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Circulation and Breathing > 056 Factors influencing coronary, cerebral, skeletal muscles > Flashcards

056 Factors influencing coronary, cerebral, skeletal muscles Flashcards

1
Q

Which circulations are predominantly controlled by local factors and which ones by remote control?

A

Cerebral and coronary circulation is predominantly controlled by local metabolic control and autoregulation. Skeletal circulation is predominantly controlled by neurohumoral control

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2
Q

What effect does paO2 have on cerebral blood flow?

A

There is no effect, unless paO2 falls below 50mmHg, of which vasodilation occurs e.g. adenosine release by smooth muscles.

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3
Q

What effect does paCO2 have on cerebral blood flow?

A

In physiological limits, the increase in paCO2 causes a direct increase in cerebral blood flow. Increasing pCO2 reduces pH as H+ ions are released. This directly increases vasodilation but also enhances NO and opens K+ channels. There is a decrease in intracellular Ca2+.

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4
Q

Which area of circulation has the highest oxygen consumption?

A

Coronary blood circulation

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5
Q

What is the blood flow rate of coronary circulation at rest?

A

60-80ml/min/100g

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6
Q

During exercise, how much can coronary circulation increase by?

A

5 fold

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7
Q

How would you calculate coronary perfusion pressure?

A

Coronary perfusion pressure = aorta diastolic pressure - end diastolic pressure

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8
Q

When does the lowest coronary perfusion pressure occur?

A

When there is isovolumetric contraction and there is strong mechanical compression that is coupled with low aorta pessure, reducing flow into coronary arteries.

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9
Q

What are the two factors that affect coronary perfusion pressure?

A

Mechanical compression by ventricle compression

Aortic pressure

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10
Q

What happens to perfusion pressure when aortic valves first open during ejection?

A

It will increase slightly because of the quick ejection. As aortic pressure decreases, it will slowly fall again.

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11
Q

When is coronary perfusion pressure highest?

A

When aortic valves first close, as aortic pressure is still high and ventricles have stopped contracting, resulting in low mechanical compression allowing blood through coronary arteries.

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12
Q

What is the difference between the right coronary perfusion pressure and left coronary perfusion pressure?

A

Right coronary perfusion pressure peaks during ejection phase. Mechanical compression does not have a large effect on coronary perfusion pressure because it contracts with much less force.

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13
Q

How long does systole last?

A

0.2sec

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14
Q

What happens to coronary perfusion pressure if heart rate increases?

A

If heart rate increases, the diastolic time will decrease giving less time for coronary perfusion. Pressure decreases.

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15
Q

What are 3 determinants of coronary circulation?

A

Coronary perfusion pressure
Perfusion time
Vessel diameter

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16
Q

How does atherosclerosis affect perfusion pressure?

A

It decreases both vessel diameter, reducing perfusion pressure.

17
Q

How is vasomotor tone regulated by neurally?

A

Sympathetic nervous system will cause vasoconstriction through a1 receptors and vasodilation on B2 receptors. Parasympathetic nervous system will stimulate M receptors that lower heart rate.

18
Q

How is vasomotor tone regulated by humorally?

A

Angiotensin II, adrenaline, ADH

19
Q

How is vasomotor tone regulated locally?

A

Endothelin, thromboxane, bradykinin, prostacyclin, NO, EDRF, autoregulation by shear forces, adenosine detecting hypoxia

20
Q

What does adenosine do?

A

detects hypoxia and catalyzes cAMP which causes vasodilation

21
Q

Define unstable angina

A

When during rest there is 80% of stenosis due to lipid deposition and smooth muscle proliferation

22
Q

Define exercise induced angina

A

When during exercise, there is 50% stenosis due to lipid deposition and smooth muscle proliferation

23
Q

What rate does cerebral blood flow occur at?

A

50ml/100g/min

24
Q

Why must cerebral blood flow be maintained?

A

To ensure constant delivery of O2 and substrates along with the removal of waste products

25
Q

Why cant the brain sustain periods of ischemia?

A

The brain has low capacity to metabolize anaerobically

26
Q

How would you calculate cerebral perfusion pressure?

A

Cerebral perfusion pressure = mean arterial pressure - intercranial pressure

27
Q

What are 4 determinants of cerebral blood flow?

A

Cerebral metabolic demand
Autoregulation by stretch receptors
CO2 & O2 levels
Neural control

28
Q

What is the myogenic mechanism that maintains blood flow?

A

Autoregulation - when stretch receptors in cerebral blood vessels maintain constant blood flow through release of adenosine etc.

29
Q

What does autoregulation keep the intercranial pressure at?

A

60-160mmHg

30
Q

What is the physiological limits of CO2 in cerebral blood pressure?

A

30-80mmHg

31
Q

What vasoactive metabolic factors control functional hyperaemia?

A

adenosine, H+ CO2, K+, NO

32
Q

How does extradural haematoma affect cerebral blood circulation?

A

Extradural haematoma is caused by bleeding from a torn meningeal artery. The swelling of blood causes and increase in pressure. Cushings reflex tries to maintain perfusion pressure but this causes CSF and blood out. There is increased swelling and decreased blod flow and perfusion, causing unconsciousness.

33
Q

How would you treat and extradural haematoma?

A

Anesthesia and intubation reduces metabolic demand. Head is also tilted up to allow venous drainage

34
Q

How does meningitis affect cerebral blood circulation?

A

Inflammation in the meninges causes an increase in intercranial pressure. This leads to lowered cerebral blood flow, which causes headaches, coma, photophobia etc.

35
Q

What is the blood flow rate at rest in skeletal circulation?

A

1-2ml/min/100g

36
Q

During exercise, by how much can skeletal circulation increase by?

A

x5 fold

37
Q

What are the 3 determinants of skeletal circulation?

A

Extrinsic muscle contraction
Neurohumoral factors
Metabolic control

38
Q

Explain the relationship between extrinsic muscle contraction and skeletal circulation, with reference to beginning of exercise and continued exercise.

A

Skeletal muscle pumps are able to maintain pressure difference between arterioles and venules by the skeletal pump mechanism that enhances blood flow. When muscle is contracted and vessels are compressed, the myoglobin that are oxygen binding proteins found in muscle tissue provide oxygen. Howe

Circulation and Breathing (13 decks)

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