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factors influencing coronary, cerebral, skeletal, skin circulations Flashcards

1
Q

what are the four different types of special circulation

A

-coronary circulation
cerebral circulation
skeletal circulation
skin circulation

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2
Q

clinical scenario-ischaemic heart disease
a 58 year old man is admitted with acute myocardial infarction
he is transferred for coronary angiography and has a stent inserted to his critically stenosed right coronary artery
prior to discharge he is started on secondary prevention drugs
anti platelet drugs
ace inhibitors
beta blockers
why

A

anti platelet drugs- to prevent rethrombosis
beta blockers- reduce heart rate and increase perfusion time diastolic time, reduce blood pressure and myocardial work
ace inhibitor- to lower the blood pressure to reduce cardiac work

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3
Q

what is the coronary blood flow in ml/100g/min at rest

A

60-80ml/100g/min at rest

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4
Q

what is the oxygen consumption in ml per minute

A

250ml/min

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5
Q

what percentage of oxygen does heart extract at rest

A

heart extracts 70-80% oxygen at rest

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6
Q

what does increased oxygen demand require

A

increased coronary blood flow

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7
Q

by how many times does the coronary blood flow increase during exercise

A

5 times

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8
Q

what is the relationship between supply and demand of oxygen in coronary ischaemia

A

oxygen demand>oxygen supply

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9
Q

what are the 4 determinants of coronary blood flow

A

vasomotor tone
vessel wall diameter
coronary perfusion pressure
perfusion time

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10
Q

which of the following increases coronary blood flow
a) arrhythmia
b)atheroma in coronary arteries
c)hypotension
d)exercise
e)tachyarrhythmia

A

d) exercise
coronary blood flow increases by 5 times in exercise as increased oxygen demand requires increased coronary blood flow

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11
Q

coronary blood flow is lowest when

A

during contraction systole

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12
Q

coronary blood flow is highest when

A

during diastole during relaxation

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13
Q

what does hypertension increase

A

hypertension increases myocardial work

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14
Q

how does hypertension lead to increased myocardial work

A

renin angiotensin aldosterone and sympathetic activity

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15
Q

what does increased sympathetic activity and renin angiotensin aldosterone lead to

A

increased left ventricle hypertrophy

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16
Q

what does left ventricle hypertrophy cause

A

decreased myocardial flow but increased oxygen demand

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17
Q

what do ace inhibitors and beta blockers do to blood pressure and LV hypertrophy

A

reduces blood pressure and hypertrophy.

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18
Q

what is the perfusion time

A

flow occurs during diastole
time in systole is fixed 0.2 seconds
perfusion time depends on heart rate

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19
Q

what increases the perfusion time

A

lower heart rate

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20
Q

how does vessel wall diameter affect coronary blood flow

A

flow proportional to radius
atheroma narrows artery
flow is reduced

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21
Q

what do coronary stents do

A

restore vessel wall diameter to prevent ischaemia

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22
Q

what do antiplatelet drugs do

A

prevent artery/stent occlusion by platelet plug

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23
Q

how does vasomotor tone of large arteries affect coronary blood flow

A

endothelial control
increased flow causes shear stress
normal nitric production
normal vasodilation

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24
Q

how does vasomotor tone of medium arterioles affect coronary blood flow

A

myogenic control
increased blood pressure arteriolar stretch
activates calcium channel
normal vasoconstriction

