Heat and water transfers in the bronchi: clinical insights from a theoretical modeling study

Introduction: Conditioning of air during respiration occurs in the upper airways, but also in the bronchi (McFadden et al., 1985). Because it is related to the evaporation of the water contained in the mucus (Karamaoun et al., 2018), it could affect its dynamics, but also the body water and thermal balance.Aim and objectives: To assess theoretically the influence of the bronchial evaporation on the mucus dynamics and on the body water and thermal balance. Then, to issue recommendations for the management of airway pathologies. Methods: A theoretical model, previously developed (Karamaoun et al., 2018), is used with parameterssimulating resting and exercise respiration in room conditions. Heat and water losses are computed forevery bronchial generation. Results:At rest:power loss is 5 W and water loss is 150 mL/day. Air saturation occurs in generation 10; peak of heat dissipation in generation 4.Exercise: power loss rises to 45 W and water loss is 1.4 L/day. Air saturation occurs in generation 15; peak of heat dissipation in generation 8. Discussion: The magnitude of thermal and hydric losses in the bronchi suggests that evaporation can modify the dynamics of bronchial mucus. This could influence its properties, such as its viscosity, which is critical in several pathologies, as in cystic fibrosis (CF). Body water and thermal balance are likely to be impacted too, especially during exercise. Conclusion: Our results confirm that bronchial evaporation is critical regarding mucus dynamics, and body water and thermal balance. They highlight the importance of inspired air conditions for the management of sensitive subjects, such as CF patients or athletes with exercise-induced asthma.