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Probing atelectasis using spherical indentation and optical coherence tomography

Understanding of atelectasis is important for respiratory physiology, pathology, and clinical anesthesia. Studies of this occurrence are often limited to causal, because the specific mechanistic conditions are not controlled. In this investigation, we systematically induced atelectasis near the surface of excised lungs using load‐controlled indentation. Physiologic pressures were applied using spherical tips over spatial dimensions far larger than alveolar size to allow continuum discussions of stress‐induced collapse. After indentation, non‐invasive sub‐surface observation of the deformation was performed using optical coherence tomography (OCT). Experimental observations of atelectasis are compared with finite element model calculations of maximum stress loci. Tests were performed over a range of transpulmonary pressures, using air, 100% O2 and isoflurane mixtures. Significant differences were found in the atelectatic occurrence and recovery between inflation gases. These differences manifested within minutes, suggesting gas‐surfactant interaction. Accordingly, here we provide surfactant‐based arguments for our experimental observations.