MECHANICS OF THE HEART-BEAT 



95 



still rises, reaches a summit, and then slowly falls; and (4) a relaxa- 

 tion period (Fig. 32). 



Without entering further into a technical discussion, we may say 



rig. 32. Intraventricular Pressure Curves with Optical Recording (Wiggers). Three 

 types of normal curves are reproduced, taken with manometers of different 

 degrees of sensitiveness. The second at the left-hand side was taken with the 

 least sensitive, a b, auricular systolic; b d, isometric period, during which 

 the auriculo-ventricular and the semilunar valves are both closed; d /, ejection 

 period; after/, diastole. 



the bulk of the evidence goes to show that the plateau is not, as the 

 advocates of the peak have claimed, an artificial phenomenon, but 

 does in reality correspond to that continuation of the systole of the 



Fig. 33. Simultaneous Record of Pressure in Left Ventricle (V) and Aorta (A). 

 (Hiirthle.) The tracings were taken with elastic manometers; o indicates a 

 point just before the closure of the mitral valve; i, the opening of the semilunar 

 valve; 2, beginning of the relaxation of the ventricle; 3, the closure of the semi- 

 lunar valve; 4, the opening of the mitral valve. The ventricular curve shows 

 a ' plateau.' 



ventricle, that dogged grip, if we may so phrase it, which it seems to 

 maintain upon the blood after the greater portion of it has been 

 expelled. 



