Tbr cbt 7 #103

[zzomg]

OK, this one's driving me nuts.

103. The RQ is measured during steady states metabolism, but the respiratory exchange ratio (RER) is the term for the same measurement made during nonsteady states. If a person were to hyperventilate, their RER would:

A. not change.
B. decrease.
C. increase.
C is the best answer. During hyperventilation, a person expires more CO2 than during normal ventilation. This means the CO2 value (the numerator of the RQ and RER) is higher, so the RER increases during hyperventilation. The best answer is C.
D. first decrease and then begin to increase.

So, the passage defines RQ as: "the ratio of the steady-state volume of CO2 produced to the volume of O2 consumed per unit of time", and that it could be measured "by collecting breath samples, or for a single organ by measuring arteriovenous differences in O2 and CO2 across the organ". My understanding of hyperventilation was that it increased the rate of breathing, which does increase CO2 output, but also increases a proportional amount of O2 intake and decreases CO2 in the blood, leading to a smaller CO2/O2 ratio in the blood (respiratory alkalosis). Shouldn't that result in a decrease in RER?

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[ljc]

Edit: On second thought..

 

[Remxed]

http://en.wikipedia.org/wiki/Respiratory_exchange_ratio

Wikipedia explains that RQ of greater than 1 is possible during exercise, when CO2 production by the muscles is greater than the O2 being inhaled. I believe you can apply the same thinking to hyperventilation.

 

[ljc]

http://en.wikipedia.org/wiki/Respiratory_exchange_ratio

Wikipedia explains that RQ of greater than 1 is possible during exercise, when CO2 production by the muscles is greater than the O2 being inhaled. I believe you can apply the same thinking to hyperventilation.

But the reason CO2 production increases during exercise is that the muscles metabolize more O2. When hyperventilating, the muscles do not need more energy/O2 and thus do not metabolize into more CO2. So I don't feel like this is the answer..

OK, this one's driving me nuts.

My understanding of hyperventilation was that it increased the rate of breathing, which does increase CO2 output, but also increases a proportional amount of O2 intake and decreases CO2 in the blood, leading to a smaller CO2/O2 ratio in the blood (respiratory alkalosis). Shouldn't that result in a decrease in RER?

Perhaps the key is in the method of measurement? You are correct in saying that CO2 levels in the blood decrease during hyperventilation - however, this CO2 must go somewhere. In this case, you breathe it out, which is how they state RER is measured. So when you are blowing out the CO2, your blood CO2 is dropping, however examination of exhaled air would show increased levels of CO2.

Although I feel like the RATE at which you breath out CO2 would be the thing to rise, not the CO2 concentration of an individual breath (which is how they state that they measure RER). Moral of the story: this problem sucks.