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DNURS 827 Advanced Physiology/Pathophysiology for Anesthesia I > Lecture 4: Physical Principles Of Gas Exchange > Flashcards

Lecture 4: Physical Principles Of Gas Exchange Flashcards

1
Q

What is diffusion?

A

Random molecular motion of molecules

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2
Q

Movement of a gas in one direction is the effect of…

A

A concentration gradient

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3
Q

Direction of diffusion occurs from areas of ___ to ___

A

High to low concentration

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4
Q

Rate of diffusion is dependent on ___

A

Pressure

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5
Q

Total pressure of mixture =

A

The summation of partial pressures of gases in a mixture

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6
Q

Respiratory gases include (3)

A
  • Oxygen
  • Nitrogen
  • Carbon dioxide
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7
Q

Composition of air

A
  • 79% nitrogen

- 21% oxygen

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8
Q

Total pressure of air mixture =

A

760 mm Hg

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9
Q

1 atmosphere =

A

760 mm Hg

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10
Q

Nitrogen partial pressure

A

79% of 760 mm Hg = 600 mm Hg

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11
Q

Oxygen partial pressure

A

21% of 760 mm Hg = 160 mm Hg

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12
Q

Henry’s Law—Solubility of a gas in a liquid depends on what 4 things?

A
  • Temperature
  • Partial pressure of gas over the liquid
  • Nature of the solvent
  • Nature of the gas
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13
Q

When dissolved molecules are attracted by water more and can be accumulated without building up excess pressure in solution = ___ soluble

A

Highly soluble

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14
Q

Molecules which are repelled by water will dissolve less and have lower concentration = ___ soluble

A

Poorly soluble

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15
Q

Carbon dioxide is ___ times more soluble than oxygen

A

20 times

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16
Q

Rate of net diffusion of gases is determined by…

A

Difference of partial pressures (pp)

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17
Q

If pp of gas in alveoli > blood, then…

A

Gas moves into blood (i.e.: oxygen)

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18
Q

If pp of gas in blood > alveoli, then…

A

Gas moves into alveoli (i.e.: carbon dioxide)

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19
Q

What is vapor pressure?

A

Partial pressure of water escaping surface into gas phase

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20
Q

Vapor pressure is ___ mm Hg when gas mixture is fully humidified at 37 degrees Celsius

A

47 mm Hg

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21
Q

Vapor pressure depends on ___

A

Temperature

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22
Q

At greater temperature, the ___ the kinetic energy and ___ water escaping into the ___ phase

A

Greater the kinetic energy, more water escaping into the gas phase

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23
Q

How do you calculate the pp of O2 in the upper airway?

A

760 mm Hg (total) = 713 mm Hg (pp Air) + 47 mm Hg (pp H2O vapor)
Pp of O2 in upper airway = 713 mm Hg x 0.21 = 150 mm Hg

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24
Q

What are 6 factors that affect gas diffusion rates?

A
  • Pressure differences
  • Gas solubility in fluid
  • Area of fluid
  • Distance which gas must diffuse
  • Molecular weight of gas
  • Temperature of fluid (constant in body)
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25
Q

What are 2 characteristics of the gas which affect the ability and rate of net diffusion?

A
  • Solubility of gas molecule

- Molecular weight

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26
Q

Diffusion coefficient is proportional to…

A

The relative rates at which different gases diffuse

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27
Q

D =

A

Diffusion coefficient

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28
Q

D is directly proportional with ___

A

Solubility

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29
Q

D is inversely proportional to…

A

The square root of the gas’ molecular weight

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30
Q

Respiratory gases are highly soluble in ___

A

Lipids (the main component of cell membranes)

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31
Q

Cell membranes are highly permeable to…

A

Respiratory gases

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32
Q

Rate of gas movement into tissues is limited by…

A

Diffusion rate of gas through tissue water

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33
Q

Movement of gas into and out of tissues =

A

Diffusion rate of gas through water

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34
Q

Does alveolar air have the same gas concentrations as atmospheric air?

