Abstract:We present a three-dimensional computer simulation of the dynamics of a vein valve. In particular, we couple the solid mechanics of the vein wall and valve leaflets with the fluid dynamics of the blood flow in the valve. Our model captures the unidirectional nature of blood flow in vein valves; blood is allowed to flow proximally back to the heart, while retrograde blood flow is prohibited through the occlusion of the vein by the valve cusps. Furthermore, we investigate the dynamics of the valve opening area a… Show more
“…Using this combined technique, we investigated the spatial and temporal variations of the velocity fields of perivalvular blood flow in a superficial vein. Although a few experimental [23,24] and computational [25] studies have been conducted so far to estimate hemodynamic information coupled with venous valve motion, it is still unexplored to measure the velocity field of valvular blood flow and the valve motion simultaneously.…”
This study aims to investigate the blood flow around the perivalvular area in a human superficial vein using high-frequency ultrasound (HFUS) speckle image velocimetry. HFUS B-mode images were captured from the superficial veins of human lower extremity with a 35-MHz transducer. To measure the instantaneous velocity fields of blood flow, a cross-correlation particle image velocimetry (PIV) algorithm was applied to two B-mode images that were captured consecutively. The echo speckles of red blood cells (RBCs) were used as flow tracers. In the vicinity of the venous valve, the opening and closing motions of valve cusps were simultaneously visualized with the phasic variation of velocity fields. Large-scale vortices were observed behind the sinus pockets while the main bloodstream was directed proximally. This measurement technique combining PIV algorithm and HFUS B-mode imaging was found to be unique and useful for investigating the hemodynamic characteristics of blood flow in the perivalvular area and for diagnosing venous insufficiency and valve abnormality in superficial blood vessels.
“…Using this combined technique, we investigated the spatial and temporal variations of the velocity fields of perivalvular blood flow in a superficial vein. Although a few experimental [23,24] and computational [25] studies have been conducted so far to estimate hemodynamic information coupled with venous valve motion, it is still unexplored to measure the velocity field of valvular blood flow and the valve motion simultaneously.…”
This study aims to investigate the blood flow around the perivalvular area in a human superficial vein using high-frequency ultrasound (HFUS) speckle image velocimetry. HFUS B-mode images were captured from the superficial veins of human lower extremity with a 35-MHz transducer. To measure the instantaneous velocity fields of blood flow, a cross-correlation particle image velocimetry (PIV) algorithm was applied to two B-mode images that were captured consecutively. The echo speckles of red blood cells (RBCs) were used as flow tracers. In the vicinity of the venous valve, the opening and closing motions of valve cusps were simultaneously visualized with the phasic variation of velocity fields. Large-scale vortices were observed behind the sinus pockets while the main bloodstream was directed proximally. This measurement technique combining PIV algorithm and HFUS B-mode imaging was found to be unique and useful for investigating the hemodynamic characteristics of blood flow in the perivalvular area and for diagnosing venous insufficiency and valve abnormality in superficial blood vessels.
“…An increase in pressure behind the closed leaflets forces them to push back towards the vessel wall and create an opening while the stagnated blood between the leaflets and the sinus wall is pushed forward. Once open, the leaflets remain suspended in the flowing bloodstream and undergo self-excited oscillations [15], while the blood flow through the valve orifice separates at the oscillating edges of the valve leaflets to create one axial flow jet in the middle of the opening and two recirculation vortices of lower speed in the sinus, causing distention of the valve sinus [15, 16]. While the pressure in the recirculation vortex is in equilibrium with the pressure exerted on the inflow side of the leaflets, the valve remains open.…”
Section: Fluid Dynamics Of the Valvementioning
confidence: 99%
“…These hemodynamic events are predetermined by the solid mechanics of the valve leaflets and the perivalvular area, and constitute a self-sustained mechanism for competent valve operation [15, 17]. A similar flow separation model has been validated [16, 18, 19] at the orifice of the aortic valves of the heart, first proposed by Leonardo da Vinci [20], and was recently suggested to apply to lymphatic valves, as similar opening and closing motions of the lymphatic valve leaflets have recently been recorded in excised vessels and in vivo [21, 22]. Fig.…”
The efficient transport of blood and lymph relies on competent intraluminal valves that ensure unidirectional fluid flow through the vessels. In the lymphatic vessels, lack of luminal valves causes reflux of lymph and can lead to lymphedema, while dysfunction of venous valves is associated with venous hypertension, varicose veins, and thrombosis that can lead to edema and ulcerations. Despite their clinical importance, the mechanisms that regulate valve formation are poorly understood and have only recently begun to be characterized. Here, we discuss new findings regarding the development of venous and lymphatic valves that indicate the involvement of common molecular mechanisms in regulating valve formation in different vascular beds.
