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 (βfit) against the theoretically calculated value βref which strongly correlated (r = 0.98, p < 0.05). The systolic PWV (PWVs) was approximately 20% higher than diastolic PWV (PWVd). The group average PWVs and PWVd 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.
Background and Aim: Given the knowledge of the noninvasive assessment of local pulse wave velocity (PWV) for cardiovascular risk stratification, it is apparent that it is necessary to develop a practically feasible solution to measure and trace instantaneous variations in local PWV (incremental local PWV) from the target arteries.Methods: From the arterial blood pulse propagation characteristics, wave nature of the transmural pressure, and the distending vessel wall geometry, a mathematical model was developed to evaluate incremental local PWV using arterial diameter waveform. Its practical feasibility and the measurement accuracy were demonstrated invivo using a custom image-free ultrasound device, with the Bramwell-Hill method as the reference.Results: The proposed technique and developed device reliably captured incremental local PWV from the carotid artery. The locus of instantaneous variations in carotid local PWV obtained using the developed model traced the reference values, with a root-mean-square-error lesser than 0.05 m/s. Study results further established the practical feasibility and accuracy of this novel approach.Conclusion: The theoretical basis and measurement method of this work is a solution for non-invasive, realtime assessment of incremental local PWV and its locus.
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