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

Resumen

The nasal cavity is a vital component of the respiratory systemthat heats and humidifies inhaled air in all vertebrates. Despitethis common function, the shapes of nasal cavities vary widelyacross animals. To understand this variability, we here connectnasal geometry to its function by theoretically studying the airflow and the associated scalar exchange that describes heatingand humidification. We find that optimal geometries, which haveminimal resistance for a given exchange efficiency, have a constant gap width between their side walls, while their overallshape can adhere to the geometric constraints imposed by thehead. Our theory explains the geometric variations of naturalnasal cavities quantitatively, and we hypothesize that the tradeoff between high exchange efficiency and low resistance to airflow is the main driving force shaping the nasal cavity. Our modelfurther explains why humans, whose nasal cavities evolved tobe smaller than expected for their size, become obligate oralbreathers in aerobically challenging situations.