Function follows form and form follows function
The flexiVent makes assessing mechanical properties of the lung a relatively simple undertaking. However, understanding the underlying physiological processes and mathematical modelling can be daunting. A background in pulmonary structure, function, and of the forces at play within the system are key to making the most of the provided outcomes.
A great resource for lung physiology is the recently published review article by Dr. Lars Knudson and Dr. Matthias Ochs, “The micromechanics of lung alveoli: structure and function of surfactant and tissue components”, published in Histochemistry and Cell Biology. Beginning with the axiom that “In biology, function follows form and form follows function”, the review elaborates with an in-depth tour of the fundamentals of respiratory function and architecture, from macro to micro structures, under normal conditions and with dysfunction, using lung injury and fibrosis as examples.
This paper gives a detailed and highly accessible account of the current understanding of parenchymal micromechanics and structure. It provides a comprehensive discussion about the lung surfactant system, the fiber network, and surfactant/fiber network interaction (an interaction that largely determines the elastic recoil of the lung). In particular, it examines how this fiber network is organized, transmits stress, maintains alveolar duct and airspace patency, along with the evidence for how the microarchitecture changes dynamically with changing volumes and pressures (see figure 1). This image depicts a model with folding and pleating of inter-alveolar septal walls at low lung volumes and stretching of alveolar epithelial cells at high volumes.
Figure 1: Model of alveolar micromechanics during deflation limb of a pressure-volume loop.
Building on the comprehensive review of the mechanisms and structure of the microarchitecture, the review article ties these relationships back to the current thinking around injurious processes and the experimental evidence those models previously presented. The outlook of the field and key issues, along with the current technical limitations we are facing, are discussed.
In summary, this review paper provides an excellent up-to-date resource on the structural and functional microarchitecture of the lung and a valuable framework to understanding lung mechanics – as measured by the flexiVent. Researchers of all levels will find food for thought.
Knudsen, L. and Ochs, M. (2018) ‘The micromechanics of lung alveoli: structure and function of surfactant and tissue components’, Histochemistry and Cell Biology. Springer Verlag, pp. 661–676. doi: 10.1007/s00418-018-1747-9.