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Respiratory Physiology > Gas Exchange > Flashcards

Gas Exchange Flashcards

1
Q

‘What is the basal gas exchange requirement?

A

250ml O2 per minute
200ml CO2 per minute

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2
Q

What is the common physiological challenge to gas exchange in health?

A

Excercise

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3
Q

What is maximal exercise limited by?

A

Cardiac output

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4
Q

What cells are present in the alveolar wall?

A

Epithelial cell (type 1 pneumocyte) - basal membrane
Endothelial cell

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5
Q

What does gas exchange depend on?

A

Partial pressure gradient from pulmonary arteriole to pulmonary venule
Passive

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6
Q

Define Fick’s Law.

A

Volume of gas diffusing across a membrane per minute is directly proportional to surface (A) of membrane, partial pressure gradient across membrane (P1 - P2) and inversely proportional to membrane thickness (T)
Vgas = D.A.(P1-P2)/T

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7
Q

What is the diffusion constant proportional to?

A

Solubility/(molecular weight)^0.5 of gas

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8
Q

In the liquid phase what is the amount of dissolved gas in solution proportional to?

A

Partial pressure of the gas and its solubility

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9
Q

What 3 things is adequate gas exchange in lung enabled by?

A

Large SA of gas exchange membrane
Thin gas exchange membrane
Maintaining partial pressure gradient across gas exchange membrane

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10
Q

What makes the lung vulnerable to oedema?

A

Thin gas exchange region

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11
Q

What 2 thingscauses damage to the gas exchange membrane?

A

Destruction and loss of alveolar walls
Thickening of alveolar capillary membrane

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12
Q

What causes thickening of alveolar wall?

A

Fibrotic Process

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13
Q

How many ml of blood is in the capillaries at any time?

A

70ml

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14
Q

How many ml of air is FRC

A

3500ml

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15
Q

At rest how many ml of blood does the heart pump through the lung?

A

5L/min

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16
Q

What is atmospheric O2 and CO2?

A

O2 - 21%
CO2 - 0.05%

17
Q

How can alveolar ventilation be changed?

A

Decreasing/increasing ventilation
Decreasing/increasing tidal volume

18
Q

What happens in increased alveolar ventilation (VA)?

A

Hyperventilation -> decreased CO2 in lungs = new steady state reached to compensate

19
Q

What happens in decreased VA?

A

Hypoventilation -> increased CO2 in lungs = new steady state reached

20
Q

What happens in half ventilation?

A

CO2 doubles
Rate of CO2 return remains constant

21
Q

What is the effect of changes in VA on Hb saturation?

A

Increasing - not a huge difference
Decreasing - decreases saturation by 5%

22
Q

What is the calculation for O2 uptake by blood?

A

Amount inspired - amount expired
VI.FIO2 - VE.FEO2

23
Q

What does hyperventilation cause?

A

Reduced PACO2 (hypocapnia)
Increased PAO2

24
Q

What does hypoventilation cause?

A

Increased PACO2 (hypercapnia)
Reduced PAO2

25
Q

What is the effect of acute reduced alveolar ventilation?

A

Respiratory compensation for acidosis

26
Q

What is the effect of chronic reduced alveolar ventilation?

A

Renal compensation for acidosis

27
Q

Why does blood flow have to increase during excercise?

A

Required increase rate of O2 and CO2 exchange in the alveolus to maintain normal arterial blood gases

28
Q

What happens to capillaries as CO increases>

A

Greater proportion of capillaries are recruited and perfused - increases gas exchange SA

29
Q

What do ,ore parallel pathways for blood through lungs cause?

A

Reduced velocity of flow at any given CO
More time for loading of O2 into RBCs

30
Q

What prevents an increase in PACO2 and reduction in PAO2?

A

Alveolar ventilation increases - must match increased CO2 delivery and O2 removal

31
Q

In normal lung, what is oxygen uptake in maximal exercise limited by?

A

Cardiac output

32
Q

In normal lung, what limits maximal oxygen uptake?

A

Perfusion

33
Q

Do reductions in diffusion capacity impair oxygen uptake at rest?

A

No

34
Q

How do you asses info about gas exchnage membrane?

A

Examine uptake of gas that is diffusion limited - CO

35
Q

What 3 properties must a gas have to assess diffusion capacity?

A

Extremely soluble in blood
Blood must not fill up during transit through lung
Must have gradient always driving gas from blood

Respiratory Physiology (17 decks)

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