Haemodynamics

Question 1

Define haemodynamics

Answer 1

Movement of blood around the body

Question 2

What is serum ?

Answer 2

Serum in the blood is the solute and fluid component found after clotting. It is plasma , just without clotting factors.

Question 3

Changes In viscosity is relatively uncommon for which substance - blood or plasma ?

Answer 3

Whole Blood

Question 4

How do minor changes in plasma viscosity arise ?

Answer 4

• acute plasma proteins such as fibrinogen , compliment , C-reactive protein (CRP)
• CRP is used to measure plasma viscosity as an indicator of inflammation

Question 5

What dictates delivery of blood around the body ?

Answer 5

Metabolic demands

Question 6

blood moves from a high/low pressure to a high/low pressure

Answer 6

High to low pressure

Question 7

What is laminar flow ?

Answer 7

Laminar flow is movement of blood through vessels through a regulated flow , it is very smoothly driven

• it helps to maintain energy
• typical for most arteries , arteriolar , venules and veins
• with laminar flow , blood flows quicker at the centre of the vessel than at the edges

Question 8

Turbulent flow

Answer 8

Movement of blood through a vessel in a disorganised flow

• energy is lost through this process
• typically happens during a pathological state

Question 9

Define flow

Answer 9

Volume transferred per unit time (L/min)

Question 10

Define pressure

Answer 10

Force per unit area (mmhg)

Question 11

Define conductance

Answer 11

Measure of ease of low

Identified as K

Question 12

Define resistance

Answer 12

Measure of difficulty of flow

Identified as R

Question 13

What is the equation for flow ?

Answer 13

flow = K x ( difference in pressure)

Question 14

What is the equation for resistance ?

Answer 14

r =-1/k

Question 15

DARCY’s LAW

Answer 15

FLOW (Q) = Change in pressure /R

Question 16

What are a few factors that cause

Resistance to flow ? And which one is most important ?

Answer 16

• diameter
• length of vessel
• viscosity

DIAMETER is most important because vessel length doesn’t change and blood viscosity is tightly regulated within a narrow range

Question 17

Poiseulle’s law

Answer 17

R = 8n(viscosity)x L(length) / pi r^4

• vascular resistance increases with vessel length , blood viscosity but decreases with increased radius.

Flow = change in pressure / R so if resistance decreases due to a 19% decrease in radius , then flow would halve.

Question 18

In the arteries eg the aorta , is resistance high or low ?

Answer 18

The resistance is low

because R= change in pressure / Flow and there is little change in pressure in the aorta

Question 19

In the arteriolar and smallest arteries , is resistance high or low ?

Answer 19

• contribute greatest to total peripheral resistance because there is the biggest jump in pressure across vessel class
• arterioles are the seat for peripheral resistance

R= change in pressure / flow

Question 20

Resistance in the pulmonary circulation is much higher/lower than the systemic circulation ?

Answer 20

Lower in the pulmonary circulation than systemic

-because they have shorter and wider vessels

Question 21

Define velocity (V)

Answer 21

Distance fluid moves in a given time (cm/s)

Question 22

How is velocity and flow related ?

Answer 22

FLOW ( F) = V x A

Where A is the cross sectional area of the vessel (pi r^2)

Therefore F ~ V x r^2

At a constant flow V is inversely related to r^2 V~ 1/r^2

Question 23

Why is velocity at capillary level much slower than at aorta or large arteries ?

Answer 23

Because cross sectional area is vast - thousands times greater than that of aorta or large arteries

V~ 1/r^2

Question 24

what is pulse pressure

Answer 24

Difference between systolic pressure and diastolic pressure

Measure in mm of mercury (mmhg)

Question 25

Define Mean arterial pressure

Answer 25

Average blood pressure in an individual during a single cardiac cycle

Mean arterial pressure = CO x total peripheral resistance

Question 26

What causes an increase in pulse pressure ‘ described as a bounding pulse ‘

Answer 26

• heart block = bradychardia
• vasodilation - decreases peripheral resistance this occurs in the hot bath, pregnancy
• elite athletes : systolic increases and diastolic decreases

Question 27

Define thrill

Answer 27

When something can be felt

Question 28

Bruit

Answer 28

When we can hear

Question 29

What are korotkoff sounds ?

Answer 29

• blood flow sounds that practitioners use observe when taking blood pressure
• these sounds appear and disappear when the cuff is inflated or deflated.

Question 30

What can be heard and felt over a stenosed vessel ?

Answer 30

If an abnormal sound sound called a bruit is heard , it could reflect turbulent flow of blood which could indicate carotid artery disease

Question 31

What are the changes in flow and velocity through a stenosed vessel ?

Answer 31

V ~ 1/r^2

• during stenosis ( narrowing of a blood vessel) , the radius ,of the blood vessel decreases which means that the velocity would increase.
• if velocity increases then flow of blood would also increase ( F= VxA)