Question

When co2 concentration in blood increases breathing becomes

Answer 1

Breathing will become rapid in the event that CO2 concentration increases in the blood. This is because the body will compensate for the accumulation of CO2 by increasing breathing to aid in the removal of the CO2. The more one breathes, the more the gaseous exchange and hence the more the CO2 will be removed from the body. 

Answer 2

Carbon dioxide concentration increases in the blood whenever there is a general obstruction to normal rate of breathing, a change in the affinity of haemoglobin for oxygen, increased work by body tissues or even in certain cases of acidosis.

As a general rule, the faster and deeper you breathe, the greater is the air exchange happening in your lungs. This means there is increase in the rate of oxygen uptake by blood and also of carbon dioxide wash-out. So if you breathe fast and deep, that will clear out maximum amount of carbon dioxide from your blood. Hence a decrease in blood CO2 concentration