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25
how does vasomotor tone of small arterioles affect coronary blood flow
metabolic control cardiomyocyte metabolites co2 adenosine local vasodilation
26
what are some factors affecting vasomotor tone
-neurohumoral factors -physical factors -endothelial factors -endocrine and paracrine factors -metabolic factors
27
what are some neurohumoral factors affecting vasomotor tone
noreadrenaline adrenaline acetylcholine
28
what are some metabolic factors affecting vasomotor tone
adenosine po2 pco2,H+,K+
29
what are some endothelial factors affecting vasomotor tone
ET NO PGI2 EDHF
30
what are some endocrine and paracrine factors affecting vasomotor tone
angiotensin ii histamine bradykinin txa2 5-HT
31
what are some physical factors affecting vasomotor tone
arterial pressure coronary pressure RAP, LVDP, systolic compression diastolic compression
32
how does autoregulation of coronary blood flow work
constant balance of oxygen demand and supply maintains constant flow at physiological blood pressure allows for compensation example post stenotic dilation increased flow in exercise
33
how do neurohumoral factors affect coronary blood flow
sympathetic stimulation increases circulating catecholamines beta adrenoreceptor activation causes increased heart rate and contractility increased myocardial work releases co2 adenosine causes vasodilation alpha adrenoceptor stimulation can cause vasoconstriction
34
how does ischaemic heart disease work
critical coronary artery stenosis: all mechanisms to increase flow are exhausted supply can no longer meet demand more than 50% stenosis can result in exertional angina more than 80% can cause rest pain- unstable angina angina pain mechanism: adenosine, bradykinin release due to myocyte ischaemia stimulates sympathetic afferents that synapse with spinothalamic tract
35
clinical scenario cerebral circulation a 24 year old women is admitted with headache and nausea 1 hour after falling and hitting her head she becomes drowsy confused and hypersensitive an urgent ct head shows an extradural haematoma she is intubated ventilated and sedated her bp is maintained greater than 140 systolic she is transferred to a neurosurgical theatre she
she is intubated ventilated and sedated to control paco2 and po2 and to reduce cmr (cerebral metabolic rate) her bp is maintained greater than 140 systolic to maintain cerebral perfusion pressure she is transferred to neurosurgical theatre to evacuate the haematoma and reduce intracranial pressure
36
what is the cerebral blood flow
50ml/100g/min
37
what organ has highest oxygen consumption
brain
38
why does the brain only tolerate short periods of ischaemia
brain is not capable of anaerobic respiration
39
why must cerebral blood flow be maintained for
constant delivery of oxygen and nutrients removal of metabolites
40
what is the cerebrospinal fluid volume
150ml
41
what is the blood volume in the brain
150ml
42
what is the brain parenchyma volume
1400ml 80%
43
explain the cerebral anatomy
skull-rigid box of fixed volume contains brain, cerebrospinal fluid and blood -brain -csf blood increase volume will increase the intracranial pressure
44
what does cerebral perfusion pressure depend on
arteriovenous pressure gradient cpp= mean arterial pressure- intracranial pressure
45
what are the four determinants of cerebral blood flow
-autoregulation -carbon dioxide and oxygen -neurohumoral factors -cerebral metabolism
46
explain the cerebral blood flow graph and how chronic hypertension can change this
y axis cerebral blood flow x axis mean arterial pressure chronic hypertension shifts the graph to the right
47
what is the main determinant of cerebral blood flow
-autoregulation constant flow at physiological blood pressure similar to coronary autoregulation hypertension shifts the range
48
how does co2 affect cerebral blood flow
within physiological co2 limits flow is proportional to co2 concentration increased pco2 increases h+ions decreased ph causes direct vasodilation enhances nitric oxide release decreases intracellular ca2+
49
within what range of paco2 is co2 concentration proportional to cerebral blood flow
30-80mmhg or 3-10 kpa
50
what are physiological co2 limits
30-80mmhg
51
how does oxygen affect cerebral blood flow
oxygen has no effects on cerebral blood flow within normal limits hypoxia pao2 <55 mmhg 7.2kpa causes arterioles to dilate which increases oxygen delivery direct action on vascular smooth muscle stimulates adenosine release cerebral blood flow decreases in hypoxic conditions
52
what does cmr mean
cerebral metabolic rate- the rate at which brain utilises metabolic substrates
53
which organ has the highest metabolic requirement
brain
54
what does increased metabolism lead to
increased metabolism is met by increased blood flow multiple mediators eg H+ co2, adenosine k+ No
55
local changes within seconds of increased cerebral activity
functional hyperaemia-increased blood flow likely to be nitric oxide mediated
56
how do neurohumoral factors affect cerebral blood flow
play a minor role during normal conditions sympathetic activation leads to vasoconstriction plays a role in shifting autoregulation curve to the right in hypertension parasympathetic nerves contribute to vasodilation
57
what is the monro kellie principle
the skull is a rigid box increased volume of one component reduces another overall increased volume increases pressure causes systemic hypertension
