Module 2 : Venous Hemodynamics Flashcards
1
Q
Venous function
A
- primary function is to return blood back to the heart
- act as a reservoir to maintain homeostasis
- 80% of blood volume is moving through the veins
- veins offer little resistance to flow
- a pressure or energy gradient is needed for blood to flow from one point to another
2
Q
Methods of moving venous flow
A
- cardiac function
- respiratory function
- skeletal muscle contraction
- pressure gradients
- venous valves
- compliance
3
Q
LV contraction
A
- sends blood through arteries as a high pressure, pulsatile stream
- blood loses pressure as it flows through the high resistance arterioles and capillaries
- at level of venules pressure reduced to 15 mmHg
4
Q
Hydrostatic pressure
A
- defined as the weight of a colomn of blood
- measured from the heart to then point of of pressure = weight of column of fluid
- caused by gravity (gravitational pressure)
- influenced by patient position
- primary factor in determining intravascular pressure
- supine = 15mmHg, all parts at same level of RA
- standing= leg veins dilate and blood pools, 110mmHg
5
Q
Hydrostatic pressure cntd
A
- pressure gradient needed for flow to occur
+ pressure in capillaries 15mmHg
+ central venous pressure RA 0mmHg
-pressure highest in lower portion of the body - in raised arm column shorter and pressure lower
- hydrostatic pressure is relative to right atrial pressure of 0
6
Q
Hydrostatic pressure effect on lower veins in stationary person
A
- ^ transmural venous pressure distally
- ^ venous distention
- ^ venous pooling
- ¥ capillary perfusion
- ¥ venous return
- ¥ cardiac output
- hypotension v fainting
7
Q
Compliance and capacitance
A
- 80% blood located in veins
- vein walls very compliant
- internal pressure= intraluminal intramural
- external pressure = interstitial
- venous wall shape depends upon pressure volume or flow
8
Q
Capacitance
A
- venous system adapts to changes in blood volume
- depends on the limb position, muscle pump activity, venous valve function, blood volume
- surplus fluids can be stored or adjusted to blood loss
9
Q
Compliance
A
- permits increase in venous flow without significant increase in venous pressure
- veins are less elastic than arteries but more compliant
- veins act similar to a rubber band and can be stretched and collapse in variety of sizes
- extreme fluid overload or severe blood loss will affect central venous pressure
10
Q
Transmural pressure
A
- determines cross sectional shape of vein
- difference between intraluminal and interstitial pressure
- ## increased intramural pressure increase transmural pressure= rounder vein
11
Q
Low transmural pressure
A
- volume and pressure decreases vein walls collapse and become elliptical
12
Q
Valsalva maneuver
A
- increase thoracic and abdominal pressure and respiratory changes exaggerated
- increase pressure in both upper and lower extremity veins
- flow should stop or diminish in upper and lower extremities
- release of breath causes augmentation
- abnormal response is reverse in flow
- don’t do with heart disease
13
Q
Cardiac return
A
- muscular contraction f the heart = dynamic pressure
- cardiac contraction and relaxation creates suction effect on venous blood flow
- 2 periods of increases venous flow during cardiac cycle
14
Q
Ventricular systole
A
- atrial volume increase
- atrial pressure decrease
- increases flow from veins into right atrium and decreased venous system pressure
- when Sv Val es open blood enters ventricles atrial pressure decreases allowing venous blood to flow into heart
15
Q
Respiration at rest
A
- respiration creates large changes in intrathoracic and intra-abdominal pressures
- phasicity term used to refer to ebb and flow that occurs in tube veins in response to respiration
- respiratory function less effect on upper extremity veins (more pulsatile)
- respiration small effect when standing
