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　　Most carbon dioxide that travels from your musclesto your lungs for exhalation does so not as CO2proper, but as part of bicarbonate:

　　HCO?—Bicarbonate's vital to maintaining your bloodpH, and it also aids in digestion.

　　But it turns out bicarbonate also tweaks the activityof rod cells in your retina.

　　In everyday vision, photons flood your rod cells, setting off a chemical cascade that eventuallytranslates into an electrical message about what you saw.

　　But in lab tests, higher than normal levels of bicarbonate allow the rods to recover from thatphoton response 30 percent faster.

　　A 30 percent higher refresh rate, essentially—meaning your ability to detect movement wouldimprove.

　　The downside?

　　This rapid reset of the rod cells means they're less sensitive to light.

　　"If you're sitting in darkness and you turned on a steady light, it might now take brighter lightfor you to say,I can see that."

　　Study author Clint Makino, of the Massachusetts Eye and Ear Infirmary and Harvard MedSchool.

　　"Or if the light's already on, it would take a larger increment in intensity for you to say,Ok, itlooks brighter now."

　　The results are in the Journal of Biological Chemistry.

　　Makino says heavy exercise—which causes a boost in CO2—might even alter the body'sbicarbonate enough to trigger a measurable effect on the eye.

　　"I don't think it's known whether your vision changes under conditions of vigorous exercise.

　　So that'll be an interesting question for the experimental psychologists and thepsychophysicists."

　　And if you're eyeing your club soda as a shortcut to CO2?

　　He says most of those bubbles never make it past the belch.