Quantification of the calibration error in the transfer function-derived central aortic blood pressures

Abstract

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). Conclusion sNoninvasive 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. © 2011 American Journal of Hypertension, Ltd.