Matching Cardiac Output

Front 1

Describe how CO and venous return are matched, using a combination of cardiac function curves and venous return curves.

Back 1

Since the circulatory system is a closed system, cardiac output must equal venous return (although transient differences do exist)

therefore, the intersection of the VR curve and the CO curve is the true CO and VR value, giving you the central venous pressure (P right atrium)

also, there is only one right atrium, so there can be only one value of Pra

Hint 1

see graph!

Front 2

Use cardiac function curves and venous return curves to explain cardiovascular responses to:

EXERCISE

Back 2

1) sympathetic stimulation of heart increases HR and contractility

2) Sympathetic stimulation of veins increases Pmc, increasing preload and thus shifting venous return curve up/right

3) Vasodilation in heart and muscle triggered by epinephrine decreases PVR, increasing slope of venous return curve, but not changing Pmc.
-- SANS always triggers an increase in PVR (think baroreflex)
-- During exercise, metabolic regulation can trigger certain tissues (like heart and muscle) to vasodilator so much that PVR could go down.

all these events happen roughly at the same time except the arteriolar vasodilation which takes a few minutes while epinephrine is produced and circles to skeletal muscle and cardiac arterioles

Sympathetic vasoconstriction also occurs in nonessential tissues.

Increased muscle contractions increase preload via venous return

Higher capillary pressure increases filtration, slightly decreasing Pmc

Hint 2

see graph!

Front 3

Use cardiac function curves and venous return curves to explain cardiovascular responses to:

BLOOD LOSS

Back 3

1) Loss of blood volume decrease Pmc and shifts venous return curve down/left

2) Baroreflex SANS simulation increases HR, contractility, increasing slope of CO curvel

3) SANS stimulates venous constriction, increasing Pmc, shifting venous return curve right/up

ALso going on but not explicitly on the graph for simplicity
- SANS vasoconstricts non-essential arterioles
- SANS vasoconstriction triggers "automatic transfusion" from interstitial fluid increases blood volume (lower hydrostatic capillary pressure increases absorption relative to filtration)ll

note: stimulating contractility any ore than it already is won't increase CO bc VR curve is plateau-ed

Hint 3

see graph!

Front 4

Use cardiac function curves and venous return curves to explain cardiovascular responses to:

HEART FAILURE

Back 4

1) Cardiac function decrease substantially, decreasing contractility and decreasing slope of CO curve while venous return is unchanged

2) SANS reflex triggers kidney water retention and contracts veins --> increases Pmc and shifts venous return curve right/up

3) Sympathetic stimulation land compensation increases HR at first, then heart contractility with compensation, increasing slope of CO curve.

notes: hypertrophy of the heart is also decreasing wall stress, work, oxygen demand
- high atrial pressures can increase capillary filtration (edema)