Carotid Tonometry Versus Synthesized Aorta Pressure Waves for the Estimation of Central Systolic Blood Pressure and Augmentation Index

Objective: To assess the interchangeability of carotid tonometry and synthesized aorta pressure waveforms for estimating central systolic blood pressure (SBP) and augmentation index (AIx). Methods: Tonometry waveforms were acquired with a custom built hardware and software platform in 276 subjects (179 men/97 women; aged 45.5 ± 5.7 years; mean ± standard deviation) at the radial (P_wf,ra), brachial (P_wf,ba), and carotid artery (P_wf,ca). The P_wf,ba was calibrated using systolic (SBP_ba) and diastolic (DBP_ba) sphygmomanometer pressure. The DBP_ba and calculated mean (MAP_ba) brachial pressure were subsequently used for calibration of P_wf,ra and P_wf,ca. A central pressure waveform (P_wf,sao) was synthesized from P_wf,ra using a generalized pressure transfer function (TFF). The AIx and SBP were measured on P_wf,ra, P_wf,ca, and P_wf,sao. Results: The SBP_ra, SBP_ca, and SBP_sao were 138.5 ± 16.8, 130.0 ± 16.2, and 131.1 ± 16.6 mm Hg, respectively. The SBP_ra correlated well with the SBP_ca (r = 0.93) and the SBP_sao (r = 0.94), as did the SBP_ca and the SBP_sao (r = 0.97) with a mean bias of 1.35 ± 3.90 mm Hg. The AIx derived from P_wf,ra, P_wf,ca, and P_wf,sao were −20.8% ± 14.5%, 12.4% ± 13.9%, and 20.0% ± 11.7%, respectively. The correlation between radial and carotid, and radial and central AIx was 0.72 and 0.94, respectively. The correlation between AIx derived from P_wf,ca and P_wf,sao was 0.75 with a bias of 11.0% ± 14% (all correlations P < .001). Conclusions: The use of a generalized TFF in combination with well-calibrated radial pressure curves yields estimates of SBP in good agreement with carotid tonometry. Although AIx derived from a measured radial pressure curve correlates surprisingly closely with AIx measured on a synthesized aortic pressure curve, the correlation with a directly measured AIx on carotid signals is relatively poor. [Copyright &y& Elsevier]