Human lung studies: Mechanical properties of lung parenchyma and pulmonary hemodynamics.

摘要

The objective of this dissertation is to conduct human lung studies from two individual but potentially coupled aspects. One is to determine the mechanical properties of the human lung parenchyma experimentally, and the other is to build up a hemodynamics model to study the pulmonary circulation in man.;In order to have a detailed analysis of the distribution of stresses in the lung, one needs to understand the mechanical behavior of the lung material. For the stress-strain relationship of human lung parenchyma, the present state of the art is that the form of the constitutive equations is known, but the material constants are unknown, and must be determined by new measurements. In this research, dynamic biaxial loading tests were performed on 17 pieces of excised parenchyma specimens from 7 saline-filled cadaver lungs. Typical tissue stress and deformation response to biaxial loading and unloading shows the mechanical nonlinearity of the human lung parenchyma, and a small amount of hysteresis. To describe the stress-strain relationship in terms of a nonlinear form of strain energy function, we obtained the material constants of each specimen individually and the results show a high correlation between theory and experiments.;The second objective of this study is to build up a hemodynamic model of the entire pulmonary circulation of man on the basis of a set of anatomical and rheological data of the pulmonary vascular bed. This model features 16 orders of arteries and 15 orders of veins with parameters including vessel diameter, length, branching ratio, and compliance in each order. The pulmonary capillary is characterized by geometric and elastic data according to the sheet-flow theory. For the steady flow, this model yields the pulmonary pressure-flow relationship and the pressure distribution under certain physiological conditions. The resistance to blood flow is derived and compared to clinically determined values. Distinct from other theoretical studies with lumped parameter models, the present study has an advantage in examining quantitatively how the anatomical and rheological variables influence the pressure-flow relationship, if we assume that pathological factors affect those variables in pulmonary circulation.