PULSATILE BLOOD FLOW 



853 



^ ,0 



CONTROL 

 FLOW 



ACETYLCHOLINE 



FLOW 



ISO 



glOO 

 6 



SO 



AP 



VP 



VP 



-"•9-- 





fig. 19. Blood flow in a small peripheral artery and the effect 

 of vasodilation. According to the definitions of the text, the 

 control flow may be considered a resonant flow form which is 

 converted to resistant flow form by the injection of acetylcholine 

 into the arterial channel. AP represents the arterial pressure, 

 immediately proximal to the flowmeter probe applied to a small 

 artery in the dog's paw. VP represents the venous pressure in a 

 small vein of the dog's paw. Conversion of the flow from reso- 

 nant flow to resistant flow by the action of acetylcholine lowers 

 the arterial pressure and raises the venous pressure. (Tracings, 

 courtesy of M. C. Conrad and H. D. Green.) 



i/R represents the conductance at the existing pres- 

 sure, and A' represents the fact that the pressure- 

 resistive-flow relationship (excluding the dynamic 

 compliant flow term, C(dP/dt)), is not constant and is 

 a nonlinear function of pressure. Presumably this 

 results from the fact that i/R is directly dependent on 

 the pressure in a manner similar to that shown by 

 the vascular beds of the skin. If this is true, then the 

 relationship is: 



°dt + 



I 



R (v) + R (P) 



(17) 



where R {v) equals resistance controlled by vaso- 

 motor tone, and R (F) equals resistance controlled by 

 intraluminal pressure P. At present, the coefficients 

 C], Riy, and R (P ) are obtained only by measuring 

 the flow and pressure without any means of indirect 

 evaluation. Figure 20 illustrates one example of how 

 C and R of equation 16 were adjusted until the 

 dynamic flow pulse was computed from P (30). In 

 this case flow was alreadv known from simultaneous 



measurement with the square-wave electromagnetic 

 flowmeter. 



There are apparently no positive reflections from 

 the normal renal bed, hence the flow computed for 

 the total renal circuit according to equation 16 and 

 without an inertance term represents the flow in the 

 renal artery. To compute, however, the instantaneous 

 flow in other arteries from whose bed there are 

 reflections one must use the difference in pressure 

 along the artery (i.e., two pressure sources in the 

 artery itself) and the equations 9 and 12. The most 

 important term is then the inertial one of equation 

 9 although, as explained earlier, a further step in 

 precise computation brings in the compliance of 

 equation 12. 



Carotid Artery Flow 



This is illustrated in figure 18. Like the renal flow 

 there is a large constant flow component upon which 

 there is superimposed a dynamic component. It is 

 related to the carotid pressure by equation 1 6 with 

 the conductance term i/R being the largest by far. 



Because the carotid and renal flow patterns are 

 governed largely by the resistance, they are called 

 viscous or resistance flow patterns. The resting flow 

 patterns of the entire aorta, iliac, femorals, and 

 subclavian arteries are called reactance flow patterns 

 because inertance and compliance are dominant. 

 They have a small constant flow when compared to 

 their dynamic component and this frequently demon- 

 strates a period of negative flow in early diastole. 



Coronarx Blood Flow 



Coronary blood flow in the unopened artery was 

 first measured by Marston and Spencer with the 

 square-wave electromagnetic flowmeter (24). The 

 resting patterns differ little from those of Gregg (18) 

 who used a cannulating system and orifice meter. 

 The equation relating coronary flow to the vascular 

 pressures is a modification of equation 16: 



'">§++"' 



(18) 



where AP equals the aortic pressure minus the 

 ventricular pressure minus the right atrial pressure. 

 Figures 21 and 22 (27) illustrate the measured left 

 anterior descending coronary flow and the circumflex 

 coronary artery flow. 



These coronary inflow curves display a marked 

 dependence on both aortic pressure and intra- 



