where Δ𝑃 is the pressure change, ΔV is the volume change and D is the distensibility coefficient.
Herein, simultaneous measurement of two variables is essential for example, pressure and flow velocity (Doppler) or pressure and diameter (wall tracking). These are further investigated in Section 3. of this paper. A significant two-site method such as velocity-encoded MRI includes transit time [73], flow-area [79], and cross-correlation techniques [80]. In this method, flow pulses are measured at dual sites over multiple cycles and ensemble averaging are employed for accurate results. Further, specific devices employed pressure/displacement waves for PWV estimation; for example Complior [81], SphygmoCor [82,83], PulsePen [84]. However, these devices use manual external tape measurements and therefore, error prone.
Additionally, consumption of meals [85], caffeine [86], and/or cigarette [87] influenced arterial stiffness.