L3: Haemodynamics

Question 1

What is serum?

Answer 1

Plasma without the clotting factors

Clear yellowish liquid

Question 2

Does blood viscosity changes much?

Answer 2

Changes are relatively uncommon
Diseases –> Polycythaemia (↑RBCs), Thrombocythaemia (↑platelets) leukaemia (↑WBCs)
Thick blood –> dry gangrene in peripheries

Question 3

What causes plasma viscosity to change?

Answer 3

Minor changes
Typically from acute phase proteins (CRP, fibrinogen, complement)
Indicates inflammation

Question 4

What does haemodynamics mean?

Answer 4

Movement of blood

Metabolic demand dictate flow

Question 5

What causes blood to move?

Answer 5

Moves from areas of high pressure to areas of low pressure

Pressure gradient required for movement

Question 6

Define laminar flow?

Answer 6

Smooth flow
Maintaining energy
Most common

Question 7

Define turbulent flow?

Answer 7

Disorganised flow
Loss of energy
Pressure increased beyond point where it can flow linearly- flow decreases

Question 8

Define flow?

Answer 8

volume transferred per unit time (L/min)

Question 9

Define pressure?

Answer 9

Force per unit area (mmHg) –> in blood

Question 10

Why does the flow and pressure pulsate?

Answer 10

To model steady flow and pressure column

Question 11

What is the relationship between flow and resistance?

Answer 11

Inverse relationship ↑resitance ↓flow

Resistance= difficulty of flow

Question 12

How are pressure, flow and resistance related?

Answer 12

Flow= Pressure / resistance

If resistance increases, flow the same, then pressure must increase

Question 13

What affects the resistance?

Answer 13

Diameter, length of vessel and viscosity
Diameter- most important
Length of vessel (constant)
Viscosity (constant)

Question 14

Why does the diameter have the biggest impact on resistance?

Answer 14

Radius raised to 4th power (simplified R= 1/r^4)
19% decrease in radius –> half the blood flow
Small changes= big impact

Question 15

What causes the radius/diameter of blood vessel to change?

Answer 15

Vasoconstriction and vasodilation

Question 16

What is the relationship between pressure and resistance?

Answer 16

Proportional

Change in pressure= change in resistance

Question 17

What structure causes the biggest change in resistance/pressure?

Answer 17

Arterioles--> biggest jump in pressure across vessel class
Small arteries and arterioles contribute greatest component of TPR

Question 18

How does pressure and resistance change in the CVS?

Answer 18

Pulmonary circulation (heart to lungs) lower pressure than systemic
Short and wider vessels

Longer vessel- greater resistance reduced flow
Short- resistance decrease flow increases
Increased diameter, reduced resistance
Reduced diameter, increases resistance

Question 19

Define velocity?

Answer 19

The distance fluid moves in a given time (and direction) (cm/s)

Question 20

What is the relationship between flow, velocity and radius?

Answer 20

(flow= volume per unit time → therefore the quicker the blood moves more flow)
Flow= Velocity x Area
Area= πr^2
therefore Velocity is inversely related to radius
F= V x r^2
flow is constant
V =1/r^2

Squeeze a hose pipe, radius decreases, velocity that water shoots out increases

Question 21

How is the relationship between flow, velocity and radius demonstrated in the vasculature?

Answer 21

Capillaries= largest SA (radius) = slowest velocity
Allows diffusion

Large number of capillaries

Question 22

What is the pulse pressure?

Answer 22

Systolic blood pressure - diastolic blood pressure

Question 23

How is the mean arterial pressure calculated?

Answer 23

MAP= Diastolic blood pressure + (systolic blood pressure - diastolic blood pressure)/3) 
MAP = DBP + (SBP-DBP)/3
Time weighted
OR
MAP = CO x TPR

Question 24

What is total peripheral resistance? How is it calculated

Answer 24

Total resistance in the systemic circulation

TPR= ( Mean aortic pressure (SBP) - central venous pressure (DBP) ) / Cardiac output

Question 25

What determines pulse pressure?

Answer 25

(pulse pressure- pressure of the blood ejected from the heart) Compliance of arterial system (ability to expand to accommodate increased blood volume) Volume of blood ejected

Question 26

What actually is your pulse?

Answer 26

Shock wave that arrives slightly before the blood itself

Question 27

What causes the pulse pressure to increase?

Answer 27

Heart block - brachycardia--> more time in filling phase so larger volume ejected each beat (↑stroke volume) Vasodilation --> decreased peripheral resistance so diastolic pressure will drop as more of the blood ejected out the heart (more volume to fill) Elite athletes --> systolic increased (bigger heart muscle so increased output), diastolic decreased (more of the blood ejected out the heart) Age and atherosclerosis --> stiffening of the vessels, reduced compliancy of vessels

Question 28

To record blood pressure what features of blood flow does it rely on?

Answer 28

Smooth laminar flow --> silent | Turbulent flow--> noisy

Question 29

What is the name of the sounds you are listening for when taking a blood pressure?

Answer 29

Korotkoffs sounds

Question 30

What is the difference between thrill and bruit

Answer 30

Thrill --> felt Bruit --> heard Turbulent flow

Question 31

Describe the basis of taking a blood pressure?

Answer 31

Pressure cuff--> occludes blood pressure Release air Sound--> turbulent flow --> Korotoff sounds --> systolic blood pressure = pressure in cuff No sound--> laminar flow--> diastolic pressure=pressure in cuff

Question 32

What is important to remember when taking blood pressure?

Answer 32

Cuff size --> small = over estimation, large = under estimation Positioning of cuff Measure both arms --> use higher as reference point Safe comfortably, upright, legs uncrossed, feet on ground Arm supported Repeat --> mean taken Taken at level of the heart

Question 33

What are the effects of gravity on blood pressure?

Answer 33

Below level of heart--> pressure increased Above level of the heart--> pressure decreased Gravity maintains pressure gradient allowing blood to flow from heart to foot when standing Pooling--> below heart

Question 34

What causes dizziness upon standing?

Answer 34

Postural hypotension ↓ SV transient arterial hypotension Baroreceptors not detected change