Fluid dynamics of thoracic cavity venous flow in multiple sclerosis

This paper hypothesizes, based on fluid dynamics principles, that in multiple sclerosis (MS) non-laminar, vortex blood flow occurs in the superior vena cava (SVC) and brachiocephalic veins (BVs), particularly at junctions with their tributary veins. The physics-based analysis demonstrates that the morphology and physical attributes of the major thoracic veins, and their tributary confluent veins, together with the attributes of the flowing blood, predict transition from laminar to non-laminar flow, primarily vortex flow, at select vein curvatures and junctions. Non-laminar, vortex flow results in the development of immobile stenotic valves and intraluminal flow obstructions, particularly in the internal jugular veins (IJVs) and in the azygos vein (AV) at their confluences with the SVC or BVs. Clinical trials' observations of vascular flow show that regions of low and reversing flow are associated with endothelial malformation. The physics-based analysis predicts the growth of intraluminal flaps and septa at segments of vein curvature and flow confluences. The analysis demonstrates positive correlations between predicted and clinically observed elongation of valve leaflets and between the predicted and observed prevalence of immobile valves at various venous flow confluences. The analysis predicts the formation of sclerotic plaques at venous junctions and curvatures, in locations that are analogous to plaques in atherosclerosis. The analysis predicts that increasing venous compliance increases the laminarity of venous flow and reduces the prevalence and severity of vein malformations and plaques, a potentially significant clinical result. An over-arching observation is that the correlations between predicted phenomena and clinically observed phenomena are sufficiently positive that the physics-based approach represents a new means for understanding the relationships between venous flow in MS and clinically observed venous malformations.

Association between secondary flow in models of the aorto-celiac junction and subendothelial macrophages in the normal rabbit

In order to examine the association between arterial fluid dynamics and the distribution of subendothelial macrophages in the normal rabbit aorta, steady and pulsatile particle flow visualization was performed in a geometrically realistic model of the rabbit aorto-celiac junction region. Over a range of aorto-celiac steady flow ratios, particle pathlines along the upstream lateral aortic walls curved to enter the celiac orifice, while two asymmetric regions of reversing spiral secondary flow originated along the downstream lateral portions of the orifice flow divider. These regions increased in size as either the Reynolds number or flow into the celiac artery increased. In pulsatile flow studies, particles along the lateral aortic walls near the celiac orifice began to spiral into the branch during peak systole. During systolic deceleration, the size of this spiral flow region increased as particles reversed direction to enter the celiac orifice. This contrasted with flow patterns directly upstream and downstream of the orifice, which remained unidirectional throughout this period even along the distal lip of the orifice. The highest frequency of subendothelial white blood cells in the normal rabbit aorta was associated with regions where secondary flow patterns occurred, and where the orientation of endothelial cell nuclei deviated from the major direction of aortic flow. Secondary flow patterns may aid the accumulation of monocytes and macrophages about the lateral regions of the celiac artery flow divider by transporting monocytes to the walls, allowing them time to attach to the endothelial cells, or by stimulating the endothelial cells to express leukocyte adhesion molecules. These same regions are associated with increased endothelial permeability to low density lipoprotein and, under hypercholesterolemic conditions, lesion origination.

Peripheral arterial disease

An update on the epidemiology, pathology and aetiology of vascular disease