If ischemia is prolonged then when blood flow is restored the microcirculation may be permanently occluded resulting in tissue necrosis and loss.
The basis of the no reflow phenomenum is the end stage of swelling, microthrombosis, increased vasomotor tone and accumulation of leucocytes. Leucocyte trapping may result from ischemia-induced leucocyte deformability as well as swelling of the endothelial cells and neutrophils. In addition, marked accumulation of interstitial fluid will result in pressure on the microcirculation that helps occlude the capilleries. Accumulation of leucocytes appears to play a central role, as depletion of leucocytes, prevention of leucocyte adherence and migration results in a decreased prevalence of the no reflow phenomeunm. Similarly the no reflow phenomenum does not occur in neutropenic animals.