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169 Cards in this Set

  • Front
  • Back
Where in the lund is the better ventilation?
at the base
The intrapleural pressure at the lung apex is what compare to the base?
WHY?
The intrapleural pressure at the lung apex is less (more negative) than the
intrapleural pressure at the lung base, thus there is a pressure
gradient.

The reasons for this regional pressure gradient are due to the
effects of gravity on the lung and the weight of the lungs
suspended within the thoracic cavity. The consequence is that the
alveoli at the apex of the lungs are subject to greater distending
force (transpulmonary pressure) than those alveoli at the base of
the lungs, thus the aveoli at the base of the lungs are better
ventilated. However, the effect of this distending force on alveoli
size also depends on the lung volumes (i.e. TLC, FRC, RV)
Where is a greater distending force in the lung?
Greater distending force at apex than at
base of lung.
where is alveolar ventilation (VA)
during normal quite breathing is greatest ?
we can see that alveolar ventilation (VA)
during normal quite breathing is greatest at the base of the lung
(especially at FRC)
Is there an actual difference between VA at
the base and VA at the apex?
Dpend on what?
Alveolar ventilation (VA)
during normal quite breathing is greatest at the base of the lung
(especially at FRC). However, the actual difference between VA at
the base and VA at the apex will vary depending on the actual lung
volume.
Where is the transpulmonary P the highest in the lung?
at the apex
Where is in the lung the
Intrapleural pressure is more
negative?
at the apex of the lung
Where is during ventilation the
Greater transmural pressure
gradient
at the apex of the lung
Where is during ventilation the
Alveoli are larger, and less
compliant
at the apex of the lung
Where is during ventilation the
Less Ventilation
at the apex of the lung
Where is during ventilation the
Intrapleural pressure is less
negative
at the base of the lung
Where is during ventilation the
Smaller transmural pressure
gradient
at the base of the lung
Where is during ventilation the
Alveoli are smaller, and more
compliant
at the base of the lung
Where is during ventilation the
More Ventilation
at the base of the lung
What is the Nitrogen Washout Test for?
Explain the test!
Determination of Regional Ventilation
to depict the uneven ventilation
associated with the various regions of the lung.

In this method,
a single breath of 100% oxygen is inspired (to TLC). This is
followed by expiration (to RV) and monitoring of the amount of
nitrogen that is exhaled. Since the base of the lungs is better
ventilated than the apex of the lungs, most of the inhaled
oxygen will make its way into the anatomical dead space and then
into the alveoli at the base of the lung. As a consequence a
higher percentage of the nitrogen can be found in the alveoli at
the apex of the lungs. (Note that from Dalton’s Law of Partial
Pressure, the 100% inspired oxygen displaces the nitrogen more
at the base of the lung than at the apex.)
On expiration, the initial portion of exhaled air (phase i) does
not contain much nitrogen (mainly oxygen from the anatomical
dead space). The next portion of exhaled air (phase ii) shows an
increasing amount of nitrogen exhaled and represents a
decreasing contribution of oxygen from the anatomical dead space
gas and an increasing contribution of nitrogen from alveolar
gas. The third portion of exhaled air (phase iii or the alveolar
plateau phase) represents nitrogen from alveolar gas at the base
of the lungs, since this area is better ventilated. As the
expiratory effort approaches RV, dynamic compression begins to
close airways (closing capacity) to the alveoli at the base of
lungs and more air is being contributed by the nitrogen rich
alveoli at the apex of the lungs. Thus, the final portion of
exhaled air (phase iv) is characterized by a rapidly increasing
percentage of nitrogen.
How do you determine the Regional Ventilation?
Nitrogen Washout test
What is closing capacity?
Where N2 will increase due to the fact it is closer to RV (apex) and dynamic compresison close airways to the alveoli at the base of the lung and more air contributed by the nitrogen rich
alveoli at the apex of the lungs.
Local Lung Ventilation depends on what?
1) Lung Compliance and 2)
Airway Resistance
HOw do you calculate the time constant?
Time constant = Resistance * Compliance (T = R * C)
HOw do you calculate the Total Ventilation?
Total Ventilation is the total volume of air into and out of the
airways and lungs over a certain period of time. (V = f * TV)
Define Alveolar Ventilation, hhow do you calculate it?
is the volume of air into and out of the
lungs over a certain period of time and can be calculated by
either of the following equations.
VA=f*(TV-V0) or
VA=(VCO2/PaCO2)* K
Velocity of air through the respiratory passages is related to....
the pressure. If the pressure increases, then velocity
increases. If the pressure decreases, then velocity decreases.
Velocity of air through the respiratory passages also depends on
the total cross-sectional area (V 1/A).
V=Q/A
If the total cross-sectional area
increases, the velocity of air in the
respiratory passages decreases.
What is the velocity from the trachea to the alveolar duct?
If the total cross-sectional area
increases, the velocity of air in the
respiratory passages decreases.
Highest velocity at the trachea, then it decreases as you go down to the level of the respiratory bronchioles, and from there the velocity will be determined by diffusion.
From the respiratory bronchioles on down, the what determines the velocity?
process of
diffusion
List the 7 steps of inspiration in order
1. Inspiratory muscles contract.
2. Thoracic cavity expands.
3. Pleural Pressure (Ppl) becomes more negative.
4. Transpulmonary pressure increases.
5. The lung fills with air.
6. Alveolar pressure (PA) becomes subatmospheric.
7. Air flows into the lungs until
List the 7 steps of expiration in order
1. Inspiratory muscles relax.
2. Rib cage drops.
3. Pleural Pressure (Ppl) becomes less negative.
4. Transpulmonary pressure decreases.
5. The lung empties its air.
6. Alveolar pressure (PA) becomes greater than barometric
pressure.
7. Air flows out of the lungs until the alveolar pressure equals
the barometric pressure.
What are the 2 effects of gravity on alveolar ventilation?
There is regional and
local affects (history of lung)
Alveolar ventilation depends on 2 things; what r they?
regional variations (gravity)
and local variations (R and C)
What is the pleural P gradient throughout in the lung and due to what?
Apex= -10 H2O
Middle = -5 H2O
Base= -2.5 H2O
Where is a greater distending force in the lung?
at the apex is greater than at the base

