Journal of Human Hypertension (2002) 16, 525–526 2002 Nature Publishing Group All rights reserved 0950-9240/02 $25.00 www.nature.com/jhh
LETTER TO THE EDITOR The oscillometric wrist devices: an estimate of the ‘supine’ error Journal of Human Hypertension (2002) 16, 525–526. doi:10.1038/ sj.jhh.1001422 Due to the fear of mercury toxicity, the classic Riva-Rocci sphygmomanometer is expected gradually to disappear from the medical wards.1,2 Oscillometric wrist devices are becoming popular mainly for self-measurement of blood pressure (BP). Some of these instruments have the advantage that they may record and save up to 30 measurements, which makes them an interesting option for repeated BP measurements. However, only few formal comparisons with the standard Riva-Rocci sphygmomanometer are available and some are unpublished.3 Therefore, before introducing a wrist device (NAISMatsushita) in our Unit, we formally tested its validity. This device, which is widely advertised in specialist medical journals, has not been formally tested by the BHS or the AAMI protocols. Since the wrist position is critical3,4 and BP in the clinical setting is often measured with patients lying in bed, we also estimated the error introduced by allowing the wrist to lay flat at the bed level. The issue is important because, although recognised, the magnitude of this error has not been systematically evaluated. Ten normal subjects (f:8; m:2) with a mean age of 38 years (range 26–55), and 20 hypertensive patients (f:11; m:9) with a mean age of 54 years (range 34 –78) were enrolled in the study. All subjects had a normal sinus Correspondence: Dr G Enia, Divisione Nefrologica & CNR, Via Sbarre Inferiori 39, 89131 Reggio Calabria, Italy. E-mail:
[email protected] Received 15 February 2002; accepted 2 March 2002
rhythm and the difference in BP (mercury sphygmomanometer) between the two upper arms was less than 5 mm Hg. The cuff size used (12 cm wide and 23 cm long) was adequate for their mid-arm circumference. All subjects participated to two consecutive studies. In the first study subjects were sitting and the BP was simultaneously taken with the auscultatory mercury sphygmomanometer at the left arm and with the NAIS at the right wrist. The wrist was kept at the heart level using the plastic box, specifically designed and supplied with the device, to support the forearm on a table. In the second study two NAIS devices were used with the subjects lying in bed; the left wrist was allowed to stay at the bed level, while the right one was kept at the heart level by raising the forearm with the plastic box. In both studies four BP measurements were taken by two trained nurses. The nurse took the readings without being aware of the values of the other observer. The mean of the four values was used for analysis. Blood pressure was measured with the auscultatory mercury sphygmomanometer according to the technique recommended by the British Hypertension Society.5
In the first study the diastolic BP was consistently underestimated by the oscillometric device in comparison with values obtained with the standard mercury sphygmomanometer. No significant difference was found in systolic BP (Table 1). In the second study BP (systolic and diastolic) was markedly higher when the wrist was kept at the bed level (Table 1). Our data show that in the controlled context of a validation study and with the wrist properly aligned to the level of the heart, this wrist oscillometric device gave diastolic BP values substantially lower than the mercury sphygmomanometer. Therefore this device cannot replace the standard mercury sphygmomanometer for diagnosis of hypertension, particularly in children and pregnant women who are expected to have a lower diastolic BP. These findings are in line with observations made during invasive studies.6 Beside this limitation, the doctors should be aware that the error of measurement in the supine position is not negligible. It is well known that incorrect positioning of the wrist is an important source of error when the patient is sitting. Our data show that even the few centimeters between the wrist kept at the bed level and the heart when
Table 1 Blood pressure measurements in the studies. Values are presented as mean (95% CI); paired t-test **P ⬍ 0.001 Systolic
Diastolic
1st study Left arm (mercury) Right wrist (oscillometric)
135 (127–143) 134 (126–141)
85 (79–88) 79 (75–83)**
2nd study Right wrist (heart level) Left wrist (bed level)
135 (126–141) 144 (135–152)**
76 (71–79) 83 (78–88)**
Letter to the editor
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the patient is lying down cause major variations in the estimation of BP. G Caridi C Zoccali G Enia Renal Unit and Centro di Fisiologia Clinica del C.N.R. Reggio Calabria, Italy
Journal of Human Hypertension
References 1 Langford NJ, Ferner RE. Toxicity of mercury. J Hum Hypertens 1999; 13: 651– 656. 2 O’Brien E. Replacing the mercury sphygmomanometer. BMJ 2000; 320: 815–816. 3 Yarows SA, Julius S, Pickering TG. Home blood pressure monitoring. Arch Int Med 2000; 160: 1251–1257. 4 Netea RT, Lenders JW, Smits P, Thien T. Arm position is important for blood
pressure measurement. J Hum Hypertens 1999; 13: 105–109. 5 Ramsay L et al. Guidelines for management of hypertension: report of the third working party of the British Hypertension Society. J Hum Hypertens 1999; 13: 569–592. 6 Weber F, Erbel R, Schafers R, Philipp T. Wrist measurement of blood pressure: some critical remarks to oscillometry. Kidney Blood Press Res 1999; 22: 161– 165.
