 Carbon monoxide has a higher diffusion coefficient compared to oxygen and the only enzyme in the human body that produces carbon monoxide is heme <unk> which is located in all cells and breaks down heme . Under normal conditions carbon monoxide levels in the plasma are approximately 0 mmHg because it has a higher diffusion coefficient and the body easily gets rid of any CO made . When CO is not ventilated it binds to hemoglobin , which is the principal oxygen @-@ carrying compound in blood ; this produces a compound known as carboxyhemoglobin . The traditional belief is that carbon monoxide toxicity arises from the formation of carboxyhemoglobin , which decreases the oxygen @-@ carrying capacity of the blood and inhibits the transport , delivery , and utilization of oxygen by the body . The affinity between hemoglobin and carbon monoxide is approximately 230 times stronger than the affinity between hemoglobin and oxygen so hemoglobin binds to carbon monoxide in preference to oxygen . 
