8 4 8 



HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



fig. 10. Relationship between 

 the differential pressure and flow 

 through the normal aortic valve. 

 The ordinates refer to the tops of 

 these simultaneous tracings. AP 

 = left ventricular pressure {LVP) 

 minus ascending aorta pressure 

 (AAP). The pressure gradient 

 is against the direction of flow 

 in the latter part of systole. 



Stroke Vol. = 18.2 cc 



**A»«» 



^-Vvj"^ -_\w\xv^t^ ^-L^V "yJ 



Bockflow Vol. = 0.58 cc 



ventricular ejection pulse. R\ and R 2 represent periph- 

 eral resistances which may be adjusted relative to 

 Ci and C 2 to give any desired ratio of pulse pressure 

 to mean pressure at Pi. 



Ci, C2, and L form a series resonant circuit and may- 

 be adjusted to give any resonant frequency, and Rz 

 and R t are chosen to provide the proper damping 

 ratio of the observed resonant wave in the arterial 

 system, as well as the high frequency details. When 

 C 2 is smaller than Ci, the P> pulse pressure is greater 

 than Pi pulse pressure, thus explaining a time- 

 honored observation that the arterial pressure in the 

 legs rises higher than in the arms during systole. 



Figure 14 demonstrates the degree of accuracy 

 with which such a grossly lumped electronic model 

 may reproduce the observed set of pressure and flow- 

 values in the arterial network. The resonant-network 

 model embodies several concepts which provide a 

 rational explanation of the major hydraulic features 

 of the arterial system. 



/) The over-all frequency response characteristics 

 of the arterial system may be taken as that of an 

 analogous filter network (56), figure 15. 



2) The resonant frequency (v n ) varies from 2 to 10 

 cps and is increased by hypertension produced by 

 increased cardiac output and sympathetic con- 

 strictor agents. It is also increased in cardiac failure 

 due to mitral stenosis. Hypotension from decreased 



fig. 11. Electrical analogue of the windkessel model of the 

 arterial system with experimental testing. P represents the 

 pressure in the aortic arch. V represents the voltage across the 

 parallel resistor and condenser. F represents the measured 

 blood flow in the ascending aorta and the electrical input cur- 

 rent forcing the analogy. 



