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HHP > haemodynamics + microcirculation > Flashcards

haemodynamics + microcirculation Flashcards

1
Q

what is the equation for mean arterial pressure (MAP)

A

map = cardiac output (co) x total peripheral resistance (tpr)

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2
Q

how else can MAP be calculated

A

because co = hr x sv

map = hr x sv x tpr

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3
Q

what does darcys law state

A

flow in a steady state (external factors driving the flow are equal) is linearly proportional to pressure difference between two points

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4
Q

what does darcys law concern

A

fluid flow which is NOT THE SAME AS fluid velocity

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5
Q

what is fluid flow

A

volume passing in a given time period

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6
Q

what is fluid velocity

A

distance travelled by fluid over time

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7
Q

what is mean velocity

A

fluid flow divided by total cross sectional area

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8
Q

what happens to mean velocity in the capillaries

A

falls progressively because total cross sectional area increases as blood enters MICROCIRCULATION (eg capillaries)

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9
Q

what happens to total flow in the vascular system

A
  • not altered
  • remains equal to cardiac output at each level of the vascular system
  • vol going through stays same even as the velocity of it changes in diff parts of systemic circulation
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10
Q

what is aortic pressure (when blood exits left ventricle)

A

90 mmHg MAP

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11
Q

what is vena cava / venous pressure (when blood enters right atrium)

A

close to 0mmHg MAP

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12
Q

how does the MAP decrease

A

steadily over the course of systemic circulation

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13
Q

how is blood pushed through the systemic circuit

A
  • pressure gradient (effectively equal to MAP) is created

- this is a driving force to push blood

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14
Q

which 3 types of fluid flow occur in circulation

A

1) laminar
2) turbulent
3) single-file

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15
Q

what is LAMINAR FLOW

A
  • in normal arteries and veins
  • straight direction of travel
  • clean lines of movement of fluid
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16
Q

what is TURBULENT FLOW

A
  • in ventricles and sometimes ascending aorta of healthy subjects
  • turbulent flow pattern
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17
Q

what is SINGLE-FILE FLOW

A
  • occurs in capillaries
    = individual blood cells pass through in single file
  • because of how narrow the vessels are
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18
Q

what did jean poiseuille establish resistance to be

A
  • steady flow
  • along straight cylindrical tube (keeps geography of vessel simple)
    IS PROPORTIONAL TO
    1) tube length
    2) fluid viscosity
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19
Q

what causes resistance to increase

A

when tube length and fluid viscosity increase

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20
Q

resistance is inversely proportional to and what does this mean

A
  • tube radius to power of 4
  • so as radius increases, resistance decreases
  • change in radius has substantial impact on resistance to flow
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21
Q

what does poiseuilles law combine

A
  • poiseuilles definition of resistance

- with darcys law of flow (referring to gradient of pressure between 2 points)

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22
Q

what does poiseuilles law calculate

A
  • flow through a tube
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23
Q

what is poiseuilles equation for flow through a tube

A 
Q (flow)
= 
(P1 - P2) (pressure gradient)
x
equation for resistance inversed
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24
Q

what do we see when using this equation

A
  • flow is v sensitive to vessel radius
  • this is why arterioles are the main site of resistance in circulation (well structured for it wstrong vascular smooth muscle layers in tunica media in vessel wall)
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25
Q

what is an example of how flow is v sensitive to vessel radius

A
  • drop in radius from 1cm in aorta to 0.01 cm in arteriole

- causes inc in resistance by factor of 10^8

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26
Q

how does arrangement of vessels increase resistance to flow

A
  • arranged in both series and parallel circuit
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27
Q

which parts of the circulatory system are arranged in series

A

arteries -> arterioles -> capillaries -> venules -> veins

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28
Q

which parts of the circulatory system are arranged in parallel

A

all vessels are arranged in parallel with other vessels of the same type (ie inferior and superior vena cava)

EXCEPTION = aorta + pulmonary trunk

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29
Q

how do we increase resistance in a circuit

A

ADD series units (makes circuit longer)

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30
Q

how do we decrease resistance in a circuit

A

ADD parallel units (adding more units alongside each other so increases whole cross sectional area thus amount of space through which fluid can flow)

