haemodynamics + microcirculation Flashcards
(115 cards)
1
Q
what is the equation for mean arterial pressure (MAP)
A
map = cardiac output (co) x total peripheral resistance (tpr)
2
Q
how else can MAP be calculated
A
because co = hr x sv
map = hr x sv x tpr
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
4
Q
what does darcys law concern
A
fluid flow which is NOT THE SAME AS fluid velocity
5
Q
what is fluid flow
A
volume passing in a given time period
6
Q
what is fluid velocity
A
distance travelled by fluid over time
7
Q
what is mean velocity
A
fluid flow divided by total cross sectional area
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)
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
10
Q
what is aortic pressure (when blood exits left ventricle)
A
90 mmHg MAP
11
Q
what is vena cava / venous pressure (when blood enters right atrium)
A
close to 0mmHg MAP
12
Q
how does the MAP decrease
A
steadily over the course of systemic circulation
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
14
Q
which 3 types of fluid flow occur in circulation
A
1) laminar
2) turbulent
3) single-file
15
Q
what is LAMINAR FLOW
A
- in normal arteries and veins
- straight direction of travel
- clean lines of movement of fluid
16
Q
what is TURBULENT FLOW
A
- in ventricles and sometimes ascending aorta of healthy subjects
- turbulent flow pattern
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
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
19
Q
what causes resistance to increase
A
when tube length and fluid viscosity increase
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
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)
22
Q
what does poiseuilles law calculate
A
- flow through a tube
23
Q
what is poiseuilles equation for flow through a tube
A
Q (flow) = (P1 - P2) (pressure gradient) x equation for resistance inversed
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)
25
what is an example of how flow is v sensitive to vessel radius
- drop in radius from 1cm in aorta to 0.01 cm in arteriole
| - causes inc in resistance by factor of 10^8
26
how does arrangement of vessels increase resistance to flow
- arranged in both series and parallel circuit
27
which parts of the circulatory system are arranged in series
arteries -> arterioles -> capillaries -> venules -> veins
28
which parts of the circulatory system are arranged in parallel
all vessels are arranged in parallel with other vessels of the same type (ie inferior and superior vena cava)
EXCEPTION = aorta + pulmonary trunk
29
how do we increase resistance in a circuit
ADD series units (makes circuit longer)
30
how do we decrease resistance in a circuit
ADD parallel units (adding more units alongside each other so increases whole cross sectional area thus amount of space through which fluid can flow)
31
what is compliance in vessels
change in volume
| divided by change in pressure inside the vessel minus the pressure outside
32
what is pressure inside the vessel minus pressure outside
- 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
33
what is compliance defined as
- change in volume per unit change in distending pressure
34
how does gradual increase in distending pressure impact volume
causes gradual increase in volume
35
what is compliance in arteries and veins
- 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
36
how is higher compliance in veins beneficial
- 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)
37
so what do veins act as
effective at acting as volume resevoirs (stores of blood volume)
38
what do arteries act as
- by contraction function they act as pressure reservoirs
| - control amount of additional pressure which passes through a certain point of systemic circulation
39
what is the distending pressure
- pressure acting to push open vessel
| - acts on the vessel wall and stretches it
40
what would happen if distending pressure wasnt balanced by forces in the vessel wall
rupture
41
what is the law of LaPlace
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)
42
what is the LaPlace equation
T = (Pt x r) / u
43
what happens as transmural pressure increases
- in a larger vessel with wall thickness acting to lower amount of tension needed in the wall to withstand this pressure
- tension increases
44
what is the transmural pressure in large arteries and how do they prevent damage
- transmural pressure and radius large
| - wall thick to compensate + maintain integrity
45
what is the transmural pressure in veins and what does this mean
- low transmural pressure
- radius still large
- SO (as walls are thin) still signif tension generated over walls of veins
46
what is the transmural pressure in capillaries and how do they prevent damage
- low transmural pressure
- small radius
- SO allows walls to be v thin (arterioles reduce + control pressure of blood entering capillaries to prevent damage)
47
where is likelihood of vessel rupture greatest overall
in elastic arteries (ie aorta)
- aortic rupture is relatively common and usually fatal medical emergency
-
48
which vessels does rupture most often occur in
- abdominal aorta = aneurysms form stretching vessel wall
49
which ruptures are rare but most dangerous
thoracic aneurysms
50
how will questions of graphs be asked
- ie what impact will radius change have on x factor?
