VELOCITY OF PROPAGATION OF PULSE-WAVES. 153 



weight employed, in order to form a correct interpretation of the shape of the 

 pulse-waves. 



It appears from an examination of the radial curves A and B, the former of 

 which was taken with a weight of 100 grams, and the latter with a weight of 220 

 grams, from the same individual and at the same time (i vibration = 0.01613 second) , 

 that changes in the load may produce differences also in the chronological develop- 

 ment of the sphygmogram. 



When the pressure on an artery is continued for a considerable period of time, 

 the force of the pulse gradually increases. If the greater load is then removed 

 and a smaller one substituted, the sphygmographic curve not infrequently assumes 

 the form of a dicrotic pulse-wave and the recoil-elevation becomes distinctly 

 marked. During the high pressure the blood is forced to make a passage for itself 

 by dilating the collateral vessels. If, then, the main channel is again thrown 

 open, the entire bed of the stream, of course, suddenly becomes much wider. In 

 consequence, there results a greater development of the recoil-elevation. Tracing 

 X in Fig. 50 represents such a dicrotic series, taken after the application of a 

 heavy weight. 



VELOCITY OF PROPAGATION OF PULSE-WAVES. 



As the pulse-wave passes from the root of the aorta into all the arteries toward 

 the periphery, the pulse is felt earlier in the arteries nearer the heart than in those 

 at a greater distance. This phenomenon was variously confirmed and variously 

 disputed until E. H. Weber determined the movement of rapidity of the pulse- 

 wave from the difference in time of the pulse in the external maxillary artery 

 and in the dorsalis pedis artery and found it to be 9.240 meters in a second. With 

 such great velocity of the pulse-wave, says this investigator, it cannot be regarded 

 as a short wave traveling along the arteries, but so long that a single pulse-wave 

 cannot find room in the entire distance from the beginning of the aorta to the 

 artery of the big toe. 



PROPAGATION OF PULSE-WAVES IN RUBBER TUBES. 



As it is possible by the intermittent injection 6f water into rubber tubes to 

 produce waves similar to those produced by the pulse, it is important to learn 

 the results that have been obtained from a study of this undulatory movement. 



According to E. H. Weber, the propagation-velocity of these waves is 11.259 

 meters in one second. Positive and negative waves are propagated with equal 

 velocity and the velocity of the waves is the same whether they have been pro- 

 duced slowly or rapidly. 



2. According to Bonders, the velocity of the waves is directly proportional 

 to the coefficient of elasticity of the walls of the tubes. It is proportional to the 

 square root of the coefficient of elasticity of the walls of the tubes, with the same 

 lateral pressure. 



3. The velocity of the waves increases with the thickness of the walls; it is 

 proportional to the square root of the thickness of the walls, with the same lateral 

 pressure. 



4. The velocity is inversely proportional to the square root of the diameter 

 of the tubes, the pressure remaining constant. 



5. According to Marey, the velocity diminishes as the specific gravity of the 

 fluid increases. It is inversely proportional to the square root of the specific 

 gravity. 



Experiments with Rubber Tubes. In determining the time-relations Landois 

 employed the following method. He recorded the waves by means of the angio- 

 graph on a recording surface attached to a vibrating tuning-fork (Fig. 60). After 

 measuring a certain distance on a long rubber tube, the extremities a and b are 

 placed under the pad of the sphygmograph . B is a compressible bulb, by com- 

 pression of which a positive wave is thrown into the tube, Q is a portable mercu- 

 rial manometer, which indicates the pressure in the apparatus. As the pulse- 

 wave first passes through at a and then at b, two elevations, i and 2, are recorded. 

 Each small indentation is equivalent to 0.01613 second. The time-relations can 

 be determined by simply counting these indentations. 



Propagation-velocity of Water-waves and Mercury-waves within Elastic Tubes. 

 Landois' experiments, published in 1879, yielded a propagation-velocity of 11.809 

 meters in i second, with an internal pressure of 75 millimeters of mercury. 



