CHAPTER XXIII 

 THE BLOODFLOW IN THE ARTERIES 



THE PULSES 



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

 we may now consider the temporary changes produced in the bloodflow 

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

 general term of the pulses, of which three may be distinguished: (1) 

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

 each heartbeat (see page 129) ; (2) the velocity pulse, or pulsatile accel- 

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

 of the walls 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. 95) taken from the apex or 

 the carotid and radial arteries we 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 which the carotid artery springs. We shall find 

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

 of the artery involved, would work out as a transmission velocity of 

 about seven meters per second or about seventeen miles an hour. The 

 pulse therefore travels along the blood vessels at a much greater speed 

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

 about 0.5 meters per second in the larger blood vessels. 



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

 ing along a stream which is flowing in the same direction with 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 with the cue, the end balls will fly off while the others are 

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

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



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