Airflow and nanoparticle deposition in rat nose under various breathing and sniffing conditions: a computational evaluation of the unsteady effect Jianbo Jiang a and Kai Zhao a a Monell Chemical Senses Center, Philadelphia, PA 19104 Abstract Accurate prediction of nanoparticle (1~100 nm) deposition in the rat nasal cavity is important for assessing the toxicological impact of inhaled nanoparticles as well as for potential therapeutic applications. A quasi-steady assumption has been widely adopted in the past investigations on this topic, yet the validity of such simplification under various breathing and sniffing conditions has not been carefully examined. In this study, both steady and unsteady computational fluid dynamics (CFD) simulations were conducted in a published rat nasal model under various physiologically realistic breathing and sniffing flow rates. The transient airflow structures, nanoparticle transport and deposition patterns in the whole nasal cavity and the olfactory region were investigated and compared with steady state simulation of equivalent flow rate. The results showed that (1) the quasi-steady flow assumption for cyclic flow was valid for over 70% of the cycle period during all simulated breathing and sniffing conditions in the rat nasal cavity, or the unsteady effect was only significant during the transition between the respiratory phases; (2) yet the quasi-steady assumption for nanoparticle transport was not valid, except in the vicinity of peak respiration. In general, the total deposition efficiency of nanoparticle during cyclic breathing would be lower than that of steady state due to the unsteady effect on particle transport and deposition, and further decreased with the increase of particle size, sniffing frequency, and flow rate. In the contrary, previous study indicated that for micro-scale particles (0.5~4ȝm), the unsteady effect would increase deposition efficiencies in rat nasal cavity. Combined, these results suggest that the quasi-steady assumption of nasal particle transport during cycling breathing should be used with caution for an accurate assessment of the toxicological and therapeutic impact of particle inhalation. Empirical equations and effective steady state approximation derived in this study are thus valuable to estimate such unsteady effects in future applications. Keywords Computational Fluid Dynamics; Rat nasal cavity; Nanoparticle deposition; Olfactory region; Cycling breathing Jianbo Jiang Address: Monell Chemical Senses Center 3500 Market Street Philadelphia, PA 19104-3308, USA Phone Number: (267) 519-4937 Fax Number: (215) 898-2084 jjiang@monell.org Kai Zhao Address: Monell Chemical Senses Center 3500 Market Street Philadelphia, PA 19104-3308, USA Phone Number: (267) 519-4935 Fax Number: (267) 519-4935 kzhao@monell.org Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author Manuscript J Aerosol Sci. Author manuscript; available in PMC 2011 November 1. Published in final edited form as: J Aerosol Sci. 2010 November 1; 41(11): 1030–1043. doi:10.1016/j.jaerosci.2010.06.005. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript