Background: Non-invasive estimation of central blood pressure from radial artery (RA) pressure waveforms is increasingly applied. We investigated the impact of RA waveform calibration on central blood pressure assessment, with focus on the one-third rule used to estimate mean arterial blood pressure (MAP).

Methods: Pressure waveforms were non-invasively measured at the radial (RA), brachial (BA), and carotid (CA) artery in 1899 apparently healthy subjects (age 45.8±6.1 yr). RA and CA waveforms were calibrated using DBP_BA and (i) SBP_BA; (ii) MAP estimated with the one-third rule; (iii) MAP estimated as DBP_BA + 40% of BA pulse pressure (PP_BA), and (iv) MAP from the scaled BA pressure waveform (MAP_ref). Central SBP was obtained via a transfer function (SBP_TF).

Results: SBP_TF calculated by assuming SBP_BA=SBP_RA (i), with the one-third rule (ii) and 40% rule (iii) calibration was respectively 6.2±4.8, 11.9±5.5 and 3.7±5.3 mmHg (p<0.001) lower than SBP_CA calibrated with method (iv), considered as the reference value. Applying the 1/3^rd rule, brachial-to-radial amplification was negative (−6.3±4.5 mmHg), while positive (6.5±4.9 mmHg) as expected with reference method (iv). PP_BA and brachial-to-radial amplification were main determinants of the difference between SBP_CA and SBP_TF.

Conclusions: SBP_TF is highly sensitive to the RA calibration procedure which determines the extent of brachial-to-radial pressure amplification accounted for. The 1/3^rd rule should be avoided to calibrate radial artery pressure waveforms. We therefore advise to use 40% of the PP to assess MAP as advocated by Bos et al. when brachial tonometry measurements are not available.