The reasons for this regional pressure gradient are due to the
effects of gravity on the lung and the weight of the lungs
suspended within the thoracic cavity. The consequence is that the
alveoli at the apex of the lungs are subject to greater distending
force (transpulmonary pressure) than those alveoli at the base of
the lungs, thus the aveoli at the base of the lungs are better
ventilated. However, the effect of this distending force on alveoli
size also depends on the lung volumes (i.e. TLC, FRC, RV).
transpulmonary P througout the lungs
Apex= +10 H2O
Middle = +5 H2O
Base= +2.5 H2O
What is the size of the alveoli at TLC? What about transp P and Lung volume?
At TLC alveoli at the apex and at the base are the same, no difference, both places the alveolies are expanded to max. so their ventialltion is the same/max at TLC. At TLS the transpulmonary P and the lung volume the highest.
What is the size of the alveoli at FRC? What about transp P and Lung volume?
The alveoli expands more at the apex than at the base. P(trans) and is in middle same as lung volume. At FRC the ventillatin will be better at the apex.
What is the size of the alveoli at RV? What about transp P and Lung volume?
At RV the ventialtion is better at the apex, because lung volume decreased to min at Rv and P transp is also decreased in the base. Alveoli at the base at RV will close/collapse and will be smaller than at the apex.
where does a big breath of O2 goes first?
to the base and then dead space.
How many stages are there in the N washout test? How does it work? What does it tell you about?
It tells you about the regional ventilation distribution and you measure N2.
Take a deep breath 100% O2 from RV to TLC! do a complete VC and blow out.
1st stage i is from TLC mainly O2 from anatomical dead space, stage 2 ii is a transitory zone shows an
increasing amount of nitrogen exhaled and represents a
decreasing contribution of oxygen from the anatomical dead space
gas and an increasing contribution of nitrogen from alveolar
gas..
stage 3 iii is alveolar platoe. By the end of iii N2 will rise as it reaches the Closing capacity and getting closer to RV.
The final portion of
exhaled air (phase iv) is characterized by a rapidly increasing
percentage of nitrogen. At RV the air coming from the apex due to alveoli at the base closes as lung volume decreases. After cc the ventilation is from the apex.
How do you calculate the CC?
CV+RV= CC
With increasing age what happens to CC and CV?
With age cc and cv move away from RV and CC will occur at higher lung volumes, you also see that with small way obstructions. CC goes up earlier.
Effects of age on lung volumes
As you age you lose elasticity. If you lose elastic tissue, RV and FRC increases. Rib cage become stiffer. You will see shift in the compliance curves.
Shift upward due to increased C, but due to Cw decreased C. So FRC will move up!
Older people ventilate more with apex of the lung than younger people.
RV, FRC will increase.
CC, CV increase a lot
ERV, IC, VC, FEV1, FEF25-75% will decrease.
TLC should be the same if adjusted for height.
If you decrease C what happens to alveolar ventilation time? R?
time to fill the alveoli with air will be decreased
If you increase R what happens to alveolar ventilation time? C?
time to fill the alveoli with air will be increased
During the breathing cycle when is P (trans) the highest?
End of inspiration/ before expiration
During the breathing cycle when is P (trans) the lowest?
End of expiration/before inspiration
During the breathing cycle when is P alveoli the lowest?
during in the process of inspiration
During the breathing cycle when is alveolar P the highest?
during in the process of expiration
During the breathing cycle when is P pleural the lowest?
end of inpiration/ before expiration
During the breathing cycle when is P pleural the highest ?
end of expiration/ before inspiration
What is recruitment?
Resistance in the pulmonary vasculature can be altered by
increasing (recruitment) or decreasing the number of blood
vessels that blood actually goes through or by increasing or
decreasing the radius of the pulmonary vessels (distention).
Distension is not to be confused with vasodilation.
What is distension?
Resistance in the pulmonary vasculature can be altered by
increasing (recruitment) or decreasing the number of blood
vessels that blood actually goes through or by increasing or
decreasing the radius of the pulmonary vessels (distention).
Distension is not to be confused with vasodilation.
The pulmonary vasculature is a_____ resistance capillary
network of ____blood vessels.
low
highly distensible
Resistance in the pulmonary vasculature can be altered by what?
Resistance in the pulmonary vasculature can be altered by
increasing (recruitment) or decreasing the number of blood
vessels that blood actually goes through or by increasing or
decreasing the radius of the pulmonary vessels (distention).
Distension is not to be confused with vasodilation.
Contraction of smooth muscle provides for _______
resistance.
increased
constriction ability (based
on amount of smooth muscle) of pulmonary arterioles is ______than the systemic arterioles.
less
shape of the Systemic blood vessels?
round
shape of the pulmonary blood vessels?
(since they are more distensible) are
ribbon shaped (sheets of blood in flattened vessels) and
hence are better able to accommodate the shape of the alveoli
for optimal gas exchange than systemic ones.
An oxygen molecule in the diffusion process passes
through.....
1. alveolar epithelium– apical & basement membranes
2. interstitial fluid
3. blood vessel endothelium- basement & apical membranes
In the adult, the surface area for exchange of gases is
between ____?
50 and 70 m2
the size of the blood vessel can vary
depending on what 2 things?
intravascular and intraalveolar pressures.
What is radial traction?
As lung volume increases, the alveoli vessel diameter increases.

