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.