Which change most directly stimulates chemoreceptors?

Which change most directly stimulates chemoreceptors?

• A. Increased PaO2
• B. Decreased PaCO2
• C. Increased PaCO2
• D. Increased pH

Answer: (C)

Chemoreceptors respond to chemical changes in the blood and CSF, with central chemoreceptors in the medulla being especially sensitive to pH changes in the CSF. CO2 diffuses easily into CSF and forms carbonic acid, lowering pH; this pH drop directly increases the firing of central chemoreceptors, prompting increased ventilation to blow off CO2. Therefore, an increase in PaCO2 is the change that most directly stimulates chemoreceptors. Higher PaO2 reduces peripheral chemoreceptor drive, lower PaCO2 would lessen stimulation, and a higher pH (alkalosis) would also reduce stimulation.

Chemoreceptors respond to chemical changes in the blood and CSF, with central chemoreceptors in the medulla being especially sensitive to pH changes in the CSF. CO2 diffuses easily into CSF and forms carbonic acid, lowering pH; this pH drop directly increases the firing of central chemoreceptors, prompting increased ventilation to blow off CO2. Therefore, an increase in PaCO2 is the change that most directly stimulates chemoreceptors. Higher PaO2 reduces peripheral chemoreceptor drive, lower PaCO2 would lessen stimulation, and a higher pH (alkalosis) would also reduce stimulation.