200 THE CIRCULATION OF THE BLOOD 



Alteration in the rate of transmission of the pulse wave in the arter- 

 ies of man depends entirely upon an application of these principles. 

 When the arteries become hardened in old age, the rate of transmission 

 of the pulse wave is markedly increased. The pulse is also transmitted 

 more rapidly in the vessels of the lower extremities than in those of the 

 upper, since in the former the blood vessels are somewhat more rigid. 

 Delay in the transmission of the pulse wave is further observed as one 

 of the signs of aneurism in a vessel; as is well known, aneurism of the 

 subclavian artery on one side causes a delay of the pulse on that side 

 that is perceptible to the fingers. 



The Contour of the Pulse Curves 



For more particular study of the exact contour of the pulse wave, and 

 especially for determining the time relationships of the secondary waves, 



Fig. 57. Diagram of Chauveau's dromograph. a, tube for introduction into the lumen of the 

 artery, and containing a needle or vane, which passes through the elastic membrane in its side 

 and moves by the impulse of the blood current; c, graduated scale for measuring the extent of 

 the oscillations of the needle. 



a large variety of methods of varying degrees of accuracy have been 

 elaborated for each kind of pulse. 



Those devised for measuring the pressure pulse have already been de- 

 scribed (see page 127) , and for the other pulses they are as follows : 



Velocity Pulse. Much ingenuity has been displayed in the elabora- 

 tion of methods for recording the velocity pulse. In one of these the 

 artery is cut across and the ends attached to a tube, into the lumen 

 of which projects a paddle or vane articulated with a light lever, which 

 passes through its wall (see Fig. 57). The vane floats in the blood 

 stream, and the outer end of the lever to which it is attached is con- 

 nected with some device to record its movements, which vary with the 

 velocity of bloodfiW (hemodromograph). Another method consists in 

 the application of the instrument known as Pitot's tube used by phys- 

 icists. This consists of a horizontal tube having two side tubes, each of 



