SPHYGMOGRAM 



2 4 I 



conditions, generally of disease, it becomes so marked as to be quite plain 

 to the unaided finger. Such a pulse is called dicrotic. The generally ac- 

 cepted explanation of the cause of the dicrotic wave is that it represents a 



B 



FIG. 200. A , Normal Pulse Tracing from Radial of Healthy Adult Obtained by the 

 Sphygmometer; B, from same artery, with the same extra-arterial pressure, taken during 

 acute nasal catarrh. 1-2 Anacrotic limb; 2-8 Catacrotic limb; 3 Predicrotic notch; 

 5 Dicrotic crest; 6 Postdicrotic notch; 7 Postcrotic crest; 4 Dicrotic notch. 



rebound of the overdistended artery at the time of the closure of the aortic 

 valves. During systole, as the blood is forcibly injected into the aorta, 

 there is an overdistention of the artery. The systole suddenly ends, the 

 aorta by reason of its elasticity tends to recover itself, the blood is driven 

 back against the semilunar valves, closing them and at the same time giv- 

 ing rise to a wave, the dicrotic wave, which begins at the heart and travels 

 onward toward the periphery like the primary wave. According to Foster, 

 the conditions favoring the development of dicrotism are: i, a highly ex- 

 tensible and elastic arterial wall; 2, a comparatively low mean blood-press- 

 ure, leaving the extensible reaction free scope to act; 3, a vigorous and rapid 

 stroke of the ventricle discharging into the aorta a considerable quantity 

 of blood. The other secondary waves are probably due to the oscillations 

 in the elastic recoil of the arteries, though some of them at least may be 

 due to the inertia of the instruments used. 



In the use of the sphygmograph care must be taken in the regulation of 

 the pressure of the spring. If the pressure be too great, the characters of 

 the pulse may be almost entirely obscured or the artery may be completely 

 obstructed and no tracing is obtained. On the other hand, if the pres- 



