CHAP, iv." 



THE VASCULAR MECHANISM. 



243 



V 



When this instrument is applied to the right auricle and 

 ventricle some such record is obtained as that shewn in Fig. 39, 

 where the upper curve is a tracing taken from the right auricle, 

 and the lower curve from the right ventricle of the horse, 

 both curves being taken simultaneously on the same recording 

 surface. In these curves the rise of the lever indicates pressure 

 exerted upon the corresponding ampulla, and the upper curve, 

 from the right auricle, shews the sudden brief pressure b exerted 

 by the sudden and brief auricular systole. The lower curve, from 

 the right ventricle, shews that the pressure exerted by the ventri- 

 cular systole begins almost immediately after the auricular systole, 

 increases very rapidly indeed, so that the lever rises in almost a 

 straight line up to c', is continued for 

 some considerable time, and then falls 

 very rapidly to reach the base line. 

 The figure, it must be understood, does 

 not, by itself, give any information as 

 to the relative amounts of pressure 

 exerted by the auricle and ventricle 

 respectively ; indeed, the movements of 

 the auricular lever are much too great 

 compared with those of the ventricular 

 lever. The figure is chiefly useful for 

 giving a graphic general view of the 

 series of events within the cardiac cavi- 

 ties during a cardiac cycle, the short 

 auricular pressure, the long-continued FlG 39 SlMDLTANBOU8 TBACINGS 

 ventricular pressure, lasting nearly half FROM THE EIGHT AURICLE, AND 

 the whole period, and the subsequent VENTRICLE, OF THE HORSE. 

 pause when both parts are at rest or in ^^ CHAUVEAU AND MAREY -) 

 diastole. 



Among the more trustworthy methods of recording the 

 changes of endocardiac pressure we may first mention that of 

 Hoy and Rolleston. 



By means of a short cannula introduced through a large vessel, or 

 directly, as a trocar, through the walls of the ventricle (or auricle), the 

 blood in the cavity is brought to bear on an easily moving piston. 

 The movements of the piston are recorded by a lever, and the 

 evils of inertia are met by making the piston and lever work 

 against the torsion of a steel ribbon the length of which, and conse- 

 quently the resistance offered by which, and hence the excursions of 

 the piston, can be varied at pleasure. 



We give as examples of curves obtained by this method 

 two curves from the left ventricle, one (Fig. 40 A) of a 

 rapidly beating, and the other (Fig. 40 B) of a slowly beating 

 heart. 



16-2 



