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Pulm > Lec 2-3 Gas Exchange > Flashcards

Lec 2-3 Gas Exchange Flashcards

1
Q

What is minute ventilation?

step1

A

volume of gas moved through nose/mouth in one minute

Ve = Vt * RR

Vt = tidal volume = volume/breath
RR = respiratory rate
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2
Q

What is normal tidal volume?

step1

A

500 ml

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3
Q

what is normal respiratory rate?

A

12-14 breaths/min

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4
Q

What are the 2 equations for minute ventilation?

A

Ve = Vt * RR = tidal vol * resp rate

Ve = VA [alveolar] + Vd [dead space]

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5
Q

What is the equation for alveolar ventilation?

step1

A

VA = (Vt - Vd)*RR

=( tidal - dead space) * resp rate

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6
Q

What is dead space ventilation?

A

the portion of minute ventilation that does not participate in gas exchange = wasted ventilation

due to anatomic +/- functional dead space

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7
Q

What is alveolar ventilation?

A

the portion of minute ventilation that does participate in gas exchagne

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8
Q

What is anatomic dead space?

A

the volume of the respiratory tract that does not participate in gas exchange = conduction zone

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9
Q

What is normal anatomic dead space?

step1

A

150 mL [1/3 of tidal volume]

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10
Q

What is functional dead space?

step1

A

the wasted ventilation that occurs when alveoli are ventilated but not perfused so cannot participate in gas exchange

due to pulm embolism or other block in blood flow to that portion of the lung

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11
Q

What is the physiologic dead space?

step1

A

physiologic dead space = anatomic dead space + functional dead space

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12
Q

What is normal functional dead space?

A

0 in normal person; higher in disease state

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13
Q

How can you measure dead space?

step1

A

measure difference between O2 in expired air compared to pure alveolar air

use arterioal PCO2 to stand in for PaCO2

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14
Q

What is equation for dead space?

step1

A

Vd = Vt * (PaCO2 - PECO2) / PaCO2

PaCO2 = arterial PCO2
PECO2 = expired PCO2
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15
Q

What is equation for Vd/Vt ratio?

A

Vd/Vt = (PaCO2 - PeCO2 ) / PaCO2

PaCO2 = arterial PCO2
PECO2 = expired PCO2
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16
Q

What is the alveolar ventilation equation in terms of rate of CO2 production etc?

A

VA = VCo2 * K / PACO2
conversely:
PACO2 = VCO2 * K / VA

K = contant 863 for BTPS

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17
Q

What is relationship PACO2 and VA?

A

PACO2 = CO2 in alveoli

is inversely proportional to

VA = ventilation to alveoli

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18
Q

What happens if VCO2 doubles in strenuous exercise?

A

only way to maintain normal PACO2 is for VA to double also

–> when VA is doubled; PACO2 is halved

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19
Q

What is the alveolar gas equation?

step1

A

PAO2 = PIo2 - PaCO2/R

PAO2 = alveolar PO2
PIO2 = PO2 in inspired air
PaCO2 = arterial PCO2
R = respiratory quotient = CO2 produced/O2 consumed
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20
Q

What is PIO2? How do you determine it?

step1

A

PIO2 = FIO2 * (Pb - PH2O)

PIO2 = PO2 in inspired air
FIO2 = fraction of O2 in inspired air [normal = 0.21]
Pb = barometric pressure [normal = 760]
PH2O = pressure of water [normal = 47]
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21
Q

What is normal value for PIO2?

step1

A

150

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22
Q

What is respiratory quotient? Normal value?

step1

A

R = CO2 production / O2 consumption

normal = 0.8

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23
Q

What is normal PH2O in air?

A

47

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24
Q

What happens to PACo2 and PAO2 if alveolar ventilation is halved?

A
  • PACO2 is doubled

- PAO2 is reduced

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25
Q

A man has a rate of CO2 production that is 80% of rate of O2 consumption. If his arterial PCO2 = 40 mmHg and PO2 in humidified tracheal air is 150 mmHg, what is his alveolar PO2?

A

PAO2 = inspired - PACO2 / R

= 150 - 50 = 100 mmHg

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26
Q

With each inspiration, where does the air go?

A

pre-inspiration have 150mL old gas in dead space

when you inspire

  • -> that 150 mL old gas goes to alveoli
  • -> have 300 new mL fresh air that go to alveoli
  • -> have 150 mL fresh air in dead space
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27
Q

What is normal PaCO2?

A

40 = realtively constant

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28
Q

What does hypoventialtion do to arterial PaCO2?

A

increases it

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29
Q

What does hyperventilation do to arterial PaCO2?

A

decreases it

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30
Q

What will pulmonary embolism do to PaCO2?

