Pressure- and time-dependent alveolar recruitment/derecruitment in a spatially resolved patient-specific computational model for injured human lungs

We present a novel computational model for the dynamics of alveolar recruitment/derecruitment (RD), which reproduces the underlying characteristics typically observed in injured lungs. The basic idea is a pressure- and time-dependent variation of the stress-free reference volume in reduced dimensional viscoelastic elements representing the acinar tissue. We choose a variable reference volume triggered by critical opening and closing pressures in a time-dependent manner from a straightforward mechanical point of view. In the case of (partially and progressively) collapsing alveolar structures, the volume available for expansion during breathing reduces and vice versa, eventually enabling consideration of alveolar collapse and reopening in our model. We further introduce a method for patient-specific determination of the underlying critical parameters of the new alveolar RD dynamics when integrated into the tissue elements, referred to as terminal units, of a spatially resolved physics-based lung model that simulates the human respiratory system in an anatomically correct manner. Relevant patient-specific parameters of the terminal units are herein determined based on medical image data and the macromechanical behavior of the lung during artificial ventilation. We test the whole modeling approach for a real-life scenario by applying it to the clinical data of a mechanically ventilated patient. The generated lung model is capable of reproducing clinical measurements such as tidal volume and pleural pressure during various ventilation maneuvers. We conclude that this new model is an important step toward personalized treatment of ARDS patients by considering potentially harmful mechanisms-such as cyclic RD and overdistension-and might help in the development of relevant protective ventilation strategies to reduce ventilator-induced lung injury (VILI). We present a novel approach to model the (patho-)physiological dynamics of alveolar recruitment and derecruitment (RD) in reduced dimensional viscoelastic tissue elements. To determine the underlying RD parameters of the new tissue elements in a patient-specific manner when integrated into a spatially resolved physics-based computational lung model, we introduce an algorithm based on the patient's global respiratory mechanics and local pathology. Applying the proposed modeling approach to a patient with acute respiratory distress syndrome (ARDS), the comprehensive lung model can reproduce clinical measurements in simulation, allowing for a more accurate estimation of the individual local tissue straining and (cyclic) RD occurring during the patient's mechanical ventilation - a crucial aspect for the development of personalized protective ventilation strategies in the long term.image