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Pulmonary physiology > V/Q > Flashcards

V/Q Flashcards

1
Q

At what point in the bronchial tree do pulmonary arteries form a capillary network?

A

From terminal bronchioles

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2
Q

What influences pulmonary blood vessels volume?

A

Pulmonary blood pressure

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3
Q

What happens to pulmonary vessels as pulmonary pressure increases?

A

Decreases resistance via recruitment of normally closed vessels and distension of already opened ones

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4
Q

What is required for collapsed pulmonary arterial vessels to open?

A

Arterial vessels must reach critical opening pressure before blood flow occurs

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5
Q

What two factors determine pulmonary blood vessel volume?

A

Alveolar blood vessel volume (determined by alveolar pressure)

Extra alveolar blood vessels (determined by lung volume and thus pull of lung parenchyma on capillary walls)

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6
Q

What influences volume of alveolar blood vessels, what happens in inspiration?

A

Alveolar pressure

In inspiration, alveolar pressure rises compared to capillary pressure, squashing alveolar capillaries

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7
Q

How do extra alveolar blood vessels volume change?

A

Higher lung volume opens vessels via increased pull of lung parenchyma on capillary wall so less vascular resistance

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8
Q

Two ways of measuring oxygen in the body

A

Amount of oxygen taken up by lungs (spirometry)

Concentration of oxygen in arterial and mixed venous blood (catheter in pulmonary artery)

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9
Q

Describe regional perfusion of the lung

A

Less blood flow at top of lung and generally more at the bottom until at extreme base where there’s small decrease in perfusion

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10
Q

Why is there a small decrease in perfusion at very base of lung?

A

Intrapleural pressure > luminal pressure of extra alveolar vessels crushing them

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11
Q

Why does perfusion decreases linearly from base to apex of lung?

A

Gravity, lower regions perfused greater since hydrostatic pressure here is higher allowing greater recruitment and distension of vessels

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12
Q

Why are relative changes in pulmonary circulation pressure greater than for systemic?

A

Lower ambient pressure in pulmonary circulation

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13
Q

Describe why there is no blood flow in dead space (ZONE 1)?

A

Alveolar pressure>pulmonary arterial pressure so no flow

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14
Q

What happens in ZONE 2, what is blood flow determined by?

A

Pulmonary arterial pressure>alveolar pressure

Blood flow determined by arterial-alveolar difference

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15
Q

What happens in ZONE 3, what is flow determined by?

A

Venous pressure>alveolar pressure.

Flow determined by arterial venous pressure difference

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16
Q

Why is ZONE 2 not affected by venous pressures?

A

Venous pressure is so low and much lower than alveolar pressure

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17
Q

Describe in what region is regional ventilation and perfusion greater, why?

A

Going down both increases

Due to gravity

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18
Q

Is the gradient for regional ventilation or regional perfusion greater? Why?

A

Perfusion, liquid weighs more than gas so gravity has a greater effect on it

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19
Q

What does hypoxia cause in systemic circulation, why?

A

Vasodilation, to help blood flow match metabolism

20
Q

What does hypoxia cause in pulmonary circulation, why?

A

Vasoconstriction, this redirects blood flow to other parts of lung that have better V/Q ratios so match perfusion to ventilation

21
Q

At what point does hypoxia cause vasoconstriction in pulmonary vessels?

A

PO2 of alveolar gas below 100mmHg

22
Q

Why can hypoxic vasoconstriction be dangerous in the lungs?

A

Chronic global hypoxic vasoconstriction - when oxygen levels fall e.g. high altitude all vessels pulmonary vessels vasoconstrict, increasing pulmonary artery pressure (oedema, pulmonary hypertension or cor pulmonale)

23
Q

What factors can cause vasoconstriction of lung blood vessels?

A

Low blood pH or hypoxia

24
Q

What determines distribution of fluid between pulmonary capillaries and pulmonary extracellular space?

A

Starling’s forces, low capillary hydrostatic pressure (net outward flow)

25
Q

What does pathological increase in pulmonary capillary pressure cause, how is gas exchange affected?

A

Increased fluid outflow from capillaries, causes pulmonary oedema so fluid crosses alveolar epithelium into alveolar spaces and compromises gas exchange

26
Q

Where is the V/Q ratio greatest?

A

Apex

27
Q

Describe the V/Q of ideal alveolus?

A

1 Well ventilated and well perfused alveolus. Blood equilibriates with alveolar air

28
Q

Describe V/Q of upper lung regions, why?

A

> 1 Well ventilated but poorly perfused alveoli

29
Q

Describe V/Q of lower lung regions, why?

A

Poorly ventilated but well perfused alveoli V/Q<1

30
Q

Describe how ventilation and perfusion curves look?

A

Ventilation is linear (increases going down lung) not steep

Perfusion is linear at first, ( increases going down the lung, more steep so overtakes ventilation curve) but then at very bottom blood flow decreases

31
Q

Describe the alveolar PO2 and PCO2 in upper/lower regions of the lung

A

Upper -Tend to be towards levels found in inspired gas

Lower - Poorly ventilated so pO2 and pCO2 in alveoli low and high respectively and thus levels in blood found towards levels found in mixed venous blood

32
Q

Describe V/Q in dead space, what does this mean?

A

No blood flow, so infinite

33
Q

What is the typical V/Q ratio?

A

0.8

34
Q

Describe V/Q in a shunt why?

A

No fresh gas exchange, V/Q =0

35
Q

Describe how you can get V/Q mismatch in extreme cases?

A

Can have normal blood flow and normal ventilation but no gas exchange since blood never goes near fresh gas

36
Q

How does large V/Q value at top of lung, justify why TB targets apex of lungs?

A

PAO2 at top of lung higher, more oxygen for bacteria

37
Q

A mismatch reduces efficiency of gas exchange, what’s the result on arterial pCO2 and pO2?

A

Arterial pO2 less than it should be and arterial pCO2 higher than it should be (compared to if V/Q were matched)

38
Q

What is meant by a pulmonary shunt?

A

Extreme V/Q mismatch, caused by passage of blood passing through pulmonary circulation but not ventilated

39
Q

What are examples of physiological shunts?

A

Bronchial artery blood supplies lung parenchyma and drains pulmonary veins

Coronary venous blood which drains left ventricle.

40
Q

What are some abnormal shunts?

A

Abnormal connections between pulmonary artery and vein (pulmonary arteriovenous fistula)

Defects that allow blood to pass from right to left hand sides of heart

41
Q

Why is the shape of oxy Hb curve significant when considering shunted blood?

A

Addition of small amount of under oxygenated shunted blood with lower pO2 reduces saturation greatly, not linear so greater effect

Think moves further along curve of graph - steeper

42
Q

Why doesn’t shunt affect pCO2 in arterial blood?

A

Chemoreceptors sense increased pCO2 and trigger increased ventilatory rate

43
Q

How does O2 content of blood decrease and increase with low V/Q units and high V/Q units respectively?

A

Lowered more by a given fall in PaO2 for low V/Q than it is elevated by a rise in PaO2 in high V/Q

44
Q

Why are effects of V/Q mismatch worse for oxygen?

A

Over ventilated regions can’t compensate for under ventilated ones because blood from over ventilated regions doesn’t have higher oxygen content than well mached region because curve is flat at high pO2 so Hb is fully saturated.

45
Q

When can you see increased V/Q pathologically?

A

Pulmonary embolism

46
Q

Where is alveolar pO2 the highest?

A

Apex

Pulmonary physiology (3 decks)

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