Module 2 Venous hemodynamics Flashcards
What is the primary function of the veins?
Return nutrient deficient blood back to heart
Veins act a reservior to do what?
Maintain homeostasis with 65% blood volume moving through veins at one time
Vein walls can expand and contract depending on what? 3
- Pressures
- Volumes
- Flow
The different pressures that effect the vein shape are what? 2
- Intramural (internal)
- Interstitial (external)
What does the veins permit in terms of blood pressure and volume?
Increase of blood volume without a significant increase in venous pressure
Veins are less elastic than arteries but more what?
Compliant
Veins adapt to changes in blood volume as a result of what? 4
- Limb position
- Muscle pump activity
- Venous valve functions
- Blood volume
Surplus fluids can be stored or adjusted to what?
Blood loss
Veins act similarly to what?
Rubber bands and can be stretched and collapsed in a variety of sizes
Extreme fluid overload or severe blood loss will affect what?
Central venous pressure
Veins have little resistance to blood flow when in what position?
In a supine position
The pressure difference form post capillary vein and the heart is what?
Low
Venous flow is affected by what?
Posture changes
Venous return to the heart is assisted by what? 4
- Cardiac cycle
- Respiration
- Muscles
- Valves
Muscular contraction of the heart affects what?
Pressure and flow of venous blood
Cardiac activity is evident where? 2
- Large central veins
- Large head and neck veins
Two periods of heart cycle increase venous flow, what are they?
- Opening of tricuspid valve
- Ventricular systole
When the tricuspid valve opens there is more what?
Volume in the heart, dropping the pressure
When the right ventricle contracts, what does it do? ( TV, RA, volume)
- Pulls the tricuspid valve down
- Expanding the right atrium
- Increasing the volume
What is respirophasicity?
Venous flow affected by movement of diaphragm
What are the two phases of breathing?
Inspiration and expiration
Effects of breathing vary with what?
Position and area of the body
Valsalva maneuver does what?
Increases pressure above and below diaphragm
During inspiration what is the diaphragm motion like?
Moves inferior
During expiration what is the diaphragm motion?
Superior
What is the intra-abdominal pressures during inspiration?
Increase
What is the intra-abdominal pressures during expiration?
Decrease
What is the intra-thoracic pressure during inspiration?
Decrease
What is the intra-thoracic pressures during expiration?
Increase
During inspiration what happens to the IVC?
Collapses
During expiration what happens to the IVC?
Dilates
During inspiration what happens to the lower extremity venous return?
Decrease
During expiration what happens to lower extremity venous return?
Increase
During inspiration what happens to the upper extremity venous return?
Increase
During Expiration what happens during upper extremity venous return?
Decrease
Respiration effects can be diminished in what? 2
- Supine position
- Shallow breather
Upper extremities can be more pulsatile because of what?
Close proximity to the heart
Respiration has less of an effect on venous flow when in what position?
Venous flow when standing
Contraction of voluntary muscles do what for veins?
Propels blood towards the heart
In the presence of normal functional valves the blood will flow how?
In one direction
Contraction results in decreased what? (Pressure wise)
Venous pressure by interrupting the hydrostatic column of blood
At rest, with no muscle activity what does the veins do?
Act as reservoirs for blood collection
Muscle contractions results in what in the veins? 3
- Decreased venous pooling
- Decreased capillary pressure
- Increased blood flow
What does a muscle contraction do in terms of venous flow?
Assists in venous flow in the deep and superficial veins is towards the heart
What is muscle relaxation in relation to the venous system?
Small amount of flow occurs in the perforators, from the superficial to the deep veins
What is the calf pump?
Contraction of the gastronemius and soleus muscles to most efficiently move blood.
What is the calf capacitance high? (How much force is generated per pump)
Generates pressures of about 200 mmHg per contraction
What happens in a single contraction of a calf pump?
40-60% of the venous volume is ejected
What does calf pump do? 2
Acts as a venous “heart” and
1. Squeeze the calf veins
2. Propels blood towards the heart.
The efficiency of the calf pump is dependent on what? 3
- Ability of the calf muscles to contract
- Competency of the venous valves
- Patency of the outflow veins
What does the venous valves do?
Direct blood flow to the heart and prevent retrograde flow (reflux)
What kind of valves are available in venous valves?
Bicuspid and arise from the intimal layer
Valves in perferator veins do what?
Direct flow from the superficial to deep veins
At the valve site what happens to the vein?
Veins dilate slightly at the sinus and expands with increased pressure
Where is a frequent site of thrombi formation due to stagnant flow?
Venous valves
What impedes Venous return? 2
- Gravity
- Hydrostatic pressure
For every 12 inches of vertical distance what happens?
22 mmHg of pressure is added
What is hydrostatic pressure?
The weight of a column of blood at a given point
Hydrostatic pressure is relative to what?
Right atrial pressure of zero
What is hydrostatic pressure above the heart?
negative pressure
When supine hydrostatic pressure is what?
Negligible (about 15 mmHg)
When standing the ankle pressure rises to around what?
110 mmHg and the legs veins dilate to accept the blood pooling
ASVD refers to what?
Blood volume
When we walk what is the hydrostatic pressures?
25 mmHG
What does transmural pressure determine?
The cross sectional shape of the vein
What is transmural pressure?
The difference between intraluminal and interstitial pressure
Intraluminal pressure is what?
The pressure within the vein walls
Interstitial pressure is what?
The pressure exerted from outside the vein by surrounding tissue and fluid
What is low transmural pressure?
The vein wall collapses and becomes elliptical in shape
What is high transmural pressure?
The vein wall becomes circular and may even distend at higher venous pressures
What makes intraluminal pressure?
Hydrostatic pressure
Aside from the images of the vessels, we can identify normal and abnormal venous returns by evaluating what?
Doppler waveforms
What is respirophasic?
When antegrade flow between the upper and lower extremity wave form is opposite due to changes in intrathoracic and intra-abdominal pressure.
The appearances between upper and lower extremities can be the same but the difference is with inspiration/ expiration.
When a valsalva maneuver is performed what happens to intra-abdominal and intrathoracic pressure? What results from this?
Increased thoracic and abdominal pressure which in turn increases the pressure in both the upper and lower extremity veins
During valsalva maneuver flow should do what?
It should stop or diminish in upper and lower extremities
During valsalva maneuver release of breath will do what to flow?
Increase or augment flow
It is normal when we see flow during valvsalva?
Abnormal response is a reverse of flow
Some abnormal venous waveforms we will encounter are what? 3
- Continuously
- Pulsation
- Reflux
What is the abnormal waveform of continuous?
A lack of respirophasicity usually the result of a more proximal obstruction from a clot or extrinsic mass
What is the abnormal waveform of pulsatile?
When the heart beat is reflected into vessels further from the heart because of increased central venous pressure related to heart conditions
What is the abnormal wave form of reflux?
Retrograde flow as a result of valve incompetence or Venus distension. A small amount is normal, but if prolonged represents venous insufficiency.
