Changes in the local blood and lymph microcirculation in response to direct mechanical trauma applied to leg: In vivo study in an animal model

Background. The aim of this study was to investigate changes in the blood m icrocirculation of skin, subcutaneous tissue, and striated muscle, and the venous and lymphatic outflow from hind limb, after a standardized mechanica l trauma. Methods. Trauma, defined as 50% of the minimal energy needed for tibia frac ture (3.7 J/g), was applied to the leg of hairless mice. Intravenously inje cted fluorescein isothiocyanate-dextran 150 kDa and Rhodamine-6G were used for intravital fluorescence microscopy of blood vessels. Lymphatics were st ained with fluorescein isothiocyanate-dextran injected into the footpad. A computer-assisted analysis system allowed measurement of the functional cap illary density (FCD), vessel diameters, velocity of blood flow, and edema v alue expressed as extravasation index (EV). The percentage of slowly rollin g and sticking leukocytes in postcapillary venules was estimated. Results. At the site of injury, trauma resulted in significant reduction of FCD in skin, subcutaneous tissue, and striated muscle. There were no signi ficant differences in the vessel diameter (skin subcutaneous and muscle art erioles and venules, and superficial saphenous artery and vein) or velocity of blood flow (subcutaneous tissue and muscle venules). The EV increased s ignificantly in muscle venules and was higher in muscles, subcutaneous tiss ue, and superficial saphenous veins than in controls (nonsignificantly). An increased percentage of slowly rolling and sticking leukocytes was noted i n the superficial saphenous vein at the site of injury and proximal to it. The lymphatics remained patent, with faster visualization and increased sum marized cross-sectional areas in traumatized extremities. Conclusion. Early changes occurring in soft tissues in response to mechanic al injury were characterized by reduction in FCD of skin and muscles, and l ess in subcutis; increased EV, reflecting leakage of macromolecules; increa sed percentage of slowly rolling and sticking leukocytes; maintenance of ly mphatic vessel continuity; and increased lymph formation and flow rate.