> I don't understand the difference in systolic bp in each arm.
imagine a hose coming out of a spigot. The hose branches in a Y into two hoses. If one of those two hoses has an obstruction in it, then the pressure coming out of it will be less than from the other, unobstructed hose.
The obstruction can be congenital, or from an atherosclerosis.
oh am so sorry your going through this with your son i know it breaks your heart, and for him to e so young . i would be asking his cardio dr this , i know my husband had two different bp in arms and it was not good news so pl;z have him checked and i will say a prayer for ya.