An experimental rat model for studying pulmonary microcirculation by in vivo videomicroscopy

It is unclear what role pulmonary microcirculatory disorders play in the pathogenesis of adult respiratory distress syndrome. The aim of this study was to establish a rat model for the direct visualization of pulmonary microcirculation by in vivo fluorescence videomicroscopy. The pulmonary terminal vascular bed was visualized and the microcirculatory parameters of leukocyte sticking, erythrocyte velocity, capillary permeability, and interalveolar septal diameter were quantified. These parameters were examined simultaneously. The preparation was stable for 120 min. Under hyperthermia, there was increased permeability with a relative fluorescence of 0.39 +/- 0.19 compared to 0.16 +/- 0.13 in the control group, and interalveolar septal diameters were wider (30.7 +/- 2.9 microm) than in control animals (17.3 +/- 3 microm). Under hypothermia and hypovolemia, the erythrocyte velocity was lower (0.351 +/- 0.063 and 0.378 +/- 0.044 mm/s) than in control groups (0.527 +/- 0.07 mm/s). Under hypoventilation, we observed a higher amount of leukocyte sticking (3.1 +/- 1.1 vs 1.8 +/- 0.8 cells/alveolus) and increased permeability (relative fluorescence 1.03 +/- 0.37 vs 0.16 +/- 0.13 in the control group). The model of rat lung exposure for direct examination of microvascular structures in living animals was valuable because it remained stable for 2 h under baseline conditions and demonstrated distinct changes in microcirculatory parameters following specific pathophysiological interventions.