  Introduction: Characteristics of hemodynamics strongly affect the patency of
arteriovenous fistula (AVF) in hemodialysis patients. Because of pressure
balance changes among arteries after AVF construction, regurgitating flow
occurs in some patients.
  Methods: Based on phase-contrast MRI measurements, flow types around the
anastomotic site are classified to the three different types of splitting,
merging, and one-way, where merging type incorporates regurgitating flow. We
have performed computational simulations to analyze characteristic differences
among these types.
  Results: In the merging type, a characteristic spiral flow is observed in AVF
causing strong wall shear stress and large pressure drop, whereas the splitting
type shows a smooth flow and gives a smaller pressure drop. The one-way case is
intermediate between splitting and merging types.
  Conclusion: Regurgitation brings about high wall shear stress near the
anastomotic site because of instabilities induced by merging phenomena, for
which type careful follow-up examinations are regarded as necessary.
