ABSTRACT
Once an embolus lodges in an artery, or once a thrombus occludes a previously diseased artery, the vasculature distal to the obstruction goes into spasm. Clot then forms proximal to the site of the obstruction, back to the point of adequate collateralization. The distal spasm lasts for approximately 8 hours and then subsides. At this point clot forms in the arterial system distal to the site of obstruction and propagates downward, obstructing any residual collateral flow, resulting in worsening of the ischemia. As a result the skin usually becomes patchy, blue, and mottled.
