How is the ventilation/perfusion ratio (V/Q ratio) calculated?

The ventilation/perfusion ratio, commonly referred to as the V/Q ratio, is a measure used to assess the efficiency and adequacy of gas exchange in the lungs. To calculate the V/Q ratio, one takes the amount of air that reaches the alveoli (which is termed alveolar ventilation) and divides it by the amount of blood that is being perfused through the lungs (which corresponds to cardiac output).

This ratio provides critical insights into the respiratory efficiency—essentially showing how well oxygen is being delivered to the blood versus how effectively carbon dioxide is being removed. In a healthy individual, a balanced V/Q ratio ensures optimal gas exchange; therefore, understanding how to compute this ratio is crucial for evaluating pulmonary function in various clinical scenarios.

The other options do not accurately represent the established calculation of the V/Q ratio. They either misrepresent the relationship between air and blood flow or do not take the correct physiological parameters into account, which could lead to misunderstandings regarding respiratory pathology or the management of critically ill patients.