| - dont remember equations but understand different components
51
define microcirculation
circulation of blood through the smallest blood vessels
| arterioles, capillaries, venules
52
where is density of capillary networks highesr
in metabolically active tissues
53
what does blood flow in capillaries depend on
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
what is autoregulation
- 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
how do changes in local blood flow occur
1) changes in arteriole diameter
| 2) altering contraction of precapillary sphincter muscles
56
what 2 categories are instrinsic control mechanisms classified into
- metabolic
| - myogenic
57
what is the relationship between metabolism + rate of blood flow
- as rate of metabolism incs, rate of blood flow incs steadily
- clear + apparent relationship
58
what is observed between metabolism + rate of blood flow in vitro
- 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
what is metabolic control characterised as
- intrinsic property w/in microcirculation
- reacting to it not only due to external factors
- intrinsic component acts autonomously
60
what happens to rate of o2 consumption with increased rates of metabolism in tissue
INCREASES
61
what is the result when consumption of O2 exceeds delivery
localised degree of hypoxia
62
what is hypoxia
- causes relaxation of nearby arteriolar smooth muscle
63
what is the direct response to local hypoxia and arteriolar smooth muscle relaxation
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
which factors other than oxygen are involved in metabolic autoregulation
```
products of metabolism
1) adenosine
2) H+
3) CO2
4) K+
substances synthesised in vascular endothelium
1) prostocyclins
2) nitric oxide
```
65
what do the products of metabolism do in metabolic autoregulation
- diffuse out of surrounding parenchymal tissue into interstitial space
- causes relaxation of the vascular smooth muscle cells
66
what do substances synthesised in vascular endothelium do in metabolic autoregulation
- generated by endothelial cells
- they diffuse across membrane into adjacent vascular smooth muscle cells
- cause further vasodilation
67
what is nitric oxide
an endothelium derived relaxing factor (EDRF)
| causes relaxation of vascular smooth muscle
68
how is nitric oxide (an EDRF) generated and where does it act
- by nitric oxide synthase in endothelial cells
- acts on vascular smooth muscle cells via cyclicGMP
- to drive relaxtion of vascular smooth muscle
69
where is nitroglycerin used
in stable exertionally induced cardiac anginga
70
what is the cause of angina
- blood supply not meeting O2/nutrient demand of cardiac tissue
- causes rapid coronary vasodilation to increase blood flow to heart and decrease pain
71
what is wall shear stress
- 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
what is displayed if we take an isolated perfused organ in the lab
- intrinsic ability to maintain a constant rate of blood flow through its vascular bed over a wide range of perfusion pressure
73
what is an isolated perfused organ
- organ out of body
- maintained in a lab environment
- perfused with buffer fluids that stimulate profusion of normal blood
74
what does the graph for myogenic control show
- 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
why is there a wide plataeu phase
blood flow kept in tight boundaries over majority of likely pressures it is going to experience
76
what is flow equal to
what does this mean
- pressure gradient over resistance
| - there must be an increase in resistance in order to keep constant flow if theres an increased pressure gradient
77
what is the negative feedback loop in the mechanism of the myogenic response
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
what does the negative feedback loop in the myogenic response do
- leads to adjusted perfusion pressure
- so theres a control of excess pressure
OR
- could reduce constriction of arteriolar smooth muscle like the cardiomyocytes
79
at what level does the myogenic response occur
SINGLE UNIT LEVEL
| - individual smooth muscle cells respond to passive stretch with contraction in opposition to it
80
when may long term autoregulation develop
- 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
how does long term autoregulation develop
1) increase in microcirculatory vessels supplying blood to tissue (increases density of the network)
2) enlargement of existing vessels
82
which environments may elicit long term autoregulation response
chronic exposure to high altitude
| due to low partial pressure of O2
83
how can we see long term autoregulation response in the heart
gradual partial occlusion of coronary vessel
84
what are lipophilic solutes in the transcapillary solute exchange
- 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
what are hydrophilic solutes in the transcapillary solute exchange
- 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
what process is dynamic and ongoing
fluid continuously circulates between capillaries and interstitium
87
what do hydrostatic pressures result from
capillary blood pressure
88
where are hydrostatic pressures
a) highest
b) lowest
a) arterial end
b) venous end
(gradient across length of capillary in hydrostatic pressure)
89
net hydrostatic pressure is this gradient in favour of...
