Physical and geometric constraints shape the labyrinth-like nasal cavity

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 theoretic...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2018-03, Vol.115 (12), p.2936-2941
Main Authors: Zwicker, David, Ostilla-Mónico, Rodolfo, Lieberman, Daniel E., Brenner, Michael P.
Format: Article
Language:English
Subjects:
Air flow
Biological Sciences
Biological variation
Breathers
Cavities
Geometric constraints
Heat exchange
Heating
Holes
Humidification
Labyrinth
Low resistance
Nose
Physical Sciences
Respiratory system
Vertebrates
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Summary: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, while their overall shape can adhere to the geometric constraints imposed by 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.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1714795115