Estimating Central Blood Pressure from Non-Invasive Data
Central blood pressure (cBP) is the blood pressure measured at the ascending aorta next to the heart and therefore the load that the heart has to overcome when pumping. cBP is a highly prognostic cardiovascular risk factor. However, cBP can only be directly measured with catheterisation, which is costly and has associated risks due to its invasive nature.

We have produced algorithms to estimate and analyse cBP non-invasively from the aortic blood flow waveform and the aortic pulse wave velocity (Am J Physiol, 2021 & 2015; Frontiers Physiol, 2021). These are based on haemodynamic principles and on physical phenomenon occurring in the aorta itself, making them more subject-specific than mathematical transfer functions. These algorithms have been tested using in vivo data (including intra-aortic pressure waveforms measured in patients undergoing catheterisation) and in vitro data measured in thousands of virtual subjects. Our approach could improve cardiovascular function assessment in clinical cohorts with available aortic ultrasound or magnetic resonance imaging data.

We have shown that the entire cBP waveform can be generated from the aortic flow velocity waveform, aortic pulse wave velocity, and peripheral blood pressure components (diastolic decay, diastolic and mean blood pressures) using a part theoretical, part empirical algorithm (Am J Physiol, 2015). Our algorithm provided accurate estimation of early systolic components of the cBP wave that determine peak myocardial wall stress. We have also developed three algorithms of increasing complexity that use computational blood flow modelling and which we tested and compared for a wide range of cBP morphologies (Am J Physiol, 2021). These algorithms are freely available from here.

A software tool was developed in collaboration with Philips Healthcare to extract the arterial geometry and blood inflow profiles from MRI images, run Nektar1D to calculate blood pressure, and display the output pressure (Proc Comput Sci, 2016). This is a highly automated workflow allowing user-interaction to correct inaccuracies if necessary.

We have also produced a method for estimating the central pulse pressure (i.e. the amplitude of the cBP wave which increases with hypertension) by identifying the main physical determinants of pulse pressure amplification along the aortic-brachial arterial path, namely brachial flow wave morphology in late systole, and vessel radius and distance along this arterial path (Frontiers Physiol, 2021).

All our algorithms require robust methods for quantifying aortic wall stiffness which we have developed and tested as described in here.