RESPIRATION 275 



the veins are always relaxed, as well as distended ; and they con- 

 sider that the easier escape of the blood from the tissues, due to 

 relaxation especially of venules, is the cause of the larger venous 

 return and consequent rise of venous pressure. Recently Hender- 

 son, Haggard, and Coburn 14 have shown that inhalation of air 

 containing 6 or 8 per cent of CO 2 has a powerful restorative effect 

 upon the circulation, and particularly upon the venous pressure, 

 in patients after prolonged anaesthesia and major surgical opera- 

 tions. 



With great deficiency of oxygen there is also at first a very 

 marked increase in the circulation rate. This is shown by the 

 greatly increased pulse rate, deep blue flushing of the skin, etc., 

 and great rise of venous blood pressure when air very deficient in 

 oxygen is breathed. In rapid poisoning by CO there is the same 

 flushing of the skin and distention of large veins, though the color 

 is now red and not blue. The increased pressure in the great veins 

 causes the distention of the right side of the heart and rapid pro- 

 duction of oedema of the lungs so characteristic of acute asphyxia, 

 although but for the fact that the heart muscle is lamed by the 

 anoxaemia there would probably be no over-distention. As Star- 

 ling and Knowlton found, oedema of the lungs and over-disten- 

 tion of the right side of the heart are very quickly produced by a 

 quite moderate increase of the ordinary very low venous pressure 

 at the entry to the heart. 15 With moderate oxygen deficiency, pro- 

 duced rapidly, there are, just at first, distinct signs of increased 

 circulation as well as of increased respiration; but very soon the 

 increased washing out of CO 2 from the blood moderates both the 

 breathing and circulation, and after a short time the circulation, 

 as well as the breathing, quiets down, so that unless the anoxaemia 

 is considerable the increased pulse rate and other signs of in- 

 creased circulation may have practically disappeared. 



The circulation during and just after forced breathing in man 

 was meanwhile investigated by a quite different method by Hen- 

 derson, Prince, and Haggard. 16 They measured the venous pres- 

 sure by observing the height of the column of blood in a vein of 

 the arm when the subject was placed in a head down position on a 

 sloping board (Figure 70) , thus obtaining a measure of the venous 



14 Henderson, Haggard, and Coburn, Journ. Amer. Med. Assn., LXXIV, p. 783, 

 1920. 



15 Starling and Knowlton, Journ. of Physwl., XLIV, p. 206, 1914. 



18 Yandell Henderson, Prince, and Haggard, Journ. of Pharmac. and, Exper. 

 Therapeutics, XI, p. 203, 1918. 



