FLOW OF BLOOD THROUGH THE ARTERIES 1043 

 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 prolongation 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 pronounced in young people than in old people, whose arteries 

 have become rigid. Where 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 committed 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 considerable time and have influenced most of the clinical work on this 

 subject. According to these authors all the secondary waves on the pulse-curve 

 are central in origin, and can therefore be traced with slight modification on the 

 curves obtained from the aorta, the large and the small arteries. Although 

 Marey investigated the propagation of reflected waves and showed their presence 

 in the artificial schema of the circulation (vide p. 1036), he considered that they 

 could not contribute to the production of the waves on the pulse-curve, owing 

 to the enormous number of points at which reflection might occur, so that the 

 different reflected waves would tend to mutually annul each other's effects. 

 Moreover the distance of the dicrotic notch from the primary elevation was 

 found to be nearly the same at different parts of the system, pointing to a propa- 

 gation of this wave from the centre to the circumference of the arterial system. 



