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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
|
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During the breathing cycle when is P pleural the highest ?
|
end of expiration/ before inspiration
|
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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
|
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Where is the extraalveolar vessels R is the highest?
|
at RV
|
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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
|
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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
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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. |
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absolute shunt + Shunt like state (i.e. decreased V/Q)
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Intrapulmonary Shunt
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Determination of Physiological Shunt Fraction
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. .
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 |
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[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 |
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What is the % shunt of a normal individual?
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33% Shunt
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In normal individuals, breathing 100% oxygen results in an
elevation of what? |
of the PaO2.
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In individuals with intrapulmonary shunts,
when 100% oxygen is administered what happens? |
PaO2 levels fail to rise to that of normal individuals
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How do you calculate the fraction of absolute shunted blood?
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allow patients
to breath 100% O2, then assume that 1% cardiac output is shunted for every 20 mm Hg of (PA - Pa)O2 gradient. |
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breathing 100% O2 will separate out what shunts?
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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. |
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What happens with PaO2 and PaCO2 in hypoventilation?
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hypoventilation
and diffusion impairment where the PaO2 is depressed but the PaCO2 is increased. |
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In individuals with physiological shunts, PaO2 is _____and PaCO2_____
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depressed
varies from normal to low |
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What happens with PaO2 in
shunt? |
decrease
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What happens with PaO2 in
diffusion impairment? |
decrease
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What happens with PaO2 in
hypoventilation? |
decrease
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What happens with PaCO2 in
shunt? |
N to decrease
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What happens with PaCO2 in diffusion impairment?
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N to increase
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What happens with PaCO2 in
Hypoventilation? |
increase
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What happens with P(A-a)O2 in shunt?
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increase
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What happens with P(A-a)O2 in diffusion impairment?
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increase
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What happens with P(A-a)O2 in Hypoventilation?
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no change
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What is normal shunt fraction?
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8-10% normal
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Where do you get the O2a and O2v values from?
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blood gas analysis
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where do you get the O2c value from?
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from alveoli- air equation to calculate PAO2.
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Every 1 % shunt equals to what? How do you calculate absolute shunt fraction?
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every 1 % shunt equals to 20mmHg of mercury
First calculate (PA02-PaO2)=number/20= % shunt |
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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 |
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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 |
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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 |
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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 |
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Dalton’s Law of partial pressures and know the
relative partial pressures of the important respiratory gases mixed venous blood, |
PO2=40
PCO2=46 |
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Dalton’s Law of partial pressures and know the
relative partial pressures of the important respiratory gases in tissues |
PO2=40
PCO2=45 |
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Dalton’s Law of partial pressures and know the
relative partial pressures of the important respiratory gases in expired air |
PO2=0
PCO2=40 |