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31
Q

what is compliance in vessels

A

change in volume

divided by change in pressure inside the vessel minus the pressure outside

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32
Q

what is pressure inside the vessel minus pressure outside

A
  • transmural pressure (pressure across the wall)
  • its the distending pressure acting on the vessel
  • differences between the two acts on the distention of the vessel so changes the volume that occurs
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33
Q

what is compliance defined as

A
  • change in volume per unit change in distending pressure
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34
Q

how does gradual increase in distending pressure impact volume

A

causes gradual increase in volume

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35
Q

what is compliance in arteries and veins

A
  • for a given pressure
  • v1 (volume) in arteries
    and
    -v2 in veins (3x larger than v1)
  • meaning veins have HIGHER compliance / capacity that the arteries because they are thin walled and easily stretched
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36
Q

how is higher compliance in veins beneficial

A
  • beneficial in terms of veins function
  • and their role as a reservoir of blood volume (as they can show a large increase in blood volume in response to small increase in blood pressure)
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37
Q

so what do veins act as

A

effective at acting as volume resevoirs (stores of blood volume)

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38
Q

what do arteries act as

A
  • by contraction function they act as pressure reservoirs

- control amount of additional pressure which passes through a certain point of systemic circulation

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39
Q

what is the distending pressure

A
  • pressure acting to push open vessel

- acts on the vessel wall and stretches it

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40
Q

what would happen if distending pressure wasnt balanced by forces in the vessel wall

A

rupture

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41
Q

what is the law of LaPlace

A

the magnitude of force / tension (T) in wall necessary to withstand transmural pressure (Pt) is influenced by both the vessel radius (r) and wall thickness (u)

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42
Q

what is the LaPlace equation

A

T = (Pt x r) / u

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43
Q

what happens as transmural pressure increases

A
  • in a larger vessel with wall thickness acting to lower amount of tension needed in the wall to withstand this pressure
  • tension increases
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44
Q

what is the transmural pressure in large arteries and how do they prevent damage

A
  • transmural pressure and radius large

- wall thick to compensate + maintain integrity

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45
Q

what is the transmural pressure in veins and what does this mean

A
  • low transmural pressure
  • radius still large
  • SO (as walls are thin) still signif tension generated over walls of veins
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46
Q

what is the transmural pressure in capillaries and how do they prevent damage

A
  • low transmural pressure
  • small radius
  • SO allows walls to be v thin (arterioles reduce + control pressure of blood entering capillaries to prevent damage)
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47
Q

where is likelihood of vessel rupture greatest overall

A

in elastic arteries (ie aorta)

  • ## aortic rupture is relatively common and usually fatal medical emergency
48
Q

which vessels does rupture most often occur in

A
  • abdominal aorta = aneurysms form stretching vessel wall
49
Q

which ruptures are rare but most dangerous

A

thoracic aneurysms

50
Q

how will questions of graphs be asked

A
  • ie what impact will radius change have on x factor?

- dont remember equations but understand different components

51
Q

define microcirculation

A

circulation of blood through the smallest blood vessels

arterioles, capillaries, venules

52
Q

where is density of capillary networks highesr

A

in metabolically active tissues

53
Q

what does blood flow in capillaries depend on

A

level of contraction of arteriolar smooth muscles (rings of smooth muscle) on vessel wall and entry points into capillary beds
- it is not uniform blood flow

54
Q

what is autoregulation

A
  • intrinsic adjustments made to blood flow in tissue / particular microcapillary vascular bed
  • so flow meets local requirements
  • so as metabolic demands of the tissue change, the blood flow in that particular tissue is regulated / adjusted to ensure needs are fulfilled
55
Q

how do changes in local blood flow occur

A

1) changes in arteriole diameter

2) altering contraction of precapillary sphincter muscles

56
Q

what 2 categories are instrinsic control mechanisms classified into

A
  • metabolic

- myogenic

57
Q

what is the relationship between metabolism + rate of blood flow

A
  • as rate of metabolism incs, rate of blood flow incs steadily
  • clear + apparent relationship
58
Q

what is observed between metabolism + rate of blood flow in vitro

A
  • when perfusion pressure (blood flow going in) is kept constant
  • in absence of autonomic nerve input
  • change seen w/ inc’d metabolic demand / rate in tissue is met by inc’d blood flow
59
Q

what is metabolic control characterised as

A
  • intrinsic property w/in microcirculation
  • reacting to it not only due to external factors
  • intrinsic component acts autonomously
60
Q

what happens to rate of o2 consumption with increased rates of metabolism in tissue

A

INCREASES

61
Q

what is the result when consumption of O2 exceeds delivery

A

localised degree of hypoxia

62
Q

what is hypoxia

A
  • causes relaxation of nearby arteriolar smooth muscle
63
Q

what is the direct response to local hypoxia and arteriolar smooth muscle relaxation

A

1) vasodilation
2) decreased resistance to blood flow
3) increased blood flow
4) increased O2 delivery
5) increased tissue O2 concentration
CLOSING THE NEGATIVE FEEDBACK LOOP

