Abstract
Three-dimensional simulations of peripheral, deep venous flow during muscular exercise in limbs of healthy subjects and in those with venous dysfunction were carried out by a computational fluid-dynamics (CFD) approach using the STAR CCM + platform. The aim was to assess the effects of valvular incompetence on the venous calf pump efficiency. The model idealizes the lower limb circulation by a single artery, a capillary bed represented by a porous region and a single vein. The focus is on a segment of the circuit which mimics a typical deep vein at the level of the calf muscle, such as the right posterior tibial vein. Valves are idealized as ball valves, and periodic muscle contractions are given by imposing time-dependent boundary conditions to the calf segment wall. Flow measurements were performed in two cross-sections downstream and upstream of the calf pump. Model results demonstrate a reduced venous return for incompetent valves during calf exercise. Two different degrees of valvular incompetence are considered, by restricting the motion of one or both valves. Model results showed that only the proximal valve is critical, with a 30% reduction of venous return during calf exercise in case of valvular incompetence: the net flow volume ejected by the calf in central direction was 0.14 mL per working cycle, against 0.2 mL for simulated healthy limbs. This finding appeared to be consistent with a 25% reduction of the calf ejection fraction, experimentally observed in chronic venous disease limbs compared with healthy limbs.
Highlights
Proper flow of blood in the veins is important to ensure effective return of blood to the heart
Venous Computational Fluid Dynamics effects (Eiken et al, 2016), the collapsible nature of the venous wall (Kölegård et al, 2009), the presence of valves, and the large blood volume that veins can hold due to their compliance
Muscular contractions in the lower extremity squeeze venous blood in a central direction, and the veins are refilled during the muscle relaxation phase (Keijsers et al, 2015)
Summary
Proper flow of blood in the veins is important to ensure effective return of blood to the heart. Venous Computational Fluid Dynamics effects (Eiken et al, 2016), the collapsible nature of the venous wall (Kölegård et al, 2009), the presence of valves, and the large blood volume (about 64% of the total) that veins can hold due to their compliance. The purpose of this study was to contribute to identifying and validating a computational model that, using typical methods of the Computational Fluid Dynamics (CFD), allows the clinical experimenters, involved in solving vascular diseases, to optimize their diagnostic and therapeutic knowledge in patients with venous insufficiency of the lower limbs, caused by both primary pathologies of the venous structure (Eberhardt and Raffetto, 2014) and reduced or absent walking ability as a secondary effect (Crisafulli et al, 2009; Carrick-Ranson et al, 2013). From that CFD model other medical and surgical specialties like, for instance, orthopedics and traumatology could obtain useful diagnostic and therapeutic information regarding the involvement of venous vessels in lower limbs suffering as a possible consequence of bones surgery or due to accidents with bone fractures of legs (Schmidt, 2017; Massari et al, 2018), while specialties such as metabolic syndrome and obesity could obtain more accurate and numerical information about the thrombosis risk in overweight patients (Stein et al, 2005; Borch et al, 2011)
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