UC Riverside

Pulmonary diseases, a leading cause of morbidity and mortality, profoundly affect lung tissue structure, resulting in alterations in mechanical and viscoelastic properties. However, our understanding of these alterations and the underlying material properties remains limited. This dissertation focuses on studying the structural biomechanics of the lung at two levels: the whole organ and tissue level, providing a comprehensive understanding of lung functioning.At the whole organ level, a novel automated device is developed to apply volume and measure lung pressure response, surpassing conventional machines. This device enables groundbreaking viscoelastic insights of the entire lung, facilitating investigations into the mechanical differences between physiological negative pressure ventilation (NPV) and artificial positive pressure ventilation (PPV). Our findings reveal disparities in organ energetics, viscoelasticity, and local stretch between NPV and PPV, emphasizing the importance of understanding these distinctions to optimize ventilator use and enhance patient outcomes. Additionally, we explore the lung's pressure-volume response under varying inflation volumes and frequencies, discovering that lung stiffness increases with faster breathing rates and lower inflation volumes, with inflation volume exerting a stronger influence on lung behavior than frequency. These insights have practical implications for the optimization and design of mechanical ventilators. Furthermore, we investigate the tissue level by examining the mechanical properties of lung airways, where disease-induced microstructural alterations predominantly occur. Through biaxial tensile experiments, we establish baseline mechanics for the entire airway, measuring proximal and distal airways in axial and circumferential orientations simultaneously. Our investigations reveal heterogeneity and anisotropy in airway mechanics, highlighting the limitations of extrapolating proximal airway behavior to the entire bronchial tree. Additionally, we characterize the material properties of pulmonary airways using computational studies, considering the non-linear, anisotropic, and heterogeneous behavior observed experimentally. By comparing various constitutive models, we identify the most suitable model for predicting the mechanical and viscoelastic behavior of the complete bronchial tree. Furthermore, various rheological models accurately capture the lung tissue stress relaxation response in uniaxial testing. These findings significantly enhance our understanding of airway function and improve computational simulations for the diagnosis and monitoring of pulmonary diseases.