THE PULSE. 491 



ment must be appealed to whenever the determination of blood- 

 pressure is a matter of importance. 



Venous Pulse. Under usual conditions the pulse wave is lost 

 before entering the capillary regions, but as a result of dilatation in 

 the arteries of an organ the pulse may carry through and appear in 

 the veins, in which it may be shown, for instance, by the rhythmical 

 flow of blood from an opened vein. The term venous pulse, how- 

 ever, as generally used aprj'lies to an entirely different phenomenon, 

 namely, to a pulse observed especially in the large veins (jugular) 

 near the heart. The pulse in this case is not due to a pressure wave 

 transmitted through the capillaries, but to pressure changes of 

 both a positive and negative character occurring in the heart and 

 transmitted backward into the veins. The venous pulse that has 

 this origin may usually be seen and recorded in the external (or 

 internal) jugular. Under pathological conditions, especially when 

 the flow through the right heart is more or less impeded, it may 

 be plainly apparent at a further distance from the heart and may 

 cause a noticeable pulsation of the liver, which is designated as a 

 liver pulse. The venous pulse curve has been much studied in 

 recent years.* It is somewhat complicated and an explanation 

 of some of its details has not been agreed upon, but there can be no 

 doubt that when properly interpreted it will throw much light upon 

 the pressure changes in the heart, and will afford a valuable means 

 of diagnosis in cases of valvular lesions and other pathological 

 conditions of the heart. It is evident also that the venous pulse 

 gives a ready means of determining the rate of beat of the auricles, 

 just as the arterial pulse enables us to count the beats of the ven- 

 tricles. 



Fig. 205. 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 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 ; x, dilatation 

 due to auricular diastole ; y, the period of ventricular diastole. (Mackenzie.) 



The venous (jugular) pulse as given by Mackenzie is represented in 

 Fig. 205. Three positive waves are shown, a, c, and v. The a wave or auric- 



* See Mackenzie, "The Study of the Pulse," 1902; also Hirschf elder, "Amer- 

 ican Journal of the Medical Sciences," Sept., 1906, and Morrow, "British 

 Med. Journal," 1906 and 1907. 



