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Dynamique du transport et du transfert de l'oxygène au sein de l'acinus pulmonaire

Abstract : The pulmonary acinus is the exchange unit between air and blood into the pulmonary airway system. In this thesis, we were interested more specifically for the oxygen. Its uptake from air to blood in the pulmonary acinus involves several successive processes: convection, diffusion in the gas phases, diffusion through the alveolar membrane and across plasma and finally capture by hemoglobin in the red blood cells. By the determination of the pulmonary diffusive capacity called DL, we can have a clinical evaluation of the efficiency and the performance of these mechanisms. This measure is currently used for the diagnostic in order to show probable deterioration of the alveolar membrane or else an exchange surface leakage. Experimentally, DL is calculated from two clinical measures: the alveolar pressure PA and the uptake V ̇. More precisely, in the case of oxygen, we talk about the oxygen partial pressure into the pulmonary alveolus P_(〖A,O〗_2 ) and the amount of oxygen exchanged in one minute V ̇_(O_2 ). A theoretical value of the oxygen diffusive capacity can be deduced from a classic and empiric formulation well-known in medicine. This theory is always the topic of several publications because it does not exactly report the experimental values. We implemented a numerical dynamical model of the oxygen transport and transfer into the pulmonary acinus able to recover the physiological value of P_(〖A,O〗_2 ) and V ̇_(O_2 ) in healthy patients. This model depends on a single physical parameter called the permeability W. It encloses all the complexity of the oxygen transfer to the blood. It is defined as an equivalent conductance induced by the different mechanisms taking place in the transfer to the blood. Thus, by the determination of the unique parameter W, we built an artificial acinus which is able to reproduce the behavior of the real acinus. From this model, we studied the influence of the asymmetric geometry of the pulmonary acinus on the oxygen transport and transfer. This study has shown an heterogeneity of the oxygen transfer. We can explain that with a phenomenon called diffusional screening, responsible for the fact that the oxygen partial pressure along the acinar tree decreases. This phenomenon is governed by the oxygen absorption across the alveolar membrane and the diffusion along the asymmetric structure of the acinar airways. This effect leads to a bad provision in oxygen in the distal regions, the major part being absorbed in the proximal zones. At rest, the influence of the diffusional screening is important. At exercise, the effects of the screening are weak because of the higher convection velocity. Thus, the quasi-totality of the exchange surface is used.
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Contributor : Aurélie Foucquier <>
Submitted on : Wednesday, February 23, 2011 - 11:39:03 AM
Last modification on : Wednesday, March 27, 2019 - 4:18:02 PM
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Aurélie Foucquier. Dynamique du transport et du transfert de l'oxygène au sein de l'acinus pulmonaire. Biophysique [physics.bio-ph]. Ecole Polytechnique X, 2010. Français. ⟨pastel-00568656⟩

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