As the lungs fill with air, there is initially a decrease in
pulmonary vascular resistance due to radial traction applied
to the extraalveolar vessels.
As the lung fills with air, how is the extra/intra-alveoli vessels react?
As the lungs fill with air, there is initially a decrease in
pulmonary vascular resistance due to radial traction applied
to the extraalveolar vessels. IN the extra alveolar vessels the diameter increases as lung/alveoli volume increases, and R and P decreases, However, as the lungs continue
to fill with air there is a consequent increase in pulmonary
vascular resistance as the (intra)alveolar vessels are compressed by
the filled alveoli. So in the intra alveoli vessels the diameter decreases as alveoli volume increases and P and R increases as the alveoli fills with air.
draw the diagram of R vs Lung volume for alveolar, extraalveolar vessels and their total curve.
(lecture 6-slide 7)
Where is the pulm vasculature R is the lowest?
AT FRC!
Where is the pulm vasculature R is the highest?
at RV
Where is the extraalveolar vessels R is the highest?
at RV
Where is the extraalveolar vessels R is the lowest?
TLC (after FRC to TLC)
Where is the (intra)alveolar vessels R is the highest?
TLC
Where is the (intra)alveolar vessels R is the lowest?
at RV
Where do you do the least amount of work?
FRC
As lung volume increases, how is pulmonaru vascular R changes?
R will initally decrease (from RV) to FRC (lowest) than increases to TLC.
Where is the lung getting blood from?
99% from the pulmonary artery and 1 % from the bronchial arteries.
what kind of blood is in the pulmonary veins?
mixed blood due to deO2 blood from the bronchial artery is going back to the circulation/heart
where is the best perfusion in the lung?
at the base
Hypothetical blood flow in the lungs. What are the zones? What are the rules?
Rules: Assumptions:
1.Assume that the lungs can be divided into three zones
2. In addition, assume that the alveolar pressure is the same (7 mm Hg of positive pressure) throughout the lung.
3. Assume that blood enters and exits the lung in the exact
middle and the pulmonary arteriole pressure = 15 mm Hg and the pulmonary venule pressure = 5 mm Hg.
4. Between the middle region of the lung and the Apex = 13 cm.
Between the middle region of the lung and the Base = 13 cm.
Due to gravity, 13 cm of blood = 10 mm Hg
Zone A: apex of the lung. No flow. P alveolar> intravascular P. There is flow ONLY with pathological conditions: HypOtns, decrease hemorrhage, increase alveolar P. (increase ventilation). In Zone A the higher alveolar pressure would squeeze the pulmonary
capillary bed so that no blood could get by (no flow). This
condition does not normally exist, but can be simulated in persons
breathing air under extreme positive pressure, such as is the case
in individuals on a ventilator. Zone A condition can also exist if there is a systemic hemorrhage which will ultimately lower
pulmonary vascular pressures.

