Physiological effects
A high arterial partial pressure of carbon dioxide (
  
    
      
        
          
            P
            
              
                a
                
                  C
                  
                    O
                    
                      2
                    
                  
                
              
            
          
        
      
    
    {\displaystyle {P_{a_{CO_{2}}}}}
  ) causes changes in brain activity that adversely affect both fine muscular control and reasoning.
Causes
Carbon dioxide is a normal metabolic product but it accumulates in the body if it is produced faster than it is cleared. During strenuous exercise the production rate of carbon dioxide can increase more than tenfold over the production rate during rest. Carbon dioxide is dissolved in the blood and elimination is by gas exchange in the lungs during breathing. Hypercapnia is generally caused by hypoventilation, lung disease, or diminished consciousness. It may also be caused by exposure to environments containing abnormally high concentrations of carbon dioxide, such as from volcanic or geothermal activity, or by rebreathing exhaled carbon dioxide. In this situation the hypercapnia can also be accompanied by respiratory acidosis.Acute hypercapnic respiratory failure may occur in acute illness caused by chronic obstructive pulmonary disease (COPD), chest wall deformity, some forms of neuromuscular disease (such as myasthenia gravis, and obesity hypoventilation syndrome. AHRF may also develop in any form of respiratory failure where the breathing muscles become exhausted, such as severe pneumonia and acute severe asthma. It can also be a consequence of profound suppression of consciousness such as opioid overdose. During diving
Normal respiration in divers results in alveolar hypoventilation resulting in inadequate CO2 elimination or hypercapnia. Lanphiers work at the US Navy Experimental Diving Unit answered the question, "Why dont divers breathe enough?