A

in most people remains normal even though we would have expected an increased due to wasted ventilation

b/c most individuals with PE will increase total minute ventilation to adjust for the increased dead space –> can maintain normal alveolar ventilation but appear tachypneic

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31
Q

How is ventilation distributed in the lungs?

A

more ventilation to alveoli at bottom [when standing/sitting]

  • due to difference in intrapleural pressure at bottom of long
  • these differences are due to gravity
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32
Q

Where does functional residual capacity of lung mostly reside?

A

in apex of lung

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33
Q

What are the 3 zones of perfusion? their order of hydrostatic pressures Pa [arterial] vs PA [alveolar] vs Pv [venous]?

A

zone 1 = apex
PA > Pa > Pv

zone 2 = middle
Pa > PA > Pv

zone 3 = base
Pa > Pv > PA

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34
Q

What is intrapleural pressure at top vs bottom of lungs?

A 
top = -10 cm H20
bottom = -2cm H2O

avleoli at apex = more distended than at base

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35
Q

What is positive pressure in lungs? negative?

A

positive = outwardly directed distending pressure

negative = inwardly directed collapsing pressure

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36
Q

Are alveoli in lung apex or base bigger?

A

bigger in apex due to difference in pleural pressure + b/c base = compressed by weight of lung above = slinky model

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37
Q

What is PO2 and PCo2 of blood as it enters the pulmonary arteries?

A

this is mixed venous blood
PO2 = 40
PCO2 = 46
oxyhemoglobin sat = 75%

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38
Q

What are unique aspects of pulm vasculature that allow it receive more blood flow in exercise without increasing resistance?

A
  • distensibility = more distensible than ystemic, less smooth muscle
  • recruitability = in normal resting state lots of pulm vascular bed not being used so can recruit when needed
  • capacity for vasodilation
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39
Q

Does pulm arterial pressure rise after a pneumonectomy?

A

nope! this is a sign of the extreme capability for recruiting new vessels

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40
Q

What is V/Q at apex of lung?

step1

A

3 = wasted ventilation

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41
Q

What is V/Q at base of lung?

Step1

A

0.6 = wasted perfusion

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42
Q

Where is greatest ventilation in lung? what about perfusion?

step1

A

both ventilation and perfusion are greater at the base of the lung than the apex

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43
Q

What is V/Q in airway obstruction?

step1

A

approaches 0 = shunt

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44
Q

What is V/Q in blood flow obstruction?

step1

A

approaches infinity = physiologic dead space

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45
Q

What is relationship Pa and Pv in healthy lung?

A

Pa always > > Pv

pulm arterial hydrostatic P is always greater than pulm venous P in healthy lung

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46
Q

Why is alveolar pressure higher than pulm artery pressure in zone 1 of lung?

A

the pulm artery pressure is insufficient to reach/perfuse the top part of the lung

little blood flow

47
Q

What determines blood flow in zone 2?

A

perfusion pressure = Parterry - Palveoi

48
Q

What part of lung has highest V/Q? Why?

A

highest V/Q in zone 1

because regional variations in ventilation arent as great as regional variations in perfusion

49
Q

What part of lung has highest PaO2?

A

zone 1

50
Q

What part of lung has highest PaCO2?

A

zone 3

51
Q

What is PCO2 and PO2 in pulmonary veins?

A 
PaCO2 = 40 mmHg
PaO2 = 100 mmHg
52
Q

What is normal alveolar ventilation?

A

4 LPM

53
Q

What is normal lung perfusion?

A

5 LPM

54
Q

What is normal avg V/Q ratio?

A

0.8

55
Q

What does high V/Q mean?

A

high ventilation relative to perfusion
blood flow decreased; pulm capillary blood from this region has high O2 and low CO2

alveolar gas looks like inspired air [PAO2 = 150; PACO2 = 0]

== dead space

56
Q

What does low V/Q mean?

A

low ventilation relative to perfusion
ventilation decreased
pulmonary capillary blood has low PO2 and high PCO2

=== shunt

57
Q

What is PAO2/PACO2/PaO2/PaCO2 in high V/Q?

A

PAO2 = 150; PACO2 = 0 reflect outside air = no gas exchange b/c not enough perfusion

PaO2/PaCO2 = not applicable b/c no blood flow

== dead space

58
Q

What is PAO2/PACO2/PaO2/PaCO2 in low V/Q?

A

PAO2/PCO2 = not applicable b/c no ventilation

PaO2 = 40; PaCO2 = 46; reflect same as mixed venous blood b/c no gas exchange

== shunt

59
Q

What is the A-a gradient? normal value

A

PAO2 - Pao2 = alveolar - arterial

normally PaO2 is slightly lower than we would calculate if we did alveolar gas equation

normally = 10-15 mmHg

60
Q

When do you get high A-a gradient?

