152 RAPIDITY OF TRANSMISSION OF PULSE-WAVES. 



dicrotic wave again diminishes. (4) The fine elastic vibrations preceding the 

 dicrotic wave appear first when a weight of 220 to 300 grammes is used. (5) The 

 rapidity of the pulse changes with increasing weight, the time occupied by the 

 ascent becoming shorter, the descent becoming longer. (6) The height of the entire 

 curve decreases as the weight increases. In every sphygmogram the pressure 

 under which it was obtained ought always to be stated. 



In Fig. 66, A, B, C, D, are curves obtained from the radial artery of a healthy 

 student. The pressure exerted upon the artery for A was 100; B, 170; C, 220; 

 and D, 240 grms. The time occupied by the various events was : 



1-2, . . . 



1-a, . . . 



1-3, . , . 



1-4, ,. . . 



1-5, V v . 



1-b, . . . 



1-6, .... . - 



If pressure be exerted upon an artery for a long time the strength of the pulse is 

 gradually increased. If, after subjecting an artery to considerable pressure, a 

 lighter weight be used, not unfrequently the pulse-curve assumes the form of a 

 dicrotic pulse, owing to the greater development of the dicrotic elevation. When 

 strong pressure is applied, the blood is forced to find its way through collateral 

 channels. When the chief artery ceases to be compressed, the total area is, of 

 course, considerably and suddenly enlarged, which results in the production of a 

 dicrotic elevation. Fig. 58, X, is such a dicrotic curve obtained after considerable 

 pressure had been applied to the artery. 



76, Rapidity of Transmission of Pulse-Waves, 



The pulse-wave proceeds throughout the arterial system from the 

 root of the aorta, so that the pulse is felt sooner in parts lying near the 

 heart than in the peripheral arteries. E. H. Weber calculated the 

 rate of the pulse- wave as 9*240 metres [28J feet] per sec. from the 

 difference in time between the pulse in the external maxillary artery 

 and the dorsal artery of the foot. Czermak showed that the elasticity 

 was not equal in all the arteries, so that the velocity of the pulse-wave 

 cannot be the same in all. The pulse-wave is propagated more slowly 

 in the arteries with soft extensile walls than in arteries with resistant 

 and thick walls, so that it is transmitted more rapidly in the arteries 

 of the lower extremities than in those of the upper. It is still slower 

 in children. 



77. Propagation of the Pulse- Wave in Elastic 



Tubes. 



Waves similar to the pulse may be produced in elastic tubes. (1) According to 

 E. H. Weber the velocity of propagation of the waves is 11 '295 metres per sec.; 



