37 o TEXT-BOOK OF PHYSIOLOGY 



systole the condition of the arterial wall may be represented by the lines a, 

 ^3, g, which indicates that the expansion and recoil of the artery, which 

 together constitute the pulse, partake of the form of a wave the length of 

 which is represented by the line 0, 0, and the height by the distance ^3. 



The Velocity of Propagation of the Pulse-wave. The propagation 

 of ,the pulse- wave from its origin at the root of the aorta to any given point 

 of the arterial system occupies an appreciable period of time. The difference 

 in time between the systole and the appearance of the pulse-wave at the 

 dorsal artery of the foot can be appreciated by the sense of touch. The 

 absolute time occupied by the wave in reaching this point was determined 

 by Czermak to be 0.193 second. The rate at which the wave is propagated 

 over the vessels of the lower extremity has been estimated by the same ob- 

 server at 1 1. 1 6 meters per second, and for the upper extremities at but 6.7 

 meters per second. Other experimenters have obtained for the lower ex- 

 tremities somewhat different results, varying from 6.5 to 1 1 meters per second 

 Weber's original estimate was from 7.92 to 9.24 meters per second. The 

 slower rate of movement in the vessels of the upper extremities has been 

 attributed to a greater distensibility of their walls, a condition unfavorable 

 to rapid propagation. For this reason a low arterial pressure will occasion 

 a delay in the appearance of the pulse- wave in any portion of the body; a 

 high arterial pressure will of course have the opposite effect. The difference 

 in the speed of the pulse- wave and the blood-current shows that they are not 

 identical and must not be confounded with each other. 



The pulse-wave which thus spreads itself over the entire arterial system 

 with each systole of the heart can be perceived in certain localities by the eye 

 by the sense of touch, and investigated with various forms of apparatus or 

 instrumental means. The pulse-wave, or at least the elevation of the soft 

 tissues overlying it, can be seen in the radial artery, where it passes across 

 the wrist-joint, in the carotid artery, in the temporal artery, and in the arteries 

 of the retina under certain conditions, with the ophthalmoscope. 



The Radial Pulse. If the ends of the fingers are firmly placed over the 

 radial artery, not only the increase and decrease of pressure, but also many 

 of the peculiarities of the pulse-wave, may be perceived. Without much 

 difficulty it may be perceived that the expansion takes place quickly, the re- 

 coil relatively slowly ; that the waves succeed one another with a certain fre- 

 quency, corresponding to the heart-beat; that the pulsations are rhythmic 

 and are characterized by rate, force, volume, hardness, softness, etc. 



Inasmuch as the individuality of the pulse-wave varies at different periods 

 of life and under different physiologic and pathologic conditions, various 

 terms more or less expressive, have been suggested for its varying qualities. 

 Thus the rate is said to be frequent or infrequent according as it exceeds or 

 falls short of a certain average number, viz., 72 per minute; the force is 

 said to be strong or weak according to the energy with which the vessel 

 expands; the volume is said to be large, full or small, according to the 

 volume of blood ejected into the aorta, or, in other words, the degree 

 of fullness of the arterial system; the hardness or softness will depend on 

 the internal pressure or the resistance which the vessel offers to its com- 

 pression by the fingers. If the pressure is high the pulse is hard or tense; 

 if it is low the pulse is soft and easily compressible; the pulse is also said 

 to be quick or slow, according to the suddenness with which the expansion 

 takes place or strikes- the fingers. 



