FLOW OF BLOOD THROUGH THE ARTERIES 1045 



open, sets these structures into vibration and so causes the fine oscillations of 

 pressure on the aortic side of the valves. 



(c) The Peripheral Pulse. The effect of the propagation of the fairly simple 

 wave started in the aorta in an endless system of elastic tubes would be to 

 diminish the rapidity of onset of each vibration, and therefore to diminish the 

 secondary vibrations on the curve. In a closed elastic system of tubes, such 

 as the arterial system, there will be factors at work analogous in many respects 

 to those responsible for the deformation of the curve given by an imperfect 

 manometer. These will be of two kinds, namely, (1) oscillations of the column of 



C 



D 



E 



FIG. 419. Pulse-pressure curves taken by means of Frank's manometer. 



(FRANK.) 



A, B, c, aortic pressure curves at different rates of the heart ; D and E, aortic 

 pressure curve, D, compared with simultaneous record of the pressure in the 

 femoral artery E. 



fluid within the stretched arterial wall, (2) reflections of waves from different 

 points in the periphery. These reflections we should expect to be evident in certain 

 cases. Thus in the carotid there should be a reflected wave from the circle 

 of Willis ; in the descending aorta, from the bifurcation of this vessel into the 

 two iliac arteries. As a result the pulse in the peripheral arteries, such as the 

 radial or femoral, diverges considerably from the pulse in the aorta. In the figure 

 (Fig. 419 E) the primary rise of pressure in the femoral artery is even higher than 

 the primary rise in the aorta, i. e. the primary wave must be augmented here by a 

 reflected wave from the periphery. Frank acknowledges that the dicrotic depres- 

 sion in this curve is due to the propagation of the wave set up by the closure of the 

 aortic valves ; but he would regard the more pronounced dicrotisrn of the pulse, 

 of which examples have been given earlier, as due for the most part to the reflec- 

 tion of waves from the periphery. 



