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CardioRespiratory Year 1 > Physiology - Haemodynamics > Flashcards

Physiology - Haemodynamics Flashcards

1
Q

What is systole

A

contraction of the heart

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2
Q

What is diastole

A

relaxation of the heart

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3
Q

What is pulse pressure

A

difference between systole and diastole
- as arteries are elastic pulse pressure normally decreases slightly from the aorta to brachial artery

  • systolic - diastolic
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4
Q

What is systolic blood pressure

A

maximum pressure in arteries

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5
Q

what is diastolic blood pressure

A

minimum pressure in arteries

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6
Q

what are numbers for systole

A

At brachial artery systolic pressure normally 120 mmHg (16kPa). Current guidelines are:
>140 mm Hg systolic marginal hypertension.
>160 mm Hg definite intervention threshold

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7
Q

what are the numbers for diastole

A

At brachial artery systolic pressure normally 80 mmHg (10.7kPa).
>90 mm Hg diastolic marginal hypertension.
>100 mm Hg definite intervention threshold.

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8
Q

How do you calculate mean arterial pressure (MAP)

A

diastoli + 1/3 pulse pressure

e.g.
So for a systolic of 120 mmHg and a diastolic of 90 mmHg, the MAP is 100 mmHg. (90 + 1/3 of 30)

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9
Q

what is compliance

A
  • stretching

- so if the artery is high in compliance it means it can stretch more

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10
Q

what is compliance caused by

A
  • elastin fibres in the arterial walls
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11
Q

what does compliance reduce?

A
  • the starchiness reduces the work of the heart in pumping the blood as some of the blood is stored in the large arteries by the stretching and increasing their volume
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12
Q

what happens to old people and compliance

A
  • compliance decreases as arteries elastin is replaced by collagen this causes the artery to harden
  • this increases the systolic pressure as aorta cannot stretch to accommodate the stroke volume
  • it can decrease the cardiac output as the isovolumetric phase of ventricular contraction is longer
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13
Q

What is the windkessel effect

A
  • this is the effect of the compliance of the small elastic arteries
  • the walls of the aorta and elastic arteries distend when the blood pressure rises during systole and recoil when the blood pressure falls during diastole
  • ## there is therefore a net storage of blood during systole which discharges during diastole
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14
Q

what is hypertension

A

abnormally high blood pressure

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15
Q

What is hypertension a risk factor for

A

vascular disease

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16
Q

what is now done to stop hypertension being a risk factor

A

, Prehypertension is now defined as a classification for cases where a person’s blood pressure is elevated above normal but not to the level requiring medication

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17
Q

define prehypertension

A

Prehypertension is considered to be blood pressure readings with a systolic pressure from 120 to 139 mm Hg or a diastolic pressure from 80 to 89 mm Hg.

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18
Q

why is hypertension a problem

A
  • person is often unaware anything is wrong - only known when blood pressure is routinely measured
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19
Q

why do we need a blood pressure of 120/80mmHg

A
  • flow through an organ can be regulated by relaxing or constricting the arterioles that input into it
  • if the pressure is constant flow is inversely proportional to resistant, a high blood pressure ensures that a local vasodilation is effective in increasing local blood flow
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20
Q

How do you work out local flow

A

local flow = pressure/local resistance

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21
Q

How do you regulate flow

A
  • by constricting and relaxing the arterioles therefore changing the arterial diameter
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22
Q

What is poseuille’s Law

A
  • this is the idea that the flow of a liquid through a tube depends on the fourth power of the radius of the tube
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23
Q

what is poiseuille’s equation

A 
flow = pie x r^4/8n x dp/L
P - pressure 
R - radius 
L - length fo tube 
n - fluid velocity
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24
Q

what does poiseullie’s law effect the most

A

arterioles - they are smaller therefore only have to constrict a little bit for there to be a reduction in flow

