Action of Carbon Dioxide and Adrenalin on the Heart. 391 



and after injecting adrenalin, diastole was 63 per cent, of the total heart 

 cycle. The shortening of the time of the contractile period is so great 

 that, even with the increased rate of heart-beat, the heart is in a state of 

 contraction for 3 - 7 seconds in 10 seconds, as against 4 - 8 seconds in 10 seconds 

 in the preceding normal period. In the heart cooled by cooling the inflowing 

 blood, the proportion of diastole to total cycle is 50 per cent. Evans and 

 Ogawa (17) have found the metabolism of the heart to be increased by 

 about three times after injecting adrenalin. Since the time per 10 seconds 

 during which the heart is in a state of contraction is shorter than in the 

 normal period, adrenalin seems to have a specific effect in mobilising the 

 " contractile substance," or in exaggerating the changes taking place on the 

 "active surface" of the muscle fibres during contraction. That the heart 

 behaves in quite another manner after injecting adrenalin is shown in 

 fig. 8, the protocols of which are given in Table VI, 6 and 7. They show 

 the more rapid development of tension in the isometric period, the great 

 rise of maximum pressure (116 to 314 mm. Hg) as the blood is shot 

 violently out of the ventricle, and the relatively short duration of the 

 whole contractile process. For a similar effect on the right ventricle, see 

 fig. 10 (2), protocols in Table VI, 5. 



When CO2 and adrenalin are administered together, there is a slightly 

 lengthened time to get up a certain tension in the isometric period ; the 

 maximum pressure in the ventricle attains a greater height than before ; and 

 there is marked lengthening of the diastolic period, thus allowing time for 

 greater filling before the next systole begins [figs. 9 and 10 (3)]. 



Output per Beat. — During the inhalation of CO2 in percentages from 3 to 

 11, the output per beat is equal to, or even greater than, before ; but with 

 percentages of 12-20, or more, the output per beat is diminished, and there 

 may be no flow of blood at all. When the C0 2 is removed and ordinary air 

 breathed again, the output per beat is greater than before the CO2, since the 

 efficiency of contraction of the heart recovers before the rate again becomes 

 normal. 



With adrenalin, the output per beat is diminished. Inhalation of C0 2 

 combined with addition of adrenalin, gives an output per beat, if the dosage 

 is adjusted, equal to, or greater than, the normal (fig. 5). 



As-Vs Interval. — Adrenalin shortens the a-v interval. Small percentages 

 of CO2 in the air breathed cause little or no alteration in the interval, but 

 with larger percentages (above 12 per cent.) the interval is lengthened ; when 

 combined with adrenalin, C0 2 still has not much effect ; but sometimes with 

 large amounts of C0 2 the heart rate drops to half, and a 2:1 heart- block is 

 set up. Lewis and Mathison (18) found heart-block to be of regular occurrence 



