Quantification of the Calibration Error in the Transfer Function-Derived Central Aortic Blood Pressures

Background

The accuracy of the central aortic systolic (SBP-C) and pulse (PP-C) blood pressures estimated noninvasively by a generalized transfer function technique has been questioned. The purpose of the present study was to quantify precisely the impact of the input errors (differences between the oscillometric (SBP-O, DBP-O, PP-O) and invasive (SBP-B, DBP-B, PP-B) brachial systolic, diastolic, and pulse blood pressures) on the output errors (differences between the estimated and invasively measured SBP-C and PP-C).

Methods

Invasive high-fidelity right brachial and central aortic pressure waveforms, and SBP-O, DBP-O, and PP-O (=SBP-O – DBP-O) were obtained simultaneously in 40 patients during cardiac catheterization. A generalized transfer function was applied on the individual brachial pressure waveform to derive predicted SBP-C and PP-C.

Results

Observed input errors were −2.3 ± 5.8mmHg from SBP-O, 8.1 ± 5.3mmHg from DBP-O, and −10.4 ± 7.1mmHg from PP-O, respectively. The output errors were −2.2 ± 6.4mmHg and −10.3 ± 8.0mmHg for SBP-C and PP-C, respectively, when the brachial pressure waveforms were recalibrated using SBP-O and DBP-O. The outputs were determined by the inputs according to the Equation (1): SBP-C error = 0.97 × SBP-O error + 0.03 (r = 0.88, P < 0.01); and the Equation (2): PP-C error = 0.96 × PP-O error – 0.30 (r = 0.86, P < 0.01).

Conclusions

Noninvasive application of the generalized transfer function techniques produces estimates of SBP-C and PP-C with errors equivalent to those of the oscillometric blood pressure monitor in the estimation of SBP-B and PP-B. The output errors can be predicted from input errors of SBP-O and DBP-O.

American Journal of Hypertension, advance online publication 18 August 2011; doi:10.1038/ajh.2011.146

blood pressure measurement, blood pressure, calibration error, central blood pressure, generalized transfer function, hypertension

© American Journal of Hypertension, Ltd. 2011