Department of Community and Environmental Medicine, University of California, Irvine, California, USA.
Inhal Toxicol. 2010 Jan;22(1):42-8. doi: 10.3109/08958370902862442.
Nicotine in mainstream cigarette smoke is predominantly present in the particulate phase. Interestingly, however, the deposition efficiency of smoke particles in the respiratory tract is less effective than is the nicotine retention. In the literature, four nicotine deposition mechanisms are identified: (a) direct gas deposition, (b) evaporative gas deposition, (c) particle deposition with evaporation, and (d) particle deposition with diffusion. In this article we present a physically motivated fundamental model to address nicotine deposition mechanisms (b) and (c) from the vapor phase. The model incorporates nicotine mass transport through estimates for the diffusion time across the epithelial layer and the time for nicotine vapor diffusion from the gas volume to the tissue surfaces in the tracheobronchial and pulmonary regions of the respiratory tract. The model comprises four mass transfer processes for nicotine at the surface of the respiratory tract epithelium: (1) conversion of free base nicotine from protonated nicotine; (2) free base nicotine transport across the epithelium; (3) free base nicotine evaporation; and (4) diffusion of free base nicotine vapor from the surface gas layer into the airway lumen. Results of the nicotine mass transport model suggest that the principal mechanism of nicotine delivery to the lung is by direct deposition of particles to the alveolar fluid lining, followed rapidly by evaporation into the lumen and then gas diffusion back to the surface as nicotine depletes in the surface layer through its transport across the epithelium.
主流香烟烟雾中的尼古丁主要存在于颗粒相中。然而，有趣的是，烟雾颗粒在呼吸道中的沉积效率不如尼古丁的保留效率高。在文献中，确定了四种尼古丁沉积机制：（a）直接气体沉积，（b）蒸发气体沉积，（c）带有蒸发的颗粒沉积，以及（d）带有扩散的颗粒沉积。在本文中，我们提出了一个物理驱动的基本模型，以解决来自蒸气相的尼古丁沉积机制（b）和（c）。该模型通过估计穿过上皮层的扩散时间以及从气体体积到呼吸道的气管支气管和肺部区域的组织表面的尼古丁蒸气扩散时间，来整合尼古丁的质量传输。该模型包含在呼吸道上皮表面的尼古丁的四个质量传递过程：（1）从质子化尼古丁转化为游离碱尼古丁；（2）游离碱尼古丁穿过上皮层的运输；（3）游离碱尼古丁的蒸发；以及（4）从表面气体层扩散到气道腔中的游离碱尼古丁蒸气。尼古丁质量传输模型的结果表明，尼古丁向肺部输送的主要机制是通过颗粒直接沉积到肺泡液衬里，然后迅速蒸发到管腔中，然后通过其穿过上皮层的运输，当尼古丁在表面层中耗尽时，尼古丁会通过气体扩散回到表面。
