THE EVENTS OF THE HUMAN CARDIAC CYCLE 81 



When jugular tracings are taken simultaneously with a standard 

 movement, the radial pulse is usually employed on account of 

 its convenience. This method involves a third error, the variation 

 in transmission delay from the aorta to radial vessel. The varia- 

 tion in this delay is so great, and the accumulated error becomes 

 so magnified, that it is unsafe to fix the radial pulse as the 

 standard movement if the carotid to radial delay is not first 

 estimated and allowed for in the particular case. 1 



The determination of the position of closure of the semilunar 

 valves (S.C.) and of the opening of the auriculo-ventrjcular 

 valves (A.O.) upon human cardiographic and carotid curves pre- 

 sents considerable difficulties. 



In. animals it is now held that the S.C. point occurs a short 

 distance along the downstroke of intra-ventricular pressure 

 (Hiirthle ( M "), Porter ("), Bayliss and Starling ( 3 ), &c.). This 

 point is found in simultaneous tracings to correspond on the aortic 

 curve to the bottom of the dicrotic depression (aortic notch) ; 2 

 on the carotid tracing, which is slightly delayed, it falls at or 

 about the beginning of the same depression. On the cardio- 

 graphic curve it corresponds in animals to a point near the end 

 of the ventricular plateau ; thus Marey ( 33b ) (Fig. 40) places it 

 before the end of the plateau, Hiirthle's tracings ( 26a ) show it before 

 or slightly after the end of the plateau. To sum up, there is no 

 constant relationship between cardiographic and intra-ventricular 

 curves at this phase. 



In man the S.C. point is placed by Edgren ( 8 ) at the bottom 

 of the cardiographic downstroke, at a point indicated by a small 

 wave. According to Hiirthle ( 26b ) it is situated in the first third of 

 the downstroke, and it is placed at the same instant by Einthoven 

 and Geluk ( 9 ), despite the fact that they were guided by the record 

 of the second sound, which occurs later than the closure. The 

 method in which the second sound is marked on the tracing by a 

 signal worked with the hand, allowance being made for reaction 

 time, is obviously unreliable and gives varying results (cp. Edgren's 



1 The figures given and statements made are the result of a critical examination 

 of a large number of statements and tracings. The sjace at our disposal prohibits 

 a full examination of the facts. There is a good deal of divergence between the 

 figures given by different authors, and further work giving more detailed analysis 

 would l)e of much value, for at present general statements are of necessity very 

 approximate. 



1 Porter and Hurthle. 



F 



