THE PULSE 



215 



.J G. 





The depression after v, sometimes termed the // depression, is 

 usually attributed to the opening of the A.-V. valves, and the passage 

 of blood from auricles to ventricles at the beginning of common 

 diastole. 



The Arterial Pulse Curve. In the arterial record, or sphygmograph, 

 the upstroke corresponds to the systolic output of the left ventricle, 

 marking the opening of the aortic valves 

 and the pouring of the blood into the 

 arteries. 



The downstroke represents the time 

 during which the valves are shut and 

 the blood is flowing out of the arteries 

 into the capillaries. There are subsi- 

 diary waves on the downstroke. The 

 chief of these is called the "' dicrotic 

 wave," the notch preceding which marks 

 the closure of the semilunar valves 

 (c, Fig. 117). The dicrotic notch is 

 caused by the swing back of the blood 

 towards the heart when the outflow 

 ceases, and the elastic rebound of the 

 blood from the closed semilunar valves 

 and root of the aorta causes the dicrotic 

 wave. If the aortic valves move back 

 1 centimetre and the diameter of the 

 orifice of the aorta is 2-6 centimetres, 

 then 1-8 centimetres of blood move back 

 towards the heart. It is most manifest 

 when the systole is short and sharp, and 

 the output of blood from the arterioles 

 rapid; in other words, when the heart- 

 beat is strong, the systolic pressure 

 high, and the diastolic pressure low. 

 Its central origin is proved by the fact 

 that it appears in the carotid or brachial 

 at the same interval of time after the 

 primary wave as in the radial artery. A 

 smaller wave, predicrotic, preceding this 

 occurs during the period of output, 

 and sometimes is placed on the ascend- 

 ing limb of the pulse-curve. This occurs 

 when the peripheral resistance is great, 

 and the pulse is then termed anacrotic. 

 It iisually occurs when the outflow from the heart is impeded as, 

 for example, by stenosis of the aortic valves. By compression of the 

 abdominal aorta the carotid pulse can easily be made to exhibit an 

 anacrotic wave. 



The post-dicrotic waves are due to secondary elastic swings of 

 the big arteries following the dicrotic swing. The form of these waves 



Js 



