Microvascular changes due to repeated local pressure-induced ischemia: intravital microscopic study on hamster cheek pouch.

: Pressure ulcer and tracheal injury occurring after endotracheal intubation are clinical examples of pressure-induced tissue damage where magnitude and duration of the applied pressure are of major importance. The objective of this study was to investigate the efflux of macromolecules caused by repeated short-time ischemia induced by a pressure of 60mmHg, which causes circulatory standstill. Pressure was applied to the hamster cheek pouch and the efflux of the macromolecules of the microvasculature was evaluated by using the fluorescein isothiocyanate (FITC) dextran dye and intravital microscopy. The pressure was applied for either 1 or 5 min and repeated 8 times with a 10min restitution period in between. The repeated 1min pressure caused almost no change in microvascular efflux of FITC-dextran while 5min repeated pressure did. The gross mechanical impact on the tissue seems to be equal in the 1 and 5min exposure and thus cannot explain the difference in the developed permeability. Ischemia of such short time as 1 and 5min does not alter the energy state of the tissue significantly. The reactive hyperemia and the mediating vasoactive amines can differ markedly after 1 and 5min ischemia and can thus contribute to the permeability alteration. However, the role of vasoactive amines is unclear and further experiments are needed to determine their role.