926 PHYSIOLOGY 



been called the percussion wave and the predicrotic wave. In the same 

 way the inertia of the instrument will tend to exaggerate the dicrotic 

 elevation and possibly to give rise to slight postdicrotic waves. 



The general form of the pulse-curve varies with changes in the heart, 

 in the arteries, and in the peripheral resistance. Thus some curves may 

 present secondary elevations on the ascending part, and are called anacrotic, 

 while in others all secondary elevations occur on the descending part. 

 The latter type is called catacrotic, and is the tracing usually obtained 

 from a normal radial artery. By comparing these two types of curves 

 with the corresponding intraventricular pressures, we find that in both 

 cases blood is flowing into the aorta during the whole time from the beginning 

 of the primary elevation to the notch just before the dicrotic elevation. 

 This is shown by the fact that the intraventricular pressure is all this time 

 slightly higher than the aortic pressure. So long as this is the case blood 

 must flow from ventricle into aorta. (This fact proves that there is normally 

 no part of the cardiac cycle during which the ventricle remains contracted 

 and empty, the ventricle in all cases relaxing before it has completely 

 emptied itself of blood.) 



Now it is easy to see the conditions which determine whether the systolic 

 plateau shall be ascending or descending, and therefore when the pulse 

 shall be anacrotic or catacrotic. If, after the first sudden rise of pressure 

 in the aorta, the blood can escape more rapidly through the peripheral 

 resistance than it is thrown into the beginning of the aorta, the ' systolic 

 plateau ' will sink, and a catacrotic pulse tracing is obtained. If, on the 

 other hand, the peripheral resistance is high, or an extra large amount of 

 blood be thrown into the aorta at each stroke of the heart (e.g. by prolonga- 

 tion of the diastole), the aortic pressure will rise so long as blood is flowing 

 in, and we get an ascending systolic plateau and an anacrotic pulse. Thus 

 we obtain an anacrotic pulse in old people with Bright's disease, in whom 

 the peripheral resistance is very high, and also in animals when the heart 

 is slowed by vagus action. 



The production of the dicrotic elevation is favoured by any influence 

 which increases the elastic resiliency of the arteries or causes the primary 

 elevation of the pulse to be rapid and sharp. Thus it is much more pro- 

 nounced in young people than in old people, whose arteries have become 

 rigid. When the peripheral resistance is low through relaxation of the 

 arterioles, and" the heart is beating forcibly, as in many cases of fever and 

 also to some extent after a good meal with alcohol, the dicrotic elevation 

 becomes very marked. Under such circumstances it may be easily felt 

 with the finger at the wrist, and in many cases the mistake has been com- 

 mitted of taking the dicrotic wave for a normal beat, and so doubling the 

 rate of the pulse, 



OTTO FRANK'S WORK ON THE PULSE. In the account given above of the 

 peculiarities of the pulse -curve in different parts of the system I have adopted in the 

 main the views of Marey and Hiirthle, which have been generally accepted for a con- 

 siderable time and have influenced most of the clinical work on this subject. According 



