MAREY'S SPHYGMOGRAPH 



165 



and its pressure on the artery is modified by the screw F or by an eccentric 

 as in fig. 126. On the upper surface of the spring rests the end of a screw, 

 p, which carries a small lever terminating in an upright with a knife-edge, e. 

 The knife-edge comes into contact with the recording lever L at a point very 

 close to its axis and on the metal piece a. This metal piece is not connected 

 to the screw g p. The lever is kept in contact with the knife-edge by a weak 

 spring, s 1 . By turning the screw g the knife-edge is raised or lowered, and 

 so the lever l is adjusted to record its movements on the recording surface. 



In fig. 128 is reproduced a tracing obtained by this method. Each 

 unit is seen to consist of a rapid ascent followed by a more gradual 



Fig. 128. — Sphygmogkam Taken by Marey's Sphygmograph. a b, the Primary 

 Wave ; c, the Dicrotic Notch ; d, the Dicrotic Wave ; and e, Post-Dicrotic 

 Wave. 



descent. The ascent in a normal tracing is unbroken. In the 

 descent is seen one conspicuous break in the curve at c. This is the 

 dicrotic notch. The descent from b to c shows one slight break just 

 above c : this is the pre-dicrotic wave. The descent from d to e shows 

 one or two further waves : these are the post-dicrotic waves. The 

 "main wave from a to & is termed the primary or percussion wave. 



The record is one of the changes of transverse diameter of the 

 artery, though it is complicated by the fact that the artery is 

 accompanied by veins, and the state of distension of these can exert 

 an effect upon the tracing. By comparison of the pulse tracing of 

 an animal with a simultaneously taken record of the intra-ventricular 

 and aortic pressures the meaning of the different parts has been 

 elucidated. The sudden rise of the lever from a to b is due to the 

 sudden forcing of a fresh quantity of blood by the heart into the 

 elastic aorta. This produces a sudden rise of pressure and distension 

 of the aorta, which is then propagated as a wave of distension over 

 the whole arterial system. The dicrotic notch is immediately 

 preceded by the closure of the semi-lunar valves. The dicrotic wave 

 is therefore a secondary wave produced by reflexion from the surface 

 of the valves. The pre-dicrotic and post-dicrotic waves are waves 

 of oscillation produced in the elastic arterial wall. They are more 

 conspicuous in pulse tracings taken from -persons in whom the blood 

 pressure is high. 



