264 



RESPIRATION 



appeared to depend almost entirely on the pulse rate. He concluded 

 that under normal conditions the heart is, practically speaking, 

 always adequately filled during diastole, although under abnormal 

 conditions the filling may become inadequate — for instance when 

 the carbon dioxide of the blood is greatly reduced by excessive 

 artificial respiration. If we apply Henderson's conclusions to man 

 it is evident that they cannot be reconciled with those of Krogh 

 and Lindhard. On Henderson's theory the increased absorption of 

 oxygen and discharge of CO2 from the blood passing through the 

 lungs during muscular exertion must be due to a very large ex- 

 tent to greater utilization of the oxygen in the blood passing 

 round the body, and a corresponding increase in its charge of COg. 

 The rate of circulation can only be increased in proportion to in- 

 creased pulse rate, the discharge of blood per systole remaining 

 about the same. 



There is no question that the systolic discharge may, at least 

 under abnormal conditions, vary enormously. This was very 

 clearly shown by the experiments of Starling and Patterson,^ with 

 a "heart-lung preparation" — i.e., a preparation in which the 

 only circulation was through the lungs and heart, the lungs being 

 ventilated so as to insure full oxygenation of the blood. By vary- 

 ing the venous blood pressure, the systolic discharge could be 

 varied tenfold, without any variation in the pulse rate. It does not 

 follow, however, that there are corresponding variations in systolic 

 discharge in normal men and animals with the organic regulation 

 of circulation not thrown out as in the case of a heart-lung prepa- 

 ration. 



In the nitrous oxide method there are various sources of pos- 

 sible very serious error which can hardly be discussed in detail 

 here. In order to get a more direct and accurate insight into the 

 venous gas pressures and their relation to blood flow, a new 

 method was introduced by Christiansen, Douglas, and myself.^ 

 In the first application of this method we simply determined the 

 COo pressure of the venous blood atter oxygenation but without 

 its losing any COg. As we had already discovered (see Chapter 

 V), this pressure is higher by an easily calculable amount than 

 that for the unoxygenated venous blood. Mixtures containing 

 about the required percentage of CO2 were prepared by adding 

 COo to air. A deep breath of one of these mixtures was taken in 



•starling and Patterson, Journ. of Physiol., XLVIII, p. 357, 19 14. 

 "Christiansen, Douglas, and Haldane, Journ. of Physiol., XLVIII, p. 244, 

 1914. 



