Haemodynamics

Question 1

What is haemodynamics?

Answer 1

the movement of blood and the physical factors that control blood flow

Question 2

How do metabolic demands dictate blood flow? How does blood generally move through different regions of the body?

Answer 2

High metabolic demand = high blood flow
- Kidneys have high metabolic demands, so it requires 20% of CO

Blood moves from a relative high pressure to low pressure

Question 3

What is serum?

Answer 3

Plasma without clotting factors

Question 4

In which conditions is high blood viscosity observed in?

Answer 4

polycythaemia (high RBCs), thrombocythaemia (high platelets), leukaemia (WBCs)

Question 5

Which proteins cause minor changes to plasma viscosity what are these changes an indicator of?

Answer 5

fibrinogen, compliment, c-reactive protein

indicator of infection

Question 6

Define flow

Answer 6

volume transfer per unit time (blood: mL/min)

Question 7

Define pressure

Answer 7

force per unit area
(SI unit is Pascal; mmHg used when measuring BP)

Question 8

What pattern do flow and pressure in circulation display?

Answer 8

Pulsatile
blood flow from relative high to low pressure

Question 9

equation for FLOW (Darcy’s Law)

Answer 9

Flow = ΔP/R
P: pressure difference
R: resistance

flow = K(ΔP)
R = -1/K
K: measure of ease of flow

Question 10

Define resistance and give the equation (Darcy’s Law)

Answer 10

The difference in mean pressure needed to move one unit of flow in steady state (mmHg/min/mL)

R = ΔP/Flow

Question 11

What is the relationship between i) flow and resistance ii) resistance and ΔP (at any give flow)

Answer 11

i) they are reciprocally related
ii) directly proportionate

Question 12

What is laminar and turbulent flow?

Answer 12

laminar - smooth, silent flow; parabolic flow profile; blood moves in streamlined and concentric fluid layers; blood moves fastest in the middle

turbulent - disorganised flow; noisy

Question 13

describe the relationship between flow and perfusion pressure to maintain laminar flow. And how do flow become turbulent?

Answer 13

As pressure increases, flow increases to match the increase (linear relationship). When flow can’t match the increase in pressure, the CRITICAL REYNOLDS NUMBER IS EXCEEDED

Question 14

Which factors primarily influence resistance to flow?

Answer 14

• diameter (most important)
• vessel length (doest change)
• viscosity (maintained with in a narrow range)

Question 15

Describe the changes in resistance across vessel types. (aorta to capillaries)

Answer 15

• low resistance in aorta (due to large diameter and short)
• small arteries and arterioles have higher resistance and pressure and contribute to total peripheral resistance

Question 16

What is velocity? Give the equation used to calculate flow from velocity and area of the cross-section.

Answer 16

the distance fluid moves in a given time (cm/s)

Flow = Velocity x A (area of cross-section)

Question 17

How does cross-sectional area influence velocity? Why is this factor important in capillaries?

Answer 17

High cross-sectional area = Low velocity

• capillaries have a combined cross-sectional area that is a thousand time larger than that of the aorta

Question 18

What has the greatest impact on resistance within a vessel?

Answer 18

Cross-sectional area

Question 19

Which vessel type has the greatest effect on total peripheral resistance?

Answer 19

arterioles

Question 20

What is pulse pressure and give the equation

Answer 20

PP = SYS BP - DIA BP

Question 21

Give the two arterial pressure equations (1. w/ CO and TPR 2. w/ DBP and PP)

Answer 21

MAP = CO x TPR
MAP = DBP + (1/3PP)

Question 22

What is high pulse pressure described and which factors increase pulse pressure?

Answer 22

• described as ‘bounding pulse’
• Heart block (poor heart conduction) resulting in bradycardia (slow HR) -> results in lower DIA BP and high PP
• Vasodilation - low peripheral resistance
• athletes - high SYS BP and low DIA BP

Question 23

How does blood flow differ before and after passing a stenosis? How does the velocity change as blood passes through the stenosis?

Answer 23

Before: laminar + silent
While passing: velocity increases
After: turbulent

Question 24

How is blood pressure measured using Korotkoff sounds?

Answer 24

• when cuff pressure is above systolic pressure, there is no flow
• when cuff pressure of below systolic pressure, there turbulent flow which produces Korotkoff sounds in the brachial artery
• when cuff pressure is below diastolic pressure, Korotkoff sounds stop and laminar flow resumes

Question 25

Which factors are important in accurately estimating blood pressure by auscultation?

Answer 25

• cuff size (too big = underestimate BP; too small = overestimate BP)
• arm supported
• cuff at the level of the heart
• sat comfortably, legs uncrossed
• measure both hands and use higher as reference

Question 26

what are the impacts of gravity on BP?

Answer 26

ABOVE HEART - low BP
BELOW HEART - high BP

Effects of gravity allows blood to flow from heart to feet when standing up
- pooling of blood occurs below the level of the heart in the venous system when standing

Question 27

What is postural hypotension and why does it occur?

Answer 27

Dizziness upon standing
- lower stroke volume
- upon standing blood moves to the lower part of the body from the head due to gravity; this causes a reduction of BP in the head leading to dizziness