Venous return Cardiac function Normal (reference)
0 5 10 15 2 4 6 8 RAP (mmHg) CO / VR (L/min) MSFP RAP 2.1 CO 3.5 MSFP RAP 0.3 CO 2.6 MSFP RAP 1.1 CO 4.3 MSFP RAP 6.9 CO 2.2 MSFP RAP 4.1 CO 2.1
Normal

Baseline physiology. Venous return equals cardiac output at the intersection of both curves. MSFP is the elastic recoil pressure of the venous reservoir; RAP is the back-pressure opposing it. CO = (MSFP − RAP) / RVR.

MSFP
7 mmHg
Cardiac function
Normal
Operating RAP
2.1 mmHg
Operating CO
3.5 L/min
Hypovolaemic

Volume loss ↓ MSFP → VR curve shifts left (parallel). CO falls significantly with minimal RAP change — cardiac function is preserved. Fluid boluses restore MSFP, walking the operating point back up the cardiac function curve.

MSFP
↓↓ 4 mmHg (volume loss)
Cardiac function
Preserved
Operating RAP
0.3 mmHg
Operating CO
2.6 L/min
Distributive

Venodilation ↓ MSFP and ↓ RVR — VR curve shifts left and becomes steeper. Hyperdynamic cardiac response shifts CO curve up. CO maintained or ↑ early despite low SVR. Vasopressors (noradrenaline) restore MSFP via venoconstriction.

MSFP
↓ 5 mmHg (venodilation)
Cardiac function
↑ Hyperdynamic
Operating RAP
1.1 mmHg
Operating CO
4.3 L/min
Cardiogenic

Depressed pump function shifts CO curve steeply down-right → high RAP, low CO. Backed-up blood raises MSFP (congestion). Inotropes shift CO curve up; diuretics lower MSFP; vasodilators reduce afterload. Classic high CVP, low CO picture.

MSFP
↑ ~10 mmHg (congestion)
Cardiac function
↓↓ Depressed
Operating RAP
6.9 mmHg
Operating CO
2.2 L/min
Obstructive

Tamponade or massive PE raises pericardial/pulmonary back-pressure on the RA — CO curve shifts right (heart needs more preload to generate the same CO). VR curve unchanged. RAP rises, CO falls. Definitive treatment removes the obstruction.

MSFP
7 mmHg (unchanged)
Cardiac function
Shifted right (↑ effective RAP)
Operating RAP
4.1 mmHg
Operating CO
2.1 L/min