Pressure and Flow in Veins

Question 1

How do you measure Korotkoff sounds?

Answer 1

Sphygmomanometer and stethoscope

Question 2

What are the disadvantages and advantages of using a sphygmomanometer?

Answer 2

Discontinuous, accuracy, needs care and skill
Non-invasive and cheap

Question 3

What causes Korotkoff sounds?

Answer 3

Turbulent blood flow
Silence above systolic and under diastolic

Question 4

What sounds are heard on stethoscope?

Answer 4

Silence, tapping, thumping, muffled and then silence again

Question 5

How does an oscillatory blood pressure measurement calculate arterial pressure?

Answer 5

Vibrations from turbulent blood flow are measured
Peak of vibrations at MAP
Transducer measures this

Question 6

Explain ventricular contraction on aorta and arteries?

Answer 6

Ventricle contracts, Semilunar valve open and blood ejected from ventricle to arteries and then aorta expands so can store pressure in elastic walls

Question 7

Explain ventricular relaxation on aorta and arteries?

Answer 7

Isovolumic ventricular relaxation, semilunar valves shut so prevents backflow of blood and then elastic recoil sends blood forward into circulatory system

Question 8

How does elastic arteries act as pressure reservoir?

Answer 8

Damps down pressure vibrations

Question 9

What is pressure wave affected by?

Answer 9

Stroke volume, Velocity of ejection, Elasticity of arteries and TPR

Question 10

Describe pressure and flow from arteries to veins?

Answer 10

Pressure falls throughout vascular tree and velocity is related to total cross-sectional area

Question 11

What causes small drop in pressure through arteries?

Answer 11

Low resistance conduit
around 95 to 90 mmHg

Question 12

What causes larger drop in pressure through arterioles?

Answer 12

Resistance vessels
Around 90 - 40mmHg

Question 13

Describe the pressure in capillaries?

Answer 13

Low which is good as thin walled

Question 14

Describe pressure in veins?

Answer 14

Small pressure difference pushing blood back through veins as systemic filling pressure
From 20 - 5 mmHg

Question 15

What is pulmonary circulation pressure?

Answer 15

1/5 th of systemic circulation pressure as need to be low

Question 16

Describe velocity and cross-sectional area

Answer 16

Fastest in aorta and vena cava as small total cross-sectional area
Slowest in capillaries as have high cross-sectional area

Question 17

How does external influences affect flow?

Answer 17

Vessels are distensible and collapsible

Question 18

Does gravity affect driving pressure from arterioles to veins?

Answer 18

No

Question 19

What effect does gravity have on flow and pressure in veins?

Answer 19

Venous distension in legs
Decreases EDV, preload, SV, CO and MAP
Can get orthostatic hypotension which causes venous collapse in neck

Question 20

What causes orthostatic hypotension?

Answer 20

Veins and venules are thin walled so increase in pressure causes them to distend (expand) so blood pulls here and less blood gets to heart

Question 21

Explain negative pressure on pressure and flow in veins?

Answer 21

Negative pressure means pressure inside vessel is lower than outside so causes vessels to become squished and collapse

Question 22

What happens if venous pressure increases?

Answer 22

The point of collapse will move further up and can be visible
Can rise due to stress
Can look for point of collapse in internal jugular vein
Very prominent and full of blood

Question 23

What can raised JVP cause?

Answer 23

Can show right sided heart failure

Question 24

How does the skeletal muscle pump affect the pressure and flow in veins?

Answer 24

Rhythmic contraction increases venous return and EDV
If muscle contracts it can squeeze on veins and venules so blood squeezed in both directions

Question 25

How does compression socks help?

Answer 25

Compress vessels in legs so blood can get back to heart quicker

Question 26

Describe the respiratory pump on pressure and flow in veins?

Answer 26

Increased respiratory rate and depth increases venous return and EDV

Question 27

How does inspiration lead to larger pressure gradient and increased venous return?

Answer 27

Diaphragm moves down and caused negative pressure in thorax and positive below
Causes larger pressure difference so blood is pushed back to heart and therefore causes increased venous return

Question 28

How does venomotor tone affect pressure and flow in veins?

Answer 28

Is a state of contraction of smooth muscle surrounding the venules and veins
Mobilises capacitance and increases EDV

Question 29

What is the systemic filling pressure?

Answer 29

Pressure created by ventricles and transmitted through vascular tree to veins

Question 30

What does clotting involve?

Answer 30

Formation of platelet plug and fibrin clot
Platelets are exposed to collagen and also send chemical signals to other platelets

Question 31

How is fibrin made?

Answer 31

Fibrinogen is converted to insoluble fibrin by thrombin

Question 32

What are some endothelium mechanisms for to stop platelet aggregation?

Answer 32

Stops blood contacting collagen
Produces prostacyclin and NO which inhibits platelet aggregation

Question 33

What endothelium mechanism stops thrombin production?

Answer 33

Produces tissue factor pathway inhibitor (TFPI)

Question 34

What endothelium mechanism inactivates thrombin?

Answer 34

Expresses thrombomodulin
Expresses heparin

Question 35

What endothelium mechanism causes plasmin production?

Answer 35

Secretes tissue plasminogen activator so plasminogen can convert to plasmin and digest clot