Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session L06: Lymphatic and CSF Flows I |
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Chair: Haoxiang Luo, Vanderbilt University Room: Ballroom F |
Monday, November 25, 2024 8:00AM - 8:13AM |
L06.00001: On the homogenized description of flow and transport through the trabecular network in the subarachnoid space Javier Alaminos Quesada, GUILLERMO LOPEZ NOZALEDA, Cándido Gutiérrez-Montes, Antonio L Sanchez The pulsating motion of the cerebrospinal fluid in the subarachnoid space (SAS) surrounding the brain and the spinal cord is known to be affected by the presence of trabeculae, which are thin collagen-reinforced fibers that form a dispersed web-like structure stretching across the SAS. Previous analyses have employed a homogenized treatment involving the familiar conservation equations of flow and transport in porous media. The accuracy of the resulting macroscopic equations is tested here through comparisons with direct numerical simulations in which the SAS is modelled as a parallel-plate channel populated by a random distribution of transverse cylindrical posts. The comparisons explore values of the controlling flow parameters in physiologically relevant ranges. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L06.00002: Volumetric Particle Tracking Velocimetry of Cerebrospinal Flow in the Spinal Subarachnoid space Reza Babakhani Galangashi, Pavlos P Vlachos This study investigates the impact of nerve roots on cerebrospinal fluid (CSF) dynamics within the spinal subarachnoid space (SSS). Proper regulation of CSF dynamics is critical for maintaining the physiological functions of the central nervous system (CNS). Disturbances in CSF flow can lead to various neurological disorders, highlighting the importance of understanding the underlying fluid dynamics. The nerve roots are prominent anatomical structures within the SSS and are believed to influence CSF flow patterns significantly. Computational fluid dynamics (CFD) models are commonly employed to simulate CSF flow, incorporating anatomical features such as nerve roots. However, the assumptions and spatial resolution limitations of current in-vivo imaging methods necessitate the experimental validation of these models using benchtop in-vitro experiments. We conducted controlled in-vitro experiments using volumetric Particle Tracking Velocimetry (PTV). We explore the effects of both steady and pulsatile flow conditions, employing a half-sine velocity waveform, on CSF dynamics at various locations within the geometry. We analyze the velocity fields within the SSS, providing high-resolution, three-dimensional insights into CSF flow dynamics. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L06.00003: An exploratory in vitro investigation to assess the potential of Time Inversion Spatial Labeling as a tool to quantify Lagrangian drift in the spinal canal. Obed Armando Campos, Javier Alaminos Quesada, Stephanie Sincomb, Vadim Malis, Mitsue Miyazaki, Wilfried Coenen, Cándido Gutiérrez-Montes, Antonio L Sanchez The pulsating motion of the cerebrospinal fluid in the spinal canal includes a mean Lagrangian drift, a reflection of the cumulative submillimeter net displacement experienced by the fluid particles during each motion cycle. The noninvasive quantification of this bulk motion in in vivo studies is difficult, because its associated velocities (~ cm/min) are much smaller than those of the predominant oscillatory motion (~ cm/s), making methods such as phase contrast (PC) MRI inadequate for this purpose. We hypothesize that methods based on Time Inversion Spatial Labeling, such as time-spatial labeling inversion pulse (T-SLIP), can be better suited to characterize the mean Lagrangian motion, thereby motivating the present in vitro exploratory investigation. Our study combines (PC) MRI and T-SLIP flow measurements in a simplified phantom model representing the compliant spinal canal with theoretical predictions based on asymptotic expansions for small stroke lengths. The preliminary results obtained at different spinal levels and relevant physiological conditions show the potential of T-SLIP as a non-invasive method to quantify mean Lagrangian motion in the spinal canal. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L06.00004: Fluid-structure interactions and flow rectification in elliptical gaps in the walls of brain perivascular spaces Yiming Gan, Douglas H Kelley The driving mechanism of cerebrospinal fluid (CSF) flow through annular perivascular spaces (PVSs) in the brain may partly be explained by a valve mechanism. PVSs are bounded by an outer wall formed by astrocyte endfeet, with gaps between. Pressure oscillation in the PVS causes deformation of the gap, which would act like a valve, rectifying fluid through it. