Pressure & Flow in Arteries & Veins

Question 1

How do we measure BP?

Answer 1

A sphygmomanometer to measure BP
A stethoscope to auscultate korotkoff sound below the cuff in order to tell systole vs diastole.

Automatic cuffs are becoming common so you dont need to auscultate

Question 2

How do we distinguish between systole/dyastole?

Answer 2

At a certain cuff pressure it will contrict the dyastolic flow but systolic pressure is still high enough to pass through without trouble. Therefore you will hear a continuous muffled sound or thumping to show dyastole.
At a higher pressure it will completely constrict dystolic pressure and somewhat constrict systolic pressure so you will hear tapping in time with systole showing your at the systolic pressure.

Question 3

What are the pros/cons to measuring BP with a sphygmomanometer??

Answer 3

Pros- Non invasive & Cheap

Cons - Inaccurate, Discontinuous and takes care

Question 4

Whats the function of elastic arteries?

Answer 4

To dampen any pressure variations, acting as a “pressure reservoir”

Question 5

What effects the arterial pressure wave?

Answer 5

• SV
• Ejection Velocity
• Elasticity of Arteries
• TPR

Question 6

How does ejection velocity effect the arterial pressure wave?

Answer 6

A higher ejection velocity means the elastic arteries have less time to react & stretch so a higher peak pressure is reached

Question 7

How does TPR effect arterial pressure wave?

Answer 7

If TPR all the pressures go down (MAP = CO x TPR)

Question 8

Why does pressure decrease in the vessels during/after arterioles?

Answer 8

They have a high resistance which you would think would increase pressure (Pressure = flow x resistance)
However this resistance decreases flow so so each consecutive section of arteriole and the following vessels has a lower flow and therfore pressure.

Question 9

What do we call the pressure difference pushing pressure difference driving blood back through veins?

Answer 9

Systemic Filling Pressure (quite small ~5-20mmHg)

Question 10

Why are external influences able to affect flow in veins?

Answer 10

Because theyre very distensible/collapsible.

Question 11

What external factors effect the pressure & flow of veins?

Answer 11

Gravity
The SkeletalMuscle Pump
Respiratory Pump
Venomotor Tone
Systemic Filling Pump

Question 12

Why doesnt gravity effect the pressure driving blood from arteries -> veins?

Answer 12

Because it evenly effects the veins and arteries so the pressure difference is unchanged

Question 13

How does gravity effect he veins?

Answer 13

Venous distension in the legs and collapse in the head/neck.

Pressure in the veins above the heart can become sub-atmospheric and the legs can go as much as 80mmHg higher.

Question 14

venous distension in the legs can lead to postural/orthostatic hypotension, how?

Answer 14

Venous distension in legs

• > Reduced Venous Return
• > Reduced EDV
• > Reduced Preload
• > Reduced SV
• > Reduced CO
• > Reduced MAP

Question 15

Whats the use of measuring the level of jugular collapse?

Answer 15

It can be used to estimate CVP (just well enough to tel if its roughly normal or not)
Level of jugular collapse is basically how high above the heart does the pressure become subatmospheric and the vein collapse

Question 16

How does the skeletal muscle pump work?

Answer 16

Every time it contracts it squashes the vein pushing blood in the right direction thanks to valves.
This is particularly important in the legs to counter venous distension

Question 17

What effect do rythmic vs static exercise have on the veins?

Answer 17

Rythmic exercise involves lots of contractions so lots of blood is pumped through the veins by the skeletal muscle pump.
Static exercise like weight lifting involves a sustained contraction which stops blood flow through the veins

Question 18

What happens if you sit or stand still for long periods without contractions?

Answer 18

Deep vein Thrombosis can occur, hence why fliers and palace guards are told to move about periodically.

Question 19

What is the effect of long term venous distension (for years)

Answer 19

Varicose veins

Question 20

What is the respiratory pump?

Answer 20

Every time you inhale you increase abdominal presure and decrease thoracic presssure.
This pushes and pulls (respectively) blood through veins from the abdomen into the heart.
The deeper the breath the more blood flow.

Question 21

What is venomotor tone?

Answer 21

The level of sustained contraction in smooth muscle surrounding veins and venules.

Question 22

how does venomotor tone change during exercise?

Answer 22

It increases during exercise or flight/flight so the muscle contracts and pushes blood back to the heart

Question 23

What creates systemic filling pressure?

Answer 23

The contraction of the left ventricle, its transmitted through the whole vascular tree to the veins.
Its the main force pushing blood back to the heart at rest.

Question 24

How do the veins themselves affect the next systemic filling pressure?

Answer 24

Very dilated veins pump less blood to heart
Therefore theres a smaller CO and a lower pressure produced
This means the systemic filling pressure gets lower.

Question 25

How does pressure change through the major arteries ?

Answer 25

thers a small drop as theyre a low resistance conduit,

~95 to 90 mmHg

Question 26

how does pressure change through the arterioles?

Answer 26

A big drop as theyre resistance vessels

From ~90mmHg to 40mmHg

Question 27

Why is it important blood pressure is low upon reaching the capillaries?

Answer 27

Theyre v thin walled so a high pressure would burst them?

Question 28

What is the value of systemic filling pressure?

Answer 28

~5-20mmHg

Question 29

How do the pressures of pulmonary circ compare to systemic circ?

Answer 29

Pulmonary circulation has pressure about 1/5 of systemic.

Question 30

What determines velocity in the vessels?

Answer 30

The total cross section of the vessels, hence its lowest in the capillaries and fastest in the aorta/vena Cavae.