Carbon dioxide binds to water and produces carbonic acid, which splits itself apart into bicarbonate and hydrogen ions. If you put more CO2 in your blood, your blood becomes more acidic. Your respiratory system has the capacity to get rid of the CO2. So breathe it off, breathe more rapidly, breathe quicker. You can get rid of CO2 out of your lungs, out of your blood, and hopefully could drop that acidity of the blood and vice versa. Drop It or Raise It: The Mechanics of Breathing is on BBC Radio 4 tonight at 9pm.