High altitude training and mountain climbing would be examples where the body encounters as a result of lower than normal partial pressures of oxygen. Conditions where circulation is compromised resulting in poor blood flow, as is seen with heart disease, would be an example of . Caused by a reduced number of red blood cells, is characterized by insufficient oxygen in the blood. Oftentimes, poisons might interfere with the body's ability to utilize or transport oxygen, thus causing . Regardless of the type of hypoxia, , or bluing of the skin, is a primary sign of oxygen-deficient tissues.