A

No

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35
Q

Why are there differences in alveolar air vs. atmospheric air? (4 things)

A
  • Alveolar air is partially replaced by atmospheric air during each breath
  • Oxygen constantly absorbed into blood from alveoli
  • Carbon dioxide diffused into alveoli from blood
  • As air enters respiratory passages, it becomes humidified, diluting the inspired gases partial pressures
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36
Q

What is required to exchange alveolar air?

A

Multiple breaths

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37
Q

___ ccs of air per breath

A

350 ccs

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38
Q

FRC is roughly ___ ccs

A

2500 ccs

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39
Q

Each breath replaces a ___ of FRC

A

A seventh

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40
Q

Multiple breaths to exchange alveolar air prevents…

A

Sudden change in gas concentrations; allows respiratory control mechanisms to be more stable

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41
Q

Normal alveolar ventilation removes 1/2 gas in ___ seconds

A

17 seconds

42
Q

Half normal ventilation removes 1/2 gas in ___ seconds

A

34 seconds

43
Q

Twice normal ventilation removes 1/2 gas in ___ seconds

A

8 seconds

44
Q

Partial pressure of oxygen is controlled by rate of ___ and ___

A

Absorption and ventilation

45
Q

What affects alveolar PO2? (3 things)

A
  • Rate of ventilation
  • Oxygen pressure
  • Exercise
46
Q

Normal alveolar PO2 =

A

100 mm Hg

47
Q

Normal alveolar PCO2 =

A

40 mm Hg

48
Q

Alveolar PCO2 increases in proportion to…

A

CO2 excretion

49
Q

PCO2 decreases in inverse to…

A

Alveolar ventilation

50
Q

Expired air is a combination of ___ and ___

A

Dead space and alveolar air

51
Q

First portion of inspired air is…

A

Dead space air—consists of humidified air

52
Q

Second portion of expired air is…

A

Mixture of both dead space and alveolar air

53
Q

Alveolar air is expired at ___ of exhalation

A

End

54
Q

What is the overall thickness of the respiratory membrane?

A

0.6 micrometers

55
Q

What is the total surface area of the respiratory membrane?

A

70 meters squared

56
Q

RBC squeeze through ___ micrometer diameter capillaries

A

5 micrometer

57
Q

___ diffusion rates for respiratory gases

A

Rapid!

58
Q

Why are diffusion rates rapid through the respiratory membrane?

A

Minimal transfer time and distance through plasma

59
Q

What are 4 factors that affect the rate of gas diffusion through the respiratory membrane?

A
  • Thickness of respiratory membrane
  • Surface area of respiratory membrane
  • Diffusion coefficient (D)
  • Pressure difference across respiratory membrane
60
Q

Rate of diffusion is ___ proportional to membrane thickness

A

Inversely

-Increasing thickness by 2-3 times interferes significantly with normal respiratory exchange

61
Q

What 3 things increase thickness of the respiratory membrane?

A
  • Edema
  • Fluid
  • Fibrosis
62
Q

What is the effect of decreasing surface area to 1/4 normal?

A

Impedes gas exchange significantly

i.e.: emphysema, removal of lung tissue during surgery

63
Q

Emphysema can decrease surface area as much as ___

A

5-fold

64
Q

What 2 things determine diffusion coefficient (D) of gases?

A
  • Solubility

- Molecular weight of gas

65
Q

CO2 diffuses ___ times faster than oxygen

A

20

66
Q

Oxygen diffuses ___ times as rapidly as nitrogen

A

2

67
Q

Diffusion occurs across the membrane ___ the pressure gradient by ___

A

Down, simple diffusion

68
Q

What is diffusing capacity?

A

“The volume of a gas that will diffuse through the respiratory membrane each minute for a pressure difference of 1 mm Hg”

AKA the ability to exchange gas between alveoli and pulmonary blood, expressed in quantitative terms

69
Q

What can affect the diffusing capacity?

A

Factors which affect diffusion through the respiratory membrane

70
Q

What is the diffusing capacity for O2 at rest?

A

21 ml/min/mmHg

71
Q

What is the oxygen diffusing capacity during exercise?

