ORIGIN AND PROPERTIES OF THE ELASTICITY-ELEVATION. 141 



course is that of the arteries of the lower extremity, in which the apex of 

 the recoil-elevation is formed about 0.45 or 0.52 or 0.59 second after the 

 beginning of the curve, in accordance with the size of the individual. In children 

 and in small individuals the recoil-elevation occurs accordingly earlier in all of 

 the arteries. If a rubber tube be connected with the carotid or the femoral artery 

 of a dog, the sphygmographic tracing may be recorded also from this tube. 

 Under such circumstances the interval between the beginning of the curve and 

 the dicrotic elevation will naturally be directly proportional to the length of the 

 tube. 



2. The dicrotic elevation in the descending limb of the curve will be 

 the lower and the more indistinct the greater the distance of the 

 artery from the heart. It is not surprising that the secondary wave 

 becomes smaller and more indistinct the further it must travel in the 

 arterial tube. 



3. The dicrotic elevation in the pulse will be more distinct the 

 shorter and the more vigorous the primary pulse- wave. It is, there- 

 fore, relatively largest with a short, powerful systole of the heart. 



4. The dicrotic elevation is greater the greater the tension in the 

 arterial tube. 



In Fig. 50 IX and X are recorded with low, V and VI with moderate, 

 and VII with high tension of the arterial wall. 



Influences Affecting Vascular Tens-ion. A number of influences are known 

 that affect the tension in the arterial tube. The tension is diminished by beginning 

 inspiration, vasomotor paralysis, venesection, intermission of the heart's action, 

 heat, and elevation of a part of the body. The tension is increased by beginning 

 expiration, accelerated heart-action, stimulation of the vasomotor nerves, inter- 

 ference with the flow of blood to the periphery (as by conditions of inflammatory 

 stasis), certain poisons (such as lead), compression of other large arterial trunks, 

 the effect of cold and of electricity on the small vessels of the skin, and inter- 

 ference with the venous flow. Likewise, exposure of the arterial trunks is followed 

 by increased vascular tension on account of the stimulation caused by the atmos- 

 pheric air coming in contact with the arterial wall. Increased arterial tension is 

 observed also in association with a variety of morbid conditions. When the ten- 

 sion is high, the entire sphygmographic tracing is, as a rule, lower. 



In conformity with the conditions named, increased tension will be indicated 

 by a lower, more indistinct dicrotic elevation; and diminished tension in the 

 arterial tube, on the other hand, by an enlarged and more distinct dicrotic eleva- 

 tion. A consideration of the laws governing the dicrotic elevation is of great 

 practical significance in the study of the pulse. Moens asserts that the interval 

 elapsing between the primary elevation and the dicrotic wave increases directly 

 as the diameter of the vessel, and that the thickness of the wall diminishes as the 

 coefficient of elasticity becomes smaller. 



ORIGIN AND PROPERTIES OF THE ELASTICITY-ELEVATION. 



In addition to the dicrotic elevation a series of more numerous, 

 though much less distinct, often almost imperceptible, movements are 

 appreciable in the sphygmographic tracing. These (marked e e in Fig. 

 50) are produced by the vibrations of the elastic vessel, which behaves 

 like a tense elastic membrane when it is rapidly and vigorously stretched 

 by the pulse-wave, just as a relaxed elastic sheet of rubber undergoes 

 a series of oscillations when it is suddenly and vigorously stretched 

 and made tense. Similarly, the elastic tube will exhibit oscillatory 

 movements when it passes suddenly from a condition of tension to one 

 of relaxation. These minor elevations produced in the sphygmographic 

 tracing by the elastic vibrations of the arterial wall are known as elas- 

 ticity-elevations. 



As the elasticity-elevations are due to the vibrations of the stretched 

 coat of the blood-vessel, the following facts will be readily understood: 