ZONE C: At the base of the lung. Intravascular P > alveolar P, here are the most distention. In Zone C the lower alveolar pressure would keep the capillaries permanently opened. Flow is proportional to arteriovenous pressure
and resistance can be calculated by the conventional formula. In Zone C, resistance is decreased by recruitment and distention.

Zone B: Alveolar P is btwn arteriolar and venular P. "Water jug Affect" there is some flow here, but less than in Zone C.
In Zone B the alveolar pressure is intermediate between the
arteriole and venule pressures so that the capillaries in this zone fluctuate between being open and being closed. In this case the vascular resistance to flow is not proportional to arteriovenous pressure difference, since the venous pressure has no influence on flow. In Zone B, resistance is decreased primarily by recruitment.
What kind of flow do you have in the lung when you lay down?
Zone B, same flow everywhere
What is an an anatomical shunt?
the Aortic blood (which is destined for systemic
circulation) is contaminated with unoxygenated blood (mixed
venous blood) due to input of deO2 blood from the bronchial artery. This is referred to as an anatomical shunt.
systolic pressure in the pulmonary
artery is______
24 mmhg
diastolic pressure is in the pulmonary
artery is______
9 mmhg
pulmonary vascular resistance is ______ than that of the systemic vascular resistance.
less (about
1/10th)
Perfusion in the lung is affected by what?
gravity and ventilation it is best at the base of the lungs.
perfusion is highest where and why?
Because resistance to blood flow varies inversely with vessel
caliber, resistance decreases and blood flow (Q) increases in the
apex-to-base direction. Thus, perfusion is highest at the base of
the lung.
what is the fick's principle?
Pulmonary Blood flow can be determined with it.
Q= q/ (O2pv-O2pa)
Q-flow of blood (perfusion)
q-rate of oxygen consumed by the lungs
increasing the number of blood vessels in the pulmonary vasculature where blood goes through is called ....
(recruitment)
increasing the radius of blood vessels in the pulmonary vasculature where blood goes through is called ....
distention
What regulates the pulmonary circulation?
Autonimics/baro and chemo-receptors
What innervates the pulmonary blood
vessels?
The autonomic nervous system
The pulmonary arterioles are innervated by----
parasympathetic
(vagus-release of ACH)
induces vasodilation.
and sympathetic nerves which release NE which
interact with alpha or beta receptors. Interaction of NE with
alpha receptors induces vasoconstriction while interaction with
beta receptors induces vasodilation. Alpha receptors predominate
in the pulmonary circulation.
Peripheral chemoreceptor stimulation leads to _
to vasoconstriction
of pulmonary vessels in a reflex manner.
Pheripheral Baroreceptor
stimulation leads to ___ in
to vasodilation of pulmonary vessels in a
reflex manner.
What is the most
important factor influencing pulmonary vascular tone.
Hypoxia or hypoxemia (i.e. low oxygen tension)
Hypoxia
will lead to
to vasoconstriction of pulmonary arterioles in poorly
ventilated alveoli which in turn will minimize the contamination
of pulmonary venous blood with unoxygenated blood.
CNS is not involved.
What dictates if
vasoconstriction will occur in hypoxia?
In
addition, it is the alveolar O2 concentration and not the
pulmonary arterial O2 concentration that dictates if
vasoconstriction will occur. It is possible that hypoxemia may
induce the release of (as of yet) an unknown vasoconstricting
agent
