Jonathan STEPHANO - Laboratoire JAD, Nice, France - Keywords: lung, asymmetry, respiration

Jonathan STEPHANO - Laboratoire JAD, Nice, France - Keywords: lung, asymmetry, respiration

Contribution title: Asymmetric bronchi tree model: does pruning bear fruit?

The lung is a complex system consisting in a tree-like network of bronchi whose sizes are decreasing more or less strongly when the distance from the first bronchus -the trachea- increases.
Although lung's bifurcations are asymmetric, many studies on this subject use a bronchial tree model where each bronchus divides into two smaller identical bronchi, we talk of a symmetric tree model [1]. Because they are more difficult to handle, asymmetric studies remain rare. However it has been shown in [2] that an asymmetric tree with noisy bronchi sizes is more robust in term of resistance to airflow. However this study used an asymmetric model which is not realistic for terminal bronchi sizes. Terminal bronchi have similar sizes in the lung but not in the model presented in [2], where some bronchi are too small.
What if this model is made more realistic, pruning the tree by cutting the bronchi that are too small? In this case, are we able to increase the tree's viability? What kind of tree would optimize ventilation performance?
We developed an original description of asymmetric trees using suitable parameters that are linked to the maximum and minimum numbers of successive bifurcations along a tree.
In our study, we search for configurations that optimize the network resistance to airflow for a given lung volume. Our goal is to improve our understanding of how evolution might have selected lung's geometry.
The study is still in progress. However, the first results show that the asymmetry effects on the volume and on the resistance are higher than those predicted in the previous study [2].

[1] Mauroy B, Filoche M & Al, 2003, Phys. Rev. Lett. 90
[2] Mauroy B., Bokov P., 2010, Phys. Biol. 7