Background Information:

The respiratory quotient (also know as RQ, the respiratory exchange ratio, RER, and most commonly, R) is the ratio of volume of carbon dioxide produced to volume of oxygen consumed. This is important because it provides a pretty good indication of the substrates being utilized for energy production!

• When palmitic acid (a fatty acid) is completely oxidized, the following equation is valid:

C₁₆H₃₂O₂ + 23 O₂ = 16 CO₂ + 16 H₂O

23 O₂ molecules are consumed while 16 CO₂ molecules are produced. 16/23 = .7

• When glucose is completely oxidized, the following equation is valid:

C₆H₁₂O₆ + 6 O₂ = 6 CO₂ + 6 H₂O

6 O₂ molecules are consumed while 6 CO₂ molecules are produced. 6/6 = 1.0

So, when R is near .7, then the body is using mostly fat for energy production. If R is near 1.0, then the body is using mostly carbohydrates for energy production. If R is above 1.0, then carbon dioxide is being produced by other means, usually from the buffering of lactic acid. This indicates that the person is working very hard, or that they are hyperventilating. Typically, R will be about .8 at rest. Although this is near the ‘halfway point’ (.85), it still indicates a reliance on fats for energy production at rest. RQ is the respiratory quotient and RQ reflects what is going on at the cell. RER is the Respiratory Exchange Ratio and reflects fuel utilization in the entire body.

Procedures:

You will be in fairly large groups (5-6 per group) for this lab. Using the cardboard mouthpiece, a noseclip, some tubing, a Douglas bag and a Daniels valve system, expired air will be collected and analyzed. Expired air will be collected under 3 conditions: rest, exercising at a light intensity, and exercising at a moderate to hard intensity. In all cases, the subject should be wearing the headgear and mouthpiece before the start of the condition. Be sure that you make a good seal around the mouthpiece with your lips. During expired air collection, the subject must wear the noseclips, and the Douglas bag must be hooked up to the end of the hose. Be sure that the hose is connected to the expired air side of the Daniels valve, and make sure that the bag is empty of air prior to beginning any gas collection.

Resting Air Collection:

The subject should lie quietly on a table or a bench for 5 minutes. At the end of the 5 minutes, collect expired air for 2 full minutes.

Light Exercise Air Collection:

The subject should lightly exercise on a cycle ergometer or a treadmill for 4 minutes. At the end of the 4 minutes, collect expired air for 2 full minutes. It is important to try and maintain a stable workload during this time.

Moderate to Hard Exercise Air Collection:

The subject should exercise at a moderate to hard intensity on a cycle ergometer or a treadmill for 4 minutes. At the end of the 4 minutes, collect expired air for 2 full minutes. It is important to try and maintain a stable workload during this time.

Following expired air collection, the Douglas bag should be attached to the analyzing system, and allowed to equilibrate for 2 full minutes. At the end of the 2 minutes, read the red LED panels indicating F_EO₂ and F_ECO₂. Record those values here:

Now, you have to calculate R for each condition:

R = VCO₂/VO₂

The above equation is for volume and your recording from the readout display is a percent. So, use the equation below to change the percent recordings into volumes.

R = (F_ECO₂ – 0.0003)/[(1 – F_ECO₂ – F_EO₂)(0.2648) – F_EO₂]

I realize that this formula looks really strange. If you want to know where it is derived see Appendix A of this lab posted on the website, or at the end of your Exercise Physiology Text. If not, just trust that these formulas are used to calculate VCO₂ and VO₂. We are just cutting out some steps that are similar to each (including measuring the volume of expired air).

If requested by your lab instructor, enter all of your results into the computer. These data will be posted on the website.

Results:

1. Include all data from your subject and enter the data on the computer if requested by your lab instructor. You will need to include your groups data and if requested, the data posted on the web site.

2. Make a Bar graph that represents fuel utilization (R values) as a function of exercise intensity. Use either your own groups data or calculate an average from the entire class.

Discussion:

1. Are the results from the lab regarding R values what you would predict? Why or why not.
2. Describe the substrate(s) used during each workload. See Page 151.
3. What happens to substrate choice as intensity of exercise increases?
4. Could you ever have an R value greater than 1.0? Explain why or why not.

See APPENDIX D in text book (page 648) for exact VO₂ and VCO₂ Calculations