Critical closing pressure, local perfusion pressure, and the failing skin flap

A simple apparatus was devised to perfuse the rat groin flap to study the relationship between perfusion pressure and flow. Results demonstrate that a relatively high intraarterial pressure must be applied to this skin flap before blood flow will commence. Results suggest that this critical closing phenomenon is the result of surface tension, blood rheology, venous pressure, tissue pressure, and vascular smooth muscle tone. Correlating the experiments of Milton and Landis reveals that, beyond a certain distance, local perfusion pressure in a skin flap gradually decreases with increasing distance from the flap base. These observations suggest that the perfusion boundary in a skin flap forms at the point where perfusion pressure has fallen to the level of the critical closing pressure. Methods of increasing survival length of a flap by decreasing critical closing pressure are discussed. The effects of edema and pressure dressings on flap and replant survival are examined in terms of the closing pressure concept.