Academic literature on the topic 'Blood Flow Analysis'

The cardiovascular system is the first fully functional organ system in the vertebrate embryo. Proper formation of the vasculature is essential for proper embryonic development. Blood flow plays a significant role in the adaptable characteristics of the vessels, as well as innetwork remodelling. As soon as blood flow begins, vessels respond to external stimuli such asshear stress, the tangential force created by the blood flow, which affect the surrounding tissue. Shear stress is the product of both the velocity profile in the vessel and the viscosity of the flowing fluid, and these parameters were determined in vivo. In this research, we have measured changes in the flow velocity, using micro particle image velocimetry (µPIV) at different somite stages during the development of the chick embryo. We measured the viscosity of avian embryonic blood for the first time ever, using a micro viscometer and calculated the change inshear stress during vascular remodelling. We observed that shear stress increases after the onset of blood flow (14 somites), until the stage where large vessels become obvious (25 somites) where a decrease in shear stress is observed. Furthermore, we found that the apparent hematocrit with respect to vessel diameter decreases with decreasing vessel radius, an effect known as the Fahreus-Lindqvist effect. We also found that the embryonic blood viscosity is non-Newtonian and displays shear-thinning behavior, similar to adult blood.<br>Le système cardiovasculaire est le premier organe entièrement fonctionnel chez l'embryon vertébré. Une formation appropriée de la vascularisation est indispensable pour le bon développement embryonnaire. Le flux sanguin a un rôle important autant dans les caractéristiques d'adaptation vasculaire que dans le remodelage. Dès que le flux sanguin commence, les vaisseaux répondent aux stimuli externes tels que les forces de cisaillement (shear stress) et la force tangentielle créée par le flux sanguin, ce qui affecte le tissu environnant. Le shear stress est le résultat du produit de la vitesse dans le vaisseau avec la viscosité du flux, paramètres ayant été déterminés in vivo. Dans cette étude, nous avons mesuré les changements de la vitesse de flux en utilisant la technique de micro particle image velocimetry (µPIV) à différents stades (somites) du développement de l'embryon de poulet. Pour la première fois, nous avons mesuré la viscosité du sang embryonnaire aviaire en utilisant un micro viscomètre et nous avons calculé le changement de shear stress au cours du remodelage vasculaire. Nous rapportonsque les niveaux de shear stress augmentent après le début du flux sanguin (14 somites) jusqu'au stade où de gros vaisseaux deviennent apparents (25 somites), stade auquel nous observons une diminution des niveaux de shear stress. En outre, l'hématocrite relié au diamètre vasculaire, diminue lors d'une réduction du rayon vaculaire, effet connu sous le nom d'effet de Fahreus-Lindqvist. Nous constatons aussi que la viscosité du sang embryonnaire n'est pas newtonienne et démontre un comportement de réduction du shear stress, observation similaire au sang adulte.

Laser speckle imaging, often referred to as laser speckle contrast analysis (LASCA), has been sought after as a quasi-real-time, full-field, flow visualization method. It has been proven to be a valid and reliable qualitative method, but there has yet to be any definitive consensus on its ability to be used as a quantitative tool. The biggest impediment to the process of quantifying speckle measurements is the introduction of additional non dynamic speckle patterns from the surroundings. The dynamic speckle pattern under investigation is often obscured by noise caused by background static speckle patterns. One proposed solution to this problem is known as dynamic laser speckle imaging (dLSI). dLSI attempts to isolate the dynamic speckle signal from the previously mentioned background and provide a consistent dynamic measurement. This paper will investigate the use of this method over a range of experimental and simulated conditions. While it is believable that dLSI could be used quantitatively, there were inconsistencies that arose during analysis. Simulated data showed that if the mixed dynamic and static speckle patterns were modeled as the sum of two independent speckle patterns, increasing static contributions led to decreasing dynamic contrast contributions, something not expected by theory. Experimentation also showed that there were scenarios where scattering from the dynamic media obscured scattering from the static medium, resulting in poor estimates of the velocities causing the dynamic scattering. In light of these observations, steps were proposed and outlined to further investigate into this method. With more research it should be possible to create a set of conditions where dLSI is known be accurate and quantitative.