Invigorate is an added regen effect to chakra..
The regen is 10HP/tick for 8 ticks(24 seconds) for a total gain of 80HP
Each additional merit upgrade to it does the same thing.. an extra 24 seconds.. so 80HP more with each upgrade. Just got the first level of it on my monk and love it so far.. I think I may just max out formless strikes and this... the others are worth looking at but nothing great.. Mantra isnt ideal for me because it wears off in 3 minutes.. gotta cure the additional HP right away or its not gonna help at all.. anyway yeah invigorate