Lec 2-3 Gas Exchange Flashcards Preview

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Flashcards in Lec 2-3 Gas Exchange Deck (113):
1

What is minute ventilation?

step1

volume of gas moved through nose/mouth in one minute

Ve = Vt * RR

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

2

What is normal tidal volume?

step1

500 ml

3

what is normal respiratory rate?

12-14 breaths/min

4

What are the 2 equations for minute ventilation?

Ve = Vt * RR = tidal vol * resp rate

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

5

What is the equation for alveolar ventilation?

step1

VA = (Vt - Vd)*RR

=( tidal - dead space) * resp rate

6

What is dead space ventilation?

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

due to anatomic +/- functional dead space

7

What is alveolar ventilation?

the portion of minute ventilation that does participate in gas exchagne

8

What is anatomic dead space?

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

9

What is normal anatomic dead space?

step1

150 mL [1/3 of tidal volume]

10

What is functional dead space?

step1

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

11

What is the physiologic dead space?

step1

physiologic dead space = anatomic dead space + functional dead space

12

What is normal functional dead space?

0 in normal person; higher in disease state

13

How can you measure dead space?

step1

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

use arterioal PCO2 to stand in for PaCO2

14

What is equation for dead space?

step1

Vd = Vt * (PaCO2 - PECO2) / PaCO2

PaCO2 = arterial PCO2
PECO2 = expired PCO2

15

What is equation for Vd/Vt ratio?

Vd/Vt = (PaCO2 - PeCO2 ) / PaCO2

PaCO2 = arterial PCO2
PECO2 = expired PCO2

16

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

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

K = contant 863 for BTPS

17

What is relationship PACO2 and VA?

PACO2 = CO2 in alveoli

is inversely proportional to

VA = ventilation to alveoli

18

What happens if VCO2 doubles in strenuous exercise?

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

--> when VA is doubled; PACO2 is halved

19

What is the alveolar gas equation?

step1

PAO2 = PIo2 - PaCO2/R

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

20

What is PIO2? How do you determine it?

step1

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]

21

What is normal value for PIO2?

step1

150

22

What is respiratory quotient? Normal value?

step1

R = CO2 production / O2 consumption

normal = 0.8

23

What is normal PH2O in air?

47

24

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

- PACO2 is doubled
- PAO2 is reduced

25

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?

PAO2 = inspired - PACO2 / R
= 150 - 50 = 100 mmHg

26

With each inspiration, where does the air go?

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

27

What is normal PaCO2?

40 = realtively constant

28

What does hypoventialtion do to arterial PaCO2?

increases it

29

What does hyperventilation do to arterial PaCO2?

decreases it

30

What will pulmonary embolism do to PaCO2?

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

31

How is ventilation distributed in the lungs?

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

32

Where does functional residual capacity of lung mostly reside?

in apex of lung

33

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

zone 1 = apex
PA > Pa > Pv

zone 2 = middle
Pa > PA > Pv

zone 3 = base
Pa > Pv > PA

34

What is intrapleural pressure at top vs bottom of lungs?

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

avleoli at apex = more distended than at base

35

What is positive pressure in lungs? negative?

positive = outwardly directed distending pressure

negative = inwardly directed collapsing pressure

36

Are alveoli in lung apex or base bigger?

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

37

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

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

38

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

- 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

39

Does pulm arterial pressure rise after a pneumonectomy?

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

40

What is V/Q at apex of lung?

step1

3 = wasted ventilation

41

What is V/Q at base of lung?

Step1

0.6 = wasted perfusion

42

Where is greatest ventilation in lung? what about perfusion?

step1

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

43

What is V/Q in airway obstruction?

step1

approaches 0 = shunt

44

What is V/Q in blood flow obstruction?

step1

approaches infinity = physiologic dead space

45

What is relationship Pa and Pv in healthy lung?

Pa always > > Pv

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

46

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

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

little blood flow

47

What determines blood flow in zone 2?

perfusion pressure = Parterry - Palveoi

48

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

highest V/Q in zone 1
because regional variations in ventilation arent as great as regional variations in perfusion

49

What part of lung has highest PaO2?

zone 1

50

What part of lung has highest PaCO2?

zone 3

51

What is PCO2 and PO2 in pulmonary veins?

PaCO2 = 40 mmHg
PaO2 = 100 mmHg

52

What is normal alveolar ventilation?

4 LPM

53

What is normal lung perfusion?

5 LPM

54

What is normal avg V/Q ratio?

0.8

55

What does high V/Q mean?

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

What does low V/Q mean?

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


=== shunt

57

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

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

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

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

What is the A-a gradient? normal value

PAO2 - Pao2 = alveolar - arterial


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

normally = 10-15 mmHg

60

When do you get high A-a gradient?

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

61

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

- 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

What is PAO2/PACO2 in alveoli?

PO2 = 100
PCO2 = 40

63

What is PvO2/PvCO2 in mixed venous blood?

PO2 = 40
PCO2 = 46

64

What is PaO2/PaCO2 in systemic arterial bloodi?

PO2 = 100
PCO2 = 40

65

What is PO2/PCO2 in peripheral tissue?

