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(VR) is the flow of blood back to the heart.
Under steady-state conditions, venous return must
equal cardiac output
CVS is essentially a closed loop.
Otherwise, blood would accumulate in either the
Increase in venous return can lead to a matched increase in
Two circulations (pulmonary and systemic) situated in series
between the right ventricle (RV) and left ventricle (LV).
Balance is achieved, in large part, by the Frank–Starling
If venous return is suddenly increased (e.g., changing from
upright to supine position), right ventricular preload increases
leading to an increase in stroke volume and pulmonary blood
The left ventricle experiences an increase in pulmonary
Increases left ventricular preload and stroke volume by
(VR) to the heart from the venous vascular beds is determined by a
1. Venous pressure –
2 Right atrial pressure
Therefore, increases in venous pressure or decreases in right atrial
pressure or venous resistance will lead to an increase in venous return,
VR is determined by the mean aortic pressure minus
the mean right atrial pressure, divided by the
resistance of the entire systemic circulation .
Decreased Veno capacitance
Pumping action of the heart
Resistance to Flow
Pressure change is
slight. Thus, small
increase in RA
in venous return.
Cardiac output increases with atrial pressure.
Normal atrial pressure is about 0 mm Hg.
Venous return (with heart and lungs removed)
decreases with atrial pressure.
Working cardiac output is where venous return
curve meets cardiac output curve.
Plateau: collapse of large veins
( => increased resistance)
Working Cardiac Output
Venous return with
heart and lung
Rt. Atrial Pressure (mm Hg)
Mean systemic filling
pressure ~ 7 mm Hg
Generally shift the cardiac
output curve in proportion
to pressure change
Cardiac Tamponade (filling
of pericardial sac with
fluid) lowers rate of change
of CO with right atrial
Rt. Atrial Pressure