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25
Q

What is cardiac output

A
  • the total blood flow out of the heart
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26
Q

what is the equation to work out cardiac out put

A

Heart rate x stroke volume

27
Q

what is the cardiac output typically in an healthy resting man

A

5L

28
Q

where can we measure pulse rate from and stroke volume from

A

Pulse rate - ECG

stroke volume - echocardiography

29
Q

what can be used to measure cardiac output

A

Doppler ultrasound

30
Q

How does the doppler ultrasound measure cardiac output

A
  • the blood velocity through the first part of the atria causes a doppler shift in frequency of returning ultrasound
  • shift can be used to calculate flow velocity
  • cross section can be measured using ultrasound
  • therefore the cardiac output can be obtained
31
Q

What are the advantages of using a doppler ultrasound to measure cardiac output

A
  • non -invasive
  • accurate
  • inexpensive
  • high levels of reliability and reproducibility
32
Q

How does a trans oesophageal doppler work

A
  • ultrasound probe is inserted into the oesophagus at the mid-thoracic level
  • probe measures the velocity of the blood
  • relies on a nomogram based on patient age, height and weight to convert the measured velocity into stroke volume and cardiac output
33
Q

what are the factors that effect cardiac output

A

factors affecting the heart rate

  • autonomic innervation
  • hormones
  • fitness level
  • age

factors affecting stroke volume

  • heart size
  • fitness level
  • gender
  • contractility
  • duration of contraction
  • preload
  • after load resistance
34
Q

How do you work out stroke volume

A

EDV- ESV

35
Q

What are the blood requires to go to the

  • brain
  • heart
  • kidneys
A
  • Your BRAIN needs about 700 ml per minute of blood (14% resting Cardiac Output) stays consent
  • Your HEART needs about 200 ml per minute of blood (4% resting C.O.) dependent on level of exercise
  • Your KIDNEYS take about 1250 ml/min (25% resting C.O.).
    Maintain blood pressure
36
Q

How much cardiac output does the brain heart and kidneys take up at rest

A
  • These three organs take up about 40-45% C.O at rest.

2-2.3L/MIN

37
Q

How much cardiac output is available for the rest of the body

A

2.7-3.0 L/min

38
Q

where does the rest of the cardiac output go in the body

A
  • depends on how much you have eaten
  • when you have eaten little ,little blood goes to the gut but after a meal 1.5L/min goes to the gut in order to be able to digest so only about 1.2-1.5L/min goes to the muscles and skin
  • blood Flo to the skin is variable it can increases via A-V shunts or decrease via vasocontriction to give other organs how much blood they need
39
Q

What happens to cardiac output during exercise

A
  • it increases by nearly 4 times in order to cope with the increased amount of oxygen needed
40
Q

what mechanisms increase cardiac output during exercise

A
  • either increase heat rate

- increase stroke volume

41
Q

how does heart rate increase cardiac output

A

Diastole shortens allowing for the increase in heart rate

42
Q

why is the stroke volume maintained when her excise increased

A
  • maintained due tot he contraction of the atria - this transfers blood into the ventricles during diastole there is also increased ventricular contractility causing a decreased end systolic (residual) volume
43
Q

How does oxygen uptake increase during exercise

A
  • oxygen uptake increases more than cardiac output as more oxygen is taken up by the lungs
  • resistance is bronchi and trachea decrease as they dilate
  • respiration rate and depth increases
  • increases the amount of PO2 which causes the pulmonary arterioles to relax
  • small increase in pulmonary arterial pressure which improves perfusion of the lungs causing the lungs to become more efficient at taking up oxygen
  • almost all blood becomes fully oxygenated
44
Q

What does the work of the heart depend on

A
  • the viscosity of the blood

- diameter of the arterioles

45
Q

What does the viscosity depend on

A
  • mainly depends on the haematocrit (the proportion of red blood cells in the blood)
  • if haematocrit is high the velocity is high so the heart works harder to pump blood around
  • if the haematocrit is low then not enough oxygen is transproted
  • the viscosity also depends on the mechanical properties of the erythrocytes such as there deformability e.g in sickle cell disease
46
Q

