Carbon dioxide is needed for every metabolic process and the excess is carried in the bloodstream back to the lungs where it is exhaled along with water vapour. The importance of oxygen in the body is well known. When carbon dioxide levels in the bloodstream reach a certain point, the respiratory centre in our brain sends a message to the muscles used for breathing to take in more air and breathe out excess carbon dioxide. The amount of oxygen released from haemoglobin is determined by carbon dioxide levels. This is known as the Bohr effect and basically means that the more you breathe, the less oxygen your body is actually able to use.
Carbon dioxide regulates the activity of the autonomic nervous system.
If carbon dioxide is low, it stimulates the sympathetic nervous system putting the body on red alert. This causes erratic, breathing. Carbon dioxide regulates smooth muscle or the involuntary muscle of the airways, blood vessels etc. Low levels of carbon dioxide cause smooth muscle to constrict and spasm. Low levels of carbon dioxide cause respiratory alkalosis and the body produces lactic acid to counteract this.