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haemodynamics Flashcards

1
Q

define systolic blood pressure

A

maximum blood pressure in the arteries

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2
Q

at the brachial artery, what is the systolic blood pressure?

A

120 mmHg

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3
Q

at what pressure is the systolic marginal hypertension?

A

140 mmHg

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4
Q

at what pressure is the definite intervention threshold?

A

160 mmHg

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5
Q

define diastolic blood pressure

A

minimum blood pressure in the arteries

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6
Q

define pulse pressure

A

difference between the systolic and diastolic blood pressures

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7
Q

how is the mean arterial pressure calculated?

A

diastolic pressure + 1/3 pulse pressure

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8
Q

what causes compliance in arteries?

A

the elastic fibres in the artery wall

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9
Q

why is compliance good?

A

reduces the work of the heart because some blood is stored in the arteries

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10
Q

explain the effect of smoking on arteries, systolic volume and cardiac output

A

hardens arteries
increases systolic volume because aorta cannot stretch to accommodate SV
decreases CO bc ventricular contraction is longer

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11
Q

what does the windkessel effect do?

A

helps reduce fluctuations in pulse pressure over the cardiac cycle
maintains organ perfusion during diastole

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12
Q

what are the windkessel vessels?

A

aorta

large arteries

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13
Q

explain the windkessel effect

A

arteries distend when BP rises in systole and recoil in diastole

in systole there is a net storage of blood bc of difference in rate of the blood entering and leaving the artery

net storage of blood is then released through recoil in diastole

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14
Q

define hypertension

A

abnormally high blood pressure over 140/90

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15
Q

what is prehypertension?

A

BP higher than normal but not enough to need medication

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16
Q

what are the range of pressures for prehypertension?

A

systolic: 120-139
diastolic: 80-89

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17
Q

how is local flow calculated?

A

pressure/local resistance

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18
Q

what does Poiseuille’s law state?

A

at a constant pressure, the flow is proportional to the radius of the tube to the power of 4

small changes in arterial diameter produce large changes in flow

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19
Q

how is cardiac output calculated?

A

heart rate x stroke volume

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20
Q

define cardiac output

A

total blood flow out of the heart

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21
Q

how can heart rate be measured?

A

from an ecg

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22
Q

how can stroke volume be measured>

A

from echocardiography

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23
Q

what is the usual heart rate?

A

70bpm

24
Q

what is the usual stroke volume?

A

70ml

25
Q

what is the typical cardiac output of a healthy adult male?

A

4.9L/min

26
Q

what method can be used to measure cardiac output?

A

doppler ultrasound

27
Q

explain how doppler ultrasound can be used to measure cardiac output?

A

blood velocity through the first part of the aorta causes a doppler shift in the frequency of the returning ultrasound waves

ultrasound can measure cross sectional area of the aorta and uses this to calculate CO

28
Q

what are the advantages of doppler ultrasound?

A 
non-invasive
accurate
inexpensive
reliable
reproducible
29
Q

explain how trans oesophageal doppler works

A

ultrasound probe inserted into the oesophagus at mid-thoracic level

measures blood velocity in adjacent descending thoracic aorta

30
Q

what factors affect heart rate?

A

autonomic innervation
hormones
fitness levels
age

31
Q

what factors affect stroke volume?

A 
heart size
fitness levels
gender
contractility
duration of contraction
preload
afterload
32
Q

what are the oxygen requirements of vital organs?

A

brain - 700ml/min
heart - 200ml/min
kidneys - 1250ml/min

33
Q

how is blood flow through the skin varied?

A

increased via AV shunts

decreased via vasoconstriction

34
Q

how much can cardiac output be increased by?

A

3.75 times to 19L/min

35
Q

how is stroke volume increased during exercise?

A

contraction of atria - transfers blood to atria

increased ventricular contractility - smaller residual volume

36
Q

how does oxygen uptake increase during exercise?

A

faster breathing

dilation of bronchi and trachea means less resistance

37
Q

what does the work of the heart depend on?

A

blood viscosity

arteriole diameter

38
Q

what does the viscosity of the blood depend on and which factor has the biggest impact?

A

haematocrit - strongest impact
RBC deformability
RBC aggregation
plasma viscosity

39
Q

what is haematocrit?

A

proportion of red blood cells in the total volume of blood

40
Q

what is polycythemia?

A

a disease where there’s increased haematocrit

41
Q

what are the types of polycythemia

A

absolute - excessive production of RBCs

relative - decrease in plasma volume

42
Q

explain how nitric oxide is released by blood vessels

A

edges of RBCs interact with polypeptide chains connected to proteins in the endothelium

calcium moves into the endothelium

nitric oxide forms and relaxes and dilates the walls

43
Q

what effect does nitric oxide have on the capillary wall?

A

local anticoagulant

44
Q

what does laplace’s law state?

A

the pressure an elastic vessel can withstand depends on the tension produced in the walls by their elasticity divided by the radius of the vessel

45
Q

in a cyclinder, what is the pressure withstood proportional to?

A

T/R

tension/radius

46
Q

in a sphere, what is the pressure withstood proportional to?

A

T/2R

47
Q

describe the relationship between the radius of a vessel and the pressure it can withstand

A

the smaller the radius, the greater the pressure the wall can withstand

48
Q

what is an atheroma?

A

a fatty deposit on the inside of an artery

49
Q

what happens if an artery wall weakens?

A

radius increases
balancing pressure that the tissue generates is less
walls balloon out so its less effective at withstanding pressure
aneurysm

50
Q

what is an aneurysm?

A

localised and abnormal weak spot on a blood vessel that can cause outward bulging

51
Q

what vessels are common sites for aneurysms?

A

aorta

cerebral arteries

52
Q

at what point in a blood vessel do aneurysms tend to occur?

A

just before points where the blood vessel branches

53
Q

what are risk factors for aneurysm formation?

A

hypertension

artery disease

54
Q

why do aneurysms commonly occur in cerebral arteries?

A

more convoluted and twisted than other arteries

more stress on the walls

55
Q

how can aneurysms present?

A

discovered incidentally during MRIs or angiography
rupture causing subarachnoid brain haemorrhage
symptoms of mass effect on neural structures

56
Q

how can cerebral aneurysms be treated?

A

clipping or coiling

57
Q

explain the process of coiling

A

fine wire is pushed into the swollen artery to form a coil

blood clots around the coil and takes pressure off the wall

c (25 decks)

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