Alveoli
From Memory Alpha, the free Star Trek reference
The alveoli are small sacs located in the lungs, where gas exchange occurs between the blood and the air.
In 2372, while undergoing hyper-evolution, Tom Paris's alveoli mutated to the point that they stopped processing oxygen. (VOY: "Threshold")
In 2374, B'Elanna Torres's alveoli briefly stopped processing oxygen after she was mutated by covert Srivani medical experiments. (VOY: "Scientific Method")
