Central chemoreceptors located in the medulla provide feedback to increase the rate and depth of breathing when they sense:

slight increases in carbon dioxide or a decrease in the pH of the cerebrospinal fluid.

slight decreases in carbon dioxide and an increase in the pH of the cerebrospinal fluid.

decreased levels of oxygen in the blood and an increase in the pH of the cerebrospinal fluid.

increased levels of oxygen in the blood and a decrease in the pH of the cerebrospinal fluid.