THE PULSATORY VARIATIONS IN BLOOD PRESSURE 381 



In this connection the student is cautioned against confounding 

 the velocity of the pulse- wave with the velocity of the blood-stream. 

 The latter is seldom greater than 0.5 m. in a second. Thus, a stone 

 thrown into a river produces ripples upon its surface which progress 

 in all directions with a speed which is not at all identical with that of 

 the flow of this body of water. This must be so, because the production 

 of a current necessitates the bodily onward movement of the different 

 particles of water in a-definite direction, while a ripple merely indicates 

 the passage of a wave incited by changes in the position of a relatively 

 small number of these particles. The wave, therefore, is enabled to 

 attain a much greater speed and to progress even against the stream. 

 While this phenomenon cannot be said to be identical with the arterial 

 pulse, the stone thrown into the river, really plays a part similar to 

 that of the ventricular discharge, in consequence of which those differ- 

 ences in pressure are established which give rise to the elastic excursions 

 of the arterial wall. A much better way of proving this point is to take 

 a fairly long piece of band-tubing which is connected at regular dis- 

 tances with a number of vertical glass tubes. If this tubing is now 

 filled with water by the rhythmic compression of a rubber .bulb, every 

 addition of water gives rise to a wave which may easily be traced 

 through this system, because it induces a successive oscillation of 

 the fluid in the different collaterals. 



It is possible to ascertain the length of the pulse- wave by multi- 

 plying the velocity of transmission with the time required by the wave 

 to pass a certain point. The former value is 7 m. per second and the 

 latter 0.8 sec, because each pulse-wave occupies the time of a cardiac 

 cycle, i.e., it begins with the systolic discharge and ends immediately 

 before the succeeding one. The value so found is 5.6 m. It may there- 

 fore be concluded that each pulse wave arrives at the periphery of the 

 arterial system long before its completion at its point of origin in the 

 aorta. 



The Registration of the Arterial Pulse. Sphygmography. — It has 

 previously been shown that the cardiac variations in arterial pres- 

 sure may be registered without difficulty by connecting the artery with 

 & mercury manometer. It is true, however, that the minute details 

 of these oscillations cannot be depicted in this manner, because the 

 mercury is altogether too sluggish to follow the variations in pressure 

 with accuracy. It is best, therefore, to employ a membrane manome- 

 ter or an optical manometer, such as have been described by Hlirthle 

 and O. Frank. When properly dampened, these instruments com- 

 bine a slight inertia with an exceptionally high speed of reaction. 



The graphic method of investigating the pulse was first employed 

 by Vierordt^ in 1885, but the instrument which he devised for this 

 purpose is not well suited for this kind of work, owing to its relative 

 inelasticity. A much more sensitive instrument has been constructed 



^Lehre vom Arterienpuls, Braunschweig, 1855. 



