380 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



the arterial pulse into relation with the apex-beat, as well as with the 

 venous pulse. The latter is generally noted in the region of the cen- 

 tral end of the right external jugular vein and is, of course, indicative 

 of the rate of the auricles. In this way it is possible to detect imme- 

 diately any dissociation in the rhythm of the heart. 



The Velocity of the Arterial Pulse. The fact that the pulse 

 progresses as a wave, 1 may readily be proved by the simultaneous 

 palpation of the carotid and radial arteries, because, as the former 

 blood-vessel lies closer to the heart, the characteristic systolic bump 

 will be noted sooner here than in the latter region. The interval, 

 however, is so brief that only a practised observer will be able to per- 

 ceive it. A more plastic way of demonstrating the wave-like character 

 of the pulse is furnished by the graphic method. Two receiving tam- 

 bours which in turn are connected with two recording tambours, are 

 placed upon an artery at different distances from the heart. Upon 

 being permitted to record in the same vertical line, it will be found 

 that the lever nearest the heart is always raised first, and naturally, 

 the difference in time between the upstrokes of the two levers is the 

 time which the pulse-wave requires in traversing the segment of 

 the artery situated between them. Having determined this distance, 

 it is a simple matter to calculate the velocity of this wave. 



While it may be said that the rate of progression of the pulse is 

 fairly constant, its speed must differ somewhat from moment to 

 moment, because the conditions in the vascular system are subject 

 to frequent changes. This is especially true of the elastic coefficient 

 of the arterial wall. Thus, it may be inferred that its velocity in- 

 creases whenever the arterial pressure is raised and decreases whenever 

 the latter is diminished. 2 These differences may readily be demon- 

 strated by the repeated stimulation of the vagus nerve which procedure 

 is followed by a fall in pressure incurred by the diastolic tendency of the 

 heart. For very similar reasons the velocity of the pulse is also de- 

 creased during sleep and anesthesia. The difference may amount to 

 1 m. per second and more. Concurrently, it may be reasoned that a 

 lessening of the distensibility of the arteries must induce a greater 

 velocity of this wave. A condition of this kind arises, for example, 

 during arterio-sclerosis. Landois, 3 Edgren, 4 and others have found 

 values ranging between 6.5 and 9.0 m. in a second. The arteries used 

 for these determinations were the carotid and femoral or the carotid 

 and radial. It has also been noted that the velocity of the pulse is 

 somewhat greater in the blood-vessels of the arm than in those arising 

 from the descending aorta. It seems that 7 m. per second may be 

 regarded as a fair average value. 



1 Discovered by Erasistratus, but denied by Galenus. It remained obscure 

 until the time of Haller. In 1850 E. H. Weber made the first attempts to deter- 

 mine its velocity. 



2 Moens, Die Pulskurve, Leyden, 1878. 



3 Lehre vom Arterienpuls, Berlin, 1872. 



4 Skand. Archiv fur Physiol., i, 1889, 67. 



