Comparison of invasive and brachial cuff-based noninvasive measurements for the assessment of blood pressure amplification.

Our aim was to assess the discrepancy in the blood pressure amplification (BPA) value defined as the aortic-to-brachial increase in systolic BP (SBP) between invasive and noninvasive brachial cuff-based methods. In 45 patients undergoing cardiac catheterization, BP in the brachial artery and ascending aorta were measured with an invasive catheter and a brachial cuff-based oscillometric device. To calculate aortic SBP, brachial waveforms were calibrated by the brachial systolic and diastolic BP (DBP) (C1 calibration) or by the brachial mean BP and DBP (C2 calibration). C1 calibration underestimated aortic SBP (-17.7 mm Hg (95% confidence interval: -21.9 to -13.5)), whereas C2 calibration generated an approximately accurate aortic SBP (1.8 mm Hg (-2.4 to 5.9)). Regarding brachial SBP, noninvasively measured values were markedly underestimated (22.2 mm Hg (-26.4 to -18.0)), resulting in a slightly low BPA value in C1 calibration (11.9±6.3 mm Hg) and a paradoxical negative BPA value in C2 calibration (-7.6±6.7 mm Hg). Multiple linear regression analysis showed that the cuff-catheter difference of BPA was positively correlated with the cuff-catheter difference of brachial SBP in both calibrations (C1 calibration: β=0.51; C2 calibration: β=0.50; both P<0.01). Although noninvasively measured BPA was associated with invasively measured BPA only in C1 calibration (r=0.33, P=0.03), when using invasively measured brachial SBP instead of a cuff-based measurement, the BPA was well associated with invasively measured BPA in both calibrations (C1 calibration: r=0.57; C2 calibration: r=0.52; both P<0.001). In conclusion, there was a trade-off in accuracy between brachial cuff-based noninvasive aortic SBP and BPA because of the inherent inaccuracies in the cuff-based method. This finding should be fully considered in establishing standardized reference values for aortic BP.