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L06.00005: Does the brain really have a fourth meningeal membrane? Cooper Gray, Dorothea Tse, Daehyun Kim, Turki Alturki, Thomas Ruhl, Silas Simpson, Anika Volker, Jeffrey Tithof The glymphatic system, a pathway for flow of cerebrospinal fluid (CSF) in the brain, is crucial for clearance of toxic cellular waste from the brain's extracellular space. Growing evidence suggests that reduction in glymphatic transport contributes to etiology of neurodegenerative diseases, such as Alzheimer's. A recent breakthrough discovery (Møllgård et al, Science 2023) reported a newly-identified 4th layer of the meninges, which they named the "subarachnoid lymphatic-like membrane" (SLYM). However, this discovery has ignited considerable controversy among neuroanatomists and neuroscientists. We will present in vivo recordings of CSF flow at the dorsal surface of the mouse brain, imaged through a cranial window using two-photon microscopy. By injecting fluorescent microspheres (1 µm diameter), we visualize CSF flow and obtain evidence that any rupture in the SLYM layer (which is only 1-3 cells thick in some locations) drastically alters CSF flow dynamics. We perform particle tracking velocimetry to quantify the impact of SLYM rupture on glymphatic flow speed. Our measurements support the notion that such a membrane does exist, separating the subarachnoid space into different compartments. We will discuss technical challenges associated with invasive surgical procedures required to obtain brain optical access which may lead to SLYM rupture. We will also argue how SLYM rupture may explain why traumatic brain injury is linked to increased risk of neurodegenerative disease. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L06.00006: Dynamics of brain valves: putative rectification mechanisms for cerebrospinal fluid flow Yisen Guo, Peter A.R. Bork, Douglas H Kelley The flow of cerebrospinal fluid (CSF) through perivascular spaces (PVSs) is an important part of the brain’s system for clearing metabolic waste. Astrocyte endfeet bound the PVSs of penetrating arteries, separating them from brain extracellular space (ECS). Gaps between astrocyte endfeet provide a low-resistance pathway for fluid transport across the wall. Recent research suggests that the astrocyte endfeet may function as valves that rectify the CSF flow, leading to observed net flow in experiments. This study uses three-dimensional fluid-structure interaction (FSI) modeling to investigate the endfeet valve mechanism. Due to the unavailability of precise in vivo measurements for the shape and dimensions of the endfeet gaps, we explore potential asymmetric geometries in the endfeet: asymmetric gap and overlapping adjacent endfeet of different sizes. Our simulation results demonstrate flow rectification with high pumping efficiency. Additionally, we quantitatively study how net flow depends on parameters such as oscillatory pressure amplitude and frequency, gap size, and endfoot length ratio. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L06.00007: Elevated Intracranial Pressure Impairs Cerebrospinal Fluid Drainage to Meningeal Lymphatic Vessels Daehyun Kim, Jeffrey Tithof Cerebrospinal fluid (CSF) has recently gained increasing recognition for its role in clearing metabolic wastes from the brain. Over the past decade, experiments have revealed the presence of meningeal lymphatic vessels (mLVs) in the tissues surrounding the brain (meninges), which play a crucial role in absorbing and draining CSF from the subarachnoid space (SAS). Counterintuitively, recent experiments demonstrate that elevated intracranial pressure (ICP) in the SAS leads to a reduction in downstream flow through the mLVs. Our research aims to model CSF efflux through mLVs using numerical analysis. We use ICP as an inlet pressure for the mLVs model. We derive an expression that relates ICP and its effect on the meninges using solid mechanics equations. Then, we use the 1D Navier-Stokes equation, coupled with an algebraic equation derived from the structural analysis of the meninges, to simulate fluid flow through the mLVs. Our preliminary results demonstrate that elevated ICP leads to reduced CSF drainage through mLVs due to decreased vessel diameter and impaired intrinsic pumping. This finding provides a novel explanation for why elevated ICP disrupts CSF circulation and drainage, as observed in hydrocephalus, traumatic brain injury, and much more. