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NON-NEWTONIAN EFFECTS IN HEMODYNAMIC SIMULATIONS OF THE CEPHALIC VEIN IN END STAGE RENAL DISEASE PATIENTS
Title
NON-NEWTONIAN EFFECTS IN HEMODYNAMIC SIMULATIONS OF THE CEPHALIC VEIN IN END STAGE RENAL DISEASE PATIENTS
Creator
Mahmoudzadeh Akherat, Seyed Mohammad Javid
Date
2013, 2013-12
Description
The objective of this research is the determination of Hemodynamic Parame- ters (HDP) in End Stage Renal Disease (ESRD) patients which is done...
Show moreThe objective of this research is the determination of Hemodynamic Parame- ters (HDP) in End Stage Renal Disease (ESRD) patients which is done via implemen- tation of Computational Fluid Dynamics (CFD) in a two dimensional computational domain which provides a non-invasive and cost e ective means of studying the pa- tient population. The medical procedure needed for these patients is essential for the success of chronic hemodialysis. The most common medical procedure currently in this eld for creating vascular access (VA) are arteriovenous stulae (AVF). However, there are many access failures reported in these patients mainly due to Cephalic Arch Stenosis (CAS), which is related to the progression of intimal hyperplasia. Although various access techniques have been developed to address this issue, still hemodialysis access dysfunctions remains one of the main causes of mortality in the hemodialysis patient population. The expense of providing medical care to this patients population for the placement and maintenance of the vascular access was estimated to be 23.9 billion dollars in 2007 in the United States alone according to United States Renal Database System (USRDS). As stated above, it is our intention to observe a cohort of ESRD patients who received VA and simulate their blood ow through their cephalic vein with their spe- ci c HDP and characteristics. In order to perform these simulations, proper viscosity models have to be taken into consideration to increase the accuracy of the outcome of the numerical solution to Navier-Stokes equations. Many articles have been published to address the proper use of constitutive functions in simulation of blood ow. However, the choice of adequate viscosity function for CFD blood ow simulation in ESRD patients receiving AVF and a ma- nipulated vascular system in general has not received proper attention. Furthermore, it was discerned that the correct choice of viscosity function to capture the non- xii Newtonian behavior of blood is of utmost importance in this context since the ESRD patient population experience drastic alteration in blood viscosity throughout the hemodialysis treatment. Various viscosity functions have been tested for this pur- pose, namely, Quemada, Walburn-Schenck and Modi ed Cross. The results exhibit no major di erences in the velocity eld and general ow characteristics compared to a corresponding identical Newtonian blood ow simulation for Reynolds of 500. The results indicate that the choice of Newtonian viscosity to simulate the blood ow in ESRD patients with VA is acceptable. However, the Newtonian simulation of these ows may over predict the sites prone to stenosis and Intimal Hyperplasia (IH) since these simulations tend to exhibit lower Wall Shear Stress (WSS) values in the recircu- lation regions compared to non-Newtonian simulations. Sites of low WSS are thought to be contributory factors to IH. Hence, the use of proper non-Newtonian constitu- tive models is suggested in this context. The di erences between non-Newtonian and Newtonian assumptions are further ampli ed when unsteady cases with Reynolds of 1000 are concerned. Navier-Stokes solutions obtained from CFD simulations re- vealed that the discrepancies between the two assumptions are very appreciable for unsteady cases. In light of the results for unsteady cases, it was concluded that for non-physiological ows in curved vessels that are encountered in this study, the non-Newtonian assumptions is the correct choice. Further investigation is required to simulate the blood ow in a three di- mensional domain. In addition, a more thorough comprehension has to be obtained regarding the correlation of HDP with the onset and progression of CAS, particu- larly in unsteady hemodynamic ows. The etiology of stenosis in cephalic veins is of scienti c and clinical importance and needs to be separately investigated.
M.S. in Mechanical and Aerospace Engineering, December 2013
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