mild fluid filtration so pressure out of capillary microcirculation into the interstitium
90
what are osmotic pressures
- 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
osmotic molecules are
mainly confined to plasma
BUT
not entirely there
92
what does net osmotic pressure gradient favour
- 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
where are osmotic pressures
a) highest
b) lowest
DOESNT VARY SIGNIFICANTLY over the length of the capillary
94
starlings forces:
| what decreases from 35 to 16 in venous end
- blood hydrostatic pressure
95
starlings forces:
| what pressure is 0
interstitial fluid hydrostatic pressure
96
starlings forces:
| what pressure is constant at 26mmHg
blood colloid osmotic pressure (pulling on fluid into vessel)
97
starlings forces:
| what pressure is constant at 1mmHg
interstitial fluid osmotic pressure
98
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
- pushing hydrostatic pressures
+
- pulling osmotic pressures
99
what does
a) net filtration at arterial end
b) net reabsorption at venous end
add up to at of microvascuture
a) 10mmHg
b) -9 mmHg
only 1mmHg causes tilt towards net filtration overall
100
what is the overall result in net fluid balance
net movement of fluid out of circulation at arterial end and back into circulation at venous capillary end
101
why is there a net loss of fluid (1.5 ml per minute) from the circulation and why is this a problem if unchecked
system doesn’t exist in perfect equilibrium
1.5ml/min = 90ml/hr = empty vascular system of plasma in 24hrs
102
what prevents the emptying of the vascular system
LYMPHATIC SYSTEM
| - returns this fluid and any plasma proteins that leaked out into circulation / interstitial fluid
103
what is the lymphatic (lymphoid) system
- 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
the primary cells of the lymphatic (lymphoid) system are
lymphocytes
| - they determine bodies ability to resist of overcome infection and disease (immunity)
105
what are the 5 components of the lymphatic (lymphoid) system
1) lymph
2) lymphatic vessels
3) lymphoid tissues
4) lymphoid organs
5) lymphoid cells
106
lymph is
- interstitial fluid
- resembles plasma (though lower conc of suspended proteins)
- NOT pumped BUT relies on contraction and relaxation of muscles to move it
107
lymphatic vessels...
- begin in peripheral tissues
- + connect to veins
- vary in size
108
lymphoid tissues...
- found throughout body
- connective tissues
- dominated by lymphocytes
109
lymphoid organs...
- found throughout body
- inc lymph nodes, tonsil, thymus, spleen
- separated from their surrounding tissues by a fibrous connective tissue capsule
110
lymphoid cells...
- consist of immune system cells (lymphocytes, smaller no of phagocytes (ie macrophages + microphages) etc)
111
what does the lymph system do
- produces, maintains + distributes lymphocytes and other lymphoid cells that provide immunity
-
112
how do lymphocytes provide defence
- circulate in the blood
- reach site of injury / infection
- can also enter/leave capillaries
113
what does the lymph system continuously circulate and what does this mean
- 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
why is there excess extracellular fluid
capillaries deliver more fluid to tissues than they carry away
115
how does the lymph system work
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
