Kidney cancers can be cystic, and differentiating between a single benign cyst of the kidney and a kidney cancer can occasionally be a problem. When many cysts are present, as in polycystic renal disease, the distinction is easier. Cysts may also be caused by some parasitic infections.
It will actually collect the oxygen in the ambient air (~21%) and convert it into a concentration of around 85-94%. One of the main reasons you would want a concentrator over a tank and regulator would be when you are using a lot of oxygen for taking ozone saunas or ozonating oils.
Humans exhale oxygen, carbon dioxide and nitrogen. Humans inhale these same gases, though in different proportions to exhalation; that is, oxygen is exchanged for carbon dioxide during breathing. When inhaling, humans take in approximately 21 percent oxygen, 0.04 percent carbon dioxide and 79 percent nitrogen. On exhalation, humans give off approximately 16 percent oxygen, 4 percent carbon dioxide and 79 percent nitrogen, according to the BBC; only the amount of nitrogen remains constant in the exchange. Exhaled air also contains water vapor.