REVIEW   

Minerva Pneumologica 2017 December;56(4):249-53

DOI: 10.23736/S0026-4954.17.01799-0

Copyright © 2017 EDIZIONI MINERVA MEDICA

language: English

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

Alessandro RUBINI ✉

Section of Physiology, Department of Biomedical Sciences, University of Padua, Padua, Italy

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 increments in lung volume. The exact mechanisms are still under debate, but these findings probably depend on the effects of the flow and volume changes on the physical-chemical characteristics of the lung tissue, on the network of the fibrous elements in the alveolar septa, and on interstitial fluid dynamics. The combined effects of volume and flow changes are reviewed, together with some energetic aspects. The consequences during quiet breathing at rest and in muscular exercise hyperventilation are described.

KEY WORDS: Respiratory mechanics - Airway resistance - Pulmonary medicine