THE ACTION OF THE HEART 149 



instrument by means of a T-piece with a mercury manometer and a pres- 

 sure bottle and then marking on the tracing, the points corresponding to 

 each 10, 20 or 50 millimeters of increase of pressure, as the case may be. 



To ascertain the time relationship between the opening and the closing 

 of the auriculoventricular valve, the tracings should be taken from the 

 right auricle and the right ventricle, and to ascertain the same with re- 

 gard to the semilunar valve, from the left ventricle and the aorta.* 



By comparing the curves it is now an easy matter to ascertain the 

 exact moment at which the pressure in the one cavity comes to equal 

 that in the other. This moment, read on the accompanying time tracing, 

 will obviously indicate that at which the particular valve is just about to 

 open or close. From the results of such experiments, the curves may be 

 superimposed as in Fig. 34. 



In the first place let us compare the curves from the right auricle and 

 ventricle. The curves begin at the very end of diastole, and they show 

 that a distinct increase in pressure is occurring in both auricle and ven- 

 tricle and lasting about 0.2 second. This is of course caused by auric- 

 ular systole, and since it occurs in both cavities, it indicates that the 

 passage between them, the auriculoventricular orifice, must be open. 

 The ventricular curve then suddenly shoots away beyond the auricular 

 because of the onset of systole in the ventricle, and the point at which 

 the two curves begin to separate indicates the moment at which the 

 auriculoventricular valves close. From this time on until ventricular 

 systole has given place to diastole, (about 0.4 second), the auricle is 

 therefore shut off from the ventricle. The exact moment in diastole at 

 which the two cavities are again brought into communication i.e., the 

 auriculoventricular valves open is indicated by the curves coming to- 

 gether. 



Having thus determined the exact moments of opening and closing 

 of the auriculoventricular valve, we may now proceed to compare the 

 intraventricular pressure curve with that taken from the aorta. After the 

 necessary calibration corrections, this curve has been placed in Fig. 34 

 in its true relationship to the ventricular curve. Beginning again at the 

 end of diastole, we find that the aortic pressure is very considerably 

 above that of the ventricles, indicating that the semilunar valves must 

 be closed; and it will be observed that the intraventricular pressure at 

 the beginning of systole does not rise sufficiently to open them until an 

 appreciable interval (0.02 to 0.04 second) after the closure of the auric- 

 uloventricular valves; that is to say, there is a period at the beginning 

 of ventricular systole during which the ventricle is a closed cavity. It 



*The connections with the heart may be made by pushing long cannul.-e down the large veins or 

 arteries, or in the case of the ventricles by inserting a cannula with a sharp point directly through 

 the wall of the ventricle. 



