496 HANDBOOK OF PHVSIOLOCn- ^ CIRCULATION 1 



250 ^-^ 



FIG. 5. LCF = left coronary 

 flow in ml/min, AF = aortic 

 flow (cardiac output minus right 

 coronary flow) in liters/min, 

 CI = cardiac (left ventricular) 

 inflow. 



250 



m 



|i^ 



^4- U- 



0^ 



I 



Figure 5 (lower, A, B, and D) shows the simuhane- 

 ous values for cardiac inflow, aortic flow (cardiac 

 output minus right coronary artery flow), and left 

 coronary artery flow before, during, and after an in- 

 crease in aortic resistance. During phase i , wlien 

 L\'ED and aortic pressures are rising, aortic flow is 

 diminishing while cardiac inflow is essentiall\- un- 

 changed. The rise in LVED pressure would thus 

 appear to be accompanied by an increased \entricu- 

 lar volume since, during this phase, more blood seems 

 to be entering the heart than is leaving it. At tiie onset 

 of phase 2, as LVED pressure declines, aortic flow 

 ri-ses to its phase 3 plateau while inflow remains the 

 same. At the moment when the increased aortic re- 

 sistance is removed (beginning of phase 4), aortic 



flow is suddenly augmented wiiile inflow remains un- 

 changed and LVED pressure falls aljriipth' to its low 

 point. At this time it would appear tiiat the ventric- 

 ular \olume is diminishing, since inore blood appears 

 to leave the ventricle than is entering it. At the point 

 of the onset of phase 2 an increase in contractility is 

 occurring, since L\'ED pressure and \olume are fall- 

 ing while stroke \olume, aortic pressure, and external 

 stroke work are risins;. Further, at the very beginning 

 of phase 4, when L\'ED pressure is substantially 

 lower tiian prior to the increase in aortic resistance, 

 it would appear that an increase in contriictility has 

 taken place, since the \entricle is putting out a sub- 

 stantially larger stroke volume ae:ainst the same aor- 

 tic pressure than it did in the control period. With 



