The view that shear is constant across the circulation appears to be dwindling, but is the view that shear increases in small arteries/microcirculation still controversial, or is there now a consensus?
David, I do not understand what you exactly mean. Could you cite some article that explains your question, please?
The below reviews are the essence of my question. People often employ experimental conditions of "physiological shear stress levels" (usually between 5 and 10 dyn), but in fact it appears shear is not the same across the circulation, even varying between different conduit arteries within a species, or in corresponding vascular region between species, and increasing quite dramatically in the microcirculation compared to its feed conduit vessel. Well, that's one side of the arguement. Until fairly recently it was thought shear was the same in the microcirculation compared to large arteries, and the same (or similar at least) between species.
I'm not a massive expert on the field but am intrigued, so I want to know whether the newer idea of variations in shear stress is one that is now generally accepted, or whether it is still controversial.
Cheng C, Helderman F, Tempel D, Segers D, Hierck B, Poelmann R, van Tol A, Duncker DJ, Robbers-Visser D, Ursem NT, van Haperen R, Wentzel JJ, Gijsen F, van der Steen AF, de Crom R, Krams R. Large variations in absolute wall shear stress levels within one species and between species. Atherosclerosis. 2007 Dec;195(2):225-35
Reneman RS, Hoeks AP. Wall shear stress as measured in vivo: consequences for the design of the arterial system. Med Biol Eng Comput. 2008 May;46(5):499-507
I think the degree of shear stress induced varies across the circulation. An article by Papaioannou and Stefanadis (Hellenic J Cardiol 46:9-15, 2005) may be worth reading.
Thanks, Yohannes. I had not seen this article before. It essentially says the same as the reviews I cited. A sharp increase in arterioles.
You mean then the wall shear stress (WSS). Fine, no I never measured it. Thanks.
You have good reference articles (Cheng and Reneman). Physic at the microcirculation level has nothing to do with what is seen in big vessels (limit 250 micrometers). This is the border. None of the laws that applies over this limit applies under the limit. It's very tricky. With strange things and their consequences, for example the notion of additional drop pressure, depending on how much red cells flow in a small capillary and if they are separated or assembled...