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 the peak of the systolic blood pressure is greater than the pressure of the cuff - a small blip of turbulent blood flow passes the stethoscope.

Noise becomes muffled as the cuff pressure is reduced because the flow becomes more laminar

The sounds disappear completely since the blood flow through the artery has returned to normal. The last audible sound is defined as the diastolic pressure

Question 2

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

Answer 2

Disadvantages - Accuracy

Discontinuous – olny use it for instantaneous measurements

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

There is a higher total peripheral resistance so the 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 is the difference between the systolic and diastolic pressurereadings

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

Why is flow constant throughout the systemic circulation?

Answer 11

Because everything is in series

Question 12

What is the pressure drop through the arteries?

Answer 12

•arteries (from ~ 95 to 90 mmHg)

–low resistance conduit

Question 13

What is the drop in blood pressure throught the arterioles?

Answer 13

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

– the resistance vessels

Question 14

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

Answer 14

–good, because they are thin-walled

Question 15

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

Answer 15

•(from ~ 20 to 5 mmHg)

–the systemic filling pressure

Question 16

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

Answer 16

Pulmonary circulation is 1/5 th of the systemic

Question 17

Where is velocity fastest?

Answer 17

In the aorta and the vena cava - slowest in the capillaries

Question 18

Look

Answer 18

Question 19

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

Answer 19

External influences affect flow

Question 20

Does gravity affect driving pressure from arteries to veins?

Answer 20

NO

Question 21

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

Answer 21

Causes venous distension - Decreased end diastolic volume, decreased preload, decreased stroke volume, decreased cardiac output and decreased mean arterial blood pressure (orthostatic hypotension)

Question 22

What is the effect of gravity in the neck?

Answer 22

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

Question 23

Where in the body has -20 mmHg?

Answer 23

Head and neck

Question 24

Where in the body is +100 mmHg?

Answer 24

Feet

Question 25

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

Answer 25

Always remains the same

Question 26

What is the pressure that causes venous collapse?

Answer 26

Pressure of the interstitial fluid

Question 27

What is the purpose of valves?

Answer 27

Ensures directional flow

Question 28

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

Answer 28

Stops blood flow due to sustain compression of the vein - less venous return (Decreased end diastolic volume, decreased preload, decreased stroke volume, decreased cardiac output and decreased mean arterial blood pressure)

Question 29

What is meant by the respiratory pump?

Answer 29

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 30

How do varicose veins arise?

Answer 30

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

Question 31

What is meant by venomotor tone?

Answer 31

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

• mobilises the capacitance

Question 32

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

Answer 32

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