Vascular Wall Shear Stress: Basic Principles and Methods

This article by Papaioannou and Stefanadis deals with the relationship between shear stress/rate and other  physiological aspects of blood vessels. These aspects range from blood viscosity, vessel diameter, vessel wall thickness, and vascular endothelium. Papaioannou and Stefanadis began by describing the basic definition of stress( the internal distribution of forces inside the body that react and balance to external forces applied on them) and strain( the change in physical form of a body as a result of external forces). They also discussed the existence of hemodynamic conditions that result in two types of stress on vessel walls( circumfrerential stress and shear stress). Shear stress is caused by friction of blood flow against the endothelial cells lining the inner membrane of blood vessels, known as the vascular endothelium(arterial). The paper was considering blood to be a Newtonian fluid or having a linear relationship between shear stress and shear rate.  The basic relationship between shear stress levels and vessel diameter and wall thickness is that at high levels of shear stress the vessel diameter increases as well as an thickening of the vessel wall, this is so that the vessel regains the accurate level of shear stress, but as the shear stress decreases there is a reduction of vessel diameter and leads to intima-media hyperplasia. The why of this vessel adaptation is being research but there are some theories. One theory is that of cellular mechanoreceptors that are activated by shear stress factors and then prompts the cell to release agents with direct or in-direct antithrombotic properties ( ex. NO). The article discussed two possible models for the mechanotransduction of signaling: 1) a localized model: the mechanoreceptors are located on the cell membrane such as calcium, potassium, or sodium channels that respond to the change in shear stress, or 2) decentralized model: the external forces act on the cell surface and the cytoskeleton of the cell responds through integrines. Papaioannou and Stefanadis also discuss possible physiological conditions that occur from low levels of shear stress as well, such as Atherogenesis, Grafts, Aneurysms, and in-stent restenosis. I found this article interesting because it described some physiological features of the cell receptor character and the role of cell signaling that we learned about in lecture. It also pertains to a research project I am working in close proximity at the moment concerning cellular adaptation to change in shear stress and flow oscillation.  

http://www.hellenicjcardiol.org/archive/full_text/2005/1/2005_1_9.pdf