“…21 Computer modeling of the dynamics of valve opening and the control of venous flow rates is just beginning. 22 The fact that venous walls are soft and compressible, and collapsible under certain conditions of reduced flow, adds to the complexity of understanding venous flow in any but a qualitative fashion. Flow through venous valves is pulsatile and separates into a central jet and vorticeal flow into the sinus pocket behind the valve cusps.…”
Section: Physiology Of Venous Outflow From Brain and Spinal Cordmentioning
There has been a recent resurgence of interest in the possibility that cerebrospinal venous outflow obstruction, venous hypertension, development of collateral channels and flow reversal might be the primary inciting factor(s) for multiple sclerosis (MS). 1 The evidence should be considered bearing in mind Hill's criteria for causation as outlined by Giovannoni and Cutter: consistency and unbiasedness of findings, strength of association, temporal sequence, biological gradient, specificity, coherence of biological background and previous knowledge, biological plausibility, reasoning by analogy and experimental evidence.2 At the present state of our knowledge, despite monumental efforts, the cause is unknown.
Anatomy Of Venous Outflow From The Brain And Spinal CordCapillaries drain into venules (10 -20 µ) that combine, almost at right angles to form larger venules within the grey matter. At a size of 50 -100 µ the venules lead on to the cortical surface at right angles to it. At the surface they combine in a two dimensional network. The craniospinal venous system is valveless and consists of veins and plexuses whose flow is potentially bidirectional. The superior cortical cerebral veins drain rostrally into the superior sagittal sinus. The inferior lateral ABSTRACT: From the earliest pathological studies the perivenular localization of the demyelination in multiple sclerosis (MS) has been observed. It has recently been suggested that obstructions to venous flow or inadequate venous valves in the great veins in the neck, thorax and abdomen can cause damaging backflow into the cerebral and spinal cord circulations. Paolo Zamboni and colleagues have demonstrated abnormal venous circulation in some multiple sclerosis patients using non-invasive sonography and invasive venography. Furthermore, they have obtained apparent clinical improvement or stabilization by endovascular ballooning of points of obstruction in the great veins in some, at least temporarily. If non-invasive observations by others validate their initial observations of a significantly increased prevalence of venous obstructions in MS then trials of angioplasty/stenting would be justified in selected cases in view of the biological plausibility of the concept.RÉSUMÉ: Étiologie vasculaire de la sclérose en plaques. La localisation périveineuse de la démyélinisation a été observée dès les premières études anatomopathologiques sur la sclérose en plaques (SP). L'obstruction du flux veineux ou la présence de valves veineuses inadéquates dans les grandes veines du cou, du thorax et de l'abdomen pourraient causer un reflux dommageable à la circulation cérébrale et la moelle épinière selon une hypothèse récente. Paolo Zamboni et ses collègues ont démontré la présence d'une circulation veineuse anormale chez certains patients atteints de SP au moyen l'échographie non effractive et de la veinographie effractive. De plus ils auraient obtenu une amélioration clinique ou une stabilisation de l'état des patients par dilatation endovasculaire de points d'obstruction d...
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