150 APPLIED PHYSIOLOGY 



aortic orifice, therefore, and cases in which the diastolic 

 pressure within the arteries is high are characterized by 

 a pulse wave of gradual ascent. 



The apex of the curve will be well or ill sustained, and 

 the downstroke gradual or abrupt, in accordance with the 

 ease with which the blood can escape through the arte- 

 rioles into the capillaries. When the arterioles are con- 

 tracted, therefore, the apex is blunt and the pulse ' well 

 sustained ' ; when they are dilated, it is pointed and the 

 pulse ' collapsing.' 



The predicrotic wave will be well marked when the 

 artery tends to flatten itself slowly between the beats, 

 and so allows the lever to rest upon it for a moment 

 before collapsing. A well-marked predicrotic wave is, 

 therefore, a sign of a high diastolic pressure in the 

 artery. The dicrotic wave, on the other hand, is best 

 marked when the pressure tends to fall rapidly after the 

 pulse, so allowing the secondary rebound from the aortic 

 cusps the opportunity to make its presence felt, which it 

 could not do in a full vessel. A ' dicrotic ' pulse is, 

 therefore, usually met with in cases of low pressure due 

 to rapid escape of blood into the capillaries, especially 

 when combined with a short, sharp systole. Its presence, 

 however, is not incompatible with high systolic pressure, 

 provided the latter be of ventricular origin. 



The pulse wave travels along the arteries at the rate of 

 about 30 feet per second. Owing to the elasticity of the 

 great vessels, part of the work of the heart is spent in 

 distending them, and this causes a delay in the trans- 

 mission of the wave of pressure, so that the pulse is not 

 synchronous with the heart-beat, but follows it at an 



