Incorporating Arterial Viscoelastic Modelling for the Assessment of Changes in Pulse Wave Velocity Within a Cardiac Cycle Using Bramwell-Hill Equation

Aims: This work presents a method & instrumentation to measure pressure-dependent intra-cardiac cycle variations in local blood pulse velocity PWV
(P)
using Bramwell-Hill (BH) equation by incorporating Kelvin-Voigt type viscoelastic modelling.Methods: A pilot in-vivo study on 8 subjects was conducted to verify the technique’s functionality. The carotid diameter D and pressure P waveforms (sampled at 1 kHz) were measured using our extensively validated image-free ultrasound technology ARTSENS and a calibrated tonometer respectively.Results: Measurement system captured high fidelity P and D signals. Employing the viscoelastic modelling, elastic P-D curves were obtained and PWV
(P)
was calculated. The reliability of these curves was verified by comparing the stiffness index derived from the fit (β
fit
) against the theoretically calculated value β
ref
which strongly correlated (r = 0.98, p < 0.05). The systolic PWV (PWV
s
) was approximately 20% higher than diastolic PWV (PWV
d
). The group average PWV
s
and PWV
d
were higher for hypertensive subjects.Conclusion: The proposed technique reliably measures the intra-cardiac cycle variations in PWV
(P)
and addresses various key considerations associated with non-invasive implementation BH equation for the same.