CHAPTER XXXIV 

 THE EFFECTS OF EXCESS OF CARBON DIOXIDE 



BREATHED in very high percentages, 30 per cent, and upwards, 

 C0 2 acts as an anaesthetic and narcotic. There is first induced a 

 spasm of respiration, then consciousness is lost, the respiration becomes 

 quiet, the heart-beat enfeebled, and death ensues owing to the direct 

 action of C0 2 upon the heart-muscle. In smaller percentages C0 2 

 has an excitatory effect at first upon the respiration, then upon the 

 circulation also. A small increase of C0 2 in the air breathed in causes 

 a marked increase in pulmonary ventilation. With an increase of 

 3 per cent, this becomes noticeable to the person breathing; with 

 5 per cent, the hypcrpncea is very marked, the respirations are quick- 

 ened, the pulse becomes quicker and fuller; with 6 per cent, there 

 begins to be a retent r'on of CO 2 within the body, breathing is distressful, 

 headache develops, profuse sweating breaks out. The blood-pressure 

 is greatly raised, and the pulse may be felt drumming in the ears. 

 Later, the mind becomes confused, and loss of consciousness ensues. 

 It is possible for a man, having filled his lungs with oxygen, and then 

 holding his breath, to run himself into a state of unconsciousness. 

 In such cases, as much as 11 per cent, of C0 2 is found in the alvedar 

 air. Athletes who run themselves out are overcome by the excess 

 of acid in the bloorl. 



Most deaths attributed to excess of carbon dioxide are in reality due 

 to oxygen-want. High percentages of CO 2 sufficient to cause death 

 cause spasm of the glottis and choking. Divers have often been over- 

 come by an excess owing to defective supply of air in deep water. 

 At a pressure of, say. 4 atmospheres (100 feet) there is four times 

 the volume of air in the helmet, and to ventilate it four times as 

 much air must be pumped through it as at 1 atmosphere. It has 

 not been recognized until recently that the deeper the diver goes, the 

 more air must be given him. 



Effects of Deficiency of Carbon Dioxide. If carbon dioxide be 

 washed out of the body by forced breathing, the desire to breathe 

 disappears for a time, and a condition of apncea ensues, which may 

 laat as long as two to three minutes, and even longer (Fig. 164), 

 If oxygen be forcibly breathed, the apnoea ma}- last five to seven 

 minutes, and even nine minutes. Forced breathing produces a curious 

 condition of spasm of the hand, sensations of " pins and needles " in 

 the hands and feet, with coldness and pallor, and a sensation of tight- 



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