In hypoxic state what happens in the cells?
New evidence suggest that hypoxia may directly inhibit the
outward K+ conductance causing the vascular smooth muscle to
depolarize thus opening voltage gated Ca++ channels which
ultimately leads to contraction of the muscle.
Hypoxia
Depolarization Opens
Ca++ Channels and
Cell Contracts
PAO2 = 100mm Hg
Channel Reduced
Channel Closed
Conductance is decreased
Causes Cell to Depolarize
Graded Response
The Lower the PAO2,
the More Reduction
the More depolarization and
the More Contraction
If PaO2= 100 mmHg
in smooth m cell
Hypoxia
Channel Reduced
Channel Closed
Conductance is decreased
Causes Cell to Depolarize
gK+ is relatively low
Depolarization Opens
Ca++ Channels and
Cell Contracts
If PAO2 = 150mm Hg
in smooth m cell
PAO2 = 150mm Hg
Channel Oxidized
Channel Open
gK+ is relatively high
Ca++ Channel
Closed
l
Water balance in the lungs depends on
Starling*s Law which
states...
Net Fluid Movement = k[(Pc + Oncotic Pi) - (Pi + oncotic Pc)]
k = filtration coefficient, describes the ease of fluid flow
into or out of a vessel.
Pc = capillary hydrostatic pressure
Pi = interstitial fluid hydrostatic pressure
In the lungs, net fluid flow is_
out of the
lungs.
In the lung there is normally a net positive outward movement of
fluid from the blood. This is called_
The consequences of this
outward movement is_
(filtration)
interstitial edema
Fortunately, there are
allot of lymphatics in the lung which remove this outward flow
of fluid. If the lymphatics are backed up or if there is left
heart failure this could lead to 1) interstitial followed by 2)
pulmonary (alveolar) edema.
Increasing O2 tension of inspired air will lead to
decreased Perfusion P
Reduce O2 tension of inspired air
lead to hypoxia and increase in perfusion P.
Blood flow will increase if alveolar PO2 (O2 tension)----?
increases
What are the Starling forces?
Hydrostatic P and Oncotic P
What might happens to Pi in a
Net Fluid = K [(Pc + Bi) - (Pi + Bp)]
Movement filtration absorption
patient with acute respiratory
distress syndrome (ARDS)?
Surface T increases, alveolar P decreases, more fluid results in edema.
Outward movement from the blood increases- result in edema.
Pulmonary oncotic P increases with Pulmonary hydrostatic P
the ratio of alveolar
ventilation to blood flow _____ in the apex to base
direction.
decreases
Where is the best ventilation-perfusion match occurs ?
somewhere
in the middle of the lung.
Va is what in L/ min normally?
Alveolar ventilation = VA = (normally 2 L/min)
Alveolar blood flow (perfusion) in L/min?
2.5 L/min)
VA/Q = ventilation/perfusion ratio normally about what?
0.8
What is the most common cause of
hypoxia?
VA/Q mismatching
A VA/Q ratio that is lower than normal indicates?
that there is
not enough ventilation with respect to perfusion. The blood that
passes through the lungs is therefore said to be "shunted blood"
since it is deficient in oxygen.
define "shunted blood"
A VA/Q ratio that is lower than normal indicates that there is
not enough ventilation with respect to perfusion. The blood that
passes through the lungs is therefore said to be "shunted blood"
since it is deficient in oxygen.
A VA/Q ratio higher than normal indicates__
increased ventilation
with respect to perfusion such that oxygen is said to be
"wasted". An increase in physiological (alveolar)dead space
results when the VA/Q ratio is increased. In the physiological
dead space, ventilation occurs but perfusion (and hence gas
exchange) does not.
oxygen is said to be
"wasted" in some situations, why?
