152 Properties of the Arterial and Venous Walls. [Oct. 24, 



Relaxed Artery. — When there is zero pressure within the artery, to 

 b>egin with a pulsatile rise of pressure of a certain amount causes an 

 extensive pulsatile change in volume ; e.g., the oil in the graduated 

 tube may move 15 mm. at each pulsation. (The tube is. 3 mm. in 

 calibre.) 



When the pressure within the artery is originally 50 mm. Hg., the 

 same rhythmical injection of air causes a much smaller expansion of 

 volume, e.g., 10 mm. 



With higher pressures there is a smaller and smaller pulsatile ex- 

 pansion, e.g., with an original pressure of 100 mm. the movement is 

 ■6 mm., with an original pressure of 200 mm. the movement is 3 mm. 



Contracted Artery. — When a contracted artery is tested in the same 

 way, the pulsatile expansion is very small in amount, and there is no 

 very evident difference in the amount of pulsatile expansion at dif- 

 ferent (pre-existing) pressures. From the fact that (as has been 

 described) a contracted artery is most distensible at a high pressure, 

 one might expect that with a tolerably high pressure a further pulsatile 

 rise would give larger expansion than when the pressure is at or near 

 .zero. But the rapid oscillations of pressure such as are now under 

 consideration are much too brief in duration to have much effect ; for 

 the expansion of a contracted artery is slowly and gradually effected, 

 and a rise of pressure, from whatever level it starts, has to last for 

 fsome time if it is to exercise its full effect upon the arterial wall. 



In accordance with this, in the intact arteries of men and animals 

 there would be much less pulsatile expansion in a contracted artery 

 than in a relaxed one ; and in a relaxed artery expansion would be 

 very much more extensive when the mean blood-pressure is low. Further, 

 .elongation would occur markedly in the relaxed artery as compared 

 with the contracted one. And when a long stretch of artery is con- 

 cerned the increase in length is very much greater than the increase in 

 transverse diameter. 



Illustrations of the above conclusions may be seen in healthy human 

 .arteries, the pulsatile changes in the relaxed temporal artery, also the 

 ■extensive pulsation of arteries in inflamed parts, &c. 



Various observers have described an apparent absence of transverse 

 .expansion at each heart-beat in arteries in situ. A. W. Volkmann* 

 remarks that when an artery is laid bare in the living animal the only 

 perceptible evidence of expansion of the vessel during pulsation is the 

 tortuous form assumed by it at every pulse, and that the transverse 

 expansion which (on other grounds) he believes to take place is 

 inappreciable. 



Listerf states that the arteries are not increased in diameter by the 

 strokes of the powerful cardiac pump — " The surgeon when tying a 

 * * Haemodynamik,' 1850. 

 f ' Brit. Med. Journ.,* 1879, vol. 1, p. 924. 



