Expert: John Locke - 8/27/2010

Question
If CO2 is produced by living/decaying carbon and exhaled by living mammals and the moisture and grasses produce sugars that can be ingested by the mammals (the horse)and these sugars can revert back to CO2 by respiration and breathing can this CO2 accumulation become toxic?  Produce acidosis?  Inflammation? Increase in IL-1b/COX2/ADAMTS-4 along with MMP2&9/14?

Please advise,  I'm not a student asking u to do my homework ,I'm a retired Blacksmith/Farrier with a need to know.  TY

Answer
Thanks for using AllExperts. Your question gets at some basic biochemical processes in the body that convert the sugars found in food into energy, with waste products being produced that need to be eliminated. As a general principle, if you are unable to get rid of a waste product, it will accumulate within the body; depending on the particular process, there may be alternate pathways to handle this waste product or it may simply build up.

The digestion of sugars, proteins, and fats produces energy in the form of a molecule called adenosine triphosphate (ATP). ATP carries high-energy chemical bonds that can be broken to release energy to supply critical life processes. The major by-product of this reaction is carbon dioxide. Carbon dioxide is carried in the bloodstream from the tissues  to the lungs, where it is excreted. Carbon dioxide can be transported in three forms:

1. Directly as a dissolved gas in the bloodstream; this accounts for about 5-10% of carbon dioxide in the bloodstream
2. Carbon dioxide is combined with water to create bicarbonate (H2CO3); this represents about 75% of the total. Bicarbonate splits into a free hydrogen ion, H+, and an ion, HCO3.
3. Carbon dioxide may be bound to the hemoglobin in red blood cells; this is about 5-10%

Upon reaching the lungs, forms (2) and (3) are converted back to carbon dioxide, which crosses from the blood into the small airways of the lungs, from which it is exhaled. If the lungs are unable to handle the amount of carbon dioxide produced by the body, or if blood cannot be delivered to the lungs quickly enough, then carbon dioxide will begin to accumulate in the bloodstream.

As you noted, the buildup of carbon dioxide does produce acidosis. This is a tendency of the pH of the blood to decrease because of an increase in hydrogen ions (H+); in other words, the blood becomes more acidic, which produces a whole host of problems if the process goes on long enough. The buildup of CO2 will eventually become toxic to the brain, also, if it is allowed to proceed long enough. Some of the symptoms of carbon dioxide poisoning are due to this brain toxicity: respiratory disturbances, headache, confusion, and irritability.

Finally, as you noted also, carbon dioxide is pro-inflammatory. It promotes the production of inflammatory compounds such as those you listed. A study that looked at the effect of carbon dioxide on lung inflammation can be found here:
http://ajplung.physiology.org/cgi/content/full/296/4/L657

Ultimately, this study found that exposure to carbon dioxide above a certain threshold greatly increased the production of inflammatory chemicals in human skin cells. This is a relatively new view of carbon dioxide, which has traditionally been thought to not have any effect on promoting inflammation, only its toxic effect on the brain in large quantities. I hope this answers your question. I will be happy to help with future questions.