Module 2 : Venous Hemodynamics

Question 1

Venous function

Answer 1

• 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

Question 2

Methods of moving venous flow

Answer 2

• cardiac function
• respiratory function
• skeletal muscle contraction
• pressure gradients
• venous valves
• compliance

Question 3

LV contraction

Answer 3

• 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

Question 4

Hydrostatic pressure

Answer 4

• 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

Question 5

Hydrostatic pressure cntd

Answer 5

• 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

Question 6

Hydrostatic pressure effect on lower veins in stationary person

Answer 6

• ^ transmural venous pressure distally
• ^ venous distention
• ^ venous pooling
• ¥ capillary perfusion
• ¥ venous return
• ¥ cardiac output
• hypotension v fainting

Question 7

Compliance and capacitance

Answer 7

• 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

Question 8

Capacitance

Answer 8

• 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

Question 9

Compliance

Answer 9

• 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

Question 10

Transmural pressure

Answer 10

• determines cross sectional shape of vein
• difference between intraluminal and interstitial pressure
• ## increased intramural pressure increase transmural pressure= rounder vein

Question 11

Low transmural pressure

Answer 11

• volume and pressure decreases vein walls collapse and become elliptical

Question 12

Valsalva maneuver

Answer 12

• 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

Question 13

Cardiac return

Answer 13

• 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

Question 14

Ventricular systole

Answer 14

• 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

Question 15

Respiration at rest

Answer 15

• 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

Question 16

Skeletal muscle contraction

Answer 16

• with muscle contraction
  + venous pressure decreased
  + hydrostatic column of blood interruption
  + decreased venous pooling
  + decreased capillary pressure
  + increased blood flow
• at rest with no muscle activity veins act as reservoir
• muscle contraction = venous flow in the deep and superficial veins toward heart
• ## muscle relaxation = small amount of flow occurs in perforators

Question 17

Calf pump

Answer 17

-gastroc and soleal muscle contractions most efficient of the pumps
- capacitance in the calf is here th and during a single contraction
+ 200mmHg pressure generates
+ 40-60% venous volume ejected
- act as venous heart
-chronic venous insufficiency failure to decrease venous pressure with exercise

Question 18

Venous valves

Answer 18

• direct flow to heart
• prevent retrograde flow
• valves
  + bicuspid
  + arise from intimal layer
• valves in perforating veins direct flow from superficial to deep veins
• valve numbers
  + greater in calf veins due to increased hydrostatic pressure
  + veins less than LE veins
• venous valve sinus
  + normal dilation of a vein st the site of a valve
  + wider than vein
  + expand with increase pressure
  + frequent site of thrombi formation due to stagnant flow