THE PULSE. 



473 



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. 



The pulse wave obtained from the radial artery is represented 

 in Fig. 199. It will be seen from this figure that the artery dilates 

 rapidly and then falls more slowly. The ascending portion of the 

 wave is spoken of as the anacrotic limb, the descending as the 

 catacrotic limb. Under usual conditions the anacrotic limb is 

 smooth, that is, shows no secondary waves, while the catacrotic 



198. 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, FI, and thence to 

 the bent lever, FZ, whose 

 movement is effected through 

 the weight, g. The writing 

 point S, of this lever makes 

 the record on the smoked sur- 

 face, A. 



Fig. 199. Sphygmogram from the radial artery, Dudgeon sphygmograph : D, The dicrotic 

 wave; P, the predicrotic wave. 



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 approximately at the middle of the descent 

 (D) and is designated as the dicrotic wave. A less conspicuous wave 

 between it and the apex of the pulse wave is known usually as the 

 predicrotic wave, P, while the wave or waves following the dicrotic 