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L06.00008: Modeling interstitial fluid flow induced by traveling waves in the brain Saikat Mukherjee Interstitial fluid (ISF), located in the spaces between the cells in the brain cortex, can be driven by traveling ionic waves that induce osmotic cellular swelling, although the precise mechanism of the coupling is not fully understood. Using volume-averaged constitutive equations, a modified Darcy's law for swelling-porous media is developed to fundamentally understand how traveling waves in the brain during different phases of sleep (slow waves) and depolarization waves during acute conditions like stroke, migraine, brain injury, and seizures, drive cortical ISF flow. The research can provide fundamental insights into (1) how traveling wave properties in healthy and diseased brains alter ISF flow physics and (2) how ISF flow can be therapeutically engineered during neurological disorders. |
Monday, November 25, 2024 9:44AM - 9:57AM |
L06.00009: On the effect of nerve roots and denticulate ligaments on flow and transport in the spinal canal. Francisco J Parras-Martos, Cándido Gutiérrez-Montes, Wilfried Coenen, Carlos Martínez-Bazán, Antonio L Sanchez MRI-informed direct numerical simulations are used to quantify effects of micro-anatomical elements, namely nerve roots and denticulate ligaments, on the flow of cerebrospinal fluid (CSF) and the transport of solutes along the spinal canal. The computations utilize an anatomically correct model of the canal along with a physiologically correct flow rate. The resulting oscillatory flow is used to evaluate the time-averaged Eulerian velocity as well as the mean Lagrangian velocity. These steady velocities are used to develop and test different reduced models for solute transport that circumvent the need to track the periodic flow oscillations, thereby significantly reducing the associated computational cost. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L06.00010: Numerical and experimental investigation of phase differences in lymphatic vessel chains Amir Poorghani, Martin Brandenbourger, Alexander Alexeev We use experiments and numerical simulations of lymphatic vessels to investigate the valve dynamics within lymphangion chains. Our goal is to understand the impact of phase differences between consecutive lymphangions on lymphatic pumping efficiency. In the simulations we systematically vary the phase differences to identify the optimal configuration for fluid transport, characterized by pumping efficiency, work done by the vessel, and flow rate. We also consider the pumping performance under an adverse pressure gradient. We compare our numerical results with experimental data obtained using a lymphatic vessel mimetic. We find close agreement between the computational results and our experiments. This research offers insights into the biomechanics of lymph transport and can be useful for designing biomedical devices to enhance lymphatic drainage. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L06.00011: Determining the effective Taylor dispersion in an annulus with a pulsatile inner boundary Drik Sarkar, Saikat Mukherjee We develop analytical expressions for the spread of concentration of a solute in an annular channel with a spatiotemporally pulsating inner boundary. The problem is motivated by perivascular spaces (PVSs; annular channels surrounding the arteries in the brain) that provide a medium for cerebrospinal fluid (CSF) to flow and transport metabolic waste products and solutes from the brain interstitium. We study the dispersion dynamics in an annular channel where the inner wall corresponds to the pulsatile arterial lumen, and the outer wall is constant, corresponding to the astrocytic end feet and the brain parenchyma. Using the invariant manifold theory, we derive a second-order asymptotic expression to determine the effective Taylor dispersion equation and dispersion parameters in the annulus for various wavelengths and frequencies of pulsations expected in the brain. The research introduces a generalized framework to quantify solute dispersion in spatiotemporally varying annular channels, and provides important insights on controlling CSF flow and solute transport in the PVSs. |
Monday, November 25, 2024 10:23AM - 10:36AM |
L06.00012: Abstract Withdrawn |
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