1906.] Obstruction of the Vence Cavce and the Portal Vein. 275- 



It has for many years been known that ligature of either the inferior vena 

 cava or the portal vein causes a great fall in the arterial pressure owing to- 

 accumulation of blood in the splanchnic area (3). 



On the following day, when ascites is present, the arterial blood-pressure is 

 usually belovj what it was before the operation, if the animal survives. 



Venous Pressure. 



Inferior Cava. — A gradually increasing constriction of the inferior vena 

 cava in the chest produces no rise of pressure at the lower end of that vein 

 until its diameter has been reduced to 3 mm., when the pressure rises about 

 20 to 30 mm. MgS0 4 solution. 



Constriction to a diameter of 2 mm. produces a rise of about 50 mm. 

 MgS0 4 solution, and complete ligature a rise of 100 mm. or more. 

 Whatever be the degree of constriction, however, the pressure in the inferior 

 vena cava gradually falls and after an hour or longer has reached the normal. 



Moreover, on the following day, when the animal has develojied ascites, the 

 pressure in the inferior vena cava still remains normal. 



The following experiment shows the relative effects of constriction of the 

 inferior vena cava in the chest to a diameter of 2h mm., and of complete 

 ligature. The arterial pressure was taken in the carotid artery and the venous 

 pressure in the external iliac vein. 



Sept. 22, 1906. Cat ; weight, 2600 grammes. Morphia, -f grain. Ether and 



artificial respiration. 



Pressures, 



Carotid artery. 



External iliac vein. 



Before obstruction 



90 mm. Hg 

 66 



82 „ 

 30 „ 

 30 



95 mm. MgS0 4 solution 

 115 „ 

 130 

 210 

 215 



Obstruction to 2| mm 



8 minutes later 



Vein completely occluded 



2 minutes later 





Veins of Foot. — Complete ligature of the inferior vena cava in the chest 

 produces a rise of pressure in the veins of the foot of 60 mm. MgS0 4 

 solution or more. Constriction to a diameter of 2 mm. may cause a rise of 

 50 mm. MgS0 4 solution in the veins of the foot. This is a more gradual 

 rise than that in the inferior vena cava, because it is produced in veins 

 farther removed from the seat of obstruction. 



The pressure in these veins falls to the normal limit again in about one hour- 

 after the occlusion has been produced. 



The following experiment shows the effects of obstruction of the inferior 

 vena cava in the chest upon the venous pressure in the foot. 



