P.04 A Transfer-Function-Free Technique for the Non-Invasive Estimation of Central Arterial Pressure

Abstract

Background: Central aortic pressure (CAP) is important for the determination of the cardiovascular risk. Transfer function (TF)-based techniques allow for estimating CAP non-invasively from pressure waveforms acquired distally in the circulation. However, TF-based CAP might preserve the high frequencies of the distal waveform [1]. Therefore, we propose a new method where CAP is estimated from local direct non-invasive measurements of diameter (D) and blood velocity (U) waveforms. Methods: Aortic root D and U were measured using an ultrasound scanner (GE, Vivid E95) in 10 healthy volunteers (46 ± 15 years, 5 men), and used to determine local wave speed (PWV) using the lnDU-loop method [2]. Brachial systolic (Ps) and diastolic blood pressure (Pd), as well as central Ps, were also estimated using a sphygmomanometer (Uscom, BPPLUS-R7). CAP was determined as: , where, and blood density = 1060 kg/m3. Results: Mean brachial Ps and Pd were 124.1 ± 9.5 and 77.9 ± 5.4 mmHg, respectively. Mean PWV was 3.07 ± 0.71 m/s, leading to = 1.00 ± 0.46. The average calculated Ps was only –0.4% lower than TF-Ps (116.4 ± 11.2 vs. 116.9 ± 8.9, mmHg). Estimated calculated aortic and measured brachial mean pressure were almost identical with a difference of 0.01% (97.8 ± 6.9 vs. 97.8 ± 6.5, mmHg). Discussion: This proof-of-concept study shows that the CAP waveform can be estimated non-invasively from measurements of brachial Pd, and aortic D and U obtained using equipment available in almost every cardiovascular clinic. Further studies are warranted to establish the full utility of the new technique. FigureA: typical example of aortic D converted into CAP. B: Bland-Altman comparison between calculated and TF Ps.

Keywords

• Non-invasive pressure estimation