390 THE MECHANICS OF THE CIRCULATION, HEMODYNAMICS 



3. The y-wave appears normally from 0.1 to 0.2 second after the commence- 

 ment of the a-wave and finds its origin in the pressure changes resulting from 

 ventricular systole. 



In view of the fact that the c-wave appears in the external jugular 

 vein before the corresponding cardiac impulse has had sufficient time to 

 make itself felt in the carotid artery, it seems that this explanation of 

 Mackenzie cannot be correct. In this connection it should also be 

 remembered that a venous pulse is present in the pulmonary veins, 

 and that its cause is precisely the same as that producing these pulsa- 

 tions in the systemic veins. • 



The Pathological Venous Pulse. — This phenomenon is most com- 

 monly associated with an incompetency of the tricuspid valve, but may 

 also appear in the pulmonary vein in consequence of mitral regurgita- 

 tion. It may be surmised that this regurgitation of the blood into the 

 auricle gives rise to a much larger c-wave than the normal upward 



movement of the auriculoventricular 

 '^..'•>. septum could possibly produce. In 



fact, a severe insufficiency often in- 

 creases the amplitude of this wave 

 so greatly that it completely over- 

 laps the a-wave. Under this condi- 

 tion, the phlebogram presents only 

 Fig. 204.— Diagrammatic Representa- one large initial rise which is followed 

 TioN OF THB Pai^. Venous Pui^e. ^y ^ ^^^^^^ ^^^^ previously desig- 



In tricuspM^regurd^^^^^^^^ ^^^^ ^^ ^^^ ^_^^^^ j, ^^^, ^^ 



evident that the conspicuousness of 

 the pathological venous pulse must differ with the severity of the 

 valvular lesion, a severe regurgitation increasing the radius of these 

 pulsations so that they may be perceived even in the distalmost veins. 

 The venous engorgement always accompanying the regurgitation 

 eventually produces a hyperemic condition of different organs and 

 preeminently of the Uver. It is then possible to obtain these pulsa- 

 tions directly from this organ by applying a flat metal cup to the skin 

 overlying it, but naturally, the minute details of the individual waves 

 are difficult to record, because the intervening mass of tissue does not 

 readily transmit the rapid oscillations in pressure. A third type of 

 venous pulse is observed at times in the veins of glands, but only 

 when the latter are actively secreting. These pulsations are nothing 

 more than the arterial pulse propagated through the highly distended 

 capillaries of the gland. 



C. THE RESPIRATORY VARIATIONS IN ARTERIAL AND VENOUS BLOOD 



PRESSURE 



The General Character of the Respiratory Variations. — Besides 

 the small cardiac oscillations, the blood pressure also exhibits fluctua- 

 tions of a much larger amplitude which occur synchronously with the 



