BLOOD-PRESSURE IN THE PULMONARY ARTERY. 177 



blood-pressure gradually and rapidly falls, and the animal dies very quickly. If 

 the ligature be removed before the blood-pressure falls too much, the animal may 

 recover. 



Ligature Of the Veins Of a Limb. The effect of ligaturing or compressing all 

 the veins of a limb is well seen in cases where a bandage has been applied too 

 tightly. It leads to congestion and increase of pressure within the veins and 

 capillaries, increased transudation of fluid through the capillaries, and consequent 

 cedema of the parts beyond the obstruction. Ligature of one vein does not always 

 produce cedema, but if several veins of a limb be ligatured, and the vaso-motor 

 nerves be divided at the same time, the rapid production of cedema is ensured. 

 In pathological cases the pressure of a tumour upon a large vein may produce 

 similar results.] 



88. Blood-Pressure in the Pulmonary Artery. 



Methods. (1.) Direct estimation of the blood-pressure in the pulmonary artery 

 by opening the chest was made by C. Ludwig and Beutner (1850). Artificial re- 

 spiration was kept up, and the manometer was placed in connection with the left 

 branch of the pulmonary artery. 



The circulation through the left lung of cats and rabbits was thereby completely 

 cut off, and in dogs to a great extent interrupted. There was an additional dis- 

 turbing element, viz. , the removal of the elastic force of the lungs owing to the 

 opening of the chest, whereby the venous blood no longer flows normally into the 

 right heart, while the right heart itself is under the full pressure of the atmo- 

 sphere. The estimated pressure in the dog = 29 '6; in the cat = 17 '6 ; in the 

 rabbit, 12 mm. Hg. i.e., in the dog 3 times, the rabbit 4 times, and the cat 5 

 times less than the carotid pressure. 



(2.) Hering (1850) experimented upon a calf with ectopia cordis. He introduced 

 glass tubes directly into the heart, by pushing them through the muscular walls of 

 the ventricles. The blood rose to the height of 21 inches in the right tube, and 

 33-4 inches in the left. 



(3.) Chauveau and Faivre (1856) introduced a catheter through the jugular vein 

 into the right ventricle, and placed it in connection with a manometer (p. 87). 



Indirect measurements have been made by comparing the relative thickness of the 

 walls of the right and left ventricles, or the walls of the pulmonary artery and 

 aorta, for there must be a relation between the pressure and the thickness of the 

 muscle in the two cases. 



Beutner and Marey estimated the relation of the pulmonary artery 

 to the aortic presssure as 1 to 3 ; Goltz and Gaule as 2 to 5 ; Tick 

 and Badoud found a pressure of 60 mm. in the pulmonary artery of 

 the dog, and in the carotid 111 mm. Hg. The blood-pressure within 

 the pulmonary artery of a child is relatively higher than in the adult 

 (Beneke). 



The lungs within the chest are kept in a state of distension, owing 

 to the fact that a negative pressure exists on their outer pleural surface, 

 When the glottis is open, the inner surface of the lung and the walls 

 of the capillaries in the pulmonary air-vesicles are exposed to the full 

 pressure of the air. The heart and the large blood-vessels within the 

 chest are not exposed to the full pressure of the atmosphere, but only 



12 



