Hypoventilation would tend to what effect on respiratory quotient (RQ) measurements?

• A. Increase RQ
• B. Reduce RQ measurements
• C. No effect on RQ
• D. Variable effect on RQ

Answer: (B)

Respiratory quotient is the ratio of CO2 produced to O2 consumed, derived from the expired air during gas exchange. When ventilation is reduced (hypoventilation), CO2 is not expelled as efficiently, so the measured amount of CO2 in the expired gas (VCO2) tends to be lower relative to actual production. O2 uptake (VO2) is affected too, but the key point is the CO2 output is underestimated due to poor alveolar ventilation. That underestimation pulls the VCO2/VO2 ratio downward, making the measured RQ appear reduced. It’s an artifact of the gas-exchange measurement rather than a true shift in substrate oxidation. Therefore, hypoventilation would tend to lower the respiratory quotient measurements.