How does pH affect respiration rate?

First of all the pH of your blood plays the major role in controlling the respiration rate. Blood pH is directly linked to C02 levels as H+ + HC02- = C02 + H20 so as C02 levels rise the pH decreases. Your respiratory system is the body's number one way to immediately control pH while the kidneys and intestines are important for longer range control.

Secondly when one hyperventilates they breath off their CO2 making the blood basic creating a metabolic alkalosis rather than an acidosis. People are told to breath into a paper bag, so that they can re-intake the CO2 they are breathing out to restore the appropriate pH before they pass out.