A

Diffusing capacity increases three-fold, to max of 65 ml/min/mmHg

72
Q

What is the diffusing capacity of CO2 at rest?

A

400 ml/min/mmHg

73
Q

What is the diffusing capacity of CO2 during exercise?

A

1200 ml/min/mmHg

74
Q

What is the diffusing capacity for CO?

A

17 ml/min/mmHg

75
Q

Which gas has the highest diffusing capacity rate?

A

CO2

76
Q

What is the V/Q ratio?

A

Highly quantitative concept of imbalance between alveolar ventilation and blood flow

77
Q

V/Q is normal when…

A

Alveolar ventilation and blood flow are normal

78
Q

V/Q is zero when…

A

When ventilation is zero but perfusion is present

79
Q

V/Q is infinity when…

A

If ventilation is present but there’s no perfusion

80
Q

If V/Q ratio = zero or infinity, there is ___ exchange of gases

A

No exchange

81
Q

V/Q = zero

A
  • Blood flow but no alveolar ventilation (i.e.: complete airway obstruction)
  • Gases diffuse between blood and alveolar air
  • Air in alveoli reaches equilibrium with deoxygenated blood returning to lungs in pulmonary arteries
82
Q

In normal deoxygenated blood, the PO2 is ___ mmHg and PCO2 is ___ mmHg

A 
PO2 = 40 mmHg
PCO2 = 45 mmHg
83
Q

V/Q = infinity

A
  • There is alveolar ventilation but no blood flow (i.e.: pulmonary artery obstruction)
  • Alveolar air becomes equal with humidified inspired air—no loss of oxygen into blood, no gain of CO2 from blood
84
Q

Alveolar gas partial pressures—PO2 is ___ mmHg and PCO2 is ___ mmHg

A 
PO2 = 150 mmHg
PCO2 = 0 mmHg
85
Q

Normal V/Q occurs when…

A

Ventilation and capillary blood flow are normal, gas exchange is optimal

86
Q

Normal inspired air partial pressures—PO2 ___ mmHg PCO2 ___ mmHg

A 
PO2 = 150 mmHg
PCO2 = 0 mmHg
87
Q

Normal venous blood partial pressures—PO2 ___ mmHg PCO2 ___ mmHg

A 
PO2 = 40 mmHg
PCO2 = 45 mmHg
88
Q

Normal alveolar partial pressures—Alveolar PO2 is ___ mmHg

A

100 mmHg

89
Q

Normal alveolar partial pressures—Alveolar PCO2 is ___ mmHg

A

40 mmHg

90
Q

Physiologic shunt—V/Q is ___

A

Below normal

91
Q

Shunt =

A

Perfusion but no ventilation (i.e.: airway obstruction)

92
Q

In a physiologic shunt, blood is being shunted from pulmonary ___ to pulmonary ___ without…

A

Pulmonary artery to pulmonary vein without participating in gas exchange

There is inadequate ventilation with a fraction of deoxygenated blood passing through capillaries and not becoming oxygenated

93
Q

Shunted blood is not ___

A

Oxygenated

94
Q

Physiologic shunt is total amount of…

A

Shunted blood per minute

95
Q

The greater the physiologic shunt, the greater the amount of…

A

Blood that fails to be oxygenated in the lungs

96
Q

Physiologic dead space—V/Q is…

A

Greater than normal

97
Q

Dead space =

A

Ventilation but no perfusion—ventilation to alveoli is good, but blood flow is low

More available oxygen in alveoli than can be transported away by flowing blood

98
Q

Physiologic dead space includes (2 things):

A
  • Wasted ventilation

- Anatomical dead space

99
Q

When physiologic dead space is great, much of the work of breathing is ___ because ventilated air ___

A

Wasted effort because ventilated air does not reach the blood

100
Q

V/Q is below normal in…

A

Physiologic shunt

101
Q

V/Q is greater than normal in…

A

Physiologic dead space

DNURS 827 Advanced Physiology/Pathophysiology for Anesthesia I (11 decks)

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