Physical and geometric constraints explain the labyrinth-like shape of the nasal cavity

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Proceedings of the National Academy of Sciences of the United States of America

The nasal cavity is a vital component of the respiratory system that heats and humidifies inhaled air in all vertebrates. Despite this common function, the shapes of nasal cavities vary widely across animals. To understand this variability, we here connect nasal geometry to its function by theoretically studying the airflow and the associated scalar exchange that describes heating and humidification. We find that optimal geometries, which have minimal resistance for a given exchange efficiency, have a constant gap width between their side walls, but their overall shape is restricted only by the geometry of the head. Our theory explains the geometric variations of natural nasal cavities quantitatively and we hypothesize that the trade-off between high exchange efficiency and low resistance to airflow is the main driving force shaping the nasal cavity. Our model further explains why humans, whose nasal cavities evolved to be smaller than expected for their size, become obligate oral breathers in aerobically challenging situations.

Copyright 2017 Proceedings of the National Academy of Sciences of the United States of America. Recommended citation: Zwicker, David, Rodolfo Ostilla-Mónico, Daniel E. Lieberman, and Michael P. Brenner. "Physical and geometric constraints shape the labyrinth-like nasal cavity." Proceedings of the National Academy of Sciences 115, no. 12 (2018): 2936-2941. (2017). doi:10.1073/pnas.1714795115. Reproduced in accordance with the original publisher's licensing terms and with permission from the authors.