3.2.4. Venous System Function Flashcards
Function of arterial system
- Maintain pressure to ensure perfusion of organs
2. Act as a filter to modulate pulsatile blood flow
central venous pressure range
2-8 mmHg
Venous pressure at the head when standing
-44 mmHg
Venous pressure at the feet when standing
88 mmHg
venous pulse: a wave pulse
corresponds to atrial contraction
venous pulse: c wave pulse
corresponds to tricuspid bulging into atria during systole
venous pulse: x decent
corresponds to atrial relaxation
venous pulse: v wave pulse
venous pressure rises slowly as atria fills
venouse pulse: y descent
corresponds to atria emptying into ventricles while AV valves open during diastole
% of blood volume in venous system at normal resting conditions
70%
% of blood volume in venous system during exercise
stored blood in venous system reduced from 60% - 70%
Vascular function curve: Hemorrhage
Hemorrhage will reduce cardiac output but not change slope of the curve
Vascular function curve: Volume infusion
Volume infusion such as saline IV will increase cardiac output but not change slope of the curve
Venous system function
- Blood storage and liberation
2. Regulate return of blood to the heart
Mean systemic filling pressure
A point on the vascular function curve in which cardiac output drops to zero L/min. Ultimately, flow will terminate once mean arterial pressure equalizes with central venous pressure at 7 mmHg
Vascular function curve: central venous pressure = 0
Here the cardiac output is at it’s maximum. Below this, no venous return to the heart will occur and veins will collapse.
Vascular function curve: increasing venous tone
increase cardiac output but not change slope of the curve
Vascular function curve: decreasing venous tone
Decrease cardiac output but not change the slope of the curve
Vascular function curve: increase total peripheral resistance such as arteriolar constriction
Mean systemic filling pressure does not change. Slope of vascular function curve decreases and cardiac output decreases for a given right atrial pressure
Vascular function curve: arteriolar dilation
Mean systemic filling pressure does not change. Slope of the vascular function curve increases and cardiac output increases for a given right atrial pressure
Cardiac function curve: Right atrial pressure of zero
Yields cardiac output of zero. There is no preload. As a mental exercise the flask of water or preload is below the heart and the heart will not fill. The cardiac function curve is a representation of the heart with no vessels.
Cardiac function curve: maximum cardiac output
Based on the maximum preload to get max cardiac output. The heart can not fill with any further increase in preload pressure.
cardiac function curve: increase in contractility, decrease in afterload, or increase in heart rate
cardiac function curve is shifted up and to the left
Cardiac function curve: decrease contractility, increase afterload, decrease heart rate
cardiac function curve shifts down and right
integrated vascular and cardiac function curve intersection
represents the only conditions where the heart and vessels can functionally coexist
integrated vascular and cardiac function curve: heart failure
contractility decreases. cardiac function curve shifts down and right. Cardiac output must remain at a certain value, so the body compensates by increasing blood volume, so the vascular function curve shifts right to restore cardiac output
integrated vascular and cardiac function curve: increase in arteriolar constriction (increase in total peripheral resistance).
vascular function curve slope decreases and cardiac output decreases. The body compensates by increasing cardiac contractility to restore cardiac output. The cardiac function curve shifts up and left.
integrated vascular and cardiac function curve: exercise
sympathetic stimulation increases contractility, so the cardiac function curve shifts up and left. Sympathetic stimulation decreases peripheral resistance and increases venous tone which increases the slope of the vascular function curve and shifts the curve to the right. This leads to a major increase in cardiac output.