Enhancement of gas transfer due to the convective resonance in the bifurcating tube of the airway

由于气流的振荡作用，气体在气道内发生交换，气体交换机制受多种因素的影响，如气道形态、气道开度、气道内表面分泌的表面活性物质等。在自然肺中，气体交换过程非常有效，并且对氧气需求高度敏感，因此有必要弄清呼吸道中的气体交换过程。在风道中，气体在多分支网络中通过振荡流传输，在弯曲处诱导的二次流使气体传输过程得到强化，这一过程被称为对流共振。因此，我们关注对流共振现象，并对其进行研究，旨在阐明对流共振引起的气体在自然肺内传递的流体力学特性。对流共振对高频振荡技术可能是有效的，而利用传递共振效应将使人工通风变得更加有效。在这项研究中，我们进行了实验和数值研究，以证实由于弯曲部分的二次流而产生的对流共振的有效性。并考虑了气道扩张性的影响，建立了逼真的气道模型。气道的膨胀性会限制湍流的产生，从而影响气体在气道内的强化传递。

The gas is exchanged in the airway due to the oscillatory flow and the gas exchange mechanisms are affected by various factors such as morphology of airway, opening of airway, surfactant secreted on the inner surface of airway and others. In the natural lung, the gas exchange process is remarkably efficient and is highly sensitive to the oxygen demand, thus it is necessary to clarify the gas exchange process in the airway. In the airway, the gas is transported by the ocillatory flow in the multi-branching network and the secondary flow induced in the curved portion of bifurcating tube causes to enhance the gas transfer process, and this process is called "convective resonance". So we payed attention to the phenomena of convective resonance and the purpose of this study it to clarify the fluid mechanical feature of convective resonance causing to enhance the gas transfer in the natural lung. The convective resonance may be effective to the high frequency oscillation technology and artificial ventilation will become more effective by utilizing the effect of convetive resonance. In this study we performed both experiments and numerical studies to confirm the effectiveness of convective resonance due to the secondary flow in the curved portions. We also took into acount the effect of distensibility of the airway and constructed the realistic airway model. The distensibility of the airway will restrict the generation of turbulence, which affects the enhancement of gas transfer in the airway.