A VA/Q ratio higher than normal indicates increased ventilation
with respect to perfusion such that oxygen is said to be
"wasted". An increase in physiological (alveolar)dead space
results when the VA/Q ratio is increased. In the physiological
dead space, ventilation occurs but perfusion (and hence gas
exchange) does not
Compare V and Q in different locations in the lung.
Both higher at the base but Q>V at the base and V>Q at the apex. So V/Q at the base is small. and V/Q at the apex is higer ratio. So at the base there is larger blood flow with small alveoli, and at the apex large alveoli has less capillaries. So, there are more ventialtion than needed at the apex (some ventillation is wasted), and more blood flow at the base than needed (not enough ventilation).
Both can lead to Hypoxia.
What is mixed venous point?
at the base, decreased ventillation with good flow, decreased V/Q ratio.
O2=40, Co2=45
What is inspired point?
increased ventilation with not enough blood flow/perfusion at the apex of the lung, large V/Q ratio. O2=150 Co2=0
Which has more affect of PP of O2? High V/Q or small V/Q
small V/Q at the base. because venous flow comes in at 14.6, and leaves at 16 ml/100 (normal would be 20ml/100 ml) due to not enough ventilation.
Pt with chronic bronchitis and emphysema is wasting what? Ventilation or perfusion?
there are a lot of wasted ventilation and shunted blood.
But more wasted ventialtion. You get them in different part of the lung.
O2 concentration comes in from veins at 14.6 ml/100ml and leaves to the heart at 20. At the apex where there are higher ventialtion
Why don't you see an increase in PP of O2 in the blood?
Because there are not enough blood vessels/capillaries to increase perfusion, all the Hb in the blood are maxed out, so it does not matter if there are more O2 available.
Actual number actually smaller than normal. 17.9/100 ml
What is inner gap elimination technique?
inject a number of inner gases and you measure V/Q ratios in the different compartments.
Differences of bloof flow and ventialltion curve due to their differences at the apex and at the base.
What is the difference btwn shunt like state and absolute shunt?
in COPD you get shount like state the V/Q is small but not 0, the alveoli are not collapsed.
In absolute shunt the alveoli are collapsed
waisted ventialtion is the same as ___
dead space
name the important respiratory gases found in air and know
the relative amount of each of these gases at sea level.******
Air = 79% N2, 21% O2, < 1% CO2
Barometric pressure = 760 torr at sea level
= 625 torr in Denver
= 250 torr at the top of Mt. Everest
1 torr = 1 mm Hg
5 cm H2O = 3.6 mm Hg
fraction (F) of N2 in air is
0.79
PP of Inspired air
about 150 mm Hg of oxygen and for all
practical purposes, no carbon dioxide.
PP of alveolar air
Alveolar gas contains about
100 mm Hg of oxygen and about 40 mm Hg of carbon dioxide.
Why do these differences in the partial pressures of oxygen
(between inspired and alveolar) exist?
1) PH2O -water vapor displacement
2) in the alveolar, O2 is constantly be removed, going into
the blood.
3) CO2 is constantly being added to the alveolar gas from
the blood.
Water Vapor also has pressure.Why?
1) water added to inspired gases and humidified in the
conducting zone
2) water gas displaces other gases
3) Partial pressure of water is determined solely by
temperature.
at 38oC PH2O = 50 mm Hg
Water vapor P
at 38oC PH2O = 50 mm Hg
fraction (F) of O2 in air is
0.21
fraction (F) of CO2 in air is
< 0.01
Dalton’s Law
The sum of all the gases are equal to barometric
pressure.

