An image-based biophysical model of the lung to investigate the effect of pulmonary surfactant on lung function.

Lung biomechanics aims to understand the structure-function relationship in the lung under normal and pathological conditions. Pulmonary surfactant has a key structural role in lung function with a significant contribution to the mechanical response of the lungs during respiration. Pulmonary surfactant dynamically regulates surface tension at the air-liquid interface to decrease stiffness during respiration and prevent alveolar collapse during lower volumes. Many lung injuries involve alterations to the contribution of surfactants to lung function. We developed a novel biophysical model using a poroelastic formulation that incorporates pulmonary surfactant dynamics and aims to quantify the contribution of the pulmonary surfactant toward lung compliance. The effect of pulmonary surfactant was modeled as a surface energy function, and the surface behavior was converted to bulk behavior by assuming uniform spherical alveoli. The model was used to simulate respiration and investigate the effect of altered surface tension caused by surfactant dysfunction. The model captured the characteristic sigmoidal inspiratory pressure-volume curve and hysteresis observed during clinical measurements. In addition, the model predicted the expected behavior in surfactant dysfunction in lung injuries. We expect this work to serve as an essential step towards de-convoluting and predicting the contributions of the lung parenchyma and pulmonary surfactant to global and regional lung compliance in health and disease.