IiitiavcuLriciilar and Aortic Pressure Curves. 43 j 



j vagus excitation). The rate of increase; of pressure during the quick 



1 ascent is, as already mentioned, loOO mm Hg. per second and in -our 

 curves (B'ig. 2) it reached the amount of 87 mm Hg., that is, supposing 

 the heat produced during the compression of th(i air to liave been 



i dissipated as fast as formed. If tlie compression were adiabatic, the 

 amount of pressure needed to produce the observed deflection can be 



{ calculated by the formula: 



j (n ~p 



I where V is the original volume of the air under the original pressure 

 I P, i. e., in our experiment, the atmospheric pressure, and V is the 

 I Yolume under the pressure P', that is, the intraventricular pressm-e, 

 I plus the atmospheric pressure, and K is the ratio of the two specific 

 heats of a gas, that is, 1"4. When calculated out by this formula, 

 the maximum pressure produced in the left ventricle amounts to 

 128 mm Hg. as against 87 mm Hg. The real value is probably some- 

 where between these two, but as said above, we lay no stress upon 

 absolute measurements of pressure based upon our curves. 



The three waves constituting the plateau vary considerably in 



relative height. Sometimes the first is the highest, as in Figs. 5 and 6, 



and at other times, the second is higher than the first, as in Figs. 2, 



J 3 and 4. When the heart is beating quickly, the third wave is not 



' very distinct, but is quite marked in Fig. 6, and is always to be seen. 



It shows itself better when the heart is slowed by moderate excitation 



of the vagus, as in Fig. 4. We are not prepared to give an inter- 



\ pretation of these waves, nor do we think that a sufficient one has 



\ been as yet suggested. Roy and Adami ^) consider the second wave 



I to be due to contraction of the papillary muscles. This much we can 



say positively, that the three waves are not of instrumental origin, 



and this for several reasons. In the first place, we have sho^^^l our 



instrument to be aperiodic for such rates of change as occur in tlie 



heart-beats investigated by us. In the second place, if the waves were 



due to vibrations set up in the column of fluid in the tube, the second 



') The Practitioner. 1S90. I pp. SS— Q-i 



