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Dear Editor: Arterial blood pressure (BP) measurement in obese patients, mainly in those with cone-shaped arms, is a controversial issue. This topic was discussed in The Journal of Clinical Hypertension (JCH) by Townsend,1 who suggested that, in these cases, the solution would be to perform the BP measurement in the forearm or at the wrist with an appropriate device. The reason for this is that the use of the thigh cuff on the arm overlaps the antecubital fossa, making auscultation of the Korotkoff sounds difficult or impossible. Nevertheless, these recommendations deserve special attention, since the proposed alternative solutions present problems.

Studies conducted in our hypertension unit2 show that forearm arterial BP measurements overestimate values when compared with the values obtained through the finger arterial pressure (Finapres) instrument and through upper arm measurements with an appropriate cuff (Figure 1). The differences between upper arm and Finapres systolic and diastolic BPs were within 10 mm Hg in 34% and 22% of the patients, respectively. Between the upper arm and forearm, the differences were 19% and 28%, respectively. BP differences were more than 20 mm Hg in 25% and 28% of the patients between forearm and Finapres systolic and diastolic BP, respectively. Differences between upper arm and Finapres systolic and diastolic BPs were more than 20 mm Hg in only 3% and 16% of the patients, respectively (Figure 2).

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Figure 1. Blood pressure measurement performed with finger arterial pressure (Finapres) and with an appropriate bladder cuff on upper arm and standard bladder cuff on forearm. *P<.05: Finapres vs upper arm diastolic and forearm systolic and diastolic blood pressure.

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Figure 2. Percentage distribution of the differences in systolic and diastolic blood pressure between finger arterial pressure (Finapres) values and upper arm and forearm measurements.

Hypertension was diagnosed in 23% of the patients using upper arm measurement, while 34% were diagnosed as hypertensive based on forearm BP measurement (Figure 3). Optimal BP values were present in 53% of the patients when upper arm measurements were considered, compared with only 18% when the forearm measurement was considered (P<.05).

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Figure 3. Classification of blood pressure (in mm Hg) according to upper arm measurements performed with an appropriate bladder cuff and to forearm values obtained with standard bladder cuff.

Our study results suggested the following equations to adjust the values of forearm arterial BP assessed with a standard cuff bladder and to correct the error found for individuals with arm circumferences between 32 cm and 44 cm:

Systolic BP measurement = 33.2 + 0.68 × systolic forearm BP measurement

Diastolic BP measurement = 25.2 + 0.59 × diastolic forearm BP measurement

It was observed that forearm measurements in obese people do not replace the upper arm measurements recorded with an appropriate cuff bladder size. The forearm BP measurement could overestimate the prevalence of hypertension in obese patients.

Another aspect worth mentioning is the use of devices that record arterial BP at the wrist. Entities such as the Association for the Advancement of Medical Instrumentation (AAMI), the British Hypertension Society (BHS), and the European Hypertension Society (ESH) have been studying equipment validation. The great majority of devices that monitor arterial BP measurement at the wrist are questionable in terms of accuracy.3–5 Thus, they should not be recommended until their efficiency is proved in new studies.—Josiane Lima de Gusmão, PhD, RN; Decio Mion Jr, PhD, São Paulo, Brazil

Response:

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Drs de Gusmão and Mion raise interesting issues in response to my “Common Questions and Answers in the Management of Hypertension” column in the December 2005 issue of JCH regarding BP measurement in obese patients with a “funnel-shaped” arm. To summarize their letter they addressed 3 points and made several observations. First they note that there are limitations and possible inaccuracies as you move from the brachial to the wrist arteries and go from auscultation to oscillometry. I agree, and the discussion in my brief editorial began with attempts to obtain auscultatory readings if possible. Second, they note the magnitude of error when using the wrist monitors in the studies they quoted pointing out their experience with the Finapres monitor. Most practicing physicians will not have access to this type of research equipment because of cost issues. That is why I pointed out the usefulness of wrist monitors, which are inexpensive and widely available despite the problems with accuracy. The formula they present to correct a wrist monitor–based forearm BP is certainly worthy of more study. Third, they questioned the potential of misdiagnosis of hypertension when over-reading the BP using a wrist monitor, a caveat with which I agree and that is equally true of poorly taken brachial BPs.

Finally, they rightly observe the value of certification of monitors by testing protocols such as those of AAMI and the American National Standards Institute (ANSI). It was for that reason that I concluded the editorial with a comment that 1 wrist monitor had less variability associated with it. That particular monitor was tested according to AAMI/ANSI protocol and found to be acceptable by the investigators.

Many thanks to our Brazilian colleagues for clarifying the importance and pitfalls of this clinically challenging scenario.—Raymond R. Townsend, MD, Philadelphia, PA

References

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  3. References
  • 1
    Townsend RR. Of funnel arms, Popeye, and other-sized challenges. J Clin Hypertens (Greenwich). 2005;7:755756.
  • 2
    Pierin AM, Alavarce DC, Gusmão JL, et al. Blood pressure measurement in obese patients: comparison between upper arm and forearm measurements. Blood Press Monit. 2004;9:101105.
  • 3
    Mourad A, Gillies A, Carney S. Inaccuracy of wrist-cuff oscillometric blood pressure devices: an arm position artefact? Blood Press Monit. 2005;10:6771.
  • 4
    Palatini P, Longo D, Toffanin G, et al. Wrist blood pressure overestimates blood pressure measured at the upper arm. Blood Press Monit. 2004;9:7781.
  • 5
    Sims AJ, Menes JA, Bousfield DR, et al. Automated noninvasive blood pressure devices: are they suitable for use? Blood Press Monit. 2005;10:275281.