THE PULSE. 533 



c wave is due simply to the pulse in the underlying carotid or 

 subclavian artery, and that, therefore, it has no special significance 

 in regard to changes within the auricle itself. Discussions in re- 

 gard to the meaning of this wave have turned largely upon its time 

 relations to the pulse wave in the neighboring arteries. Some ob- 

 servers have obtained records which seem to show that the c wave 

 begins in the jugular before a pulse wave appears in the carotid at 

 thjB same level, as is shown, for example, in the tracings reproduced 

 in Fig. 218. The more sensitive and probably more reliable optical 

 methods of recording indicate, however, that the c wave appears 

 exactly at the time of the pulse in the subclavian artery,* a fact 

 which would justify Mackenzie's view that this wave is due to im- 

 pact from the neighboring arteries. Measurements made in the 

 auricle itself reveal a positive wave occurring at the beginning of 



Carotid 



J \ rv 



^ %f 



R* Int. Jugular 



Fig. 217. Simultaneous tracings of the carotid and venous pulses. In the venous 

 tracing (internal jugular) a indicates the auricular wave due to the contraction of the auri- 

 cle; c is the carotid wave due (Mackenzie) to an impulse from the neighboring carotid 

 artery; v is the ventricular wave due to the checking or stagnation of the flow into the 

 auricle as this chamber fills during the period of closure of the auriculo ventricular valves. 

 (Mackenzie.) 



ventricular systole and explained as due to a protrusion of the 

 closed auriculo ventricular valves toward the auricle as the pressure 

 rises in the contracting ventricle. If this auricular positive wave 

 is transmitted back to the jugular vein it may enter as a factor in 

 the production of the c wave as usually recorded. Following the 

 c wave is a second negative wave, usually quite marked, which 

 occurs during the period of systolic output of blood from the ven- 

 tricles. It has been explained as due to the shortening of the 

 ventricle from base to apex, resulting in a downward movement of 

 the closed auriculo ventricular valves. The sudden forcible pulling 

 down of the floor of the auricle would tend to lower intra-auricular 

 pressure, and the negative wave thus produced if transmitted back 

 to the jugular vein would coincide in time with the fall in pressure 

 following the c wave. This negative wave is converted into a posi- 

 tive wave by the steady inflow of venous blood -, which continues to 

 * Wiggers, loc. cit. 



