Caption: Carbon Monoxide in Smokers

It is interesting to note that CO is also generated by burning tobacco, and it enters the blood of smokers. While CO binds to hemoglobin more tenaciously than oxygen, it slowly leaves the blood and re-enters alveoli and is exhaled. Hand-held devices that measure the concentration of exhaled CO provide a simple and very useful way of monitoring the success of people who are trying to quit smoking (or who claim to be trying).