130 BLOOD-PRESSURE IX THE PULMONARY ARTE1JY. 



(7) Gravity exercises a greater effect upon the blood-stream in the extensile 

 veins than upon the stream in the arteries. It acts on the distribution of the 

 blood, and thus indirectly on the motion of the blood-stream. It favours the 

 emptying of descending veins, and retards the emptying of ascending veins, 

 so that *he pressure becomes less in the former and greater in the latter. If 

 the position of the limb be changed, the conditions of pressure are also altered. 

 If a person be suspended with the head hanging downwards, the face soon 

 becomes turgid, the position of the body favouring the inflow of blood through 

 the arteries and retarding the outflow through the veins. If the hand hangs 

 down it contains more blood in the veins than if it is held for a short time over 

 the head, when it becomes pale and bloodless. [As Lister has shown, the condition 

 of the vessels in the limb is influenced not only by the position of the limb, but 

 also by the fact that a nervous mechanism is called into play.] 



[Ligature of the portal vein causes congestion of the rootlets and dilatation of all the blood- 

 vessels in the abdomen ; gradually nearly all the blood of the animal accumulates within its 

 belly, s<> that, paradoxir.il as it may seem, an animal may be bled into its own belly. As a 

 consequence of sudden and complete ligature of this vein, the arterial 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. Schiff and Lautenbach regard the 

 symptoms as due chiefly to the action of a poison, for when the blood of the portal vein in an 

 animal treated in this way is injected into a frog, it causes death within a few hours, while the 

 ordinary blood of the portal vein has no effect] 



[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 txdema of the parts beyond the obstruction. Ligature of one 

 vein does not always produce oedema, but if several veins of a limb be ligatured, and the vaso- 

 motor nerves be divided at the same time, the rapid production of oedema is ensured. In 

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

 (203).] 



88. BLOOD-PRESSURE IN THE PULMONARY ARTERY. Methods. (1) Direct estima- 

 tion of the blood-pressure in the pulmonary artery by opening the chest was made by C. Ludwig 

 and Beutner (1850). Artificial respiration was kept up, and the manometer was placed in con- 

 nection 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 disturbing element, viz. , the removal of the elastic force of the lungs, 

 owing to the opening of the chest, whereby the venous blood no longer flowed normally into the 

 right heart, while the heart itself was under the full pressure of the atmosphere. The estimated 

 pressure in the dog = 29 *6 ; in the cat=177 ; 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) Faivre (1856) introduced a catheter through the jugular vein into the right ventricle, 

 and placed it in connection with a recording tambour. 



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. 



Beutner and Marey estimated the relation of the pulmonary artery to the aortic 

 pressure as 1 to 3 ; Goltz and Gaule as 2 to 5 ; Fick 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. 



Elastic Tension of Lungs. 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 large blood-vessels within the chest are not exposed to the full 

 pressure of the atmosphere, but only to the pressure which corresponds to the 

 atmospheric pressure minus the pressure exerted by the elastic traction of the lungs 



