Lec 2-3 Gas Exchange Flashcards
(113 cards)
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
2
Q
What is normal tidal volume?
step1
A
500 ml
3
Q
what is normal respiratory rate?
A
12-14 breaths/min
4
Q
What are the 2 equations for minute ventilation?
A
Ve = Vt * RR = tidal vol * resp rate
Ve = VA [alveolar] + Vd [dead space]
5
Q
What is the equation for alveolar ventilation?
step1
A
VA = (Vt - Vd)*RR
=( tidal - dead space) * resp rate
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
7
Q
What is alveolar ventilation?
A
the portion of minute ventilation that does participate in gas exchagne
8
Q
What is anatomic dead space?
A
the volume of the respiratory tract that does not participate in gas exchange = conduction zone
9
Q
What is normal anatomic dead space?
step1
A
150 mL [1/3 of tidal volume]
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
11
Q
What is the physiologic dead space?
step1
A
physiologic dead space = anatomic dead space + functional dead space
12
Q
What is normal functional dead space?
A
0 in normal person; higher in disease state
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
14
Q
What is equation for dead space?
step1
A
Vd = Vt * (PaCO2 - PECO2) / PaCO2
PaCO2 = arterial PCO2 PECO2 = expired PCO2
15
Q
What is equation for Vd/Vt ratio?
A
Vd/Vt = (PaCO2 - PeCO2 ) / PaCO2
PaCO2 = arterial PCO2 PECO2 = expired PCO2
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
17
Q
What is relationship PACO2 and VA?
A
PACO2 = CO2 in alveoli
is inversely proportional to
VA = ventilation to alveoli
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
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
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]
21
Q
What is normal value for PIO2?
step1
A
150
22
Q
What is respiratory quotient? Normal value?
step1
A
R = CO2 production / O2 consumption
normal = 0.8
23
Q
What is normal PH2O in air?
A
47
24
Q
What happens to PACo2 and PAO2 if alveolar ventilation is halved?
A
- 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
