| PhD Seminar

Name of the Speaker: Mr. Rahul M (EE17D202)
Guide: Prof. Mohanasankar Sivaprakasam
Co-Guide: Dr. Jayaraj Joseph
Venue: ESB-244 (Seminar Hall)
Online meeting link: https://meet.google.com/kzj-ncca-gye
Date/Time: 2nd February 2024 (Friday), 3:00 PM
Title: Demystifying the Arterial Pulse – Methods to Quantify Arterial Pulse Wave Reflection and its Novel Applications

Abstract

The pulse wave, originating from the left ventricle's rhythmic contraction, undergoes reflections in the arterial network due to impedance mismatches. These reflections, superimposed on the forward-running wave, modulate pulse wave magnitude and morphology, influencing blood pressure and flow in the vasculature. Quantifying these reflections through wave separation analysis (WSA) enhances vascular health assessment. Current methods, limited to the aortic site, necessitate simultaneous measurement of transmural blood pressure and blood flow; however, a single pulse waveform approach for WSA can overcome this limitation, offering methodological and instrumental advantages.

My work proposes modelling and signal processing techniques for performing WSA using a single pulse waveform measured from the common carotid artery and its applications in improving the reliability of local pulse wave velocity (PWV). In the first seminar, I presented the theory and validation of the proposed methods: the multi-Gaussian decomposition model (MGDM) of a pulse wave and a multi-Rayleigh flow model for WSA. The proposed MGDM decomposes the arterial pulse waveform using weighted and shifted multi-Gaussian curves, which are then uniquely combined to yield the forward and backward waves. In the second approach, a flow waveform morphology is constructed using weighted and shifted multi-Rayleigh curves, from the fiduciary markers obtained from arterial pulse waveform, mimicking the characteristics of the carotid blood flow for WSA. The performance of these methods was validated to quantify wave reflections on simulated settings, in-silico virtual subjects database (N = 4374, healthy, age: 25 – 75 years) and in-vivo studies on human participants (N = 70, healthy, age: 18 – 51 years) against reference WSA, that uses both pressure and flow. Reliable forward and backward pulse waves were obtained using both approaches, with root-mean-square error < 2.5 mmHg. The reflection quantification indices obtained from both methods had a statistically significant and strong correlation (r > 0.75, p < 0.001) with those obtained using reference methods.

In the second seminar, I will illustrate a novel application that uses carotid WSA based on the proposed methods to improve the reliability and repeatability of measuring local PWV. Based on controlled experiments and evidence from literature, it is hypothesised that the wave reflections corrupt the PWV measurement. To test the hypothesis, a measurement apparatus consisting of a dual-channel ultrasound transducer with an integrated pressure sensor was developed to conduct the relevant studies. Results from in-vivo invasive studies on animals (N=2, male porcine) and non-invasive studies on human participants (N = 51, healthy, age: 20 – 56 years) indicate a lower coefficient of variations (~5% (from ~7.5%) at diastole, and ~10% (from ~25%) at systole) in the beat-to-beat estimates of PWV after eliminating for wave reflections. Additionally, the mean values obtained from reflection-free PWV and from theoretical estimates of PWV were statistically assessed, and the results indicated no significant difference between the means (p > 0.05) at both diastole and systole. In comparison, the PWV (with reflections) revealed a statistically significant difference between the means (p < 0.05). The seminar concludes with further research directions in this regard.