FLOW VISUALIZATION OF JET VENTILATION IN NEONATAL AIRWAY

在婴儿中，常规的辅助通气常常导致气胸 因为新生儿肺比成人肺更容易受到气压伤。 由于与传统的呼吸道压力相比， 机械通气，高频喷射通气（HFJV）已被 建议作为一种方法来帮助这一患者群体。 不幸的是，据报道，HFJV会导致新的创伤效应 包括由于高速射流冲击在 气管内皮表面，以及整体气体逐渐恶化 交换效率。 此外，在新生儿中使用HFJV获得的结果 由于喷气式飞机的设计和操作范围很广， 不同临床组使用的参数。 所有这些的核心 问题是缺乏对物理机制的清晰理解， 新生儿HFJV手术。 为了得到其中的一些 了解，研究提出调查的假设，射流 喷管的设计和位置对整个飞行器的性能有着重要的影响， 高频气体交换效率和气管壁剪切率 喷射通气（HFJV）。 我们建议通过以下方式来检验这一假设： 利用液珠流动显示实验技术， 新生儿支气管树的物理比例模型。 流动显示 将通过拍摄传统的和高速的电影来实现 模型中射流产生的振荡液体流。 物理模型中的液珠流动与气体流动相似 在新生儿肺HFJV期间通过使用流体机械 动力学和几何相似原理。 电影框架 将使用图像分析仪对所拍摄的流进行显影和分析。 通过这种分析，我们将确定实际注入的潮气量， 射流;射流对气管壁施加的剪切力;以及 对流气道气体交换过程的总效率 给定一组射流设计、操作和位置的参数。 压力 在充液模型内的不同位置， 同时，并用于预测相应的气体压力， 新生儿气道 主要的研究人员已经开发出一种技术， 支气管气道模型中的液珠流动可视化， 他成功地将其应用于正常呼吸的情况， 高频活塞振荡通风。

In infants, conventional ventilatory assistance often leads to pneumothorax since neonatal lungs are more subject to barotrauma than adult lungs. Because of relatively lower airway pressures in comparison to conventional mechanical ventilation, high frequency jet ventilation (HFJV) has been suggested as one method of assisting this patient population. Unfortunately, HFJV has been reported to lead to new traumatic effects including endothelial erosion due to the high velocity jet impinging on the tracheal endothelial surface, and gradual deterioration in overall gas exchange efficiency. Also, results obtained using HFJV in neonates have been difficult to compare due to the wide range of jet design and operation parameters employed by different clinical groups. Central to all of these problems is a lack of a clear understanding of the physical mechanisms of operation of HFJV in neonates. In order to obtain some of this understanding, research is proposed to investigate the hypothesis that jet nozzle design and location exert a major influence on the overall efficiency of gas exchange and tracheal wall shear rates in high frequency jet ventilation (HFJV) in neonates. We propose to test this hypothesis by using the experimental technique of liquid-bead flow visualization in physical scale models of the neonatal bronchial tree. Flow visualization will be achieved by taking conventional and high speed motion pictures of the oscillating liquid flow produced by the jet operating in the models. The liquid-bead flow in the physical models is made similar to the gas flow occurring during HFJV in neonatal lungs by use of the fluid mechanical principle of dynamic and geometrical similarity. The motion picture frames taken of the flow will be developed and analyzed using an image analyzer. By this analysis we will determine the tidal volume actually injected by the jet; the shearing force exerted by the jet on the tracheal wall; and the overall efficiency of the convective airway gas exchange process for a given set of parameters of jet design, operation and location. Pressures at various locations within the liquid-filled models will also be measured simultaneously and used to predict the corresponding gas pressures in the neonatal airways. The principle investigators have developed the technique of liquid-bead flow visualization in bronchial airway models and have applied it with considerable success to the case of normal respiration and high frequency-piston oscillation ventilation.