356 TEXT-BOOK OF PHYSIOLOGY. 



eral blood-pressure, as shown by the small curves on a blood-pressure tracing, 

 and for this reason the pressure which causes the expansion and recoil is 

 termed the pulse pressure. It is denned as the rhythmic change in pressure 

 at any given point of the arterial system; and in amount, is the difference 

 between the diastolic and the systolic pressures, at the corresponding points. 

 The volume of blood ejected from the ventricle is frequently termed the 

 pulse volume. 



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 11.16 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 n 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, 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 in 

 character, etc. Inasmuch as the individuality of the pulse-wave varies at 

 different periods of life and under different physiologic and pathologic con- 

 ditions, various terms more or less expressive, have been suggested for its 

 varying peculiarities. Thus the pulse is said to be frequent or infrequent 

 according as it exceeds or falls short of a certain average number 72 per 

 minute; quick or slow, according to the suddenness with which the expansion 

 takes place or strikes the fingers; hard or soft, tense or easily compressible, 

 according to the resistance which the vessel offers to its compression by the 

 fingers; 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. 



