THE PULSE. 



487 



button of the metallic spring rests over the radial artery. The movements 

 of the artery are transmitted to this spring and this latter in turn acts upon 

 the bent lever, and the magnified movement is recorded by the writing point, 

 upon a strip of blackened paper which is moved 

 under the point by clockwork contained in the 

 case. To obtain a satisfactory record or sphyg- 

 mogram, two details are of special importance: 

 First, the button of the lever must -be pressed 

 upon the artery with the proper force. Theo- 

 retically this pressure should be about equal to 

 the diastolic pressure within'' the artery. All 

 sphygmographs are provided with means to 

 regulate the pressure, and practically one must 

 learn so to place the button and to arrange the 

 pressure as to obtain the largest tracing. A 

 second detail of importance is that the weight 

 of the lever when set suddenly into motion 

 causes a movement, due to the inertia of the 

 mass, which may alter the true form of the wave. 

 To overcome this defect the lever should be as 

 light as possible, or the spring upon which the 

 artery plays should have considerable resis- 

 tance. In those sphygmographs in which the 

 inertia factor is practically eliminated the diffi- 

 culty of obtaining a tracing, especially from a 

 weak pulse, is correspondingly increased, and in 

 the sphygmographs most commonly employed, 

 such as the Dudgeon, facility in application is 

 obtained at the expense of incomplete correction of the error of inertia. 



Fig. 201. The lever of 

 the Dudgeon sphygmograph : 

 P, The button of the spring F, 

 to be placed upon the artery. 

 The movement is transmitted 

 to the lever, F\, and thence to 

 the bent lever, F 2 , whose 

 movement is effected through 

 the weight, g. The writing 

 point S, of this lever makes 

 the record on the smoked sur- 

 face, A. 



The pulse wave obtained from the radial artery is represented 

 in Fig. 202. It will be seen from this figure that the artery dilates 

 rapidly and then falls more slowly, but it must be borne in mind 

 that the very pointed apex of the wave recorded by this form of 

 sphygmograph is due to the instrumental error referred to above, 

 namely, the "fling" of the lever caused, by the sudden expansion 



Fig. 202. Sphygmogram from the radial artery, Dudgeon sphygmograph: D, The dicrotic 

 wave; P, the predicrotic wave. 



of the artery. The ascending portion of the wave is spoken of as 

 the anacrotk limb, the descending, as the catacrotic limb. Under 

 usual conditions the anacrotic limb is smooth, that is, shows no 

 secondary waves, while the catacrotic limb shows one or more 

 secondary waves, which are spoken of in general as the catacrotic 

 waves. The most constant of these latter waves occurs usually 



