THE VELOCITY OF THE PULSE WAVE. 103 



velocity of transmission and the coefficient of elasticity increase. 

 Thus Moens 1 determined that in the same individual the velocity 

 was greater when the arterial pressure was higher. In Valsalva's 

 experiment the filling of the heart is impeded by the increase of intra- 

 thoracic pressure, hence the arterial pressure falls. During this con- 

 dition, the velocity of the pulse wave has been estimated to be 7 metres 

 per second, while during quiet respiration the velocity rose to 8 metres 

 per second. 



Before stimulation of the peripheral end of the vagus, Moens 

 estimated the velocity to be 11 "5 metres per second. During the first 

 six beats, after the cessation of cardiac inhibition, the velocity was 4 - 5 

 metres, 4*5 metres, 6"0 metres, 7'5 metres, 12 metres, 13*5 metres, respect- 

 ively, per second. Similarly, when the arterial pressure is lowered by 

 a condition of deep amesthetisation, or by dividing the spinal cord, the 

 velocity is lessened, while it is increased by excitation of the divided 

 spinal cord. 2 



By placing the arm in hot water, the velocity of transmission from 

 the carotid to the radial artery may be lowered by 14 per cent., owing 

 to the local dilatation of the blood vessels. The velocity may be found 

 to be different in the arm and in the leg, owing to the variations in the 

 elastic coefficient of the arteries of these parts — variations which may 

 depend upon the structure of the arterial wall, upon the hydrostatic 

 effect of gravity, or upon the local condition of vascular dilatation. When 

 the arteries are sclerosed, and the rigidity of the wall is increased, as 

 in the degenerative condition which accompanies chronic Bright's disease, 

 the velocity is increased. 



The length of the pulse wave is the product of the velocity of trans- 

 mission of the wave into the time occupied by the wave in passing any 

 given point ; which time, in the case of the pulse wave, is about the 

 time of a cardiac cycle, i.e. 0*8 second. 



If the velocity of transmission be taken as 6 metres per second, then 

 the length of the wave will be 6 metres X - 8, i.e. about 5 metres. 

 From this it follows that the pulse wave reaches the periphery long 

 before it has left the aorta. 



The characteristic features of the pulse curve. — The radial 

 artery is surrounded by veins. A vena comes lies on either side, whilst 

 a superficial vein (a branch of the median or radial) often lies directly 

 over or just to the side of the artery (Fig. 68, c). 



In Figs. 68, 69, there is represented (drawn to scale) the arrangement of 

 the veins and artery. The plane of the section (Fig. 68) passes through the 

 spot where the radial pulse is usually explored by the ringer or the sphygmo- 

 graph. The artery and veins lie in a space between the styloid process of 

 the radius and the tendon of the flexor carpi radialis. This space may be con- 

 veniently termed the radial sulcus. 



If, after ligation of the upper forearm in a corpse, the radial artery 

 be distended from above, and the venae comites from below, it appears 

 to the finger as if one broad flat band filled the radial sulcus. If the 

 artery be then pulsed by rhythmically compressing the tube connected 

 with the arterial pressure bottle, both artery and veins seem to share in 

 the pulsatile movement. 



1 "DiePulscurve/'Leyden, 1878, S. 111. 



2 Grunmach, Arch. f. Physiol., Leipzig, 1879, S. 424. 



