146 



SPECIAL CARDIAC PHASES. 



[BOOK i. 



On the relative duration and special characters of the 

 Cardiac events. 



We may now return to a more detailed study of what is taking 

 place in the heart during a beat. We have already spoken of the 

 conclusions which may be drawn from Chauveau and Marey's curves, 

 and have incidentally (p. 138) referred to the cardiograph. 



Various forms of cardiograph have been used to record the 

 cardiac impulse. In some the pressure of the impulse as in the 

 sphygmograph is transmitted directly to a lever which writes upon 



FIG. 23. CARDIOGRAPHIC TRACING OF CARDIAC IMPULSE IN MAN (from Landois). 



An entire beat occurs between a and /. The auricular systole is marked by b, 

 the end of the ventricular relaxation by/. At c, the highest point of the curve, the 

 blood begins to be propelled from the ventricle, d and e are considered by some to 

 indicate the closure of the aortic and semilunar valves respectively, see text. Five 

 cardiac beats are represented ; the convex curve which their base line forms is due to 

 the respiratory movements. 



a travelling surface. In others the impulse is, by means of an 

 ivory button, brought to bear on an air-chamber, connected by 

 a tube with a tambour as in Fig. 22 ; the pressure of the cardiac 

 impulse compresses the air in the air-chamber, and through this 

 the air in the chamber of the tambour by which the lever is raised. 

 In such delicate and complicated movements as those of the 

 heart however, the use of long tubes filled with air is liable to 

 introduce various errors. A cardiographic tracing of ordinary 

 characters is given in Fig. 23. 



Curves of the variations in internal pressure may be obtained 

 by passing a tube connected with a mercurial manometer (as in the 

 investigation of arterial pressure, p. 122) into the right ventricle 

 through the jugular vein or into the left ventricle through the 

 carotid artery. But this method, though useful for the purpose of 

 investigating generally the pressure exerted by the cardiac walls, 

 is, by reason of the inertia of the mercury, unsuitable for detecting 

 rapid and small changes. 



