io8 



THE MECHANISM OF THE CIRCULATION. 



By recording with the sphygmograph the effect of occlusion of 

 the brachial artery, we possess a method of investigating the condi- 

 tion of the circulatory system. If the fall of the line of the curve 

 is steep and rapid on sudden compression of the artery, a high 

 arterial tension, a low venous pressure, and a rapid escape of the 

 venous blood is indicated (Fig. 72, tracing 2) ; if the fall is shallow 

 and slow, the opposite conditions exist, for then the indication is that 

 the arterial and venous pressures are more approximate to each other, 

 and that the escape of the venous blood is obstructed 1 (Fig. 72, 

 tracing 1). 



Analysis of pulse curve. Each pulse curve begins with an ascend- 

 ing limb of considerable steepness, which corresponds with the positive 

 wave produced by the systolic output of the heart. As a rule, the ascent 

 forms an unbroken line until the apex of the curve is reached, and the 

 descent commences. The descending limb is marked by several minor 

 waves, of which one, the dicrotic, is present in all forms of pulse curve. 



The minor waves on the descending limb of the curve are termed 

 katacrotic, and if such waves appear on the ascending limb these are 

 termed anacrotic? 



FIG. 73. Velocity of pulse wave. Carotid and radial pulse. After Ed gren. 



The difference in time between b and b = -0786 sec. 

 The distance between radial and carotid = about 60 cm, 



.. velocity of transmission = about 7 in. per sec. 



The dicrotic ivave. There has been much dispute over the origin of 

 the secondary waves, and the matter cannot yet be considered definitely 

 settled. It cannot be doubted that the dicrotic wave is a positive 

 centrifugal wave, for, if synchronous tracings be taken from two arteries, 

 the dicrotic wave, like the primary wave, appears earlier in time in the 

 artery which is nearer the heart. Although the dicrotic wave runs 

 centrifugally, it does not follow that it is entirely central in origin. 

 Several authors have maintained that the dicrotic wave travels with 

 less velocity than the primary w r ave down the arteries of the lower 

 limb, while it travels with approximately the same velocity down the 

 arteries of the upper limb. 3 



1 In taking such observations the sphygmograph must be arranged so as in each case to 

 give the maximal pulsation. The wrist also should be placed on the same level as the 

 heart. 



2 Landois, "Die Lehre vom Arterienpuls," S. 108. 



3 v. Kries, Arch. f. Physiol., Leipzig, 1887, S. 275 ; Edgren, Skandin. Arch. f. Physiol. , 

 Leipzig, 1889, Bd. i. S. 104 ; for the contrary conclusion, see Hiirthle, Arch. f. d. ges. 

 Physiol., Bonn, 1890, Bd. xlvii. S. 28. 



