title: How to assess mean blood pressure properly at the brachial artery level.
abstract: OBJECTIVE
  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 intra-arterial 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 +/- 2.3 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Internal Medicine, St Antonius Hospital, Nieuwegein, The Netherlands. w.bos@antonius.net
authors.forename: Willem J W
authors.initials: WJ
authors.lastname: Bos
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Verrij
authors.forename: Hieronymus H
authors.initials: HH
authors.lastname: Vincent
authors.forename: Berend E
authors.initials: BE
authors.lastname: Westerhof
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Parati
authors.forename: Gert A
authors.initials: GA
authors.lastname: van Montfrans
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000098:blood supply; D001794:Blood Pressure; D001916:Brachial Artery / Q000503:physiopathology*; D016022:Case-Control Studies; D002940:Circadian Rhythm; D005260:Female; D006339:Heart Rate; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012107:Research Design; D014664:Vasodilation