Flow and volume dependence of resistive pressure dissipation in the respiratory system

An inspiratory driving pressure must be applied to the respiratory system to inflate airflow from the external ambient to the alveolar space. This pressure is dissipated as heat after the inflation, and allows to win two resistive components named "ohmic" and visco-elastic resistances. The first depends on the frictional forces opposing airflow in the airway, while the second is exerted by respiratory tissue resistance to deformation during inflation. Both of them are here described. Experiments in animals and humans showed that both the resistances exhibit flow as well as volume dependence. The "ohmic" resistance increases with increasing values of flow rate mostly because of increased turbulence in the airway, and decreases with lung volumes increments. This decrement happens because lung inflation increases the tensile stress on the bronchial walls causing bronchodilation. On the contrary, the visco-elastic component decreases with increasing values of flow rate and increases with i...