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 ventricular curve in the diagram alluded 

 to above (Fig. 34) is 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, so that we may fitly describe the 

 contour of the ventricular curve during the sphygmic period as consist- 

 ing of a rising portion, almost continuous with the curve during the pre- 

 sphygmic period, a summit and then a declining portion, which is usually 

 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 is a sudden rather than a 

 sustained one. The column of blood in the aorta is a mighty thing to 

 move, and it would appear as if a sustained pressure brought to bear on 

 it during the sphygmic period would be far more efficient in bringing 

 about an adequate movement of the blood than a sudden jerk. In closing 

 a heavy gate a slow sustained pressure is far more effective than a 

 sudden blow. 



It is further of interest to note on the intraventricular pressure curve 

 that there is very little indication of any secondary waves or vibrations 

 at the moment during which the semilunar valves are opened or closed. 

 Nevertheless, by close scrutiny it can usually be seen that a slight 

 change in the direction of the ascending curve is evident when the valves 

 open (see Fig. 33), and similarly that the moment of closing is indicated 

 by a sharper bend in the curve. As a matter of fact, Wiggers has shown 

 that the exact contour of the curve during the sphygmic period depends 

 partly on the degree of sensitiveness of the optical manometer used and 

 partly on the tension existing in the ventricle just before contraction. 



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