RESPIRATION 



273 



cannot have been due to any other cause than diminution in the 

 circulation rate ; and this diminution is shown far more directly 

 by Yandell Henderson's experiments and numerous blood-gas 

 analyses by the ferricyanide method. The diminution in circula- 

 tion goes so far that the venous return to the heart becomes quite 

 inadequate to fill the ventricles. Hence arterial as well as venous 

 pressure finally falls, and the heart itself is inadequately supplied 

 with free oxygen or CO2, and gradually fails along with fail- 

 ure in the brain and other parts of the body. 



Slowing of the circulation through the hands during forced 

 breathing was clearly demonstrated by his calorimetric method by 

 G. N. Stewart.ii^ 



By means of the new method for determining venous gas pres- 

 sures in man we found that though there is a considerable fall, 

 after forced breathing for about three minutes, in the CO2 con- 

 tent of the mixed venous blood, there is, relatively speaking, an 

 even greater fall in the oxygen content. The experiments were 

 difficult because of the mental state of the subject. I had to be 

 watched very closely to see that I carried out the proper manipula- 

 tions, and many experiments failed because of gross errors, such 

 as taking in a deep breath of ordinary air from the room. The gas 

 mixture used had to contain less than 4 per cent of oxygen and 

 less than 5 per cent of CO2. The fall in oxygen pressure was con- 

 siderably more than could be accounted for as due to the fall in 

 CO2 pressure on account of the Bohr effect. Hence the circulation 

 rate was diminished. The mental condition was apparently due to 

 marked anoxaemia of the nervous centers ; and it may be remarked 

 that owing to the rapid normal circulation through the brain the 

 effects of the forced breathing must be felt there sooner than else- 

 where. 



We also investigated the effect on the circulation of a moderate 

 excess of CO2, sufficient to increase the breathing to about five 

 times the normal. This was easily accomplished in a respiration 

 chamber in which the CO2 percentage had been raised to a little 

 over 5 per cent. Under this condition there was a slight rise in 

 both my arterial and venous CO2 pressure ; but the difference 

 between them was not diminished. Thus there had been no ap- 

 preciable increase in the circulation rate. It was quite clear that 

 the circulation does not increase with increased arterial CO2 pres- 

 sure in a manner corresponding to the increase of breathing. The 



"'^ G. N. Stewart, Amer. Journ. of Physiol., XXVIII, p. 190, 191 1. 



