Action of Carbon Dioxide and Adrenalin on the Heart. 375 



considerable time, the output of the heart may almost cease. With recovery 

 from the effects of CO2 the output per minute is above normal, but this 

 occurs only after the CO2 is removed and ordinary air respired. Since the 

 coronary output has been found not to be increased during administration of 

 C0 2 , the total output of the left ventricle is proportional to the observed 

 output and is thus never increased but suffers more or less diminution. 



After adding adrenalin to the blood circulating through a good heart, the 

 systemic output is observed to be about the value obtained before, unless the 

 heart was failing ; but since the coronary flow is markedly raised, the total 

 output of the left ventricle is usually increased. Adrenalin sometimes can 

 improve the condition of a heart that is working badly, or make the heart 

 better able to work against a greater resistance ; but with some hearts 

 adrenalin is incapable of bringing about an improvement. 



When adrenalin and C0 2 are combined in suitable proportions, the systemic 

 output has been found to be increased ; and, since there is also increased 

 coronary flow, the total output of the heart may be greatly increased. 



Examples of such findings are given in the protocols of Table II. 



In Experiment 1, 5 per cent. C0 2 reduced the systemic output from 130 to 

 96 c.c. in 10 seconds, 0*1 mgrm. adrenalin also reduced the output to 103 c.c. 

 per 10 seconds, while with combination of the two together the systemic 

 output was 125 c.c. In Experiment 5, combining CO2 and adrenalin 

 increased the systemic output to more than normal. Experiment 2 shows 

 the greater effect of larger percentages of C0 2 in reducing the output ; 

 while Experiment 3 shows that the same percentage of CO2 has a more 

 marked effect when the arterial resistance is high and the load on the heart 

 consequently greater. 



The constancy of the output with constant venous inflow, even in the presence 

 of varying rate and arterial resistance, has been insisted on in previous papers 

 from this laboratory. How then is it possible for the output to be increased 

 or diminished by C0 2 , or adrenalin, with constant venous inflow ? The clue 

 to the interpretation of the results is given in the effect of CO2 and adrenalin 

 on the venous pressures (see below). The question is one of the diastolic 

 pressure and diastolic filling of the heart. The higher the diastolic pressure, 

 the smaller is the inflow under a given head of pressure ; and it will be seen 

 that CO2 raises the venous pressure, while adrenalin usually lowers it. 



Pressures in the Inferior Vena Cava and Left Auricle. — These pressures 

 represent (i) the side pressure of the blood flowing into the right and left 

 ventricles, (ii) the damming back (Stauung) of the blood in the auricles 

 during the ventricular systole. These two factors are present in the 

 normally acting heart ; but there may be also (iii) a more marked abnormal 