64
Q

which factors other than oxygen are involved in metabolic autoregulation

A 
products of metabolism
1) adenosine
2) H+
3) CO2
4) K+
substances synthesised in vascular endothelium 
1) prostocyclins
2) nitric oxide
65
Q

what do the products of metabolism do in metabolic autoregulation

A
  • diffuse out of surrounding parenchymal tissue into interstitial space
  • causes relaxation of the vascular smooth muscle cells
66
Q

what do substances synthesised in vascular endothelium do in metabolic autoregulation

A
  • generated by endothelial cells
  • they diffuse across membrane into adjacent vascular smooth muscle cells
  • cause further vasodilation
67
Q

what is nitric oxide

A

an endothelium derived relaxing factor (EDRF)

causes relaxation of vascular smooth muscle

68
Q

how is nitric oxide (an EDRF) generated and where does it act

A
  • by nitric oxide synthase in endothelial cells
  • acts on vascular smooth muscle cells via cyclicGMP
  • to drive relaxtion of vascular smooth muscle
69
Q

where is nitroglycerin used

A

in stable exertionally induced cardiac anginga

70
Q

what is the cause of angina

A
  • blood supply not meeting O2/nutrient demand of cardiac tissue
  • causes rapid coronary vasodilation to increase blood flow to heart and decrease pain
71
Q

what is wall shear stress

A
  • physical stress
  • due to passage of fluid on wall of vessel
  • different types of it affecting endothelial cells depending on if blood flow is laminar or turbulent
72
Q

what is displayed if we take an isolated perfused organ in the lab

A
  • intrinsic ability to maintain a constant rate of blood flow through its vascular bed over a wide range of perfusion pressure
73
Q

what is an isolated perfused organ

A
  • organ out of body
  • maintained in a lab environment
  • perfused with buffer fluids that stimulate profusion of normal blood
74
Q

what does the graph for myogenic control show

A
  • x-axis = pressure mmHg
  • y-axis = flow (into vascular bed)
  • relatively flat line but above a certain point when pressure gets very high the flow increases and control mechanisms are overcome
75
Q

why is there a wide plataeu phase

A

blood flow kept in tight boundaries over majority of likely pressures it is going to experience

76
Q

what is flow equal to

what does this mean

A
  • pressure gradient over resistance

- there must be an increase in resistance in order to keep constant flow if theres an increased pressure gradient

77
Q

what is the negative feedback loop in the mechanism of the myogenic response

A

1) increased profusion pressure
2) increased stretch of arteriolar smooth muscle
3) increased constriction
4) increased resistance
5) decreased flow
negative feedback
6) increased flow

78
Q

what does the negative feedback loop in the myogenic response do

A
  • leads to adjusted perfusion pressure
  • so theres a control of excess pressure
    OR
  • could reduce constriction of arteriolar smooth muscle like the cardiomyocytes
79
Q

at what level does the myogenic response occur

A

SINGLE UNIT LEVEL

- individual smooth muscle cells respond to passive stretch with contraction in opposition to it

80
Q

when may long term autoregulation develop

A
  • if needs for O2 and nutrients of tissue chronically higher than delivery from blood supply (ie due to gradual partial occlusion of a coronary vessel)
  • chronic exposure to high altitude
  • develops over a period of weeks to months
81
Q

how does long term autoregulation develop

A

1) increase in microcirculatory vessels supplying blood to tissue (increases density of the network)
2) enlargement of existing vessels

82
Q

which environments may elicit long term autoregulation response

A

chronic exposure to high altitude

due to low partial pressure of O2

83
Q

how can we see long term autoregulation response in the heart

A

gradual partial occlusion of coronary vessel

84
Q

what are lipophilic solutes in the transcapillary solute exchange

A
  • inc O2 + CO2
  • non polar molecules that diffuse in an out of lipids easily enter / leave capillary over transcellular route so lipid cell membranes can be crossed
85
Q

what are hydrophilic solutes in the transcapillary solute exchange

A
  • water soluble
  • cross using intercellular clefts (up to 60 angstroms diameter)
  • clefts easily traversed by H2O, ions and small organic solutes
  • BUT albumin (70 angstroms diameter) and other plasma proteins cannot cross and difficulty of them crossing impacts how easily fluids shift across
86
Q

what process is dynamic and ongoing

A

fluid continuously circulates between capillaries and interstitium

87
Q

what do hydrostatic pressures result from

A

capillary blood pressure

88
Q

where are hydrostatic pressures

a) highest
b) lowest

A

a) arterial end
b) venous end

(gradient across length of capillary in hydrostatic pressure)

89
Q

net hydrostatic pressure is this gradient in favour of…

A

mild fluid filtration so pressure out of capillary microcirculation into the interstitium

