L13 Coupling of Heart & Peripheral Vasculature

Question 0

Central Venous Pool

Answer 0

Volume of blood in the right atria and the great veins

Question 1

Venous Return

Answer 1

The amount of blood returning to the thorax from periphery

Question 2

Cardiac Output

Answer 2

The amount of blood that leaves the central venous pool via pumping

Question 3

Vascular Function Curve & influence by volume and tone

Answer 3

As the cardiac output increases, the Central Venous Pressure (CVP) goes down. As the CO goes down (blood is backed up), the CVP increases.

Volume influence: more volume increases the vascular function curve and increases venous return.

Tone influence: more tone makes the system more full, has same effects^

Question 4

Mean Circulatory Pressure (Pmc)

Answer 4

Pmc is the pressure when the heart stops pumping (Peripheral P = Central P). It is the “fullness” of the venous system and is affected by:

Tone: increase tone (venoconstrict) makes the system smaller, so it appears more full.

Volume: giving more volume would make the system more full

Question 5

Factors affecting Venous Return

Answer 5

1. Cardiac suction
2. Cardiac contraction
3. increase blood volume
4. Sympathetic Venoconstriction makes blood flow faster
5. Respiratory pump creates negative P in thorax
6. Skeletal leg pump creates venoconstriction
7. Venous Valves prevent gravity from taking over

Question 6

Cardiac Function-Vascular Function graph

Answer 6

Only valid at the intersection points!!!!!!!!

CVP is determined by the relation between the CO and the vascular function

When the CO is 5L/min, the CVP is 2mmHg

Question 7

Influences on Cardiac Function Graph

Answer 7

This graph is moved up by positive inotropes and depressed by negative inotropes.
Sympathetic nerve stimulation and inotropic drugs cause the graph to move up, giving at higher CO at the same CVP

Heart failure is a failure in contractility. The CO decreases. This decrease in CO meets the vascular function curve at a higher CVP.

Question 8

Adjusting the vascular-cardiac function graph in response to hemorrhage & Heart failure

Answer 8

Hemorrhage: Venous return curve is depressed, but IN RESPONSE, the cardiac function curve is elevated based on Sympathetic innervation. The new *CVP is *lower but the *CO stays the *same.

Heart failure: The cardiac function curve is depressed, which means CO is depressed. IN RESPONSE: The kidneys sense this as hemorrhage and increase reabsorption of water, thus increasing volume. THIS IS BAD BC THE HEART CAN’T HANDLE THE INCREASE IN PRELOAD. Therefore, the vascular function curve shifts up, and the ultimate result is *CVP is *high and *CO is *low