Pressure and Flow in arteries and veins

Question 1

How are a sphygmomanometer and a stethoscope used to measure arterial pressure?

Answer 1

Cuff is inflated - constricts brachial artery

First audible tapping noise through stethoscope is because peak of systolic Bp is greater than pressure of cuff - small blip of turbulent blood flow passes stethoscope

Noise muffles as cuff pressure is reduced because flow becomes more laminar

Sounds disappear completely since blood flow through artery has returned to normal.

Last audible sound defined as diastolic pressure

Question 2

What are the advantages/disadvantages of this method of measurement of blood pressure?

Answer 2

Disadvantages:

Accuracy

Discontinuous – only for instantaneous measurement

Needs care – constant surveillance, not automated

Advantages:

Cheap and non-invasive

Question 3

What is the effect of high diastolic pressure on the aorta?

Answer 3

higher total peripheral resistance so aorta finds it harder to release blood

Question 4

What is the effect of elastic vessels on pressure variations?

Answer 4

Dampens them down

Question 5

What is the pressure wave affected by?

Answer 5

• stroke volume
• velocity of ejection
• elasticity of arteries
• total peripheral resistance (If TPR increases, stroke volume will go down (more energy is “wasted” building up sufficient pressure to open the aortic valve))

Question 6

Define pulse pressure

Answer 6

Pulse pressure = difference between systolic and diastolic pressure readings

Question 7

What feature of arteries allows maintainance of high pressure during high systolic pressure?

Answer 7

Elastic fibres

Question 8

How does pressure change from arteries - arterioles - capillaries - venules?

Answer 8

Decreases

Question 9

What is name given to the blood pressure left to bring the blood back to the heart?

Answer 9

Systemic filling pressure

Question 10

What is normal arterial pressure?

Answer 10

“Normal” arterial pressure

= 120/80 mmHg

Arterial pressure (especially pulse pressure) increases with age

Question 11

What is the pressure drop through the arteries?

Answer 11

arteries (from ~ 95 to 90 mmHg)

• low resistance conduit

Question 12

What is the drop in blood pressure throught the arterioles?

Answer 12

Large drop through arterioles (from ~ 90 to 40 mmHg)

• resistance vessels

Question 13

Why is it good that blood pressure is low when blood reaches the capillaries?

Answer 13

Capillaries are thin-walled

Question 14

What is the small pressure difference pushing blood back through the veins?

Answer 14

From ~ 20 to 5 mmHg

• systemic filling pressure

Question 15

What is the pulmonary pressure in relation to the systemic pressure?

Answer 15

Pulmonary circulation is 1/5 systemic

Question 16

Where is velocity fastest?

Answer 16

aorta and vena cava - slowest in capillaries

Question 17

Look

Answer 17

Question 18

Vessels of veins are distensible and collapsable what does this mean?

Answer 18

External influences affect flow

Question 19

Does gravity affect driving pressure from arteries to veins?

Answer 19

NO

Question 20

What is the effect of gravity in venous blood in the leg?

Answer 20

Causes venous distension

Decreased:

• end diastolic volume
• preload
• stroke volume
• cardiac output
• mean arterial blood pressure (orthostatic hypotension)

Question 21

What is the effect of gravity in the neck?

Answer 21

Causes venous collapse in the neck - can be used to estimate central venous pressure

Question 22

Where in the body has -20 mmHg?

Answer 22

Head and neck

Question 23

Where in the body is +100 mmHg?

Answer 23

Feet

Question 24

If pressure in the arteries always remains constant what does this mean for the driving force of the blood?

Answer 24

Always remains the same

Question 25

What is the pressure that causes venous collapse?

Answer 25

Pressure of the interstitial fluid

Question 26

What is the purpose of valves?

Answer 26

Ensures directional flow

Question 27

What is the effect of sustained muscle contraction in the legs?

Answer 27

Stops blood flow due to sustain compression of vein

Less venous return

(Decreased end diastolic volume, preload, stroke volume, cardiac output, mean arterial blood pressure)

Question 28

What is meant by the respiratory pump?

Answer 28

During inspiration, decreases in intrathoracic pressure draws air into the trachea, bronchi, and lungs and draw blood into the vena cava and right atrium of the heart

Question 29

How do varicose veins arise?

Answer 29

Result from poor valves – more pooling of blood and high pressure in deep veins

Question 30

What is meant by venomotor tone?

Answer 30

State of contraction of the smooth muscle surrounding the venues and veins

• mobilises the capacitance

Question 31

What are all the factors that affect venous pressure and blood flow in veins?

Answer 31

• Gravity
• skeletal muscle pump
• respiratory pump
• venomotor tone
• systemic filling pressure