142 THE DICROTIC PULSE. 



1. In the same artery the variations in elasticity increase in num- 

 ber as the tension of the arterial wall increases. Especially high 

 tension has been encountered chiefly during the cold stage of malarial 

 fever (intermittent fever), and precisely in this connection has the most 

 obvious increase in the elevations also been observed. 



2. If the tension of the arterial wall is greatly diminished, the elas- 

 ticity-elevations may disappear. As diminution in the tension favors 

 the development of a dicrotic elevation, the two kinds of elevations have, 

 with respect to their magnitude, an inverse relation to each other. 



3. In the presence of diseases of the vessel-wall that diminish or 

 even destroy its elasticity, the elasticity-elevations are either greatly 

 diminished 'in size or altogether abolished. 



4. The greater the distance of the artery from the heart, the greater 

 will be the elasticity-elevations in the descending limb of the curve. 



5. When the mean pressure in an artery is heightened on account of 

 interference with the flow of blood in the arteries, the elasticity-eleva- 

 tions are nearer the apex of the curve. 



6. The elasticity-elevations vary in number and position in the 

 sphygmographic tracings from the different arteries in the human body. 



When the arm is held in the vertical position, relaxation and diminution in 

 the elastic tension appear in the course of five minutes in the arteries of the upper 

 extremity, which at the same time contain less blood. 



The elevations that are designated elasticity-elevations are believed by Moens 

 to owe their origin to numerous small waves that appear to be superadded to 

 the dicrotic elevation. Grashey thinks them only in part due to elastic vibrations. 



The laws governing the movement of the pulse may be most readily demon- 

 strated by means of investigations in regard to the undulatory movements in 

 elastic rubber tubes, as has been done by Marey, Landois, Moens, Grashey, G. v. 

 Liebig, and others, 



THE DICROTIC PULSE. 



Under the influence of excessive elevation of temperature the pulse in man 

 is sometimes observed to be composed of two beats (Fig. 50), the first being large 

 and the second small and apparently secondary to the first. A couple of these 

 beats always correspond to a single systole of the heart. By the sense of touch 

 it is quite possible to feel the two unequal beats separately. The study of the 

 pulse with the sphygmograph has taught that the dicrotic pulse is only an 

 exaggeration of the normal pulse. The palpable secondary beat is only a greatly 

 magnified dicrotic elevation, which under normal conditions cannot be recognized 

 by the palpating finger, but which, when increased by some morbid condition, 

 becomes recognizable by the sense of touch. As regards the causes that are 

 responsible for this increase in the size of the dicrotic elevation, Landois' investiga- 

 tions have yielded the following results : 



1. The production of a dicrotic pulse is favored by a short primary pulse- 

 wave, such as occurs usually in the presence of fever, a condition in which the 

 contractions of the heart are comparatively rapid and unproductive. 



2. The dicrotic pulse is favored by reduction of the tension in the arterial 

 system. A short systole combined with diminished arterial tension offers the 

 most favorable condition for the production of the dicrotic pulse. Sometimes 

 the dicrotic pulse is felt only in a certain arterial distribution, while in all the 

 others the pulse-beat is single. This happens especially in the brachial artery on 

 one or other side of the body. Under such circumstances the conditions for 

 the production of dicrotism in the corresponding arterial area must be especially 

 favorable. These conditions will be found in the local diminution of vascular 

 tension in this area in consequence of paralysis of the vasomotor nerves con- 

 trolling it. If the tension be increased, as can readily be done by compressing 

 adjacent or other arterial trunks of considerable size or the corresponding veins, 

 the dicrotic pulse is converted into a single pulse. In the presence of fever, dicro- 

 tism appears to be due to the elevation of temperature (from 39 to 40 C.), which 

 causes greater distention of the artery and shorter and quicker heart-beats. 



