Under the enthusiastic and elaborate study of Mahomed the sphygmograph has attained a certain degree of usefulness. Though difficult in its application and limited in its results, yet many of the points demonstrated by it are of sufficient importance to justify their consideration. The sphygmographic tracing of the normal pulse is shown in Fig. 50.
| FIG. 50. |
| AB. The Up-stroke. ABC. Percussion Wave. E. Aortic Notch. D. Dicrotic Wave. |
Now, the points which distinguish an aneurismal tracing from the normal are—1, a sloping up-stroke; 2, impairment or loss of the percussion wave; 3, obliteration of the secondary waves; 4, diminished volume of the curve; 5, vibratile waves; 6, a different blood-tension.
| FIG. 51. |
| Right and Left Radial Pulse in Aneurism of Aorta. |
In comparing the curves shown in Fig. 51, taken from Powell's article upon aneurism, it will be noticed that the up-stroke AB is more sloping in the curve of the right wrist than in that of the left. The percussion and dicrotic waves are entirely smoothed out into an almost uniform wavy slope. As one writer has expressed it, an aneurism acts like an air-chamber in an engine, and tends to break up the intermittent pulse into a steady stream. The relative difference of the blood-tension of two arteries is determined by the relative amount of pressure required of the instrument to develop the tracing. This amount of pressure is sometimes greater and sometimes less on the affected side.
In comparing the tracings from the radials the following points are to be noted: 1. Is there any difference in the percussion waves?—i.e. is the up-stroke more sloping or the apex less pointed in the one than in the other? 2. Is the tidal wave equally high and sustained in both? 3. Is the dicrotic wave equally developed?
If a difference exist in the tidal wave alone, it need not, and probably will not, be due to aneurism. It is the loss of the percussion wave and of the dicrotism which characterizes aneurism.
It must be conceded here that the use of the sphygmograph and the interpretation of its tracings are beset by the greatest difficulties. Mahomed, to whom I am chiefly indebted for these sphygmographic details, declares that the use of the instrument requires great care and skill, and it may easily lead to error. "No one should attempt to use it who cannot readily obtain similar tracings from the two radials of a healthy person." Great care in the application of the instrument should be exerted, and we must guard against all causes of transient excitement. It is well to let the patient see the instrument applied to others before attempting it on him, in order that he may not fear it. The patient must be placed in a comfortable position, with both arms alike, and the points of application of the instrument must be alike on the two sides. The amount of pressure on the two sides must be equal, or the difference carefully noted. Moreover, one should never be contented with one tracing, but a number on each wrist should be taken. If, then, the two radials appear to differ, the precautions must be redoubled, and the pulse tested again on another day. Inequalities of the tracings may be produced by abnormal distribution of the radials, and an old fracture or other injury of one arm may affect the flow of blood in the arm.