When organs are not receiving enough oxygen the breathing rate is increased in an attempt to get more oxygen. (mysweetpuppy.net)
They then had their metabolism measured via a highly reliable method called indirect caliometry (essentially a gas mask that measures exact amounts of oxygen you breathe in and out). (instantknockout.com)
The heart and bloodstream are responsible for taking oxygen breathed in through the lungs and circulating it around throughout the body. (whfoods.com)