CIRCULATION 



265 



By recording the changes produced by the pulse wave as it 

 passes any point in an artery the shape of the wave may 

 be deduced. 



This may be done by any of the various forms of sphygmo- 

 graph. (Practical Physiology.) 



Such a tracing is not a true picture of the wave, but 

 simply of the effect of the wave on one point of the arterial 

 wall. Its apparent length depends upon the rate at which 



Medium Pressure. 



Medium Pressure. 



Low Pressure, 



FIG. 123. Three Sphygmographic Tracings made from the radial artery of a 

 healthy man in the course of one hour without removing the Sphygmo- 

 graph. 1 was made immediately after muscular exercise ; 2 was made 

 after sitting still for half an hour ; and 3, after an hour. 



the recording surface is travelling and not on the length of 

 the wave. 



Its height depends in part upon the length of the recording 

 lever, in part upon the resistance offered by the instrument, 

 in part upon the degree of pressure, with which the instru- 

 ment is applied to the artery, and in part on the thickness of 

 the arterial wall. 



Such a trace shows (fig. 123) 



1st. That the pulse waves generally follow one another with- 

 out any interval. 



