Blood pH can be disturbed by a number of respiratory and metabolic causes. Respiratory alkalosis is a condition in which the pH of the blood is above normal. The increase in pH is often caused by hyperventilation (excessively deep breathing). When a person hyperventilates they exhale more carbon dioxide than normal. As a result the carbon dioxide concentration in the blood is reduced and the bicarbonate/carbonic acid equilibrium shifts to the left. The corresponding drop in H3O+ concentration causes an increase in pH.
2 H2O + CO2 H2CO3 + H2O H3O+ + HCO3-
Respiratory alkalosis is treated by having the hyperventilating person breathe into a paper bag. In doing so, they rebreathe some of expelled carbon dioxide, and blood carbon dioxide levels return to normal.
Respiratory Acidosis
Respiratory acidosis is caused by the reverse process. A hypoventilating (excessively shallow breathing) person does not expel enough carbon dioxide and has elevated blood carbon dioxide levels. This causes the equilibrium to shift to the right, the H3O+ concentration increases and pH drops.
H2CO3 + H2O 
