A stroke occurs when a blood clot blocks a blood vessel or artery, or when a blood vessel breaks and interrupts blood flow to an and bleeding occurs into an area of the brain. Every stroke is different.
ETA Chlorophyll works on the Liver and probably works a little. No it really doesn't, you are not a plant. Tea will oxygenate the blood. No it won't Also don't do as someone else said and drink liquid oxygen, that's really not a good idea.
Any significant increase in total oxygen levels in the blood volume will likely need an increase in red blood cells. Other answers have provided ways to accomplish that. However, it should be noted excess can be detrimental to your health and it only gives you an edge if you're a seasoned, well-trained athlete.