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FBS2 > Gaseous diffusion 1 > Flashcards

Gaseous diffusion 1 Flashcards

1
Q

What is FO2?

A

Fractional concentration of oxygen

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2
Q

What is PIO2?

A

Partial pressure of inspired oxygen

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3
Q

What is PAO2?

A

Partial pressure of alveolar oxygen

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4
Q

What is PaO2?

A

Partial pressure of arterial oxygen

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5
Q

What is Dalton’s Law?

A

In a mixture of non-reacting gases, total pressure exerted is sum of individual partial pressures

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6
Q

How can you calculate PO2?

A

FO2 x PB

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7
Q

What is Henry’s Law?

A

C = kP

As the partial pressure of the gas increases, more of the gas dissolves in the liquid

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8
Q

Which is more soluble - oxygen or nitrogen?

A

Oxygen is twice as soluble as nitrogen (higher Henry’s Law constant)

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9
Q

Which is more soluble - carbon dioxide or oxygen?

A

Carbon dioxide is 20x more soluble than oxygen (much higher Henry’s Law constant)

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10
Q

What is the bends?

A

Nitrogen less likely to dissolve in plasma than oxygen
Pressure surrounding you is greater during diving
More nitrogen goes into solution
When you ascend, if you go to quickly, nitrogen will rapidly come out of solution and form bubbles in muscles/SC

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11
Q

What 2 factors does the water vapour pressure (PH20) depend on?

A

Temperature

Saturation

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12
Q

What is the water vapour pressure in the lungs?

A

6.3kPa

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13
Q

Is the water vapour pressure in the lungs constant or does it change?

A

Constant at 6.3kPa

100% saturated

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14
Q

What is the alveolar gas equation?

A

PAO2 = PIO2 - PACO2/R

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15
Q

What is the respiratory exchange ratio, R?

A

CO2 production/O2 consumption

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16
Q

What is the PO2 of atmospheric air?

A

21kPa

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17
Q

What is the PO2 in alveolar gas?

A

13.5kPa

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18
Q

What is the PCO2 in alveolar gas?

A

5.3kPa

19
Q

What is the PH20 in alveolar gas?

A

6.3kPa

20
Q

What is the PO2 in mixed venous blood?

A

5.3kPa

21
Q

What drives O2 movement across alveoli into capillary?

A

Partial pressure gradient

22
Q

What determines the rate of gas transfer?

A

Partial pressure gradient NOT concentration gradient

23
Q

What limits diffusion of gases in the lung?

A

Respiratory disease - disrupts the alveolar/capillary unit

24
Q

Which factors affect rate of diffusion across a membrane?

A

Pressure gradient
Surface area
Thickness

25
Q

What is the equation for rate of transfer of a gas?

A

DLg (PA - PC)
Where DLg = transfer factor
PA = alveolar pp
PC = capillary pp

26
Q

Why can’t we use O2 to measure transfer factor?

A

Because mean capillary PO2 is unmeasurable

27
Q

What gas is used to measure transfer factor and why?

A

Carbon monoxide - has a higher affinity for Hb than oxygen (240x higher)

28
Q

What is the equation for gas transfer factor of CO?

A 
DLCO = VCO/ PACO
VCO = rate of CO uptake
PACO = conc of CO in alveolar air
29
Q

Which factors reduce the surface area of the lungs?

A

Emphysema
Lung resection
Decreased venous return

30
Q

Which factors increase the thickness and reduce gas transfer factor in the lungs?

A

Fibrosis
Collagen vascular diseases
Congestive heart failure

31
Q

What 3 factors decrease DLCO?

A

Reduction in alveolar-capillary area
Increased thickness of alveolar-capillary membrane
Anaemia

32
Q

Which 2 factors increase DLCO?

A

Increased pulmonary blood volume (exercise)

Polycythaemia (increased no of RBCs)

33
Q

What is the normal concentration of Hb in the blood?

A

150g/L

34
Q

What is the oxygen capacity of normal blood?

A

200ml/L

35
Q

What is the oxygen saturation of pulmonary venous blood?

A

Nearly 100%

36
Q

What is the oxygen saturation of mixed venous blood returning to the heart?

A

75%

37
Q

What is the Bohr shift?

A

Shift of oxygen-Hb dissociation curve to the right due to decrease in pH etc - easier to offload oxygen, e.g. in respiring tissues

38
Q

What happens to the oxygen capacity, content and saturation at high altitudes?

A

Capacity - normal
Content - reduced
Saturation - reduced

39
Q

What happens to the oxygen capacity, content and saturation at high altitudes?

A

Capacity - normal
Content - reduced
Saturation - reduced

40
Q

What happens to the oxygen capacity, content and saturation in anaemia?

A

Capacity - reduced
Content - reduced
Saturation - normal

41
Q

What is the PO2 in mixed expired air?

A

16kPa

42
Q

What is the PCO2 in mixed expired air?

A

3.5kPa

43
Q

What is the PH20 in mixed expired air?

A

Variable

FBS2 (16 decks)

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