Evaluate lungs ability to deliver oxygen to the blood. Arterial blood is leaving the heart after traveling through the pulmonary system so arterial blood will tell us how well the lungs are working 2. Venous blood has been exposed to the cellular level where oxygen has been consumed and carbon dioxide has been dumped for delivery back to the heart. Oxygen is a vital substance for cellular metabolism and must be delivered to all cells to sustain life. Lack of oxygen will result in cell death and will eventually result in death of the organism.
Carbon dioxide is a normal waste product of cellular metabolism.
Build up of carbon dioxide in the cell or in the blood is toxic to the body. Blood is coming to the right heart via venous system. Its represented in blue because the oxygen level is this blood is lower than arterial. The oxygen has been used by the cells as blood circulated through the capillaries. Once the venous blood reaches the right heart it exits into the pulmonary artery then through the pulmonary capillaries where it picks up oxygen and releases carbon dioxide via the lungs.