154 VELOCITY or THE PULSE-WAVE IN MAN. 



7 mm. diameter. If 1 metre of the tube is weighted with 1 kilo, it elongates 68 

 cmtr. An ampulla, B, capable of containing 50 cmtr., is fixed to one end of the 

 tube, while to the other end of the ampulla is fixed a mercurial manometer, Q. 



Fig. 67. 



Pulse-curve from an elastic tube registered upon a plate attached to a vibrating 



tuning-fork. 



The tube, A, is shut close to the ampulla every time the pressure is mea- 

 sured, in order to obviate the occurrence of oscillation in the mercury. A certain 

 portion of the tube, say 8 metres, is measured. The beginning, a, and end, b, 

 of this stretch of tubing are placed under the pad, x , of the angiograph. When 

 a positive wave is produced by compressing the ampulla, the writing-lever is raised 

 twice, the first time when the wave passes the first part of the tube, o, under the 

 pad, and the second time when the end part of the tube, b, is distended by the 

 wave. The curve obtained is shown in Fig. 67, in which the two elevations, 

 1 and 2, are obvious. The time between the two may be ascertained by counting 

 the number of vibrations of the tuning-fork. The experiments gave the following 

 results : 



(A.) The velocity of the wave is 11 '809 metres per sec. 



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

 in the tube, A, with 18 cmtr. (Hg.) pressure, the velocity per metre = 0'093 sec., 

 while with 21 cmtr. pressure (Hg.) = 0'095 sec. per metre. 



(C.) The specific gravity of the liquid influences the velocity of the pulse-wave. 

 In mercury the wave is propagated four times more slowly than in water (Marey 

 and Landois). 



(D.) The velocity in a tube which is more rigid and not so extensile is greater 

 than in a tube which is easily distended. 



78, Velocity of the Pulse-Wave in Man. 



Landois obtained the following results in a student whose height was 174 centi- 

 metres : Difference between carotid and radial = 0*074 sec. (the distance being 

 taken as 62 centimetres); carotid and femoral = '068 sec.; femoral (inguinal 

 region) and posterior tibial = 0'097 sec. (distance estimated at 91 centimetres). 



The velocity of the pulse-wave in the arteries of the upper extre- 

 mities=:9-43 metres per sec., and in those of the lower extremity 9'40 

 metres per second. The velocity is greater in the less extensible arteries 



