It is a good question. If you look at the physiology of injury again inflammation and vasodilatation go hand in hand. Various substances such as the amines (histamine, seratonin etc.) and prostaglandins, cause vasodiltation as part of the inflammation process. However I feel there is a misperception about blood flow. Dilating blood vessels does not increase blood flow, it increases blood volume. The rate of blood flow is important in good body function and if a blood vessel dilates, the rate will slow, just as a river will flow slower when it becomes wider. If the rate of blood flow is maintained by increase heart function then this is OK, but if not then there will be a slowing of blood flow rate.
At the same time blood pressure in the vessels can only increase if 1) The heart works harder to counter the dilated blood vessels and initial drop in pressure, or 2) if there is a blockage at the end of the vessel causin a backlog of blood. The reason for vasodilation in the injured area is to allow better permeability of fluids in and out othe the blood vessels, but also to allow a slowing of the rate of bloo so the necessary cells have an oppertunity to adhere to the damaged blood vessels or penetrate the blood vessels and adhere to the injured tissues. This is done electrically, as the injured area will be initially positively charged (internal cell fluid leakage), and all red and white blood cells and platelets are negetively charged. It is not a chemical attraction.
So again my question is: if vasodilatation is normal in injury (and apparently only lasts 10 to 15 mins), as a part of the inflammatory process then how can we be doing the body any favours by causing vasoconstriction? Logic indicates that this would reduce the inflammatory process as the necessary mast cells, red blood cells and other chemicals cannot get there in enough quantities to do what they are meant to do. It seems that we have been brainwashed into believing that if we do not treat with ice we will continue swelling or bleed to death, yet the blood vessels are immediately repairing themselves and vasodilatation only last 10 to 15 mins, so the body has the ability to control these factors, but it needs the process to continue to be able to do a sufficient job.
Again, are we helping the longer-term repair by icing or are we hindering it? Should we go against the body's natural practice and treat symptoms or should we allow the body to continue its natural methods and assist where we can?
Pete