FLOW OF BLOOD THROUGH THE ARTERIES 1039 



when moving, a magnified record of the expansion of the artery under the 

 knob P. 



Either form of sphygmograph is generally applied to the radial 

 artery, since this is near the surface and is supported by bone, and the 

 arm is well adapted for the application of the sphygmograph. The 



Fio. 413. Dudgeon's sphygmograph, showing its mode of application to 



the radial artery. 



pulse-curve obtained by means of a sphygmograph varies according 

 to the artery employed and the force with which the lever presses on 

 the artery, but all the curves present the same general features. 



The velocity of the pulse can be measured by taking simultaneous 

 tracings from two arteries separated by some 

 distance from one another, such as the femoral 

 artery and the dorsalis pedis, or from the carotid 

 and radial arteries. In a healthy individual the 

 velocity varies between 7 and 10 metres per 

 second. The more rigid the arteries the greater 

 will be the velocity, so that the velocity of 

 propagation gradually increases with advancing 

 age, and is higher in the arteries of the lower 

 extremities than in the more distensible arteries 

 of the arm. 



The length of the pulse-wave can be found 

 by multiplying the velocity of transmission by 

 the time occupied by the wave in passing any 

 given point. The duration of the wave at any point corresponds to 

 the time of a cardiac cycle, viz. 0-8 sec., so that if the velocity of 

 transmission be taken as 7 metres per second, the length of the wave 

 is about 5-6 metres. The pulse-wave thus reaches the periphery long 



Fio. 414. Diagram of 

 arrangement of re- 

 cording lever in 

 Dudgeon's sphygmo- 

 graph. 