90
Q

what are osmotic pressures

A
  • result from presence of large, non-diffusible molecules (eg plasma proteins)
  • they can filter out in the interstitium
  • so lots of them in the bloodstream
91
Q

osmotic molecules are

A

mainly confined to plasma
BUT
not entirely there

92
Q

what does net osmotic pressure gradient favour

A
  • fluid absorption by capillaries
  • so gradient of osmotic pressure into and out of the capillary
  • net effect favours fluid absorption back into the vessel
93
Q

where are osmotic pressures

a) highest
b) lowest

A

DOESNT VARY SIGNIFICANTLY over the length of the capillary

94
Q

starlings forces:

what decreases from 35 to 16 in venous end

A
  • blood hydrostatic pressure
95
Q

starlings forces:

what pressure is 0

A

interstitial fluid hydrostatic pressure

96
Q

starlings forces:

what pressure is constant at 26mmHg

A

blood colloid osmotic pressure (pulling on fluid into vessel)

97
Q

starlings forces:

what pressure is constant at 1mmHg

A

interstitial fluid osmotic pressure

98
Q

starlings forces:
what results in net filtration pressure over all those promoting filtration, blood hydrostatic pressure and pressures promoting absorption of fluid back into vessel

A
  • pushing hydrostatic pressures
    +
  • pulling osmotic pressures
99
Q

what does
a) net filtration at arterial end
b) net reabsorption at venous end
add up to at of microvascuture

A

a) 10mmHg
b) -9 mmHg

only 1mmHg causes tilt towards net filtration overall

100
Q

what is the overall result in net fluid balance

A

net movement of fluid out of circulation at arterial end and back into circulation at venous capillary end

101
Q

why is there a net loss of fluid (1.5 ml per minute) from the circulation and why is this a problem if unchecked

A

system doesn’t exist in perfect equilibrium

1.5ml/min = 90ml/hr = empty vascular system of plasma in 24hrs

102
Q

what prevents the emptying of the vascular system

A

LYMPHATIC SYSTEM

- returns this fluid and any plasma proteins that leaked out into circulation / interstitial fluid

103
Q

what is the lymphatic (lymphoid) system

A
  • maintain blood pressure, avoid swelling
  • central role in maintaining health
  • includes cells, tissues + organs responsible for defending the body
  • acts against environmental hazards (ie pathogens) and internal threats (ie cancer cells)
104
Q

the primary cells of the lymphatic (lymphoid) system are

A

lymphocytes

- they determine bodies ability to resist of overcome infection and disease (immunity)

105
Q

what are the 5 components of the lymphatic (lymphoid) system

A

1) lymph
2) lymphatic vessels
3) lymphoid tissues
4) lymphoid organs
5) lymphoid cells

106
Q

lymph is

A
  • interstitial fluid
  • resembles plasma (though lower conc of suspended proteins)
  • NOT pumped BUT relies on contraction and relaxation of muscles to move it
107
Q

lymphatic vessels…

A
  • begin in peripheral tissues
    • connect to veins
  • vary in size
108
Q

lymphoid tissues…

A
  • found throughout body
  • connective tissues
  • dominated by lymphocytes
109
Q

lymphoid organs…

A
  • found throughout body
  • inc lymph nodes, tonsil, thymus, spleen
  • separated from their surrounding tissues by a fibrous connective tissue capsule
110
Q

lymphoid cells…

A
  • consist of immune system cells (lymphocytes, smaller no of phagocytes (ie macrophages + microphages) etc)
111
Q

what does the lymph system do

A
  • ## produces, maintains + distributes lymphocytes and other lymphoid cells that provide immunity
112
Q

how do lymphocytes provide defence

A
  • circulate in the blood
  • reach site of injury / infection
  • can also enter/leave capillaries
113
Q

what does the lymph system continuously circulate and what does this mean

A
  • excess / extracellular fluid and returns it to the bloodstream
  • helps transport lymphocytes + WBCs from 1 organ to another while maintaining normal blood vol + eliminating local variations in composition of interstitial fluid by distributing hormones, nutrients + waste from their tissues of origin to general circulation
114
Q

why is there excess extracellular fluid

A

capillaries deliver more fluid to tissues than they carry away

115
Q

how does the lymph system work

A

1) lymphatic vessels carry lymph from peripheral tissues to venous system
2) lymph drains into major lymph collecting vessels (trunks + ducts)
3) as lymph flows through lymph node 99%+ of its antigens are removed and lymphocytes diffuse into lymph (lymph nodes filter lymph)
4) cleansed lymph flows into left or right subclavian veins

HHP (10 decks)

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