Unsteady Mass Transport During Liquid Ventilation

液体通气是一种非常有前途的人工通气方法，特别是在严重的急性呼吸窘迫综合征（ARDS）中，传统的通气方法不起作用。然而，由于缺乏对气体交换过程的详细了解和缺乏临床经验，液体通气方法尚未在临床常规应用。为了评估通气/灌注比，了解溶解气体分别通过全氟碳（PFC）和支气管树的传输行为是非常重要的。只有这样，呼吸参数（频率、潮气量）才能设置得最优。只有进入气道前的气体浓度以及肺泡和血气浓度是已知的或可以测量的。在本研究项目的范围内，将研究溶解氧和二氧化碳通过人体上呼吸道模型的运输。在这里，将采用PFC液体通气。为了进行研究，采用了新的方法，如在PFC中使用氧敏感示踪粒子光学测量氧浓度。颗粒将在肺模型中均匀分布。由于受激粒子的氧猝灭，荧光强度的差异是在相机系统的帮助下光学测量的。除了收集氧浓度分布外，还需要分别分析速度和质量流量分布。只有这样才能评价溶解气体的输运机制。根据液体通气时典型的呼吸参数（潮气量、呼吸频率）和PCF较低的运动黏度，上气道一直到第6代都以湍流为特征。这与层流占主导地位的传统通风的边界条件不同。因此，可以预期不同的质量传递途径。这将通过粒子图像测速（PIV）测量来研究。

The method of liquid ventilation is a very promising alternative of life saving, artificial ventilation, especially at severe forms of the Acute Respiratory Distress syndrome (ARDS), where conventional ventilation methods fail. Nevertheless, due to a lack of detailed knowledge about the gas exchange processes and little clinical experience, the method of liquid ventilation has not been used in clinical routine, yet. In order to evaluate the ventilation/perfusion ratio, it is of high importance to gain knowledge about the dissolved gas transport behavior through the perfluorocarbon (PFC) and the bronchial tree, respectively. Only this way, the breathing parameters (frequency, tidal volume) can be set up optimally. Only the gas concentrations before entering the airways as well as the alveolar and blood gas concentrations are known or can be measured.Within the scope of this research project, the transport of dissolved oxygen and carbon dioxide through a model of the upper human airways will be investigated. Here, liquid ventilation with PFC will be applied. For the investigations, novel methods such as the optical measurement of the oxygen concentration by using oxygen sensitive tracer particles in PFC are applied. The particles will be distributed homogeneously in the lung model. Differences in fluorescence intensity due to oxygen quenching of the excited particles are measured optically with the help of a camera system. Besides gathering the oxygen concentration distribution it is necessary to analyze the velocity and mass flow distribution of the , respectively. Only this way the transport of mechanisms of dissolved gas can be evaluated. According to the typical breathing parameters (tidal volume, breathing frequency) during liquid ventilation and the low kinematic viscosity of PCF the upper airways down to the 6th generation are characterized by turbulent flow. This differs from the boundary conditions of conventional ventilation where laminar flow predominates. Consequently, different pathways of mass transport can be expected. This will be investigated by Particle Image Velocimetry (PIV) measurements.