THE CIRCULATION OF THE BLOOD 



371 



The three qualities which are of most value to the clinician are rate, 

 strength or force, and volume. 



Frequency of the Pulse. As the pulse or the arterial expansion and 

 recoil is the direct result of the heart's action, its frequency must, under 

 physiologic conditions, coincide with that of the heart. (See page 290.) All 

 conditions which modify the rate of the heart will modify at the same time 

 the rate of the pulse. 



For the purpose of accurately studying and analyzing the pulse-wave and 

 its characteristic features, it is necessary to obtain graphic records of the 

 alternate expansion and recoil of the artery under normal and abnormal 

 conditions. This is accomplished by means of 



The Sphygmograph. The sphygmograph is, therefore, an apparatus 

 designed to take up, reproduce, and record the alternate expansion and recoil 

 of an artery caused by the temporary increase and decrease of pressure fol- 

 lowing each heart-beat. The tracing pr record obtained with it is termed the 

 pulse-curve or the sphygmogram. Different forms of this apparatus have been 



FIG. 170. VON FREY'S SPHYGMOGRAPH. GS. Metal framework. P. Button attached to spring. 

 F. Vertical rod. U. Clock-work which turns the recording cylinder. VI. Time marker. 



devised by Marey, Dudgeon, v. Frey, and many others. The instrument 

 of v. Frey is shown in Fig. 170. This consists, first, of a metal framework 

 GS by which the apparatus is fastened to the arm and support given to the 

 lever, recording surface, etc. The essential part is the spring carrying a but- 

 ton P, which is placed over the artery, usually the radial, before it crosses the 

 wrist-joint. A vertical rod F transmits the 

 movement of the spring to the recording lever; 

 the movements of the latter are recorded on a 

 small cylinder inclined slightly so that the 

 upstroke may be vertical. A small electro- 

 magnet serves to record the time relations of the 

 changes in the blood-pressure. The artery 

 usually selected for obtaining a sphygmogram is 

 the radial. This artery lies quite superficially, 

 is covered only by connective tissue and skin and is supported by the flat 

 surface of the radial bone, conditions most favorable to technical investiga- 

 tion. When the apparatus is properly adjusted a tracing similar to that 



FIG. 171. THE PULSE-CURVE 

 OR SPHYGMOGRAM OF THE RADIAL 

 ARTERY. 



