924 PHYSIOLOGY 



ventricle (Fig. 416). We are enabled in this way to dissociate the waves 

 caused by the ventricular systole from those which have their origin in 

 the arterial system. In Fig. 416 is given somewhat diagrammatically 

 typical tracings of the mtra-auricular, intraventricular, and aortic pressures 

 during one heart-beat, and in dotted lines is represented approximately 

 the sort of a curve which would be given by a sphymograph applied to the 

 aorta, taking into account the greater inertia of the latter instrument. 

 The auricular systole begins at the ordinate 1. It gives a slight rise of 



Aorta 



Ventricle 

 Auricle 



67 



FIG. 416. 



pressure in the ventricle, but as a rule is not transmitted to the aorta, 

 though often some small traces of it can be seen. As the auricular con- 

 traction is dying away, the ventricular contraction begins at 2. The first 

 effect of this rise of pressure is to close the auriculo-ventricular valves, 

 as is shown by the elevation at 3 in the auricular curve, and the shock 

 of the closure is occasionally transmitted to the aorta. The pressure in 

 the ventricles then rapidly rises. At the point 4 it surpasses the pressure 

 in the aorta and then rapidly rises above it. Since the aortic valves offer 

 no resistance to the flow of blood from ventricles to aorta, they must open 

 as soon as the intraventricular exceeds the aortic pressure, and this is 

 shown by the rise of pressure in the aorta at 5. The shock of the inrush 

 of blood may give rise to a distinct secondary wave at this point. The 

 pressure then continues for a time to rise rapidly both in the ventricle and 

 in the aorta, blood flowing from the heart into the arterial system. As 

 the first rush of blood diminishes and as the blood begins to escape more 

 rapidly under the influence of the rise of pressure from the peripheral end 

 of the arterial system, the rise of pressure in the ventricle and aorta slows 

 off and the junction between these two periods at 5, where the rise of 



