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.
We used previously recorded resting intrabrachial pressure and Riva–Rocci Korotkoff blood pressure measurements in 57 subjects (study A) and 24-h intra-arterial recordings obtained in 22 ambulant subjects (study B).
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 ± 2.3 mmHg (P < 0.01) when calculated from intra-arterial pressure readings, and by 4.9 ± 5.3 mmHg (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).
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.