How to assess mean blood pressure properly at the brachial artery level

Objectives Mean arterial pressure at the upper arm is traditionally calculated by adding one-third of the pulse pressure to the diastolic pressure. We questioned the general validity of this formula. Methods We used previously recorded resting intrabrachial pressure and Riva - Rocci Korotkoff blood pressure measurements in 57 subjects ( study A) and 24-h intraarterial recordings obtained in 22 ambulant subjects ( study B). Results In study A the intra-arterially measured 'real' mean pressure was found at 39.5 +/- 2.5% of pulse pressure above diastolic pressure, namely at a level higher than the expected 33.3% of pulse pressure, in all individuals. Results were not related to age, blood pressure, pulse pressure or heart rate levels. Mean pressure calculated with the traditional one-third rule therefore underestimated 'real' mean pressure by 5.0 +/- 2.3mmHg ( P < 0.01) when calculated from intra-arterial pressure readings, and by 4.9 +/- 5.3mmHg ( P < 0.01) when calculated from Riva - Rocci Korotkoff readings. In study B we showed activity-related variations in the relative level of the 'real' mean pressure, which increased by 1.8 +/- 1.4% ( P < 0.01) during sleep, and decreased by 0.5 +/- 0.9% during walking ( P < 0.05) and by 0.8 +/- 1.3% during cycling ( P < 0.01). Conclusion The mean pressure at the upper arm is underestimated when calculated using the traditional formula of adding one-third of the pulse pressure to the diastolic pressure. This underestimation can be avoided by adding 40% of pulse pressure to the diastolic pressure. The proposed approach needs to be validated through larger scale studies. J Hypertens 25: 751 - 755 (c) 2007 Lippincott Williams & Wilkins.