Real-time imaging assessment of pulmonary vascular responses.

Real-time imaging of the intact lung allows for the visualization and analysis of pulmonary vascular responses at a unique spatial and temporal resolution. For visual access to the pulmonary microvasculature under closed chest conditions, a series of thoracic window techniques has been developed. These approaches provide singular insights into basic physiological phenomena, such as capillary recruitment and hypoxic pulmonary vasoconstriction, and into the site, extent, and mechanisms of neutrophil margination in the pulmonary vasculature. Recent advancements, such as the murine thoracic window model and the oxygen saturation mapping technique, have expanded these applications to studies in genetically modified animals and to the analysis of regional gas exchange. Although intravital microscopy may visualize vascular responses in their most physiologic context, functional imaging in isolated perfused lungs allows for targeting of individual cell subsets with functional fluorescence probes and specific interventions. This approach has proven essential for studies on the spatial arrangement and trafficking of cytoskeletal proteins such as actin, organelles such as mitochondria, or vesicles such as Weibel-Palade bodies in lung endothelial cells. Functional imaging has generated unprecedented insights into the temporal and spatial profile of intra- and subcellular second messenger systems, including signaling cascades via Ca(2+), nitric oxide, or reactive oxygen species. The rapid advancement of bioimaging capabilities at the technical level, the increasing availability of protein-based fluorescent probes, and the ongoing refinement of in vivo and ex vivo lung models provide promising prospects for the application of real-time bioimaging to the further resolution of pulmonary vascular responses in lung health and disease.