What effect does a decrease in CO2 have on respiratory rate?

• A. Increases respiratory rate
• B. Decreases respiratory rate
• C. No effect on respiratory rate
• D. Irregular respiratory rate

Answer: (B)

A decrease in carbon dioxide (CO2) levels in the blood, a condition referred to as hypocapnia, leads to a decrease in respiratory rate. This occurs because the body regulates breathing primarily through the levels of CO2 rather than oxygen.

When CO2 levels fall, it results in a state of respiratory alkalosis due to an increase in blood pH. The chemoreceptors in the brain and carotid bodies detect these changes and signal the body to decrease the rate of breathing. This is a compensatory mechanism aimed at restoring CO2 levels to their normal range. Therefore, with lower levels of CO2, the drive to breathe more frequently diminishes, ultimately resulting in a decrease in respiratory rate.

Understanding this physiological response is crucial, as it highlights the importance of CO2 not only as a waste product of metabolism but also as a key regulator of ventilation in the body.