Use of generalized transfer function-derived central blood pressure for the calculation of baroreflex gain

BACKGROUND: Peripheral blood pressure measurement underestimates pressure changes during baroreflex testing, resulting in an overestimation of baroreflex gain. This error might be reduced by measuring central blood pressure; the invasive measurement, however, may represent ethical and practical problems. The solution may be the derivation of central blood pressure from the peripheral pulse using a generalized transfer function. METHODS: In the current study, we tested the agreement between catheter-measured and generalized transfer function derived central blood pressure measurements and corresponding baroreflex gains. ECG and blood pressure waveforms were monitored continuously during a phenylephrine-induced pressure rise in 22 subjects undergoing cardiac catheterization. Pressure was measured with a catheter positioned in the aorta and with applanation tonometry in the radial artery. Radial pressure waveforms were subject to a generalized transfer function built in the SphygmoCor device to derive central pressure waveforms. Radial tonometric signal was calibrated with catheter-measured (invasive) and sphygmomanometric (noninvasive) pressures. Baroreflex gains were calculated from the linear regressions between heart period and systolic pressure changes. RESULTS: When radial tonometric signal was calibrated invasively, there was no group difference between baroreflex gains calculated from SphygmoCor-derived and catheter-measured pressures (8.2 +/- 1.2 vs. 7.2 +/- 1.2 ms/mmHg, P = NS). When radial tonometric signal was calibrated noninvasively, however, baroreflex gains calculated from SphygmoCor-derived pressures overestimated those calculated from catheter-measured pressures. CONCLUSION: Using a generalized transfer function is an accurate method to derive central pressure changes for baroreflex gain calculation. The technique, however, requires invasive pressure measurements for calibration, leaving the problem of a fully noninvasive central pressure measurement unresolved.