Pgas = Fgas * Pb
t do you calculate before the partial pressures of inspired gases (Pigas) can be
determined.
PH2O must be subtracted from the barometric pressure
Pigas = Fgas * (Pb - PH2O)

For O2 and CO2:

PiO2 = 0.21 * (760 - 50) = 149.1 mm Hg
PiCO2 = 0.01 * (760 - 50) = < 7.1 mm Hg
Alveolar- Air or Gas Equation
PAO2 = PiO2 - (PACO2/R) + F
nomogram can be used to determine what?
the partial pressure of
oxygen in the alveoli as well as determine the difference between
the PAO2 and the PaO2.
What is a P(A-a)O2 Gradient?
A small difference between the partial pressure of oxygen in the
alveoli and the partial pressure of oxygen in the systemic arterial
blood exists. This is referred to as the P(A-a)O2 gradient. An
increase in the P(A-a)O2 gradient indicates problems with gas
exchange, possibly a shunt, a diffusion limitation or a low V/Q
ratio.
List of all the Pathophysiological Causes of Hypoxemia and their effect on their A-a gradient
Respiratory
Diffusion impairment-Increased
Physiological shunt- Increased
General hypoventilation -Normal
Regional and local low VA/Q -Increased
Nonrespiratory
Intracardiac right-to-left shunt -Increased
Decreased PIO2, low PB, low FIO2 -Normal
Reduced oxygen content (anemia and CO poisoning- Normal
Anatomical shunt + intrapulmonary shunt
Physiological Shunt
Physiological Shunt
Anatomical shunt + intrapulmonary shunt
Intrapulmonary Shunt
absolute shunt + Shunt like state (i.e. decreased V/Q)

In individuals with intrapulmonary shunts,
PaO2 levels fail to rise to that of normal individuals when 100%
oxygen is administered.
absolute shunt + Shunt like state (i.e. decreased V/Q)
Intrapulmonary Shunt
Determination of Physiological Shunt Fraction
. .
QS/QT =([O2]c - [O2]a)/([O2]c - [O2]v)

.
QS = Shunted blood flow
.
QT = Total blood flow
[O2]c = CCO2 = Pulmonary end capillary O2 content
[O2]a = CaO2 = Systemic arterial O2 content
[O2]v = CVO2 = Mixed venous O2 content
[O2]c = ? ml of blood
[O2]a = ? of blood
[O2]v = ? ml of blood
[O2]c = 20 ml/100 ml of blood
[O2]a = 18 ml/100 ml of blood
[O2]v = 14 ml/100 ml of blood
What is the % shunt of a normal individual?
33% Shunt
In normal individuals, breathing 100% oxygen results in an
elevation of what?
of the PaO2.
In individuals with intrapulmonary shunts,
when 100%
oxygen is administered what happens?
PaO2 levels fail to rise to that of normal individuals
How do you calculate the fraction of absolute shunted blood?
allow patients
to breath 100% O2, then assume that 1% cardiac output is shunted for
every 20 mm Hg of (PA - Pa)O2 gradient.
breathing 100% O2 will separate out what shunts?
breathing 100% O2 will separate out the low V/Q shunt
like states from the absolute shunts. Breathing 100% O2 will allow
even the alveolar units with the real low V/Q ratios to have enough
O2 to saturate the hemoglobin, thereby eliminating any shunt like
state.
What happens with PaO2 and PaCO2 in hypoventilation?
hypoventilation
and diffusion impairment where the PaO2 is depressed but the PaCO2 is
increased.
In individuals with physiological shunts, PaO2 is _____and PaCO2_____

.
depressed

varies from normal to low
What happens with PaO2 in
shunt?
decrease
What happens with PaO2 in
diffusion impairment?
decrease
What happens with PaO2 in
hypoventilation?
decrease
What happens with PaCO2 in
shunt?
N to decrease
What happens with PaCO2 in diffusion impairment?
N to increase
What happens with PaCO2 in
Hypoventilation?
increase
What happens with P(A-a)O2 in shunt?
increase
What happens with P(A-a)O2 in diffusion impairment?
increase
What happens with P(A-a)O2 in Hypoventilation?
no change
What is normal shunt fraction?
8-10% normal
Where do you get the O2a and O2v values from?
blood gas analysis
where do you get the O2c value from?
from alveoli- air equation to calculate PAO2.
Every 1 % shunt equals to what? How do you calculate absolute shunt fraction?
every 1 % shunt equals to 20mmHg of mercury
First calculate (PA02-PaO2)=number/20= % shunt
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases (in atmospheric air/dry air
PO2=160
PCO2=0
in dry air
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
in humidified
air,
PO2=150
PCO2=0
inhumidified air
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
in alveolar air
PO2=100
PCO2=40
in alveolar air
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
in oxygenated blood,
PO2=100
PCO2=40
in oxygenated blood
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
mixed venous blood,
PO2=40
PCO2=46
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
in tissues
PO2=40
PCO2=45
Dalton’s Law of partial pressures and know the
relative partial pressures of the important
respiratory gases
in expired air
PO2=0
PCO2=40