Hindawi Publishing Corporation Journal of Applied Mathematics Volume 2012, Article ID 950323, 27 pages doi:10.1155/2012/950323 Research Article Nonlinear Fluid Models for Biofluid Flow in Constricted Blood Vessels under Body Accelerations: A Comparative Study D. S. Sankar 1 and Atulya K. Nagar 2 1 School of Mathematical Sciences, University Science Malaysia, 11800 Penang, Malaysia 2 Centre for Applicable Mathematics and Systems Science, Department of Computer Science, Liverpool Hope University, Hope Park, Liverpool L16 9JD, UK Correspondence should be addressed to D. S. Sankar, sankar ds@yahoo.co.in Received 3 January 2012; Accepted 12 February 2012 Academic Editor: M. F. El-Amin Copyright q 2012 D. S. Sankar and A. K. Nagar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Pulsatile flow of blood in constricted narrow arteries under periodic body acceleration is analyzed, modeling blood as non-Newtonian fluid models with yield stress such as i Herschel-Bulkley fluid model and ii Casson fluid model. The expressions for various flow quantities obtained by Sankar and Ismail 2010 for Herschel-Bulkley fluid model and Nagarani and Sarojamma 2008, in an improved form, for Casson fluid model are used to compute the data for comparing these fluid models. It is found that the plug core radius and wall shear stress are lower for H-B fluid model than those of the Casson fluid model. It is also noted that the plug flow velocity and flow rate are considerably higher for H-B fluid than those of the Casson fluid model. The estimates of the mean velocity and mean flow rate are considerably higher for H-B fluid model than those of the Casson fluid model. 1. Introduction Atherosclerosis is an arterial disease in large and medium size blood vessels which involve in the complex interactions between the artery wall and blood flow and is caused by intravascular plaques leading to malfunctions of the cardiovascular system 1. The intimal thickening of an artery is the initial process in the development of atherosclerosis and one of the most wide spread diseases in humans 2. In atherosclerotic arteries, the lumen is typically narrowed and the wall is stiffened by the buildup of plaque with a lipid core and a fibromuscular cap, and the narrowing of lumen of the artery by the deposit of fats, lipids, cholesterol, and so forth is medically termed as stenosis formation 3. Different shapes of