Pressure and flow in arteries and veins

Question 1

Describe the Korotkoff sounds made on auscultation to measure BP

Answer 1

Silence
Tapping - systolic BP
Then aortic valve closes (dicrotic notch) -> thumping
Then muffled/silent - diastolic BP

Question 2

What is the function of elastic arteries?

Answer 2

Dampen pressure variations

Question 3

State 4 factors that affect the pressure wave

Answer 3

Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance

Question 4

State normal arterial pressure

Answer 4

120/80mmHg

Question 5

What happens to arterial pressure, especially pulse pressure with ageing?
Why is this?

Answer 5

Arterial pressure, especially pulse pressure increases.

Due to loss of aortic elasticity

Question 6

Describe the effect of exercise on arterial pressure

Answer 6

Arterial pressure increases since velocity of ejection increase and the artery can’t respond that quickly

Question 7

State three factors that affect arterial pressure

Answer 7

Age
Exercise
Time of day

Question 8

Define pulse pressure

Answer 8

The difference between systolic and diastolic pressure

Question 9

Describe pressure changes through arteries and veins

Answer 9

Arteries have a low resistance conduit - 95-90mmHg
Arterioles are resistance vessels - 40mmHg
Pressure already low when it gets to capillaries - 20mmHg
Small pressure difference pushing blood back into veins - 5mmHg

Question 10

What name is given to the small pressure change pushing blood from the periphery back to the heart?

Answer 10

Systemic filling pressure

Question 11

What is the fraction of pulmonary circulatory pressure in relation to systemic circulatory pressure

Answer 11

1/5

Question 12

What is the relationship between velocity, cross section and surface area?

Answer 12

The bigger the cross section, the smaller the surface area and the great the velocity.
Therefore blood flows fastest through the aorta and vena gave which have the largest cross section but smallest surface area. It flows slowest through capillaries which have the smallest cross section and the largest surface area.

Question 13

Is the change in pressure driving blood back to the heart big or small?

Answer 13

The change in pressure driving blood back to the heart from the periphery is small since venous pressure is low.

Question 14

What characteristics of venous vessels make them vulnerable to external influences?

Answer 14

Collapsible and distensible

Question 15

List the 6 factors that affect pressure and flow in veins

Answer 15

Gravity
CVP (central venous pressure)
Skeletal muscle pump
Respiratory pump 
Venomotor tone
Systemic filling pressure

Question 16

Does gravity affect flow from arteries to veins?

Answer 16

No, but it causes venous distension in the legs

Question 17

Describe the effect of gravity on venous pressure between lying down and standing.

Answer 17

Lying down - 20mmHg at head, 0mmHg at arms and 20mmHg at feet
Standing: -20mmHg at head, 0mmHg at arms and 100mmHg at feet

Question 18

How much blood can accumulate in the feet due to the effects of gravity when standing?

Answer 18

1.5l

Question 19

Describe the effects of gravity on venous return.

What are the clinical consequences of this?

Answer 19

Reduced EDV
Reduced preload 
reduced stroke volume 
reduces CO
reduces MAP 
Clinical consequence: postural hypotension - less blood reaches brain -> not enough O2 -> fainting

Question 20

What is used to estimate CVP?

Answer 20

JVP/jugular collapse

Question 21

Describe the mechanism of the skeletal muscle pump

Answer 21

Muscle contracts to squeeze blood back to the heart and increasing EDV.
Rhythmic exercise is better than static explaining why travellers are more prone to DVT and varicose veins

Question 22

Describe the mechanism of the respiratory pump

Answer 22

During inspiration, there is an increase in thoracic pressure which reduces the pressure gradient between the veins and the heart, leading to a reduced EDV

Question 23

Describe the effect of venomotor tone on venous return

Answer 23

Venomotor tone - state of contraction of smooth muscle surrounding veins and venules which mobilises their capacitance -> increased EDV

Question 24

What triggers an increase in venomotor tone?

Answer 24

Increased sympathetic tone

Question 25

Define systemic filling pressure

Answer 25

Pressure created by ventricles and transmitted through vascular tree to veins

Question 26

What increases systemic filling pressure?

Answer 26

Exercise