CHAPTER XXI 1 1 

 THE BLOODFLOW IX THE ARTERIES 



THE PULSES 



Returning to the physical laAvs that govern the circulation of the blood, 

 "\ve may now consider the temporary changes produced in the bloodfloAV 

 in the arteries by each systolic discharge. These changes go under the 

 general term of the pulses, of "which three may be distinguished: (\) 

 the pressure pulse, or the pulsatile increase of pressure produced by 

 each heartbeat (see page 127) ; (2) the velocity pulse, or pulsatile accel- 

 eration of velocity; and (3) the palpable pulse, or the pulsatile expansion 

 of the Avails of the blood vessels produced by the sudden change of blood 

 pressure in their interior. The general characteristics of the three 

 pulses are the same, certain features being however more pronounced 

 in one than in another. 



General Characteristics 



Rate of Transmission of Pulse Wave. — The rate of transmission of 

 the pulse wave can be determined by taking simultaneous tracings of 

 the pulses from two far distant parts of the arterial system along with 

 accurate time-tracings. From records (cf. Fig. 98) taken from the apex or 

 the carotid and radial arteries Ave can determine how long it takes for 

 the beginning of the pulse wave to travel to the radial artery from the 

 point in the aorta from whieh the carotid artery springs. We shall find 

 that it takes about one-tenth of a second, which, considering the length 

 of the artery involved, Avould Avork out as a transmission Aelocity of 

 about seA T en meters per second or about seA'enteen miles an hour. The 

 pulse therefore travels along the blood A-essels at a much greater speed 

 than the blood itself is moving, this being, as Ave shall see immediately, 

 about 0.5 meters per second in the larger blood A-essels. 



The pulse is a Avave of sudden increase in pressure and velocity pass- 

 ing along a stream whieh is floAving in the same direction Avith a cer- 

 tain more permanent pressure and velocity. A simple physical experi- 

 ment may serve to make this clear: If the first of a row of billiard balls 

 be tapped Avith the cue, the end balls Avill fly off Avhile the others are 

 moving slowly along in the direction of the stroke. Bach ball becomes 

 accelerated by the ball behind it, and imparts ils influence to the ball 



I'.IS 