PO2 = 40
PCO2 = 46

66

What is fick's law of diffusion?

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

What is measured by pulse ox?

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

What is the relationship of PO2 to SaO2?

described by the hemoglobin saturation curve

69

What factors shift hemoglobin curve to the right?

acidemia
2, 3 DPG
hyperthermia

70

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

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

What does it mean that we have "perfusion limited gas exchange"

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

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

within first 1/3 of capillary

73

What is diffusion limited gas exchange?

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

What types of gas are perfusion limited?

O2 under normal conditions
CO2

75

What types of gas are diffusion limited?

CO [binds to Hb]
transport of O2 during exercise [have increased blood flow]

76

What happens to oxygen diffusion in emphysema?

becomes diffusion-limited
lack of adequate surface area for normal diffusion

77

What happens to oxygen diffusion in pulmonary fibrosis?

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

78

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

2% of total O2 content in blood

79

What is henry's law ?

Conc = Pressure * solubility

80

What is solubility of O2?

0.003 mL O2/100 mL blood / mmHg

81

What is normal conc of dissolved O2?

0.3 mL

82

How much of O2 in blod in bound to HbA?

98% of O2 content of blood
each Hb bind 4 O2 molec

83

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

step1

1.34 mL 02

84

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

step1

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

normal = 20.1 mL O2/dL

85

What is equation for O2 content of blood?

step1

O2 content = O2 bound to HbA + dissolved O2
= Hb conc * 1.34 * % saturation + dissolved O2

86

How much Hb normally in blood?

step1

15 g/dL

87

At what level of deoxygenated Hb do you get cyanosis?

step1

when > 5g/dL Hb deoxygenated

88

If amount of Hb decreases how are the following affected

- O2 content of arterial blood
- O2 sat
- arterial PO2

step1

O2 content of arterial blood decreases

O2 sat and arterial PO2 do not

89

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

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

What is equation for O2 delivery to tissues?

O2 deliver = blood flow * O2 content of blood

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

91

What happens to each of the following in CO poisoning

- Hb level
- %O2 sat
- dissolved O2 [PaO2]
- total O2 content

- Hb level: same

- %O2 sat: decrease [CO competes wtih O2]

- dissolved O2 [PaO2]: same

- total O2 content: decrease

92

What happens to each of the following in polycythemia

- Hb level
- %O2 sat
- dissolved O2 [PaO2]
- total O2 content

- Hb level: increase

- %O2 sat: normal

- dissolved O2 [PaO2]: normal

- total O2 content: increase

93

What happens to each of the following in anemia

- Hb level
- %O2 sat
- dissolved O2 [PaO2]
- total O2 content

- Hb level: decrease

- %O2 sat: same

- dissolved O2 [PaO2]: same

- total O2 content: decrease

94

What is P50?

PO2 at which Hb is 50% saturated

usually 25 mmHg

95

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

step1

BAT ACE
- BPG
- altitude
- temperature [increase]

- acid [H+]
- CO2
- exercise

96

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

step1

- decreased affinity of Hb for O2
- increase in P50
- O2 unloading is facilitated

97

What is 2,3 BPG?

step1

byproduct of glycolysis in RBC
under hypoxic conditions, binds Hb and reduces affinity for O2

98

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

step1

- increased affinity of Hb for O2
- decrease in P50
- decreased unloading of O2 to tissues

99

How does fetal Hb differ from O2?

step1

- higher affinity for O2 than adult Hb
- dissociation curve is shifted left

100

How does CO affect Hb O2 dissociation curve?

step1

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

What is hypoxemia?

step1

decrease in arterial PaO2?

102

What is hypoxia?

step1

decrease O2 delivery to tissue

103

What is ischemia?

step1

loss of blood flow

104

How do each of the following change in high altitude:

- paO2
- A-a gradient
- effect of supplemental O2

- paO2: decrease = hypoxemia

- A-a gradient: normal

- effect of supplemental O2: improves

105

How do each of the following change in hypoventilation:

- paO2
- A-a gradient
- effect of supplemental O2

- paO2: decrease = hypoxemia

- A-a gradient: normal

- effect of supplemental O2: improves

106

How do each of the following change in diffusion defect:

- paO2
- A-a gradient
- effect of supplemental O2

- paO2: decrease = hypoxemia

- A-a gradient: increase

- effect of supplemental O2: improves

107

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

- paO2
- A-a gradient
- effect of supplemental O2

- paO2: decrease = hypoxemia

- A-a gradient: increase

- effect of supplemental O2: improves

108

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

- paO2
- A-a gradient
- effect of supplemental O2

- paO2: decrease = hypoxemia

- A-a gradient: increase

- effect of supplemental O2: does not improve

109

How does high altitude affect O2?

low barometric pressure --> decreased PIO2 --> decrease PAO2

normal diffusion --> normal A-a gradient

giving extra O2 increases PIO2 and improves

110

How does hypoventilation affect O2?

decreases alveolar PAO2

supplemental O2 will improve

111

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

- 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

How does cyanide poisoning cause hypoxia?

decrease O2 utilization by tissues

113

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

- decreased cardiac output
- anemia
- CO poisoning