240 PHYSIOLOGY. 



endocardiac pressure with the duration of the auricular and ven- 

 tricular contractions. 



By these levers it was shown without doubt that the apex-beat 

 is due to the systole of the ventricle, as the two were synchronous. 



Pressure Curve in the Ventricle. Experiments on ventricular 

 pressure have been made with Fick's elastic manometer and the 

 differential manometer of Hiirthle. Dr. Porter, of Harvard, has 

 made a study of this subject with the instrument of Hiirthle, and 

 I shall follow him in the description of the curves obtained. 



Porter (Fig. 72), with his predecessors, has shown that the 

 systolic muscular contractions begin quite suddenty, producing a 



Line of atmospheric 

 pressure. 



yig. 72. Magnified curve of the course of pressure within the left 

 ventricle and the aorta of the dog, the chest being open; to be read 

 from left to right. Recorded simultaneously by two elastic manometers 

 with transmission by liquid. (PoRTEE. ) 



In both curves the ordinates having the same numbers have the following 

 meaning: 1, The instant preceding the closing of the mitral valve. 2, The 

 opening of the semilunar valve. 3, The beginning of the "dicrotic wave," 

 regarded as marking the instant of closure of the semilunar valve. 4, The 

 instant preceding the opening of the mitral valve. 



swift rise of pressure. The diastolic fall of pressure is nearly as 

 sudden as the rise. In the fall of diastolic pressure, the pen often 

 reaches below the pressure of the atmosphere. Between the sys- 

 tolic rise and the diastolic fall it is found that the systolic pres- 

 sure causes its curve to bend alternately downward and upward. 

 Between these two points the general direction of the curve 

 approaches the horizontal, and thus may be denominated the "sys- 

 tolic plateau." The curve of intraventricular pressure rarely gives 

 any clear indication of the beginning or end of auricular systole. 

 The ventricular pressure curve does not give any clear indication 



