968 



PHYSIOLOGY 



into account the greater inertia of the latter instrument. The auricular 

 systole begins at the ordinate 1. It gives a slight rise of 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 contraction 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 occa- 

 sionally 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 



Aorta 



Ventricle 

 Auricle 



345 



FIG. 426. 



67 



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 con- 

 tinues 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 i lie 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 

 two periods at 5. where the rise of pressure becomes suddenly slower. 

 may be marked in the aortic curve by one or two secondary waves. It must 

 be remembered however that all these secondary waves shown on the aorta 

 at 4 and r may be absent, the one at 5 boiii'j; 1 IIP one which is most frequent Iv 

 seen. .From <> to 7 the ventricle is still contracting and forcing blood into 

 the aorta. The curve <>f jnvssiire is generally rounded. It-, may present a 

 ilat top, the plnteau, or the top may be roimoVd with an inclination to fall 



