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Artificial ventilation and respiratory mechanics basic: Part 2

(BQ) Continued part 1, part 2 of the document Artificial ventilation and respiratory mechanics basic has contents: Alveolar micromechanics, how the diaphragm works in normal subjects, altered elastic properties of the respiratory system, closed ioop control mechanical ventilation, and other contents. Invite you to refer. | Artificial ventilation and respiratory mechanics basic: Part 2 Chapter 10 Alveolar micromechanics P.Y.ROMERO The mechanical behavior of the air spaces in the periphery of the lung is the result of a delicate balance of forces acting on the tissue scaffold of lung parenchyma. Static and dynamic properties of such a complex system have been an important field of research for many years. Alveolar space micromechanics have important physiological implications in terms of mechanical interdepen- den ce, alveolar stability, and the maintenance of agas exchanging surface in constant contact with air. The mechanical behavior of such system has to allow the expansion of the alveolar surface at physiological rates at a low energy cost, and without interfering with the exchange process. I will describe how the struc- ture and mechanics of the alveolar space are particularly optimized to reach these goals. Anatomical structure of the alveolar space The alveolar septum is made of a single capillary network interlaced with fibers (mainly collagen and elastine), which form a continuum embedded in the con- nective matrix, the thin membrane of epithelial cells forming the external boundary of this scaffold. This irregular surface is to some extent smoothed by an extracellular layer of lining fluid that is rather thin over the capillaries but forms small pools in the intercapillary cavities. Alveolar lining consists of an aqueous layer called the hypophase which is of variable thickness and is pre- sent mainly in the pools, and a layer of surfactant which forms a film on the surface of the hypophase. Because of the relevant physical properties of these structures, septal configuration is not exclusively determined by the structural disposition but results from the molding effect of the two main forces that have to be kept in balance: tissue tension and surface tension. Structural interaction of tissue fibers and surface lining Many .