SPHYGMOGRAM 



207 



C, called the dicrotic notch, followed immediately by a second more or less 

 marked ascent of the lever called the dicrotic wave, D. Not infrequently 

 there is also at the beginning of the descent a slight wave previous to the 

 dicrotic notch; this is called the pre-dicrotic wave, and in addition there 

 may be one or more slight waves after the dicrotic, called post-dicrotic, E. 

 The interruptions in the downstroke are called the catacrotic waves to dis- 

 tinguish them from an interruption in the upstroke, called the anacrotic 

 wave, which is sometimes met with. 



The explanation of these tracings presents some difficulties, not, how- 

 ever, as regards the two primary factors, viz., the upstroke and downstroke, 



To manometer. 



FIG. 197. Diagrammatic Sectionr.l Representation of the Sphygmometer. a, Box by which 

 the portion of the artery is covered; b, thin- walled india-rubber bag filled with water, and com- 

 municating through tap, c, with the manometer and thick- walled rubber bag, h ; d, piston con- 

 nected by rod, e, with recording lever, /; g, spiral spring, attached to axis of lever, and by which 

 the pressure in b, against the piston, d, is counterbalanced; k, skin and subcutaneous tissue; m, 

 end of radius seen in section; n, radial artery seen in section. (Roy and Adami.) 



because they are universally taken to mean the sudden injection of blood 

 into the already distended arteries, and the gradual recovery of the arteries 

 by their recoil. These points may be demonstrated on a system of elastic 

 tubes, with a pump to inject water at regular intervals, just as well as on the 

 radial artery, or on the arterial schema, a more complicated system of tubes 

 in which the heart, the arteries, the capillaries and veins are represented. 

 If we place two or more sphygmographs upon such a system of tubes at in- 

 creasing distances from the pump, we may demonstrate, first, that the rise 

 of the lever commences earliest in that nearest the pump, and, second, that 

 it is higher and more sudden. So in the arteries of the body the wave gradu- 

 ally gets less and less as we approach the periphery of the arterial system, 

 and is lost in the capillaries. 



