What is the normal respiratory quotient used in the alveolar gas equation for normal pulmonary function?

What is the normal respiratory quotient used in the alveolar gas equation for normal pulmonary function?

• A. 0.6
• B. 0.8
• C. 1.0
• D. 1.2

Answer: (B)

In the alveolar gas equation, the respiratory quotient reflects the balance of substrates the body is burning and is the ratio of CO2 produced to O2 consumed by tissues at rest. For a typical mixed diet, this value is about 0.8, which is why it’s used for normal pulmonary function. The different substrates have characteristic quotients: fats around 0.7, carbohydrates about 1.0, and proteins near 0.8, so a mixed diet lands near 0.8. Using 0.8 links the amount of CO2 in the blood to the expected alveolar oxygen pressure, via the equation that relates PaCO2 to PAO2. If the diet were mainly carbohydrate-dominated, the RQ would rise toward 1.0; if mainly fat-dominated, it would fall toward 0.7. Values like 1.2 aren’t typical for normal physiology and aren’t used in the standard calculation.

In the alveolar gas equation, the respiratory quotient reflects the balance of substrates the body is burning and is the ratio of CO2 produced to O2 consumed by tissues at rest. For a typical mixed diet, this value is about 0.8, which is why it’s used for normal pulmonary function. The different substrates have characteristic quotients: fats around 0.7, carbohydrates about 1.0, and proteins near 0.8, so a mixed diet lands near 0.8. Using 0.8 links the amount of CO2 in the blood to the expected alveolar oxygen pressure, via the equation that relates PaCO2 to PAO2. If the diet were mainly carbohydrate-dominated, the RQ would rise toward 1.0; if mainly fat-dominated, it would fall toward 0.7. Values like 1.2 aren’t typical for normal physiology and aren’t used in the standard calculation.