arXiv subjects

Cyril Karamaoun

Publications and source records attributed to Cyril Karamaoun.

5 recordsLinked to original sources

arXiv2024

Curvature-driven transport of thin Bingham fluid layers in airway bifurcations

The mucus on the bronchial wall forms a thin layer of non-Newtonian fluid. One of the roles of mucus is to protect the lungs by capturing inhaled pollutants. It is transported by mucocilliary clearance toward the tracheo-pharyngeal bifurcation, where it is eliminated. Due to the corrugation of its interface with air, the mucus layer is subject to surface tension forces that interact with its rheology. It is still not clear whether these forces can affect mucus displacement and, if they can, under what conditions and how this displacement can occur. In this work, we model the mucus as a thin Bingham fluid layer located on the wall of idealized, multi-scaled airway bifurcations. We analyze the resulting physical system using lubrication theory and 3D simulations. The theoretical analysis allows us to characterize the nonlinear behavior of the system and determine the geometric conditions under which the Bingham fluid can be moved by surface tension. 3D simulations are then used to quantify the effects in idealized airway bifurcations on a range of scales corresponding to those of bronchial bifurcations. Our results suggest that surface tension effects can displace overly thick mucus layers in airway bifurcations, a typical situation in obstructive lung pathologies (asthma, BPCO, cystic fobrosis, etc.). Moreover, our results indicate that this movement can disrupt mucociliary clearance and the homogeneity of the layer thickness, thus increasing the risk of lung infection.

physics.flu-dyn↗

arXiv2022

Water and heat exchanges in mammalian lungs

A secondary function of the mammals' respiratory system is during inspiration to heat the air to body temperature and to saturate it with water before it reaches the alveoli. Relying on a mathematical model, we comprehensively analyze this function, considering all the terrestrial mammals (spanning six orders of magnitude of the body mass, $M$) and focusing on the sole contribution of the lungs to this air conditioning. The results highlight significant differences between the small and the large mammals, as well as between rest and effort, regarding the spatial distribution of heat and water exchanges in the lungs, and in terms of regime of mass transfer taking place in the lumen of the airways. Interestingly, the results show that the mammalian lungs appear to be designed just right to fully condition the air at maximal effort: all generations of the bronchial region of the lungs are mobilized for this purpose. For mammals with a mass above a certain threshold ($\simeq 5$ kg at rest and $\simeq 50$ g at maximal effort), it appears that the maximal value of this evaporation rate scales as $M^{-1/8}$ at rest and $M^{-1/16}$ at maximal effort and that around 40\% (at rest) or 50\% (at maximal effort) of the water/heat extracted from the lungs during inspiration is returned to the bronchial mucosa during expiration, independently of the mass, due to a subtle coupling between different phenomena. This last result implies that, above these thresholds, the amounts of water and heat extracted from the lungs by the ventilation scale with the mass such as the ventilation rate (i.e. as $M^{3/4}$ at rest and $M^{7/8}$ at maximal effort). Finally, it is worth mentioning that these amounts appear to remain limited, but not negligible when compared to relevant global quantities, even at maximal effort (4-6\%).

physics.flu-dyn↗

arXiv2021

The origin of the allometric scaling of lung ventilation in mammals

A model of optimal control of ventilation has recently been developed for humans. This model highlights the importance of the localization of the transition between a convective and a diffusive transport of respiratory gas. This localization determines how ventilation should be controlled in order to minimize its energetic cost at any metabolic regime. We generalized this model to any mammal, based on the core morphometric characteristics shared by all mammalian lungs and on their allometric scaling from the literature. Since the main energetic costs of ventilation are related to convective transport, we prove that, for all mammals, the localization of the shift from a convective transport to a diffusive transport plays a critical role on keeping this cost low while fulfilling the lung function. Our model predicts for the first time the localization of this transition in order to minimize the energetic cost of ventilation, depending on mammal mass and metabolic regime. From this optimal localization, we are able to predict allometric scaling laws for both tidal volumes and breathing rates, at any metabolic rate. We ran our model for the three common metabolic rates -- basal, field and maximal -- and showed that our predictions reproduce accurately experimental data available in the literature. Our analysis supports the hypothesis that mammals allometric scaling laws of tidal volumes and breathing rates at a given metabolic rate are driven by a few core geometrical characteristics shared by mammalian lungs and by the physical processes of respiratory gas transport.

q-bio.TO↗

arXiv2019

Allometric scaling of heat and water exchanges in the mammals' lung

Mammals have a high metabolism that produces heat proportionally to the power 3/4 of their mass at rest. Any excess of heat has to be dissipated in the surrounding environment to prevent overheating. Most of that dissipation occurs through the skin, but the efficiency of that mechanism decreases with the animal's mass. The role of the other mechanisms for dissipating heat is then raised, more particularly the one linked to the lung that forms a much larger surface area than the skin. The dissipation occurring in the lung is however often neglected, even though there exists no real knowledge of its dynamics, hidden by the complexity of the organ's geometry and of the physics of the exchanges. Here we show, based on an original and analytical model of the exchanges in the lung, that all mammals, independently of their mass, dissipate through their lung the same proportion of the heat they produced, about 6-7 %. We found that the heat dissipation in mammals' lung is driven by a number, universal among mammals, that arises from the dynamics of the temperature of the bronchial mucosa. We propose a scenario to explain how evolution might have tuned the lung for heat exchanges. Furthermore, our analysis allows to define the pulmonary heat and water diffusive capacities. We show in the human case that these capacities follow closely the oxygen consumption. Our work lays the foundations for more detailed analysis of the heat exchanges occurring in the lung. Future studies should focus on refining our understanding of the universal number identified. In an ecological framework, our analysis paves the way to a better understanding of the mammals' strategies for thermoregulation and of the effect of warming environments on mammals' metabolism.

physics.bio-ph↗

arXiv2017

A new role for exhaled nitric oxide as a functional marker of peripheral airway caliber changes: a theoretical study

Though considered as an inflammation marker, exhaled nitric oxide (FENO) was shown to be sensitive to airway caliber changes to such an extent that it might be considered as a marker of them. It is thus important to understand how these changes and their localization mechanically affect the total NO flux penetrating the airway lumen (JawNO), hence FENO, independently from any inflammatory status change. A new model was used which simulates NO production, consumption and diffusion inside the airway epithelium wall, then, NO excretion through the epithelial wall into the airway lumen and, finally, its axial transport by diffusion and convection in the airway lumen. This model may also consider the presence of a mucus layer coating the epithelial wall. Simulations were performed that showed the great sensitivity of JawNO to peripheral airways caliber changes. Moreover, FENO showed distinct behaviors depending on the location of the caliber change. Considering a bronchodilation, absence of FENO change was associated with dilation of central airways, FENO increase with dilation up to pre-acinar small airways, and FENO decrease with intra-acinar dilation due to amplification of the back-diffusion flux. The presence of a mucus layer was also shown to play a significant role in FENO changes. Altogether, the present work provides theoretical evidences that specific FENO changes in acute situations are linked to specifically located airway caliber changes in the lung periphery. This opens the way for a new role for FENO as a functional marker of peripheral airway caliber change.

q-bio.TO↗