Tolerance
CO2 toxicity in animal models
Tests performed on mongrel dogs showed the physiological effect of carbon dioxide on the body of the animal: after inhalation of a 50% CO2 and 50% air mixture, respiratory movement increased for about 2 minutes, and then, it decreased for 30 to 90 minutes. Hill and Flack showed that CO2 concentrations up to 35% have an exciting effect upon both circulation and respiration, but those beyond 35% are depressant upon them. The blood pressure (BP) decreased transiently during the increased respiratory movement and then rose again and maintained the original level for a while. The heart rate slowed slightly just after the gas mixture inhalation.
The effects of high 
  
    
      
        
          
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    {\displaystyle {P_{a_{CO_{2}}}}}
   can take several minutes to hours to resolve once the cause has been removed.