THE PULSE 113 



3. Upon the elasticity of the bloodvessel walls. An abnormal 

 change in either of the three will modify its character. An 

 artery not only increases in its girth as the pulse wave sweeps 

 over it, but also in its length, which can readily be seen when 

 the vessel has a sinuous course. The increase in girth can be 

 felt when the artery is pressed upon with the finger, and forms 

 a constant means of diagnosis. The rate of the pulse wave 

 is from 6 to 9 meters a second. As the blood moves on an 

 average in the arteries only one-half a meter in the same time, 

 it is clear that it is not the travelling of the blood that pro- 

 duces the pulse, but a wave of pressure." A number of terms 

 describe the character of the pulse. In regard to its tension 

 it may be: 



Of high tension or of low tension. 



Incompressible or compressible. 



Hard or soft. 



Very hard (wiry) or very soft (gaseous). 



High tension is indicative of high blood pressure, which 

 can be measured by a sphygmomanometer. In regard to its 

 size the pulse may be : 



Large or small. 



Very large (bounding) or very small (thready). 



A large pulse often indicates a low mean blood pressure. 

 Finally, the pulse may be short or long. It is long when the 

 upstroke takes place slowly. 



While an experienced physician can appreciate slight varia- 

 tions in the character of the pulse, it is only by means of the 

 graphic method that different kinds of pulse can be investigated 

 successfully and records kept. The sphygmograph is an instru- 

 ment which measures the succession of alternate dilatations 

 and contractions of an artery, magnifying them, and register- 

 ing them on a surface moving at a uniform rate by clockwork. 

 The tracings show variations of the pulse too slight to be 

 appreciated by the most experienced fingers. The record of 

 a sphygmograph is called a sphygmogram. Each pulsation 

 of the artery is seen to be made up of a sudden and direct 

 upstroke and a gradual oscillating downstroke* The latter 

 in typical tracings is made up of three waves, of which the 

 middle one is the most pronounced, and is known as the dicrotic 

 /rare. \Yhrn the dicrotic wave can be felt with the finger, 

 8 



