Sitting on the Evidence: What Is the Proper Patient Position for the Office Measurement of Blood Pressure?

Abstract

The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7)—as well as earlier reports—states that the proper position for the measurement of blood pressure (BP) is sitting.1 Two questions come to mind regarding this recommendation: Are there significant differences between BPs obtained in the supine and sitting positions? and What is the evidence that BP should be measured in the seated position? There are conflicting data regarding the relationship between supine and sitting BPs in otherwise healthy (i.e., not hypovolemic) individuals. Although both the International Society of Hypertension of the World Health Organization2 and the Hypertension Task Force of the American Heart Association3 assert that the two approaches to BP measurement are equivalent (assuming all measurements are performed with the arm at the level of the right atrium), numerous prospective studies have challenged this notion. Whereas some authors have demonstrated that systolic BP is lower and diastolic BP higher in the sitting, compared with the supine position,4 others have shown that both the systolic and diastolic BP are lower in the sitting position.5, 6 Conversely, another group has demonstrated that mean intra-arterial ambulatory systolic and diastolic BP were higher in the sitting position.7 It is noteworthy that the differences in BPs recorded in these studies were as high as 10 mm Hg. Some of the discrepancies between these studies can be explained by differences in technique (i.e., sphygmomanometric vs. oscillometric vs. intra-arterial) and research subject characteristics (i.e., hypertensive or diabetic status). Nevertheless, it is unclear if there is a consistent relationship between these two methods of BP measurement. Furthermore, it is unclear which method better approximates intra-aortic pressure and would thus be a better predictor of cardiovascular outcomes. The strongest argument in favor of routinely measuring BP in the sitting position is that the overwhelming majority of data associating hypertension with poor cardiovascular outcomes and the treatment of hypertension with improved outcomes were derived from studies in which the BP was measured, by protocol, in the sitting position. Specifically, the Framingham study measured BPs in the sitting position.8 Furthermore, the large BP treatment trials of the 1960s and 1970s, namely the Veteran's Affairs Cooperative Study Group on Antihypertensive Agents9 and the trial of the Medical Research Council (MRC) Working Party on Mild to Moderate Hypertension10 both measured BPs, by protocol, in the sitting position. In addition, two large trials from the late 1980s and early 1990s, the Multiple Risk Factor Intervention Trial (MRFIT)11 and the Systolic Hypertension in the Elderly (SHEP) trial,12 also measured BP in the sitting position. Finally, the major trials of antihypertensive therapy over the past decade, namely the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT),13 the Second Australian National Blood Pressure Study (ANBP2),14 the Hypertension Optimal Treatment (HOT) trial,15 and the Losartan Intervention for Endpoint (LIFE) Reduction in Hypertension Study,16 all measured BPs in the sitting position only. In conclusion, it is unclear if there are significant differences between BPs measured in the sitting vs. the supine position or which position best approximates intra-aortic pressure. It certainly is more convenient in most instances to take the BP when someone is sitting—and virtually all of the evidence linking hypertension with poor cardiovascular outcomes, as well as the data that support treating hypertension to improve these outcomes—were derived from studies that measured sitting BPs. The published guidelines recommending specific target BPs in certain populations were all based on measurement of BPs in the sitting position. Therefore, for the routine measurement of BP in the office setting, patients should be seated.