ELASTIC ELEVATIONS. 105 



is best developed in a soft pulse]. In fig. 83, IX and X were obtained when the 

 tension of the arterial was low ; V and VI, medium ; and VII with high tension. 



Conditions influencing Arterial Tension. It is diminished at the beginning of inspiration 

 ( 74), by haemorrhage, stoppage of the heart, heat, an elevated position of parts of the body, 

 amyl nitrite, nitro-glycerine, and the nitrites generally. [Both drugs accelerate the pulse-beats 

 and produce marked dicrotism ; with amyl nitrite the full effect is obtained in from 15 to 20 

 sec. after the inhalation of the dose (fig. 84, A, A'), but with nitro-glycerine not until 6 or 7 

 min. (fig. 84, B, B') and in the latter case the effects last longer.] It is increased at the 



Fig. 84. 

 Pulse-tracings. A, normal ; A', one minute after inhalation of amyl nitrite ; B, normal ; B', 

 after a dose of nitro-glycerine (Stirling after Murrell). 



beginning of expiration, by accelerated action of the heart, stimulation'of vaso-motor nerves, 

 diminished outflow of blood at the peripher}' - , and by inflammatory congestion by certain 

 poisons, as lead ; compression of other large arterial trunks, action of cold and electricity on 

 the small cutaneous vessels, and by impeded outflow of 

 venous blood. When a large arterial trunk is exposed, the 

 stimulation of the air causes it to contract, resulting in an 

 increased tension within the vessel. In many diseased con- 

 ditions the arterial tension is greatly increased [e.g., in 

 Bright's disease, where the kidney is contracted ("granu- 

 lar "), and where the left ventricle is hypertrophied]. 



In all these conditions increased arterial tension is indi- 

 cated by the dicrotic wave being less high and less distinct, 

 while with diminished arterial tension it is a larger and 

 apparently more independent elevation. Moens has shown 

 that the time between the primary elevation and the dicrotic 

 wave increases with increase in the diameter of the tube, ^ig 85. 



with diminution of its thickness, and when its coefficient of Aortic regurgitation, 



elasticity diminishes. 



[The dicrotic wave is absent or but slightly marked in cases of atheroma and in aortic 

 regurgitation (fig. 85). In this fig. observe also the vertical character of the up-stroke.] 



Elastic Elevations. Besides the dicrotic wave, a number of small less-marked 

 elevations occur in the course of the descent in a sphygmogram (fig. 83, e, e). 

 These elevations are caused by the elastic tube being thrown into vibrations by the 

 rapid energetic pulse- wave, just as an elastic membrane vibrates when it is suddenly 

 stretched. The artery also executes vibratory movements when it passes suddenly 

 from the distended to the relaxed condition. These small elevations in the pulse- 

 curve, caused by the elastic vibrations of the arterial wall, are called "elastic 

 elevations " by Landois. 



(1) The elastic vibrations increase in number in one and the same artery with 

 the degree of tension of the elastic arterial wall. A very high tension occurs in 

 the cold stage of intermittent fever, in which case these elevations are well marked. 



(2) If the tension of the arterial wall be greatly diminished, these elevations may 

 disappear, so that, while diminished tension favours the production of the dicrotic 

 wave, it acts in the opposite way with reference to the " elastic elevations." (3) 

 In diseases of the arterial walls affecting their elasticity, these elevations are either 

 greatly diminished or entirely abolished. (4) The farther the arteries are distant 

 from the heart, the higher are the elastic elevations. (5) When the mean pressure 

 within the arteries is increased by preventing the outflow of blood from them, the 

 elastic vibrations are higher and nearer the apex of the curve. (6) They vary 



