Variability in Indirect Blood Pressure Measurement

Abstract

fully appreciate the reproducibility of ABPM, the variability of office blood pressures (OBPs) using a standard mercury sphygmomanometer should be presented in comparison. We presented a direct comparison of the variability of office and 24-hour ABPs in a subsequent article,3 which, although not referenced by the authors, contributes new information on the variability of indirect blood pressures and, thus, deserves comment.For the purposes of this discussion, reliability ofblood pressures for an individual can be represented by the standard deviation of the differences (SDD) of repeated mea¬ surements obtained in patients at different visits. The re¬ liability of standard OBPs has been shown to be wide, av¬ eraging approximately ±14 mm Hg for systolic blood pressure (SBP) and ±10 mm Hg for diastolic blood pres¬ sure (DBP) across different studies (presented in reference 3). In comparison, the reliability of mean 24-hour aver¬ age ABPs between visits was found to be significantly less than that for OBPs in the same group of 50 hypertensive patients (SDDsbp, 10.6 vs 17.9mm Hg;F=2.85;P<.01;and SDDDBP, 5.8 vs 8.9 mm Hg; F=2.35; P<.01).3 Thus, in di¬ rect comparison with OBPs, ABPs proved to be more re¬ liable as an estimate of the patient's true blood pressure.Use of a more reliable estimate of blood pressure has some important clinical implications. Using OBPs alone, the false-positive diagnostic rate for hypertension may be as high as 20% to 25%, even with repeated office visits.45 At present, there is no general agreement on the defini¬ tion of a "normal" (mean±2 SDs) 24-hour ABP. However, once normal values are established, the use of the more reliable ABPs in the evaluation of patients with potentially abnormal elevations in blood pressure should reduce the number of patients labeled hypertensive. Without data com¬ paring cardiovascular morbidity and mortality in patients treated on the basis of ABPs vs OBPs, the question of the broader use of ABPM in the evaluation and management of hypertension will continue to be debated. Nevertheless, techniques to improve the reliability ofindirect blood pres¬ sure measurements should be examined-a point empha¬ sized by the authors of the current article.1 of automated ambulatory blood pressure measurements. J Fam Pract. 1992; 34:569-574.3. Bottini PB, Carr AA, Rhoades RB, Prisant LM. Variability of indirect methods used to determine blood pressures: office vs mean 24-hour automated blood pressures. Arch Intern Med. 1992;152:139-144. 4. A report by the management committee of the Australian Therapeutic Trial in mild hypertension. Lancet. 1982;1:185-191. 5. Pickering TG, James GD, Boddie C, Harshfield GA, Blank S, Laragh JH. How common is white coat hypertension? JAMA. 1988;259:225-228. New Do-Not-Resuscitate PoliciesThe article by Murphy and Finucane on new do\ x=r eq-\ not-resuscitate (DNR) policies1 leaves the reader perplexed. First, the policies are not new; second, the rationale for the new policies is contradicted by the authors themselves and the data available...