Science Buddies: "Ask an Expert"

Hi Could you please guide me on how to do a biology project on effect of exercise on carbon di oxide production in humans.I do not have acess to hi tech physiology labs -so it should be supported by school lab/home lab only
Thanx

I've been trying to find a way to measure the carbon dioxide production without lab equipment. Having a human do this gets more difficult as humans aren't small, and rooms they are breathing in are big.

There may be some way to breathe out of a tube (snorkel of sorts) into water, which will raise the dissolved CO2 concentration of the water, but the total exhaled volume won't be known.

Obviously, with the equipment in an exercise physiology lab this isn't that difficult to do. You just exhale through a snorkel, an instrument measures the CO2 concentration, and a separate flow meter measures the flow of exhaled gas (the minute ventilation, to use the medical term.) From this, CO2 production can be easily calculated.

It's the fact that it must be done at home / school lab that's the difficult part.

Thanx.but i thought there may be an indirect way -a change in pH indicator or something.I hope somebody can help me-i have to submit a proposal in class soon

bio student,

This sounds an awful lot like a lab you were assigned . . . not so much like a science fair project. But science is science, so here goes.

The College Board's AP Biology course has a lab very similiar to what you are describing, using chemical reactions to measure the respiration of peas. It is commonly called AP Bio Lab 5: Respiration. Take a look at the procedures for this lab and think about how you can adapt them to your specific needs.

Interesting procedure in that AP Biology Lab. You would have to scale up the experiment to deal with the production of 300-500ml PER MINUTE of CO2, which would be produced during strenous exercise. I would also have concerns with inhaling KOH, which I can't imagine is terribly good to your lungs, so one way valving will be important (you'll need 2). Then you need measured amounts of O2 added to the circuit.

BTW, this is a wonderful description of an anesthesia circuit (although we do it with dry soda lime instead of in solution), and is, in fact, how we scrub CO2 from our semi-closed systems.

I didn't even consider this complicated an apparatus when I answered.



Of course, this type of circuit doesn't measure CO2 that is absorbed. You can easily measure the O2 that is consumed by closing down the popoff valve and lowering O2 intake until it matches consumption (the bag doesn't empty.)

The ratio of O2 consumed / CO2 produced isn't constant in humans. It depends on which fuel is being utilized (fats, carbs) amongst other factors.

Basically, a good question for the Anesthesiology boards. A little advanced for a science fair experiment. To really get meaningful results, I think you really do need the equipment in an exercise lab.