In the schematic of double circulation, the Vena Cava collects deoxygenated blood from the body parts and delivers it to the right atrium (auricle). The partial pressure of carbon dioxide ($pCO_2$) in deoxygenated blood is 45 mm Hg and the partial pressure of oxygen ($pO_2$) is 40 mm Hg . The Pulmonary Artery carries deoxygenated blood (pO2 = 40 mm Hg), not 90 mm Hg. The Pulmonary Vein carries oxygenated (pure) blood, not impure blood .