P.037 Pressure Waveform Estimation in the Common Carotid Artery — Different Methods in Comparison

Abstract

Non-invasive blood pressure waveform estimation in the common carotid artery (CCA) would yield an indirect estimation of its mechanical properties. Assuming both diastolic (P_d) and mean arterial pressure (MAP) to be constant over the arterial tree and considering arteries as rotationally symmetrical, CCA pressure waveform (P_CCA(t)) can be estimated by rescaling the diameter waveform in the CCA (D_CCA(t)) on the radial artery (RaA) blood pressure waveform (P_RaA(t)), using either a linear or an exponential estimation method.

11 normotensive volunteers were included. For each subject, 3 repeated measurements over three days with a weekly interval were performed in the RaA and the CCA simultaneously. P_RaA(t) was measured using applanation tonometry, whereas D_CCA(t) was measured with ultrasound.

Linear Estimation: D_CCA(t) was linearly rescaled over P_RaA(t) by equalizing diastolic and mean values of both waveforms: P_CCA(t) = δ*D_CCA(t)+P_d. Exponential Estimation: the CCA cross sectional area waveform, A(t), was exponentially rescaled over P_RaA(t) according to: PCCA(t) = P_d*Exp (α*((A_C-_CA(t)/Ad,CCA) -1)), iteratively adjusting α (stiffness index) to equalize RaA and CCA mean pressures.

The difference between systolic pressure values estimated by means of the two methods in the CCA is on average 2.6 ± 1.1 mmHg, approximately pressure-independent. The mean difference between the systolic pressure in the RaA and the CCA, using the exponential method, is 17.6 ± 6.3 mmHg. The difference between the radial MAP computed as integral mean and the one estimated with [1/3*P_s + 2/3*P_d] is -0.3 ± 3.4 mmHg. Estimation quality is not depending on the MAP value.