272 RESPIRATION 



like the breathing, is delicately regulated in accordance with the 

 local requirements for the supply of oxygen and removal of CO 2 . 



The idea that the local circulation is regulated in accordance 

 with the local CO 2 pressure was brought forward in a very definite 

 form by Yandell Henderson in a series of papers on "Acapnia and 

 Shock." 10 He showed, firstly, that the local circulation and func- 

 tional activity in the exposed intestines depends upon the main- 

 tenance in them of a sufficient pressure of CO 2 , and secondly, that 

 on the removal of an excessive quantity of CO 2 from the body by 

 excessive artificial or natural respiration the circulation fails, 

 whereas excessive ventilation with air to which sufficient CO 2 has 

 been added produces no such effect. These are evidently facts of 

 fundamental importance as regards the regulation of the circula- 

 tion, and as showing the intimate connections between respiration 

 and circulation. On these and other observations he also based the 

 theory that the immediate cause of shock may be excessive res- 

 piratory activity. 



The blood-gas changes caused by excessive artificial respira- 

 tion were first investigated by Ewald in connection with apnoea. 11 

 He not only found that there is a slight excess of oxygen and very 

 large deficiency of CO 2 in the arterial blood, but also (though of 

 this he did not realize the significance) that there is great de- 

 ficiency of both CO 2 and oxygen in the mixed venous blood. The 

 changes in the arterial blood have already been discussed in earlier 

 chapters, and it was pointed out in Chapter VII that owing to the 

 deficiency of CO 2 a state of anoxaemia must, other things being 

 equal, be produced by forced breathing. Ewald's analyses show, 

 however, that there is something more to cause anoxaemia than 

 mere deficiency of CO 2 . The latter would not by itself account 

 for the deficiency of oxygen combined with haemoglobin in the 

 venous blood. In long experiments Ewald found this oxygen down 

 to about a third of the normal, and the CO 2 down to half the 

 normal. Taking into account both the direct effect of deficiency 

 of CO 2 in diminishing the free oxygen present in the venous blood, 

 and the effect in the same direction of the diminished proportion 

 of oxyhaemoglobin present, the artificial respiration must have 

 brought about a condition of very intense anoxaemia in the tis- 

 sues. But the diminution in the proportion of oxyhaemoglobin 



10 Yandell Henderson, Amer. Journ. of Physiol., XXI, p. 126, 1908; XXIII, 

 p. 345, 1909; XXIV, p. 66, 1909; XXV, p. 310, 1910; XXV, p. 385, 1910; 

 XXVI, p. 260, 1910; XXVII, p. 152, 1910; XLVI, p. 533, 1918. 



"Ewald, Pfluger's Archiv., VII, p. 575, 1873. 



