Chapter 8, Problem 1RQ

Overall, the normal $\text{V/Q}$ ratio is about

0.2

0.4

0.6

0.8

Summary Introduction

Introduction:

The ventilation-perfusion $\frac{V}{Q}$ ratio represents the ratio of alveolar ventilation to pulmonary capillary blood flow. It is the ratio of receiving of air in the alveoli to the reaching of blood in the alveoli per minute. This ratio varies within the region of the lungs based on the range of ventilation and blood flow to each part.

Answer to Problem 1RQ

Correct answer:

0.8

Explanation of Solution

Justification/ Explanation for the correct answer:

Option (d) is given that the normal $\frac{V}{Q}$ ratio is about 0.8, the normal rate of alveolar ventilation (V) is 4 liters/minute, while the normal rate of blood flow to pulmonary capillary (Q) is 5 liters/minute. So, the normal $\frac{V}{Q}$ ratio is $\frac{4}{5}$, which is 0.8. Hence, option (d) is correct.

Explanation for the incorrect answers:

Option (a) is given that the normal $\frac{V}{Q}$ ratio is about 0.2, the normal rate of alveolar ventilation is 4 liters/minute, while the normal rate of blood flow to pulmonary capillary is 5 liters/minute, so the normal V/Q ratio is $\frac{4}{5}$, that is 0.8, $0.2\ne 0.8$. So, it is an incorrect option.

Option (b) is given that the normal $\frac{V}{Q}$ ratio is about 0.4, the normal rate of alveolar ventilation is 4 liters/minute, while the normal rate of blood flow to pulmonary capillary is 5 liters/minute, so the normal V/Q ratio is $\frac{4}{5}$, that is 0.8, $0.4\ne 0.8$. So, it is an incorrect option.

Option (c) is given that the normal $\frac{V}{Q}$ ratio is about 0.6, the normal rate of alveolar ventilation is 4 liters/minute, while the normal rate of blood flow to pulmonary capillary is 5 liters/minute, so the normal V/Q ratio is $\frac{4}{5}$, that is 0.8, $0.6\ne 0.8$. So, it is an incorrect option.

Hence, options (a), (b), and (c) are incorrect.

Conclusion

The normal alveolar ventilation rate is about 4 litres/minute and the normal perfusion rate is about 5 liters/minute to perfusion ratio. Thus, the normal ventilation-perfusion $\frac{V}{Q}$ ratio is about 0.8.