242 



ENDOCARDIAC PRESSURE. 



[BOOK i. 



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 ventricular 

 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. But 

 it may be doubted whether the instru- 

 ment can be trusted to tell much more 

 than this. The pressure recorded by 

 each lever is the pressure exerted on 

 the ampulla and this may continue to 

 be exerted after all blood has been dis- 

 charged from the cavity, the walls of the 

 emptied cavity closing round and press- 

 ing on the ampulla. But as we shall 

 presently see, it is of great interest to 

 determine, not only the force and dura- 



tion of the exerted 



, , 



VENTRICLE, OF THE HORSE, ventricular systole, but also whether 

 ( AFTER CHAUVEAU AND MARET.) or no the fibres continue contracted 



and exerting pressure for an appreciable 



time after the blood has been forced out of the cavity. The figure 

 moreover, it need hardly be said, does not, by itself, give any in- 

 formation as to the relative amounts of pressure exerted by the 

 auricle and ventricle respectively. In the curve the auricular lever 

 rises about half as high as the ventricular lever ; but we must not 

 infer from this that the auricular stroke is half as strong as the 

 ventricular stroke ; the former is arranged so as to move much 

 more readily, to be much more sensitive than the latter. The 

 instrument it is true may be experimentally graduated, and may 

 then be used to determine the actual amount of pressure ; but 

 for this purpose is not wholly satisfactory. We may add that 

 the irregularities seen on the ventricular curve during the ven- 

 tricular systole and on the auricular curve at the same time 

 have given rise to much debate and need not be discussed here. On 

 the whole the method, though useful for giving a graphic view 

 of the series of events within the cardiac cavities during a cardiac 

 cycle, the short auricular pressure, the long continued ventricular 

 pressure, lasting nearly half the whole period, and the subsequent 

 pause when both parts are at rest or in diastole, cannot with 

 safety be used for drawing more detailed conclusions. 



Perhaps the least untrustworthy method of recording the 

 changes of endo-cardiac pressure is that recently introduced by 

 Roy and Rolleston, though difficulties present themselves in the 

 interpretation of the curves obtained by it. 