A

hypoxemia due to shunting, V/Q mismatch, fibrosis [impaired diffusion], etc

61
Q

What is PO2 in each of the following places:

  • dry inspired air
  • humidified tracheal air
  • alveolar air
  • mixed venous blood in pulm artery
  • systemic arterial blood in pulm vein
A
  • dry inspired air = 160
  • humidified tracheal air = 250
  • alveolar air = 100
  • mixed venous blood in pulm artery = 40
  • systemic arterial blood in pulm vein = 100
62
Q

What is PAO2/PACO2 in alveoli?

A 
PO2 = 100
PCO2 = 40
63
Q

What is PvO2/PvCO2 in mixed venous blood?

A 
PO2 = 40
PCO2 = 46
64
Q

What is PaO2/PaCO2 in systemic arterial bloodi?

A 
PO2 = 100
PCO2 = 40
65
Q

What is PO2/PCO2 in peripheral tissue?

A 
PO2 = 40
PCO2 = 46
66
Q

What is fick’s law of diffusion?

A

rate of transfer of gas by diffusion directly proportional to:

  • driving force [partial P dif]
  • diffusion coefficient
  • surface area available

inversely to:
- thickness of membrane barrier

67
Q

What is measured by pulse ox?

A

SAO2% = oxyhemoglobin saturation percent

measures the O2 loading onto hemoglobin in arterial blood

usually correlates with the O2 content of blood

BUT: assumes normal amount of normally functioning hemoglobin

68
Q

What is the relationship of PO2 to SaO2?

A

described by the hemoglobin saturation curve

69
Q

What factors shift hemoglobin curve to the right?

A

acidemia
2, 3 DPG
hyperthermia

70
Q

What are the rules for using PO2 and SAO2 in clinic?

A
  1. changes in PO2 above 60 mmHg usually not of therapeutic significance EXCEPT changes in PO2 may reflect significant alteration in lung function and may help diagnose
  2. changes in SaO2 from high 90s to low 90s are of diagnostic signifiance; may reflect significantly increased A-a even though may not have much therapeutic significance
71
Q

What does it mean that we have “perfusion limited gas exchange”

A

total amount of gas transported across alveoli/capillary barrier is limited by blood flow [perfusion]

only way to increase amount of gas transported is to increase blood flow

72
Q

Where in capillary do O2 partial pressures equilibrate with those in alveoli?

A

within first 1/3 of capillary

73
Q

What is diffusion limited gas exchange?

A

total amount of gas transported across barrier is limited by diffusion

as long as partial pressure gradient is maintained, diffusion wlll continue along length of cpaillary

74
Q

What types of gas are perfusion limited?

A

O2 under normal conditions

CO2

75
Q

What types of gas are diffusion limited?

A

CO [binds to Hb]

transport of O2 during exercise [have increased blood flow]

76
Q

What happens to oxygen diffusion in emphysema?

A

becomes diffusion-limited

lack of adequate surface area for normal diffusion

77
Q

What happens to oxygen diffusion in pulmonary fibrosis?

A

thickening of alveolar capillary barrier –> increased distance for diffusion –> slow rate of diffusion –> prevents equilibration

78
Q

How much of O2 in blood is free in solution/dissolved?

A

2% of total O2 content in blood

79
Q

What is henry’s law ?

A

Conc = Pressure * solubility

80
Q

What is solubility of O2?

A

0.003 mL O2/100 mL blood / mmHg

81
Q

What is normal conc of dissolved O2?

A

0.3 mL

82
Q

How much of O2 in blod in bound to HbA?

A

98% of O2 content of blood

each Hb bind 4 O2 molec

83
Q

How much O2 can 1 gm of HbA bind when 100% saturated?

step1

A

1.34 mL 02

84
Q

What is the O2 binding capacity of blood? equation? normal?

step1

A

binding capacity = Hb conc [gm/dL] * 1.34 mL O2/gm

normal = 20.1 mL O2/dL

85
Q

What is equation for O2 content of blood?

step1

A

O2 content = O2 bound to HbA + dissolved O2

= Hb conc * 1.34 * % saturation + dissolved O2

86
Q

How much Hb normally in blood?

step1

A

15 g/dL

87
Q

At what level of deoxygenated Hb do you get cyanosis?

step1

A

when > 5g/dL Hb deoxygenated

88
Q

If amount of Hb decreases how are the following affected

  • O2 content of arterial blood
  • O2 sat
  • arterial PO2

step1

A

O2 content of arterial blood decreases

O2 sat and arterial PO2 do not

89
Q

What is O2 content of the blood of a patient with anemia (Hb 10 gm/dL)?

