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Analyse de l'efficacité de la ventilation par oscillation haute fréquence (VOHF)

Abstract : High Frequency Oscillatory Ventilation (HFOV) consists of insufflation at high frequency of current volumes lower than anatomical dead space, in order to purify carbon dioxide, which are residues of the cellular activities.This work consists in proving the effectiveness of the HFOV. Indeed, treatment of patients using HFOV allows satisfactory care of them, but with empirical adjustments of parameters involved in its use. Moreover, because of, the inhomogeneity of the patients, in one hand, and the impossibility of making clinical tests on people suffering from HMD (Hyaline Membrane Disease) or ARDS (Acute Respiratory Distress Syndrome), etc?, in the other hand, the use of the HFOV become increasingly complex for hospital staff.To analyze these difficulties, we, first, identified the influence of the amplitude of pressure and that of the frequency on the purification of two simple models of analogues. The results of these models prove that these parameters support the increase in alveoli?s volume according to their elasticity. Other results of these models are the basis for the development of future work in a numerical model of HFOV. Then, because of the limitation of the control range of certain parameters of the HFOV's machine, we designed and conducted series of tests with two types of analogues, the first one having rigid closures in the last generation of branches and the second having flexible closures in the same generation of branches. Thus, with this new device, we carried out the analysis of the influence of each one of these factors over the time of purification of the two models according to 12 sets of parameters of the Taguchi?s table L12 (23x31). With the introduction of the elasticity of flexible membranes, we noted not only, the significant reduction in the purification time, but also that the existence of an optimal frequency, function of the length of respiratory airways of the patients (age), which increases this efficiency. According to this study, the forced diffusion remains the principal mechanism, responsible for the efficiency of the HFOV. The analysis of influence of the parameters setting- entry velocity of oxygen, amplitude of pressure, oscillatory frequency and gravity- has been made in this work.Then, we simulated numerically the two experimental models of the tests, in order to confirm the experimental trends of these factors. Indeed, these two models were implemented in the software CFD (Computer Fluid Dynamic) Fluent. The results from these numerical models are agreed with those of the experimental models.Furthermore, we set up a model of Spontaneous Ventilation (SV) by using a more complex analogue with all the 23 generations of branches that has a human lung. Indeed, the movement of the 300 millions and the rib cage were modeled by that of 2,097,152 pistons. The results of this model confirm those of existing work on the SV.The future goal would be to conduct a comparative study between two numerical models, the SV and the HFOV by taking into account of alveolar diffusion mechanism.
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http://docnum.univ-lorraine.fr/prive/METZ_T_2010_Novinyo.Kossi.Edem.SMZ1010.pdf
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Kossi Edem Novinyo. Analyse de l'efficacité de la ventilation par oscillation haute fréquence (VOHF). Autre. Université Paul Verlaine - Metz, 2010. Français. ⟨NNT : 2010METZ010S⟩. ⟨tel-01752679⟩

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