58
how are brain injuries managed
aims to prevent secondary injury anesthetise and intubate reduces metabolic demand controls ventilation to maintain o2 and co2 head up tilt to enhance venous drainage if brain tissue directly affected by trauma, autoregulation cannot occur
59
if brain tissue directly affected by trauma what cannot occur
autoregulation
60
clinical scenario skeletal circulation a 78 year old man presents to the vascular clinic he has a 3 year history of worsening pain in the left leg on exertion he now gets pain even at rest and can barely walk surgeon lists him for an angioplasty
3 year history of worsening pain in the left leg on exertion- intermittent claudication- ischaemia due to inadequate blood flow during exercise he now gets pain even at rest and cannot walk critical ischaemia- inadequate blood flow even at rest angiplasty-balloon dilation of narrowed vessels (coronary or peripheral) restores blood flow to reduce supply/demand mismatch
61
what are the three determinants of the skeletal muscle circulation
neurohumoral control extrinsic muscle contraction metabolic control
62
what is the skeletal muscle blood flow
1-2ml/100g/min
63
during exercise how much does blood flow increase
by 50 fold
64
what is the skeletal muscle blood flow during exercise
50-100ml/min/100g
65
why does the blood flow increase need to occur quickly
fight or flight response
66
during exercise blood flow to which organ is sacrificed
during exercise blood flow to other organs e.g the gut is sacrificed to allow for the increase in skeletal muscle blood flow
67
what does skeletal muscle vascular make a huge contribution to
peripheral vascular resistance
68
what is the main determinant of skeletal muscle blood flow at rest
sympathetic innervation contributes greatly to total vascular resistance
69
what do alpha 1 and alpha 2 receptors do
vasoconstriction
70
what do beta 2 receptors do
vasodilation
71
how does metabolic control affect skeletal muscle blood flow
during exercise local metabolic control becomes dominant functional hyperaemia- increase blood flow associated with metabolic activity at the start of exercise demand exceeds supply lactate co2 and h+ accumulate adenosine is produced and k+ channels open all contributes to rapid vasodilation
72
why does rapid vasodilation occur under metabolic control of skeletal muscle blood flow
to restore oxygen delivery remove metabolites
73
how does extrinsic muscle contraction affect skeletal muscle blood flow
co-ordinated contractions enhance blood flow skeletal pump mechanism ensures venous blood is sufficiently cleared atroventricular pressure difference is maintained during sustained contraction skeletal blood flow is interrupted or reduced demand exceeds supply-fatigue
74
what happens when demand exceeds supply
fatigue
75
what is claudication
peripheral vascular disease muscle ischaemia on walking collateral flow sufficient at rest during exercise demand>supply pain caused by muscle ischaemia rest pain-critical ischaemia
76
at normal body temperature what is the skin flow
5ml/min/100g
77
what is the skin blood flow in cold environments
3ml/min/100g
78
what is the skin blood flow in hot environments
7-8ml/min/100g
79
what is the key role of skin circulation
thermoregulation
80
what are arteriovenous anastomoses
av anastomoses shunt blood from arterioles to venules bypassing capillaries greatest number of arteriovenous anastomoses in hands toes ears nose lips
81
what is the determinants of skin blood flow
neurohumoral control local metabolic control
82
how does neurohumoral control affect skin blood flow
on exposure to cold, peripheral blood cools this then circulates to thermoregulatory centre in posterior hypothalamus sympathetic activity is increased skin arterioles have numerous alpha2 receptors alpha 2 receptors these constrict and blood is diverted through av anastomoses reduces superficial capillary blood and therefore heat loss
83
how does local metabolic control affect skin blood flow
hot environments- sweat glands activated activated sweat glands stimulate bradykinin production-vasodilation increased blood flow through capillary beds-heat loss
84
what is raynauds syndrome
excessive sympathetic response to cold on exposure to cold alpha2 receptors become more sensitive their vasoconstrictor effect seems to be enhanced
85
what are some key points about circulations
in coronary and cerebral circulations autoregulation and local metabolic control are the major factors influencing blood flow in contrast neurohumoral control has the greatest control in resting skeletal muscle and skin circulations in all tissues, if oxygen demand exceeds supply by blood flow tissue ischaemia occurs skeletal muscle contraction enhances blood flow arteriovenous anastomoses in the skin have a key role in thermoregulation clinical practice requires knowledge of normal physiology and how it is deranged by disease
86
what does the left coronary artery supply
87
what does the right coronary artery supply
supplies the right ventricle posterior wall of left ventricle and posterior 1/3 septum
88
what does the left coronary artery supply
lateral and anterior walls of left ventricle and anterior 2/3 septum
89
what is the formula for coronary perfusion pressure
aortic diastolic pressure- left ventricle end diastolic pressure

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