TRANSMISSION OF PULSE-WAVE. 



13 



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. 95, A, B are curves obtained from the radial artery of a healthy student. The pressure 

 exerted upon the artery for A was 100 ; B, 220 grms. (1 vibration = '0161 3 sec). 



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 



Fig. 95. 

 Various forms of curves (radial) obtained by gradually increasing the pressure. 



unfrequently the pulse-curve assumes the form of a dicrotic pulse, owing to the greater develop- 

 ment 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. 83, X, is such a dicrotic curve obtained after considerable pressure had 

 been applied to the artery. 



76. TRANSMISSION OF PULSE-WAVES. The pulse-wave proceeds through- 

 out 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 calcul- 

 ated the velocity of the pulse-wave as 9*240 metres [28 J feet] per second, 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 resistent 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. 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 "205 

 metres per sec. ; according to Donders, 11-13 metres (34-42 feet). (2) According to E. H. 

 Weber increased internal tension causes only an inconsiderable decrease ; Rive found a great 

 decrease ; Donders found no obvious difference ; while Marey found an increased velocity. (3) 

 Donders found the velocity to be the same in tubes 2 mm. in diameter as in wider tubes, but 

 Marey believes that the velocity varies when the diameter of the tube changes. (4) The 

 velocity is less, the smaller the elastic coefficient. (4) The velocity increases with increased 

 thickness of the wall, while it diminishes when the specific gravity of the fluid increases. 



Moens has recently formulated the following laws as to the velocity of propagation of waves in 

 elastic tubes : (1) It is inversely proportional to the square root of the specific gravity of the 

 fluid ; (2) it is as the square root of the thickness of the wall, the lateral pressure being the 

 same ; (3) it is inversely as the square root of the diameter of the tube, the lateral pressure being 

 the same ; (4) it is as the square root of the elastic coefficient of the wall of the tube, the lateral 

 pressure being the same ( Valentin). 



(A) The velocity of the wave is 11 # 809 metres per second. 



(B) The intra-vascular pressure has a decided influence on the velocity : thus, in the tube, 



H 



