168 



THE PULSE. 



[BOOK i. 



Less constant and conspicuous than the dicrotic wave but yet 

 appearing in most sphygmograms is an elevation which appears 

 higher up on the descending limb of the main wave; it is marked 

 B on some of the curves and is frequently called the predicrotic 



FIG. 33. ANAGBOTIC SPHTGMOGBAPH TRACING FROM THE ASCENDING AORTA (Aneurism). 



wave ; it may become very prominent. Sometimes other secondary 

 waves are seen following the dicrotic wave as at D in Fig. 28; but 

 these are very inconstant and usually even when present incon- 

 spicuous. 



When tracings are taken from several arteries or from the same 

 artery under different conditions of the body, these secondary 

 waves are found to vary very considerably, giving rise to many 

 characteristic forms of pulse-curve. Moreover in the same artery, 



FlG. 34. PULSE-TRACING FROM THE DORSALIS PEDIS. 



and with the same instrument, the form and even the special features 

 of the curve vary according to the amount of pressure (expressed 

 either in ounces or in mm. of mercury) with which the lever is 

 pressed upon the artery. Figs. 35, 36 shew a series of changes 

 thus brought about by varying the pressure of the lever ; and Fig. 37 

 shews the effect of this extra vascular pressure on the form of a 

 fully dicrotic pulse. This effect of pressure in fact varies according 

 to the condition of the vascular system. 



"Were we able with certainty to trace back the several features 

 of the curves to their respective causes, an adequate examination 

 of sphygmographic tracings would undoubtedly disclose much 

 valuable information concerning the condition of the body pre- 

 senting them. Unfortunately the problem of the origin of these 

 secondary waves is a most difficult and complex one ; so much so 

 that the detailed interpretation of a sphygmographic tracing is still 

 in most cases extremely uncertain. 



