Enhanced condensational growth (ECG) is a newly proposed concept for respiratory drug delivery in which a submicrometer aerosol is inhaled in combination with saturated or supersaturated water vapor. The initially small aerosol size provides for very low extrathoracic deposition, whereas condensation onto droplets in vivo results in size increase and improved lung retention. The objective of this study was to develop and evaluate a CFD model of ECG in a simple tubular geometry with direct comparisons to in vitro results. The length (29 cm) and diameter (2 cm) of the tubular geometry were representative of respiratory airways of an adult from the mouth to the first tracheobronchial bifurcation. At the model inlet, separate streams of humidified air (25, 30, and 39 °C) and submicrometer aerosol droplets with mass median aerodynamic diameters (MMADs) of 150, 560, and 900 nm were combined. The effects of condensation and droplet growth on water vapor concentrations and temperatures in the continuous phase (i.e., two-way coupling) were also considered. For an inlet saturated air temperature of 39 °C, the two-way coupled numerical (and in vitro) final aerosol MMADs for initial sizes of 150, 560, and 900 nm were 1.75 μm (vs. 1.23 μm), 2.58 μm (vs. 2.66 μm), and 2.65 μm (vs. 2.63 μm), respectively. By including the effects of two-way coupling in the model, agreements with the in vitro results were significantly improved compared with a one-way coupled assumption. Results indicated that both mass and thermal two-way coupling effects were important in the ECG process. Considering the initial aerosol sizes of 560 and 900 nm, the final sizes were most influenced by inlet saturated air temperature and aerosol number concentration and were not largely influenced by initial size. Considering the growth of submicrometer aerosols to above 2 μm at realistic number concentrations, ECG may be an effective respiratory drug delivery approach for minimizing mouth-throat deposition and maximizing aerosol retention in a safe and simple manner. However, future studies are needed to explore effects of in vivo boundary conditions, more realistic respiratory geometries, and transient breathing.

中文翻译：

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应用于呼吸药物输送的增强凝结生长 (ECG) 的 CFD 模拟与体外数据的比较

增强凝结生长 (ECG) 是一种新提出的呼吸药物输送概念，其中吸入亚微米气溶胶与饱和或过饱和水蒸气。最初较小的气溶胶尺寸提供了非常低的胸外沉积，而在体内凝结到液滴上会导致尺寸增加并改善肺滞留。本研究的目的是开发和评估简单管状几何形状的心电图 CFD 模型，并与体外结果进行直接比较。管状几何形状的长度 (29 cm) 和直径 (2 cm) 代表了成人从口腔到第一气管支气管分叉处的呼吸道。在模型入口处，分开的加湿空气流（25、30、和 39 °C) 和质量中值空气动力学直径 (MMAD) 为 150、560 和 900 nm 的亚微米气溶胶液滴相结合。还考虑了冷凝和液滴生长对连续相（即双向耦合）中水蒸气浓度和温度的影响。对于 39 °C 的入口饱和空气温度，初始尺寸为 150、560 和 900 nm 的双向耦合数值（和体外）最终气溶胶 MMAD 分别为 1.75 μm（与 1.23 μm）、2.58 μm（与. 2.66 μm）和 2.65 μm（对比 2.63 μm）。通过在模型中包含双向耦合的影响，与单向耦合假设相比，体外结果的一致性得到显着提高。结果表明，质量和热双向耦合效应在 ECG 过程中都很重要。考虑到 560 和 900 nm 的初始气溶胶尺寸，最终尺寸受入口饱和空气温度和气溶胶数浓度的影响最大，而不受初始尺寸的影响很大。考虑到亚微米气溶胶在实际数量浓度下会增长到 2 μm 以上，ECG 可能是一种有效的呼吸药物输送方法，可以以安全和简单的方式最大限度地减少口喉沉积和最大限度地增加气溶胶滞留。然而，未来的研究需要探索体内边界条件、更现实的呼吸几何学和瞬态呼吸的影响。考虑到亚微米气溶胶在实际数量浓度下会增长到 2 μm 以上，ECG 可能是一种有效的呼吸药物输送方法，可以以安全和简单的方式最大限度地减少口喉沉积和最大限度地增加气溶胶滞留。然而，未来的研究需要探索体内边界条件、更现实的呼吸几何学和瞬态呼吸的影响。考虑到亚微米气溶胶在实际数量浓度下会增长到 2 μm 以上，ECG 可能是一种有效的呼吸药物输送方法，以安全和简单的方式最大限度地减少口喉沉积和最大限度地增加气溶胶滞留。然而，未来的研究需要探索体内边界条件、更现实的呼吸几何学和瞬态呼吸的影响。