Visualization and quantification of pulmonary microcirculation with microspectroscopy

We developed a video-rate polarizing microscope system to visualize the pulmonary capillary bed continuously and clearly under physiological and pathological conditions during continuous mechanical ventilation. We evaluated the effect of positive end-expiratory pressure (PEEP) on hemodynamic parameters such as erythrocyte number and velocity, tissue blood flow, hemoglobin oxygenation, and leukocyte adhesion to pulmonary vessels. The optimal PEEP required to maintain the pulmonary microcirculation was 3 cm H₂O in our anesthetized and thoracotomized rat model. Acute dysfunction in the pulmonary microcirculation was examined in lipopolysaccharide-treated rats. Blood circulation in the capillaries, but not in the arterioles and venules, deteriorated in a time-dependent manner that resulted in a slight but significant decrease in blood oxygenation. These results suggest the presence of pathological shunts in the pulmonary circulation in response to lipopolysaccharide administration and also suggest that leukocyte adherence to the vascular endothelium plays an important role in the development of pathological shunts.