ENDOCARDIAC PRESSURE 



193 



closure of the valve occurs probably in the lower third of the rise AB, figure 

 165, and does not produce any notch or wave. It is shown that the semilunar 

 valve opens at the point in the ventricular systole, situated at c, about or a 

 little above the junction of the middle and upper thirds of the ascending line 

 AB, and the closure about or a little before the shoulder, D, The figures 

 show, finally, that the minimum pressure in the ventricle may fall below 

 that of the atmosphere, but that the amount varies considerably. 



On the whole, the most satisfactory recording instrument for the measure- 

 ment of endocardiac pressures is the membrane manometer devised by 

 Hurthle. This instrument avoids mechanical errors in a most satisfactory 

 manner. By simultaneous tracings of the pressure in the ventricle and in 

 the aorta by Hiirthle's differential manometer, the exact moment of the 



PA H SE 



DIASTOLE 



AURICLE 



VENTRICLE 



IMPULSE 



FIG. 167. Diagrammatic Representation of the Events of the Cardiac Cycle. For 

 events which occur in sequence, read in the direction of the curved arrow; for synchronous 

 events, read from the center to the periphery in any direction. (Coleman.) 



opening and closing of the semilunar valve has been determined. By 

 similar methods we have been able to fix synchronism between other events 

 occurring during the beat. These we will summarize in the following section. 



