The CO2 reduces the CSF pH, thus stimulating the chemoreceptors. CO2 can also act directly on the chemoreceptors. The cardiovascular response of the central chemoreceptors is to increase sympathetic nerve activation. These mechanisms lead to increased blood flow to the brain. The peripheral chemoreceptors are located in the carotid and aortic bodies, which reside in the carotid arteries and aortic arch, respectively.
Carotid bodies are more importrant in humans.
Their major stimulus is low pO2, but they are also sensitive to high pCO2, particularly if pO2 is also low. However, the response of the peripheral chemoreceptors to arterial pCO2 is less important than that of the central chemoreceptors . However, at high altitudes, a large increase in ventilation occurs in response to hypoxia. Remember there is vagal innervation of coronary and cerebral arteries. When the latter are stimulated and ventilation maintained constant, the heart rate and cardiac contractility are decreased, and the coronary vessels are dilated owing to increased vagal activity.