Effect of Fiduciary Point Choice on Pulse Wave Velocity-based Cuffless Pulse Pressure Estimation: Ex-vivo Study

Superiority of central blood pressure (BP) (especially its pulsatile component; pulse pressure (PP)) over that of brachial has been underlined recently through several clinical studies. Local pulse wave velocity (PWV) based cuffless methods using Bramwell-Hill (BH) equation are popularly employed to assess PP. These approaches assume PWV to be constant, whereas, it changes with pressure. Pertaining to this, literature is unclear on which instantaneous local PWV value should be chosen within the cardiac cycle for PP evaluation. Since local PWV can be measured from various fiducial points spread across the blood pulse cycle, it may be relevant to investigate on the choice of particular one(s) for reliable PP calculation. We have conducted an ex-vivo study in this regard employing an excised ovine artery, emulating 21 independent flow conditions by changing the PP and mean arterial pressure (MAP). The measured end-diastolic (ED) PWV was lower than the peak-systolic (PS) PWV by 32%, and in theory they are the extremities of PWV within a cardiac cycle. An underestimation of 26% was observed in the PP evaluated using ED-PWV and overestimation of 30% using PS-PWV. The PWV that is expected to yield an exact PP value corresponded to the instant in the blood pulse cycle where its mean occurred. The ED-PWV underestimated and the PS-PWV over-estimated the expected PWV by 17% and 14%, respectively, which explains the deviations in the estimated PPs. The time instant of the first derivate maximum being closer to that of the cycle's mean makes it a potential choice for measuring PWV for PP estimation.