To speculate on human responses from animal studies, scale-up factors (body weight, lung volume, or lung surface area ratios) are currently used to extrapolate aerosol lung deposition from animal to human. However, those existing scale-up methods between animals and humans neglected two important inter-subject variability factors: (1) the effect of anatomical differences in respiratory systems from mouth/nose to peripheral lungs between human and rat, and (2) the effect of spatial distributions and temporal evolutions of temperature and relative humidity (RH) on droplet size change dynamics between the two species. To test the above-mentioned inter-species variability effects on droplet fates in pulmonary routes and generate correlations as a precise scale-up method for lung deposition estimation, this study simulated the transport of pure-water droplets in both human and Sprague-Dawley (SD) rat respiratory systems. Employing an experimentally validated Euler-Lagrange based Computational Fluid-Particle Dynamics (CFPD) model, simulations were performed for droplets with Stk/Fr between 8.36 × 10⁻⁵ and 1.25 × 10⁻². Droplets were inhaled through human and rat nostrils with resting breathing conditions. Numerical results indicate that RH becomes uniformly distributed in rat airways sooner than in human airways, which significantly influences droplet size change dynamics and the resultant trajectories in pulmonary paths. Using the Stokes-Froude dimensionless number group (i.e., Stk/Fr) as the independent variable, the regional deposition fractions and evaporation fractions in both rat and human respiratory systems collapsed into unified correlations. The correlations can be used as a new rat-to-human scale-up method, estimating the lung depositions with consideration of anatomical differences. Furthermore, the necessity to employ realistic RH and temperature boundary conditions at airway walls was also confirmed for the accurate prediction of droplet size change using CFPD. Employing idealized boundary conditions leads the droplets to evaporate slower and deposit more than using realistic RH and temperature boundary conditions.

为了推测来自动物研究的人类反应，目前使用放大因子（体重、肺体积或肺表面积比）来推断从动物到人类的气溶胶肺沉积。然而，现有的动物和人类之间的放大方法忽略了两个重要的主体间变异因素：（1）人和大鼠之间从口/鼻到外周肺的呼吸系统解剖学差异的影响，以及（2）影响温度和相对湿度 (RH) 的空间分布和时间演变对两个物种之间液滴大小变化动力学的影响。为了测试上述物种间变异性对肺部路径中液滴命运的影响，并生成相关性作为肺沉积估计的精确放大方法，这项研究模拟了纯水滴在人类和 Sprague-Dawley (SD) 大鼠呼吸系统中的运输。采用经过实验验证的基于欧拉-拉格朗日的计算流体-粒子动力学 (CFPD) 模型，对 Stk/Fr 介于 8.36 × 10^-5和 1.25 × 10 ^-2. 在静息呼吸条件下，通过人和大鼠的鼻孔吸入液滴。数值结果表明，RH 在大鼠气道中比在人体气道中更快地均匀分布，这显着影响了液滴尺寸变化动力学和肺路径中的最终轨迹。使用 Stokes-Froude 无量纲数群（即 Stk/Fr）作为自变量，大鼠和人类呼吸系统中的区域沉积分数和蒸发分数塌陷成统一的相关性。这些相关性可以用作一种新的大鼠-人类放大方法，在考虑解剖学差异的情况下估计肺沉积。此外，为了准确预测使用 CFPD 的液滴尺寸变化，还证实了在气道壁上使用实际 RH 和温度边界条件的必要性。使用理想化的边界条件会导致液滴蒸发得更慢，并且比使用实际的 RH 和温度边界条件沉积更多。