<P> The use of oxygen as treatment began in 1868 . The use of hyperbaric oxygen in rats following poisoning was studied by Haldane in 1895 while its use in humans began in the 1960s . </P> <P> Carbon monoxide is produced naturally by the body as a byproduct of converting protoporphyrin into bilirubin . This carbon monoxide also combines with hemoglobin to make carboxyhemoglobin, but not at toxic levels . </P> <P> Small amounts of CO are beneficial and enzymes exist that produce it at times of oxidative stress . Drugs are being developed to introduce small amounts of CO during certain kinds of surgery, these drugs are called carbon monoxide - releasing molecules . </P>

How does inhaling carbon monoxide decreased oxygen level in blood