148 



APPLIED PHYSIOLOGY 



are two secondary waves, the upper called the 'pre- 

 dicrotic ' or tidal wave, and the lower the * dicrotic ' 

 wave (Fig. 8). 



Physiologists seem to vary in their interpretation of 

 the meaning of the predicrotic wave, but it would appear 

 that it indicates the true summit of the pulse wave, and 

 that the primary wave is merely the result of instrumental 

 error, and due to the sudden jerking upwards of the lever 

 of the sphygmograph.* 



If the tension in the artery rises very slowly, as it 

 does in aortic stenosis, the lever is not jerked upwards 



FIG. 8. SPHYGMOGRAM OF EADIAL PULSE. (MACKENZIE.) 



E = Period of systole when aortic valves are open ; G = Ventricular 

 diastole ; s = pulse wave due to systole ; n = aortic notch ; d = dicrotic 

 wave ; p = wave due to instrumental defect. 



so abruptly, and in that case the predicrotic wave comes 

 to form the apex of the pulse curve, whilst the tidal 

 wave is represented by a notch on the ascent ; this is 

 termed the ' anacrotic pulse.' 



The most probable explanation of the dicrotic wave is 

 given by Mackenzie as follows : t ' The semilunar valves 



* This view, though supported by Mackenzie, is not universally 

 accepted. Lewis, for instance, as a result of a recent careful study 

 of the subject (Journ. of Anat. and Physiol., 1906-7, xli. 137), 

 concludes that, in the great majority of cases, the primary and 

 predicrotic waves are both genuine, and are of central origin. 



f ' The Pulse,' p. 20. 



