Noses are great. Noses allow us to smell and they humidify, heat and clean the air for us. Although, it fulfills the same tasks in all vertebrates, nasal geometries vary highly among species. The question is, what determines the form of the nasal cavity. One answer to this question can be found in the paper from David Zwicker at al. They calculated the optimal nasal cavity structure regarding the air flow and the heating and humidifying of the air. While narrower geometry improves the efficiency of heating and humidification, the airflow resistance increases. So the optimum lies somewhere in the middle: narrow enough to guarantee the right heat and humidity and wide enough so that the lung power allows air to go through the structure. In their paper, David Zwicker at al. transformed all this in physical equations and calculated the optimal nasal cavity: a narrow tube with a constant diameter and a certain length. So why the most animals have a labyrinth shaped instead of a tube-shaped nose cavity? Is there something wrong with the equations? No. The problem is the length. The nose (and the skull) restrict the possible space, and a straight tube structure of the optimal length would just not fit in. Therefore, the nasal cavities have this labyrinth-like structure. It also has a constant narrow diameter, as calculated. And Zwicker et al. showed that the branching and bending, does not change the airflow resistance. So messages of the day: 1. There are people which calculate the optimal nasal cavity. 2. The nasal cavities found in nature are quite optimal. STOP. The last point is not true for humans. The paper shows that the nasal cavity gap width and surface area is smaller as assumed by the model. The authors assume that the resulting higher resistance in air flow is the reason why humans are obligate oral breathers: during heavy physical activity, we don’t get enough airflow through our nose and therefore we tend to breathe through our mouth. Remember that, the next time you take a deep breath :)
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IdeaI love to increase my general science knowledge by reading papers from different fields of science. Here I share some of them. Archiv
März 2018
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