To know how blood will get saturated with oxygen, You should understand about the air sacs in the lungs named alveoli. There are an incredible number of these microscopic air sacs during the lungs. They Trade oxygen and carbon dioxide molecules to-and-within the bloodstream. It appears they use two tanks https://allhealthmarket.com/product/medical-supplies/portable-oxygen-concentrator-generator/oxygen-concentrator-machine-camping-use-oxygenator-driving-oxygen-bar-with-24-hours-battery-lasting-oxygen/