Breathing air with CO2 more than 7% leads to
Breathing air with CO2 up to 6% in healthy individuals increases the rate and depth of respiration. This is by an increase in alveolar PCO2 concentration leading to an increase in arterial PCO2 which stimulates respiration and increased rate and depth of respiration occurs. Increased respiration, reduces alveolar PCO2 concentration
When CO2 concentration in breathing air rises above the 7% increased rate and depth of respiration will not be able to reduce alveolar PCO2 concentration. This failure raises the blood level of CO2 leading to respiration depression and CO2 narcosis.