246 ENDOCARDIAC PRESSURE. [BOOK i. 



that the point c in the three figures under discussion, where the 

 descent of the lever changes in rate, becoming less rapid, corre- 

 sponds to the end of the outflow from the ventricle ; but this is 

 not certain, and indeed the exact interpretation of this part of the 

 curve is especially difficult. 



The escape from the ventricle is rapid and forcible ; the flow 

 ceases suddenly. Hence, as we have already stated 127, owing 

 to the column of blood tending to move on by virtue of its 

 inertia after the propelling force has ceased to act, a negative 

 pressure makes its appearance behind the column of blood dis- 

 charged from the ventricle, and as soon as the column is lodged 

 in the aorta leads to a reflux towards the ventricle. This 

 reflux would of itself have the effect of closing the valves even 

 were the aorta a rigid tube. But the aorta is extensible and 

 elastic and the effects of the movement of the column of fluid are 

 combined with the effects of the movement of the arterial walls : 

 the elastic action of the arterial walls, in a manner which we shall 

 discuss later on in dealing with the pulse, also leads to a reflux. 

 It has been urged that the reflux due to the negative pressure of 

 the mere movement of the column of blood being more rapid, occurs 

 independently of and earlier than the reflux due to the elastic 

 recoil, the former closing the valves, the latter securing their com- 

 plete closure. Be this so or no the valves are probably closed almost 

 immediately after the escape of the ventricular contents, though 

 observers are not agreed on this point, some urging that the 

 valves are not closed until so late a period as the point d, just as 

 relaxation is about to begin. In the curves we are now con- 

 sidering, a notch, followed by a rise, or at least a more or 

 less abrupt change in the course of the curve at c', is some- 

 times observed in that part of the curve which intervenes 

 between the first large rise and the final sudden fall ; and this 

 secondary rise has been taken to indicate the closure of the 

 semilunar valves. Sometimes two such notches and peaks are 

 seen, and the occurrence of the two has been attributed to a 

 want of synchronism in the closure of the pulmonary and aortic 

 semilunar valves, the latter closing some little time before the 

 former. But it is by no means clear that these notches and peaks 

 are thus due to the closure of the valves ; they may possibly 

 have another origin, they are not always present, and indeed it 

 does not seem certain that the closing of the valves should neces- 

 sarily make an impress on the ventricular curve. 



134. In the performance of the ventricle then (and what 

 has been said of the left ventricle applies also to the right 

 ventricle) there appear to be four stages : 



1. A rapid "getting up" of pressure within the ventricle, all 

 the valves being as yet closed ; this continues until the pressure 

 within the ventricle, becoming greater than that in the aorta, 

 throws open the aortic valves. 



