Every 30 points of bonus health gives Vladimir 1 ability power and every 1 point of ability power gives Vladimir 1.6 bonus health (does not stack with itself).
From my experiences, it will always serve vlad better to build pure ability power, as when building health, you get .25 of your health from items as ability power, where you will get double your ability power from items back as health. In a typical vlad game building ability power, I usually get around 700 ability power, which gives me 1400 extra health, this helps me end most games close to 4000 health. At the same time,the ability power gives transfusion a much better boost, meaning more self healing.
A great passive that means the item Rylai's Crystal Scepter gives massive boosts to Vladimir
Basically the single reason Vladimir will always have brick loads of health
tl;dr, ap wins
Basically the single reason Vladimir will always have brick loads of health