THE DIASTOLIC FILLING OF THE HEART. 



45 



rises to about 60 mm. soda solution. By a pressure of at most 240- 



300 mm. oil, the arterial pressure is driven to zero. 1 By no possible 



means can the vena cava pressure rise beyond this pressure, and thus the 



heart is unable to fill. " The quantity of blood 



thrown into the aorta by each contraction of 



the left ventricle, should accurately correspond 



to that issuing from the arteries into the 



capillaries during the period which elapses 



from the commencement of the systole to the 



end of the following diastole. It is the main- 

 tenance of tliis proportion that is the source of 



the constant mean tension of the arteries" 2 



In the dog either the vena cava superior or 



the vena cava inferior below the liver may be 



completely occluded, and yet no change of 



pressure is indicated by the arterial mano- 

 meter. On compressing the vena cava inferior 



between the liver and the heart, on the other 



hand, there is an immediate and marked 



descent of the arterial tension. Thus, too, a 



rabbit, in which the portal vein has been 



ligatured, perishes within a few minutes, 



owing to the rapid accumulation of the blood 



in the portal tributaries. The capacity of 



these is so great that they are sufficient to 



hold all the blood at a low tension. The filling of the heart is thus 



enormously diminished while the aorta continues to empty itself, by 



its elastic reaction, into the portal system. 



Stefani 3 found that the intrapericardial pres- 

 sure must, in order to stop the diastole of the 

 heart, be raised to a higher point if the vagi 

 are intact than if the vagi are divided. This 

 need not prove, as Stefani believes, that the 

 vagus actively influences the diastole of the 

 heart muscle. The result can be explained by 

 the alteration in the action of the respiratory 

 pump which follows division of these nerves. 

 By dividing both vagi the rate of respiration is 

 greatly slowed, and thus the action of the re- 

 spiratory pump, so far as regards the filling of 

 the heart, is lessened. 



On compression of the thorax of a dog, the 



FIG. 28. Compression of the 

 thorax (A-B). Compensa- 

 tory effect of powerful in- 

 spirations, alternating with 

 forced expiratory efforts 

 (glottis closed). Hill and 

 Barnard. 



FIG. 29. A, vertical feet- 

 down position ; B-C, 



effect of compressing the arterial pressure falls towards zero, owing to 

 thorax. Hill and Bar- the increased in tra thoracic pressure, while the 

 vena cava pressure rises. The gravity of the 



effect depends greatly on the rigidity of the thorax and resisting power 

 of the animal. 4 In man, compression of the chest produces the same 

 result, and Weber thereby induced in himself loss of consciousness and 



1 Cohnheim, "Lectures on General Pathology," New Syd. Soc. Trans., vol. i. p. 23. 



2 Cohnheim, ibid., p. 25. 



3 " Cardiovolume pressione pericardica e attivita della diastole," Mem. Accad. med.- 

 chir. di Ferrara, il 5 Agoste 1891. 



4 Hill and Barnard, Journ. Physiol., Cambridge and London, 1897, vol. xxi. p. 333. 



