There is a simplier way
You need a unit ability, damage bonus (item ability), make it 100 levels, each level with 1 damage increment
You need a trigger that activates Trigger2
Then
Trigger2(disabled at start)
Every 0.5 seconds of the game
local int life = 0
local real lifemissing = 0
set lifemissing = unit maxlife - unit currentlife
life = converttoINT(lifemissing/4)
if (level of item damage bonus <1)
add item damage bonus to unit
endif
set damage bonus of unit to life
Hope you get it, sorry about no trigger tags =(