The role of the endothelium in the regulation of vascular function is widely recognized. Endothelial dysfunction being a precursor to clinically observable vascular deformations, suggests that early detection and proper interventions might arrest disease progression. The percentage flow-mediated dilation index (FMD%), which is defined as the relative change in artery diameter during hyperemia, has been commonly used to quantify endothelial function and is said to be a strong predictor of future cardiovascular events. However, conventional FMD measures only the diameter response to shear stress leaving out the changes in artery material properties that influence dilation. This may be addressed by measuring the arterial material response during reactive hyperemia (transient increase in blood flow in the artery as a response to a shear stimulus) using simultaneous and continuous brachial blood pressure, diameter, and flow measurements, all of which are intrinsically responsible for dilation.

In this seminar, we will explore the state-of-the-art method for endothelial reactivity assessment, the research gaps and instrumentation challenges. We will discuss the development of hardware and software architecture of a multimodal image-free ultrasound system for real-time measurement of arterial vessel wall dynamics (pressure and diameter) during reactive hyperemia. We will also cover the developed models to normalize endothelial reactivity with input shear and to establish associations with artery wall dynamics, material properties with age and disease conditions. Further, we will also present the design and development of a dual bladder cuff system, which is a simple, and cost-effective yet feasible alternative of the state of art. To support the hypothesis, we will also discuss the initial results on the feasibility of the developed endothelial reactivity assessment model in clinical applications through in-vivo (N=50+), in-silico (N=4374) and clinical experiments.

Further research would include the development of: instrumentation for simultaneous measurement of pressure, diameter and flow from the target artery, mathematical models that relate endothelial function with bio-availability of nitric oxide and extensive studies of the developed hardware using in-vitro, ex-vivo and in-vivo experiments.