The vascular function curve is affected more by changes in peripheral resistance compared to the cardiac function curve. As a result, when peripheral resistance increases, equilibrium point B shifts below and to the left of point A, leading to a decrease in both cardiac output and Pv. Conversely, if the cardiac function curve is displaced more than the vascular function curve, point B falls below and to the right of point A, causing a decrease in cardiac output but an increase in Pv.

In a simplified model of the cardiovascular system, which includes the left and right ventricles, systemic and pulmonary vascular resistance, and arterial and venous compliance, the pressures in the systemic arteries and veins (Psa and Psv) as well as in the pulmonary arteries and veins (Ppa and Ppv) are represented. This model helps understand the interrelationships among ventricular output, arterial pressure, and atrial pressure in a more comprehensive manner.

However, in reality, the cardiovascular system is even more complex, involving both the systemic and pulmonary circulations and two pumps: the left and right ventricles. In this complete model, the flow pumped by the two ventricles must be nearly equal over a significant period of time to prevent blood accumulation in either vascular system. Since the cardiac function curves for the two ventricles differ, the filling pressures for each ventricle must also differ appropriately to ensure equal stroke volumes.

[Paraphrased excerpt ends]
in peripheral resistance shifts the vascular function curve more than it does the cardiac function curve, equilibrium point B is below and to the left of point A; that is, both cardiac output and Pv diminish. Conversely, if the cardiac function curve is displaced more than the vascular function •Fig. 19.11 Anincreaseinperipheralresistanceshiftsthecardiacandvascularfunctioncurvesdownward.Atequilibrium,cardiacoutputisless(pointB)whenperipheralresistanceishighthanwhenperipheralresistanceisnormal(pointA).
•Fig. 19.12 Simplifiedmodelofthecardiovascularsystemthatconsistsoftheleftventricle(LV)andrightventricle(RV),systemicvascularresistance(Rs)andpulmonaryvascularresistance(Rp),systemicarterialandvenouscompliance,andpulmonaryarterialandvenouscompliance.PsaandPsvarethepressuresinthesystemicarteriesandveins,respectively;PpaandPpvarethepressuresinthepulmonaryarteriesandveins,respectively.
curve, point B falls below and to the right of point A; that is, cardiac output decreases, but Pv rises.
A More Com﻿plete Theoretical Model: The Two-Pum﻿p System﻿
The preceding discussion shows that the interrelationships between cardiac output and Pv are complex, even in an oversimplified circulation model that includes only one pump and just the systemic circulation. In reality, the cardiovascular system includes the systemic and pulmonary circulations and two pumps: the left and right ventricles. Thus the interrelationships among ventricular output, arterial pressure, and atrial pressure are much more complex.
Fig. 19.12 depicts a more complete (but still oversimplified) cardiovascular system model that has two pumps in series (the left and right ventricles) and two vascular beds in series (the systemic and pulmonary vasculature). The series arrangement requires that the flow pumped by the two ventricles be virtually equal to each other over any substantial period; otherwise, all the blood would ultimately accumulate in one or the other of the vascular systems. Because the cardiac function curves for the two ventricles differ substantially, the filling (atrial) pressures for the two ventricles must differ appropriately to ensure equal stroke volumes (see
Fig. 18.13