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Title: Micro-particle image velocimetry for lymphatic flow
Author: Margaris, Konstantinos
ISNI:       0000 0004 5361 4348
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2014
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The lymphatic system constitutes a vital part of the systemic circulation, maintaining tissue fluid homeostasis; its biological significance is not limited to fluid balance, as it is a part of the immune system, facilitating immune cell trafficking and initiating the immune system response to pathogens. However, the hydrodynamics/biomechanics of the lymphatic system have been relatively understudied when compared to the cardiovascular system. In contrast with the latter, where the heart provides the necessary energy for blood flow, the lymphatic system relies on the active contraction of vessels and one-way valves to generate and sustain flow. The present thesis describes the development of an optical flow diagnostic method for resolving the 2-dimensional flow field at the mid-plane of isolated contracting mesenteric rat lymphatic vessels, in-vitro. The aim was to develop an experimental protocol for accurately estimating flow parameters, and in addition, estimate lymphatic functional parameters, with high spatial and temporal resolution. Previous studies in-situ have relied on lymphocytes as tracers, but their low density however resulted in a reduced spatial resolution. The time-resolved micro-Particle Image Velocimetry technique, a well established method has been employed to study this transient flow. To that end, a bespoke light source was developed, utilising high-power light-emitting diodes, as well as associated control and image processing software. Image analysis was performed with PIV cross-correlation algorithms and was facilitated by custom vessel wall detection algorithms. In terms of flow parameters, flow velocity, flow rate and shear stresses were estimated from the raw images. Additionally, the dynamic pressure was estimated allowing for extraction of pressure volume curves and estimation of work performed during contraction by the lymphatic vessels. It was also possible to obtain an estimation of lymphatic wall stress. The results were extended to lymphatic functional parameter estimation, such as contraction amplitude and fractional pump flow. Statistical analysis was undertaken, in order to reveal possible relationships between the experimental parameters and the derived hydrodynamic/biomechanical results. Analysis of the uncertainty of the measurements showed that method employed provides exceptional accuracy. The results demonstrated the successful application of the micro-PIV technique in lymphatic vessels and yielded interesting observations, either previously unreported in the literature or contradicting previous reports. The wall velocity was shown that it may be comparable to the fluid one; an observations that questions the assumptions of previous attempts to study lymph flow. It was also observed that the flow rate may not increase during contraction depending on the hydrodynamic conditions. Although an incidental finding, vibrations were shown to increasethe contraction frequency of lymphatic vessels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral