Veins in right leg swell and then other times really small. had 3 stents in lad. also have some type of autonomic disfunction. bp dropping. causes?

Normal veins: Veins are thin walled, low pressure structures that fill and become engorged or empty and lie flat depending on gravity and position with state of hydration also contributing. When you sit with your legs down, they'll swell. When you sit or lie and elevate them, they'll empty. Arterial disease (as in stenting of your lad) has nothing to do with your venous system.