82 



PEACTICAL PHYSIOLOGY 



elastic vibrations of the wall of the large arteries which result from 

 their sudden distension. The first, secondary, or predicrotic wave may 

 perhaps be produced by reflection of the primary wave from the 



FIG. 80. Marey's sphygmograph. 



periphery. The second or dicrotic wave follows the dicrotic notch. 

 The dicrotic notch is synchronous with the tension of the closed 

 semilunar valves and the second sound of the heart. 



The dicrotic wave, depending as it does on the elastic swing of the 

 arterial wall, is most marked when the arteries are healthy, the 

 arterial pressure low, and the heart-beats slow and powerful. The 

 elastic wall of the aorta and large arteries, suddenly expanded by 



FIG. 81. Dudgeon's sphygmograph. 



the systolic output, then swing in and out like a stretched string when 

 it is plucked. 



Take another pulse tracing and forcibly inspire and expire during 

 the record. The line of the tracing falls during inspiration and rises 

 during expiration. This is due to the effect of respiration on the 



