At what level of PO2 do peripheral chemoreceptors respond to initiate a reaction?

• A. 70 mmHg
• B. 60 mmHg
• C. 50 mmHg
• D. 80 mmHg

Answer: (B)

Peripheral chemoreceptors play a crucial role in regulating respiratory drive by responding to changes in the gas concentrations in the blood, primarily oxygen (O2) and carbon dioxide (CO2) levels. These chemoreceptors are located in the carotid and aortic bodies and are particularly sensitive to decreases in arterial oxygen tension (PO2).

The main threshold at which peripheral chemoreceptors initiate a strong ventilatory drive occurs around 60 mmHg of PO2. Below this level, there is a significant increase in the firing rate of these chemoreceptors, leading to deeper and more frequent breaths to improve oxygen uptake. This response is a critical compensatory mechanism during hypoxemia, where maintaining adequate oxygen delivery to tissues becomes essential.

In contrast, at PO2 levels above 60 mmHg, peripheral chemoreceptors are less activated and do not trigger significant respiratory changes. Therefore, when assessing when these receptors respond to initiate a reaction, it is clear that the threshold of 60 mmHg is the critical level for stimulating increased respiratory effort due to hypoxemia.