haemodynamics

Question 1

what is haemodynamics?

Answer 1

the physical factors that control the flow of blood e.h. pressure, resistance, velocity

Question 2

what gradient does blood move down?

Answer 2

pressure gradient. high to low
in the legs the pressure is higher than the heart! how does blood flow to the legs then?
gravity helps produce a slight negative pressure gradient

Question 3

what is the difference between plasma and serum?

Answer 3

serum is plasma without clotting factors!

Question 4

does whole blood viscosity change?

Answer 4

not really- only change when disease occurs e.g. leukaemia

thick blood is difficult to transport

Question 5

does plasma viscosity change?

Answer 5

yes, a small amount due to differing levels of plasma proteins

Question 6

what do we use plasma viscosity to measure?

what now measures this?

Answer 6

inflammation

however we usually use CRP (C reactive protein) now to measure inflammation rather than plasma

Question 7

what is flow and what units are used?

Answer 7

it is the volume of blood transferred per unit time

L/min or ml/min (blood)

flow will pulsate as it moves through the body but we model as a steady line

Question 8

what is pressure? what units?

Answer 8

pressure is the force per area
mm of mercury (mmHg)- used to measure blood pressure

pulsates as it moves through the body and decreases

Question 9

what is resistance and what is conductance?

Answer 9

resistance is a measure of the difficulty of flow (R)
mmHg min/ml

conductance is a measure of the ease of flow (K)

Question 10

darcy’s law?

Answer 10

flow = change in pressure/R

Question 11

what is vascular resistance?

equation for resistance - done have to know but helps understand

Answer 11

resistance to flow in blood vessels
R= change in pressure/flow

if flow decreases, R increases
if pressure change increases, R increases

Question 12

what are the 2 types of blood flow?

explain them both.

Answer 12

laminar and turbulent

laminar is smooth, silent and steady and stream lined - it is the most common type of flow and maintains energy

turbulent is disorganised and noisy - is used to hear a pulse in BP, energy is lost. It occurs after there is a change of direction or a stenosed valve/artery

Question 13

what are the factors for resistance?

main one?

Answer 13

diameter is the main one / radius - in the equation piR is raised to the power of 4 = big effect on resistance
length of vessel
viscosity

length of vessel and viscosity don’t often change therefore diameter is the most important

Question 14

what is the resistance like in the aorta and why?

Answer 14

resistance is low

the diameter is large and the vessel length is small

Question 15

what vessels are the seat of total peripheral resistance?

Answer 15

small arteries/arterioles
they have the biggest change in pressure across them therefore a big change in resistance
R= change in pressure / flow

Question 16

what is velocity?

how is flow related to velocity?

Answer 16

the distance the fluid (blood) moves over a given time
cm/s
F= V X Area2 , flow is proportional to V XA2

at constant flow V is inversely proportional to A2
increase velocity = decrease area

Question 17

why is velocity at capillaries slow?

why is this important?

Answer 17

because the cross sectional area is huge- velocity is inversely proportional to area (big area = small V)

it allows exchange of waste and nutrients and also the small vessels couldn’t handle a large velocity

as the capillaries change to veins the velocity increases again as the area becomes smaller

Question 18

why is blood pressure considered at regulated variable?

Answer 18

because it changes between individuals and also changes depending on situation- it can be controlled so is considered regulated

Question 19

what is SBP, DBP and PP?

Answer 19

SBP = systolic blood pressure (peak)

DBP = diastolic blood pressure (lowest)

PP = pulse pressure (SBP-DBP) the difference

Question 20

honestly this is just info

not even sure if you need this but is equations

Answer 20

R (TPR)= pressure / flow (CO)

R = resistance (total peripheral resistance TPR)
Flow = cardiac output (CO)
pressure difference = mean aortic pressure - mean venous pressure- venous pressure is often 0 so can just be mean aortic pressure

TPR= aortic mean pressure/CO

mean arterial pressure = CO X TPR

mean arterial pressure is determined by SV and HR as CO= SV X HR

Question 21

what governs pulse pressure?

what things can change pp?

Answer 21

the volume of blood ejected per beat (SV)
compliance of arterial system (how well it can accommodate the bigger volume/expand)

increase SV and no increase compliance = increase PP

haemorrhages can change pp - less blood volume = less SV = lower PP
age can change pp - atherosclerosis = blockages = smaller diameter = bigger pp

Question 22

what is a pulse

Answer 22

the shock wave that arrives just before the blood- I think its the aortic valve closing, not sure??

Question 23

how to increase pulse pressure (pp)?

Answer 23

when it increases you would feel a strong bounding pulse at a decent rate

Bradycardia - this allows more time for diastolic pressure to fall creating a big difference in DBP and SBP = big pp

vasodilation = lowers resistance therefore pressure = bigger PP

elite athletes - bigger systolic pressure = bigger difference = bigger pp

Question 24

what is thrill?

what is bruit?

Answer 24

thrill = pulse than can be felt

bruit = pulse that can be heard

Question 25

describe how to measuring blood pressure including laminar and turbulent flow

Answer 25

1. increase pressure on cuff round arm until it stops blood flow (cannot hear a pulse)
2. gradually release the pressure until you hear a pulse (this is created by turbulent flow/noisy flow) = systolic pressure- these are called korotkoff sounds
3. continue to release pressure until you cannot hear the pulse anymore (laminar flow/silent flow) = diastolic pressure

the cuff creates a stenosis - this causes turbulent flow/increase velocity

Question 26

what is MAP?
how to calculate?
what is the low threshold of MAP?

Answer 26

mean arterial pressure
MAP= DBP+ 1/3PP

70mmHg- below this organ perfusion becomes impaired and organs may get damaged/fail

Question 27

what to ensure when taking BP?

Answer 27

right cuff size + positioning of cuff
meant to measure both arms and take highest BP
sat down, feet flat
arm supported
several takings and mean taken
assume measurement is at the level of the heart (upper arm is in line with position of he heart)

Question 28

what is the pressure of blood below and above the level of the heart?

Answer 28

above the pressure is lower therefore blood flows down pressure gradient to head

below the pressure is greater BUT gravity is involved and allows a pressure gradient to be created meaning blood can reach the feet

Question 29

what is postural hypotension?

Answer 29

it happens when a persons blood pressure drops when standing up
this can be because of blood pooling in the lower limbs
this means there is a smaller SV and less blood to brain = dizzy