The purpose of this paper is to demonstrate the importance of a compliant wall approach in modeling of non‐Newtonian and non‐physiological blood flows. A case study of a stenosed and symptomatic carotid bifurcation was considered to show the influence of the wall‐resilience assumption on the flow parameters obtained with numerical simulations. Patient‐specific data concerning the geometry and flow conditions were collected and used to carry out two‐way coupled fluid structure interaction simulations of the pulsatile blood flow through carotid artery. The wall compliance was considered separately as related to the wall‐elasticity and as associated with the reaction of the loose connective tissue surrounding the carotid bifurcation. The obtained hemodynamic parameters were compared to those which were found in rigid‐wall simulations. The difference between the results obtained for rigid‐wall and compliant‐wall approaches for the peak‐systolic area‐averaged wall shear stress achieved 35%, whereas the difference between the time‐averaged local vorticity and shear strain reached, respectively, 42% and 43%. The influence of the highly resilient wall on the monitored hemodynamic parameters was significant even if time‐averaged values are compared, which suggests that these metrics are considerably overestimated if the wall compliance is not considered. Moreover, the findings show that the mechanical response of the loose connective tissue cannot be neglected in blood flow simulations. Additionally, this study indicates that stiffening of the arterial wall due to atherosclerosis significantly rises hemodynamic parameters. This explains the therapeutic benefits of surgical removal of plaque lesions formed in the carotid bifurcation (endarterectomy).

Arteriovenous fistula (AVF) is the preferred vascular access for hemodialysed patients. AVF is created surgically using the patient’s artery and vein. Once the connection (anastomosis) is made, the maturation process begins. Studies have shown that most AVFs do not survive beyond one year. This study presents fluid–structure interaction (FSI) modelling of non-Newtonian blood flow through an end-to-side radio-cephalic AVF, investigated weekly during a 15-week follow-up period and 1.5 years postoperatively using ultrasound methods. The aim was to collect qualitative and quantitative data regarding changes in hemodynamics and alterations in the walls of AVF vasculature. Different material properties were assigned to the artery, suture zone (anastomosis), and vein, while the stiffening of the venous arm over time was also modelled. The proposed FSI methodology can be implemented in future follow-up studies involving groups of patients. The main findings revealed: a) counter-rotating vortices in the anastomosis cross-section affecting local pressure conditions; b) different temporal progression of vorticity, shear strain rate, and turbulent kinetic energy and similarity of the temporal progression of WSS obtained under the assumptions of the rigid-walled and FSI; c) a negligible low-WSS zone in the presented thrombosis-free AVF; d) migration of the zone of maximal temporal wall deformation over time.

Background: This study investigated flow analysis inside pediatric ventricle assist devices (VADs) designed and manufactured at the Foundation for Cardiac Surgery Development (FRK), Zabrze, Poland. The main goal of the experiment was to define the minimal heart rate admissible in clinical practice. Methods: The flow was directed by mechanical, single-disc valves developed at the Lodz University of Technology, Institute of Turbomachinery in Lodz, Poland. VAD operation conditions under different heart rates were analyzed. Measurements were performed on Religa PED pediatric VADs (45 cm³ and 30 cm³) with a particle image velocimetry (PIV) system. Results: Due to the PIV method used, the measurements were made without interference of the measuring system onto the flow structure in the investigated channel, as the measurement procedure is noninvasive. During the investigations conducted in different measurement planes, the majority of the flow volume in the chamber was observable. Conclusions: The measurements at different heart rates demonstrated a significant influence of this parameter on the flow nature in the heart ventricle. Additionally, it was found that the heart rate affected the operation of heart valves in the VAD.