CHAPTER XVIII 



THE PUMPING ACTION OF THE HEART (Cont'd) 

 THE CONTOUR OF THE INTRACARDIAC CURVES 



The Ventricular Curve 



From an analysis of the contour of each curve, further interesting 

 points are brought to light. The intraventricular pressure curve recorded 

 by older methods was shown as having a flat top or plateau. By the use 

 of the more modern, optically recording, instruments it has been shown 

 that this plateau becomes displaced by a peak if every precaution is 

 taken to prevent dulling down of the pressure changes in the instrument, 

 as by opening wide the stopcock in the instrument (Fig. 33). The peak 

 is, however, by no means a sharp one (Fig. 34), so that we may fitly de- 

 scribe the contour of the ventricular curve during the sphygmic period as 

 consisting of a rising portion, almost continuous with the curve during the 

 presphygmic period, a summit and then a declining portion, which is usu- 

 ally slower than the ascending. The practical value arising from a study 

 of the curves lies in the insight which they give us into the nature of the 

 stroke of the cardiac pump. They show us that the impulse which the 

 ventricle gives to the moving mass of blood in the aorta rises quickly, 

 attains a peak, and then more gradually falls until the aortic valves close, 

 when the fall becomes much more sudden. 



Wiggers has shown that the exact contour of the curve during the 

 sphygmic period depends partly on the degree of sensitiveness of the op- 

 tical manometer used and partly on the tension existing in the ventricle 

 just before contraction. In the case of the right ventricle the contour of 

 the curve also depends on the degree of resistance to the bloodflow through 

 the pulmonary circuit. The top of the curve becomes broader when the 

 initial tension is high, and more rounded when there is a high pulmonary 

 resistance. 



The interest of studying the contour of the curve lies in the fact that 

 it indicates the nature of the stroke of the cardiac pump. It shows that 

 this is maintained so that time may be afforded to overcome the inertia of 

 the heavy load of blood in the large arteries. 



Another point of interest in connection with the ventricular curve is 

 that early in diastole it descends below the line of zero pressure, indicating 



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