Pulse generated during the systole of ventricle due to elasticity of aorta. Takayasu disease is the type of granulomatous vasculitis with massive fibrosis of intima and narrowing of vessels so, loss of elasticity restrict to generate pressure wave in aorta which goes to arteries. And it occur in upper extremities due to involvement of major branch of aorta that is left coronary, left subclavian and brachiocephalic which supply blood to upper extremities.
First of all etiology is not known (theoretically - autoimmune), then it mostly effects the branches of ascending aorta, and as v go up there is decrement in pressure. Don't know for sure (Just my thoughts)