The role of venous valves in pressure shielding

Zervides, Constantinos; Narracott, Andrew; Lawford, Patricia; Hose, D.R.

doi:10.1186/1475-925x-7-8

Cited by 11 publications

(15 citation statements)

References 26 publications

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“…Studying the spatial pressure distribution in the vein (Figure ) reveals a pressure drop over the closed proximal valve higher than the contribution of the hydrostatic column alone. This phenomenon was also reported by Zervides et al in a numerical study and observed in vitro by Raju et al . This pressure drop is associated with fluid redistribution from the proximal to distal section due to gravitational loading, lowering the pressure below the proximal valve, and thereby increasing the pressure drop over the valve.…”

Section: Discussionsupporting

confidence: 82%

“…Gravity has been included in lumped‐parameter models using an additional pressure source and can straightforwardly be included in the momentum equation of 1D pulse wave propagation models , resulting in a continuous gravity field. The inclusion of venous valves within such models allows the transient shielding of hydrostatic pressure to be simulated and their action to prevent backflow. Valves are often represented by a perfect diode in circulatory models , whereas more detailed models include gradual opening and closing behaviors based on the transvalvular pressure drop or force balance on the valve leaflets .…”

Section: Introductionmentioning

confidence: 99%

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A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function

Keijsers

Leguy

Huberts

et al. 2015

Numer Methods Biomed Eng

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The calf muscle pump is a mechanism which increases venous return and thereby compensates for the fluid shift towards the lower body during standing. During a muscle contraction, the embedded deep veins collapse and venous return increases. In the subsequent relaxation phase, muscle perfusion increases due to increased perfusion pressure, as the proximal venous valves temporarily reduce the distal venous pressure (shielding). The superficial and deep veins are connected via perforators, which contain valves allowing flow in the superficial-to-deep direction. The aim of this study is to investigate and quantify the physiological mechanisms of the calf muscle pump, including the effect of venous valves, hydrostatic pressure, and the superficial venous system. Using a one-dimensional pulse wave propagation model, a muscle contraction is simulated by increasing the extravascular pressure in the deep venous segments. The hemodynamics are studied in three different configurations: a single artery–vein configuration with and without valves and a more detailed configuration including a superficial vein. Proximal venous valves increase effective venous return by 53% by preventing reflux. Furthermore, the proximal valves shielding function increases perfusion following contraction. Finally, the superficial system aids in maintaining the perfusion during the contraction phase and reduces the refilling time by 37%. © 2015 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.

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Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

A 1D pulse wave propagation model of the hemodynamics of calf muscle pump function

Keijsers

Leguy

Huberts

et al. 2015

Numer Methods Biomed Eng

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“…The venous valves play an important role in reducing the pressure applied under dynamic load conditions but understanding is rudimentary and theoretical. 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.…”

Section: Physiology Of Venous Outflow From Brain and Spinal Cordmentioning

confidence: 99%

Multiple Sclerosis - A Vascular Etiology?

Weir

2010

Can. j. neurol. sci.

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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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“…Although these models are suitable for assessment of the hemodynamic significance of chronic venous disease, they have not yet been applied in this context. Most models used to represent venous valve dynamics are generally only able to represent the open and closed state (diode) (Fullana and Zaleski [2008]; Müller and Toro [2014]; Zervides et al [2008]), whereas reduced order heart valve models provide more detail (Werner et al [2002]; Zacek and Krause [1996]). More sophisticated reduced-order valve models have been developed by Korakianitis and Shi [2006], who included valve leaflet motion based on a force balance and Mynard et al [2012], who related valve opening state to the pressure drop over the valve.…”

Section: ∆V ∆T 90%refillingmentioning

confidence: 99%