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 an arch 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). We may 

 therefore describe 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 usually slower than the ascending. On the rising portion there 

 is usually a notch at the moment the semilunar valves open. The cause 

 for this is not satisfactorily explained. 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. The pressure is 

 maintained long enough to overcome the inertia of the heavy load of 

 blood in the large arteries. 



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. When the tension is low the arch becomes a 

 plateau. In the case of the right ventricle the contour of the curve also 

 depends on the degree of resistance to the bloodflow through the pul- 

 monary circuit. The top of the curve becomes broader when the initial 

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

 resistance. 



By the use of the older methods of observation (spring manometers) 

 it was believed that the intraventricular pressure fell below the zero 

 line in the early stage of diastole, thus indicating that a negative or 



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