Microparticle image velocimetry approach to flow measurements in isolated contracting lymphatic vessels

Abstract

We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ -PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ -PIV technique in these vessels.

The in vitro inertial positions and viability of cells in suspension under different in vivo flow conditions

“…The system design was required to be able to test a range of different conditions as cells in circulation can be subject to a wide variety of different fluidic conditions in the LS and the CS. Lymphatic capillaries are much larger (100-300 μm) [26][27][28][29][30] than blood capillaries (5-10 μm) and fluid velocities in the LS are much lower (0.35-1 mm/s) [27][28][29][30] than those found in the CS which can reach up to 300 mm/s. In addition, blood is a shear thinning fluid whereas lymph is considered a Newtonian fluid with a dynamic viscosity and density similar to those of water (approximately 1 mPas and 1000 kg/m 3 respectively) 28,31,32 .…”

Mechanotransduction activates canonical Wnt/β-catenin signaling to promote lymphatic vascular patterning and the development of lymphatic and lymphovenous valves

“…As mentioned above, LECs within the vessel lumen in vivo and in isolated vessel preparations are exposed to OSS (Dixon et al 2006(Dixon et al , 2007Sweet et al 2015;Margaris et al 2016). Approaches to prevent lymph flow and determine its role in lymphatic vascular development currently do not exist.…”

“…Lymphatic vessels are exposed to reversing fluid flow (more commonly known as oscillatory shear stress [OSS]) (Dixon et al 2006(Dixon et al , 2007Sweet et al 2015;Margaris et al 2016). In vitro, OSS promotes the expression of FOXC2 in LECs (Sabine et al 2012;Sweet et al 2015).…”

Demonstration and Analysis of the Suction Effect for Pumping Lymph from Tissue Beds at Subatmospheric Pressure

“…At the low fluid velocities inherent to these experiments, the particles either float or sink and clog the pipettes. We did manage to succeed in a short series of experiments with fluorescent microparticles, but the methodology is extremely cumbersome, interferes with pressure/diameter measurements, and is subject to its own uncertainties 46 . Most importantly, the images are only 2D, so one has to assume axisymmetry to estimate volume flow rate.…”