.
19. Wonka F, Thummler M, Schoppe A. Clinical test of a blood pressure measurement device with a wrist cuff. Blood Press Monit 1996; 1: 361–366.
20. Herpin D, Pickering T, Stergiou G, de Leeuw P, Germano G. Consensus conference on self-blood pressure measurement. Clinical applications and diagnosis. Blood Press Monit 2000; 5: 131–135.
21. Guidelines Subcommittee. World Health Organization–International Society of Hypertension Guidelines for the Management of Hypertension. J Hypertens 1999; 17: 151–185.
22. The Sixth Report of the Joint National Committee. Prevention, detection evaluation, and treatment of high blood pressure. Arch Intern Med 1997; 157: 2413–2446.
23. Wessig K, Hollinger S, Schmalzhaf I, Lenz T. Clinical evaluation of the efficacy of the Braun PrecisionSensor oscillometric wrist blood pressure monitor for use on adults versus auscultation as defined by ANSI/AAMI SP10-1992. Blood Press Monit 2000; 5: 239–245.
24. Eckert S, Gleichmann U, Zagorski O, Klapp A. Validation of the OMRON R3 blood pressure self-measuring device through simultaneous comparative invasive measurements according to protocol 58130 of the German Institute for Validation. Blood Press Monit 1997; 2: 189–192.
25. Yarows SA, Brook RD. Measurement variation among 12 electronic home blood pressure monitors. Am J Hypertens 2000; 13: 276–282.
26. Suzweiker R, Schumacher M, Fruhwald FM, Watzinger N, Klein W. Comparison of wrist blood pressure measurement with conventional sphygmomanometry at a cardiology outpatient clinic. J Hypertens 2000; 18: 1013–1018.
27. Rogers P, Burke V, Stroud P, Puddey IB. Comparison of oscillometric blood pressure measurements at the wrist with an upper-arm auscultatory mercury sphygmomanometer. Clin Exp Pharmacol Physiol 1999; 26: 477–481.
28. Heise T, Magnusson K, Grobel B, Heinemann L, Rave K, Bender R. et al
. A cross-over evaluation of different methods and devices to measure blood pressure in type 1 diabetic patients with nephropathy. Blood Press Monit 2000; 5: 175–180.
29. Watson S, Wenzel RR, di Matteo C, Meier B, Luscher TF. Accuracy of a new wrist cuff oscillometric blood pressure device: comparisons with intraarterial and mercury manometer measurements. Am J Hypertens 1998; 11: 1469–1474.
© 2002 Lippincott Williams & Wilkins, Inc.
30. Saul F, Aristidou Y, Klaus D, Wiemeyer A, Losse B. Comparison of invasive blood pressure measurement in the aorta with indirect oscillometric blood pressure measurement at the wrist and forearm. Z Kardiol 1995; 84: 675–685.