When a person stops breathing--be it from an obstruction in the airway or something like acute lung failure--the clock is decidedly ticking. Deprived of oxygen for long enough, a person can go into cardiac arrest. Brain damage sets in. Without oxygen, things go south pretty quickly. So a team of researchers at Boston Children’s hospital has designed a kind of injectable oxygen that can be quickly introduced to a person’s bloodstream to oxygenate the blood, buying paramedics or other medical personnel perhaps as much as half an hour to remedy an oxygen flow problem.