What is haematocrit

A
  • proportion of red blood cells in the blood
47
Q

what is the blood viscosity in capillaries

A

= viscosity is low - therefore heart has to do less work to push blood through the capillaries
- expected to be large because the red blood cells have a larger diameter than that of the capillary

48
Q

What happens if blood cells are too large

A
  • they clog up the capillary and oxygen delivery is compromised
  • rupture and cause haemolysis
49
Q

How does vasodilation happen

A
  1. erythrocytes interact with polypeptide chain which are in the lumen of the capillary
  2. erythrocytes move along the endothelium they deflect the chains
  3. this allows calcium to enter the endothelium
  4. calcium triggers the formation of nitric oxide which relaxes and dilates the walls and a its as a local anitcoagulant
50
Q

What does nitric oxide do

A
  • Counteracts excess contraction caused by stimulation of the autonomic nervous system
51
Q

what happen when blood does not move through a vessel

A
  • clots form
  • people with atrial fibrillation have a risk of stroke because clots can form in auricles of the atria where blood is not moving
  • if blood doesn’t move in the leg veins you can develop deep vein thrombosis (DVT)
52
Q

What is polycythemia

A
  • it is a disease state in which the hematocrits increases, can be due to an excessive production of red blood cells or to a decrease in the volume of plasma
53
Q

How do arterioles sustain arterial pressure with thin walls

A
  • use Laplace’s Law
54
Q

what does Laplace’s law state

A

Laplace’s law states that the pressure that an elastic vessel can withstand depends on the tension produced in the walls by their elasticity divided by the radius (diameter) of the vessel

55
Q

describe how to work out Laplace’s Law

A

In a CYLINDER (eg a blood vessel) the pressure withstood is proportional to T/R
In a SPHERE (eg an alveolus) the pressure withstood is
proportional to T/2R

P(withstood) = K(T/R)
- T/R - tension in the wall divided by the radius

56
Q

the smaller the radius….

A

of a vessel the greater the pressure that a given wall strength can withstand
- therefore ether small diameter arterioles only need thin walls to withstand normal arterial pressures

57
Q

describe why capillaries can withstand pressures

A

Because capillaries have such a small diameter, they can withstand fluid pressures of >20 mm Hg using only the small tension generated by the basement membrane.

58
Q

Why don’t capillaries have any smooth muscle

A
  • muscle would impede the exchange of fluids and gases
59
Q

What is an atheroma

A
  • a fatty deposit inside the artery

- because of piseuille law even a small atheroma can decrease blood flow and cause hypoxic states in tissue

60
Q

what is a common site for an aneurysm

A
  • aorta
  • at points before the blood vessels branch as pulsatile flow of blood occurs here
  • cerebral arteries - more convoluted that arteries and have twists which cause extra stress on the walls
61
Q

what happens if an artery wall gets a tear

A
  • radius increases therefore the balancing pressure that the elastic tissue generates is less
  • the wall balloons out and this reduces the effectiveness of the wall to withstand the pressure and can cause an aneurysm
62
Q

What are the factors that lead to aneurysm occurring

A
  • atheroma - narrows the lumen of the artery and if tuber lent flow happens this can cause high pressure in the artery causing the walls to break
  • if there is an inflammation reaction to the atheroma this can cause the destruction of the elastin fibres in the artery wall and weakens it so it can stretch more when there is a blood pressure spike
  • hypertension
  • artery disease
63
Q

How can you discover an aneurysm

A
  • during MRI or angiography
  • rupture causing subarchanoid brain haemorrhage
  • present with symptoms of mass effect on neural structures
64
Q

How do you treat cerebral aneurysms

A
  • clip or coil
  • coiling - fine wire is pushed into the swollen artery and forms a coil, the blood clots around the coil and takes the pressure off the wall and forms a stable structure

CardioRespiratory Year 1 (28 decks)

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