Assuming normal lungs hence normal PAO2 of 100 mmHg and normal PaO2 of 100 mmHg

Hb is 98% saturated at PaO2 of 100 mmHg

A

O2 bound to Hb = 10 gm/dL x 1.34 mL O2 / gm Hb X 98% (saturation) = 13.1 mL O2/100 mL blood

Total O2 content = above value + dissolved O2

Dissolved O2 = PaO2 X solu = 100 mmHg X 0.003 mL O2/100 mL/mmHg = 0.3 mL O2/100 mL blood

Total O2 content = sum of above two = 13.1 + 0.3 = 13.4 mL O2/100 mL blood

90
Q

What is equation for O2 delivery to tissues?

A

O2 deliver = blood flow * O2 content of blood

== CO * (O2 bound Hb + dissolved O2)

91
Q

What happens to each of the following in CO poisoning

  • Hb level
  • %O2 sat
  • dissolved O2 [PaO2]
  • total O2 content
A
  • Hb level: same
  • %O2 sat: decrease [CO competes wtih O2]
  • dissolved O2 [PaO2]: same
  • total O2 content: decrease
92
Q

What happens to each of the following in polycythemia

  • Hb level
  • %O2 sat
  • dissolved O2 [PaO2]
  • total O2 content
A
  • Hb level: increase
  • %O2 sat: normal
  • dissolved O2 [PaO2]: normal
  • total O2 content: increase
93
Q

What happens to each of the following in anemia

  • Hb level
  • %O2 sat
  • dissolved O2 [PaO2]
  • total O2 content
A
  • Hb level: decrease
  • %O2 sat: same
  • dissolved O2 [PaO2]: same
  • total O2 content: decrease
94
Q

What is P50?

A

PO2 at which Hb is 50% saturated

usually 25 mmHg

95
Q

What things shift O2-Hb dissociation curve to the right? hint. first aid mnemonic

step1

A

BAT ACE

  • BPG
  • altitude
  • temperature [increase]
  • acid [H+]
  • CO2
  • exercise
96
Q

What does a shift to the right in Hb curve mean?

step1

A
  • decreased affinity of Hb for O2
  • increase in P50
  • O2 unloading is facilitated
97
Q

What is 2,3 BPG?

step1

A

byproduct of glycolysis in RBC

under hypoxic conditions, binds Hb and reduces affinity for O2

98
Q

What does a shift to the left in Hb curve mean?

step1

A
  • increased affinity of Hb for O2
  • decrease in P50
  • decreased unloading of O2 to tissues
99
Q

How does fetal Hb differ from O2?

step1

A
  • higher affinity for O2 than adult Hb

- dissociation curve is shifted left

100
Q

How does CO affect Hb O2 dissociation curve?

step1

A

CO has much higher affinity for Hb than O2

presence of CO decreases available units to bind with O2

shift left in binding curve

101
Q

What is hypoxemia?

step1

A

decrease in arterial PaO2?

102
Q

What is hypoxia?

step1

A

decrease O2 delivery to tissue

103
Q

What is ischemia?

step1

A

loss of blood flow

104
Q

How do each of the following change in high altitude:

  • paO2
  • A-a gradient
  • effect of supplemental O2
A
  • paO2: decrease = hypoxemia
  • A-a gradient: normal
  • effect of supplemental O2: improves
105
Q

How do each of the following change in hypoventilation:

  • paO2
  • A-a gradient
  • effect of supplemental O2
A
  • paO2: decrease = hypoxemia
  • A-a gradient: normal
  • effect of supplemental O2: improves
106
Q

How do each of the following change in diffusion defect:

  • paO2
  • A-a gradient
  • effect of supplemental O2
A
  • paO2: decrease = hypoxemia
  • A-a gradient: increase
  • effect of supplemental O2: improves
107
Q

How do each of the following change in V/Q defect:

  • paO2
  • A-a gradient
  • effect of supplemental O2
A
  • paO2: decrease = hypoxemia
  • A-a gradient: increase
  • effect of supplemental O2: improves
108
Q

How do each of the following change in R–> L shunt:

  • paO2
  • A-a gradient
  • effect of supplemental O2
A
  • paO2: decrease = hypoxemia
  • A-a gradient: increase
  • effect of supplemental O2: does not improve
109
Q

How does high altitude affect O2?

A

low barometric pressure –> decreased PIO2 –> decrease PAO2

normal diffusion –> normal A-a gradient

giving extra O2 increases PIO2 and improves

110
Q

How does hypoventilation affect O2?

A

decreases alveolar PAO2

supplemental O2 will improve

111
Q

What is effect of giving extra O2 on pt with R to L shunt?

A
  • deoxygenated blood mixed with oxygenated “non-shunted” blood and dilutes it

giving supplemental O2 doesnt really help b/c the shunted blood still keeps diluting the normal oxygenated blood

112
Q

How does cyanide poisoning cause hypoxia?

A

decrease O2 utilization by tissues

113
Q

What are some examples of things that cause hypoxia but not hypoxemia?

A
  • decreased cardiac output
  • anemia
  • CO poisoning

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