Exam 4: Respiratory L3 Flashcards
Transfer of gas across the blood gas barrier:
- Occurs via the process of _____
- Transfer of gas follows basic _____
Factors facilitating gas diffusion in the respiratory system:
1.
2.
3
Occurs via diffusion (passive)
Transfer of gas follows basic diffusion laws
Factors facilitating gas diffusion:
- Large Surface Area of Alveoli (70 meters square = 750 square feet)
- Short distance to travel
- Gases with advantageous diffusion properties
Capillary network is also ideal for gas exchange:
Capillary diameter:
RBC diameter:
Erythrocytes:
- Pass through capillaries in _______
- Average transit time is ___
Capillary diameter: less than ten um
RBC diameter: 7 um
RBCS:
Pass through capillaries in single file
Average transit time is roughly a second
Total diffusion capacity for O2:
Combination of __ different diffusion constants:
12 different diffusion constants
Fick’s Law of Diffusion Through Tissues:
(Parameters: Area, thickness, diffusion constant, partial pressure)
The amount of gas transferred is Proportional to what three things?
What is it inversely proportional to?
Diffusion through tissues:
Amount of gas transferred is proportional to Area, Diffusion Constant, and the Partial Pressure
Amount of gas transferred is inversely proportional to thickness
What will happen to diffusion rate considering the following:
Pulmonary Edema
Collapsed Lung
High Altitude
PE: will cause an increase in thickness, and therefore a decrease in diffusion
Collapsed Lung: decrease in area, decrease in diffusion
High Altitude: Decrease in partial pressure, decrease in diffusion
Both CO2 and O2 can rapidly diffuse across the alveolar barrier, but which one is better?
So, CO2 is better, but both will diffuse readily under normal conditions.
Explain Diffusion Limited:
The amount of X carried into circulation is limited by ________.
Driving force will always be _____ than the rate at which molecules can pass through the barrier.
What are the two general examples of why molecules would be diffusion limited?
Draw the graph and figure for diffusion limited
Diffusion Limited:
- The amount of molecule X carried into circulation is limited by the diffusion across the alveolar membrane
Driving force will always be higher than the rate at which molecules can pass through the barrier.
Two main general examples:
- Molecule simply can’t diffuse across the barrier
- Molecule diffuses but then gets immediately converted to something or binds to something else and therefore no longer contributes to partial pressure
Perfusion Limited:
- The amount of molecule X carried into circulation is limited by _____
Diffusion will quickly ______the driving force
The only way to get more molecule X into circulation is to _______.
Draw both figure and the graph
Perfusion Limited:
Amount of molecule X carried into circulation is limited by the rate of perfusion (blood flow through pulmonary capillaries)
Diffusion will quickly decrease the driving force
Only way to get more molecule X into circulation is to increase perfusion
What is the different shape of the graph between Pressure as a function of time between diffusion limited and perfusion limited molecules
Describe the following gases as perfusion limited or diffusion limited:
N2O (nitrous oxide)
CO (carbon monoxide)
O2 and Co2
N2O is perfusion limited (gas transfer is limited by the amount of blood perfusion the alveoli)
CO is DIFFUSION LIMITED (it binds rapidly to Hb and then doesn’t count as partial pressure anymore)
O2 and CO2 both bind to Hb, but with less affinity than CO, they are perfusion limited under normal circumstaces
What happens to oxygen uptake along the pulmonary capillary under the following circumstances:
- Exercise
- Increased thickness of blood-gas barrier (like if you have fibrosis or edema)
- Exercise: increased blood flow, but under normal circumstances you’re still okay because it’s perfusion limited and at 250 milliseconds you still are at PO2 of 100mmHg
- Increased thickness of blood-gas barrier (fibrosis, or edema):
oxygen uptake may become diffusion limited
Oxygen Uptake along the pulmonary capillary at lower alveolar PO2 (like at high altitude)
What does going to higher altitude do to the driving force/pressure gradient?
Severe exercise at high altitude can lead to _________.
Going to higher altitude will decrease the pressure gradient/driving force because you are decreasing the amount of PO2 in the air.
Severe exercise at high altitude can lead to diffusion impairment of oxygen transfer.
What does DL stand for?
How does it get measured in the clinic?
DL is the diffusion capacity of the lung
DL = VCO / PalveolarCO
CO is used because it diffuses rapidly and it is also not normally present in your blood
Single Breath DL of CO
Pt will breathe in CO (and a trace amount of He), hold for ten seconds, breathe out and then their volume of CO they breathe out will be measured. If diffusion of CO decreases, the graph will not be as steep of a drop off.
Gas diffusion follows basic gas laws:
Diffusion is directly proportional to____
Diffusion is indirectly proportional to____
O2 and CO2 are normally ____ limited
Under extremes (high altitude or exercise) or disease, O2 can become _____
What is used to measure the total diffusion capacity of the lung?
Diffusion is directly proportional to: surface area, the pressure gradient, and also the diffusion constant
Diffusion is inversely proportional to thickness
O2 and CO2 are normally perfusion limited
Under extremes, or disease O2 can become diffusion limited
Single breath CO test is used to measure total diffusion capacity of the lung.
What are the only arteries in the body that carry deoxygenated blood?
Pulmonary arteries
Pulmonary arteries:
Total blood volume is like 500 mL
In the alveolar capillary network:
___ mL under resting conditions
___ during exercise
In alveolar capillary network:
70 mL under normal resting conditions
200 mL during exercise
Pulmonary arteries:
- think wall, ____ smooth muscle
- ________ compliant than systemic arteries
- easily distendable
_____ pressure circulation
Driving Pressure: systemic vs pulmonary:
Pulmonary arteries:
- think wall, minimal smooth muscle
- 7x more compliant than systemic arteries
- easily distendable
LOW pressure circulation
Driving Pressure:
Systemic: 87 mmHg
Pulmonary: 6 mmHg
What are the four factors influencing lung perfusion:
1.
2.
3.
4.
Factors Influencing Lung Perfusion:
- Pulmonary Vascular Resistance (PVR)
- Gravity
- Alveolar Pressure
- Arterial venous pressure gradient
Pulmonary Vascular Resistance:
Explain/graph how PVR changes with increasing vascular pressure (in arteries and in veins)
What two mechanisms help with this process?
PVR decreases with increasing vascular pressure
MUCH more of a change in PVR with increasing pressure in the arterial side
Two Mechanisms:
1. Recruitment : opening of closed vessels and conducting in previously non conducting vessels
- Distension: widening of open vessels
For the blood vessels within the respiratory system:
Alveolar vessel : feels pressure from ____
Extra-alveolar vessel: feels pressure from
Alveolar Vessels: subject to pressure from alveoli
Extra-alveolar vessel: subject to pleural pressure
Draw the graph showing how PVR changes with lung volumes for the alveolar and extraalveolar vessels
At which point is PVR the lowest?
PVR is the lowest at FRC (“steady state”)
At low lung volume, extra-alveolar vessels are subject to intrapleural pressure
At high lung volume, vessel stretching crishes alveolar vessels, pulls open extra-alveolar vessels
Explain the affect that gravity has on distribution of pulmonary flow
Just like with ventilation,
most of the blood flow goes to the base instead of the apex.
Blood flow distrubution depends on posture
Difference between apex and base becomes less during exercise
Both _____ and ____ are increased towards the base of the lungs
Both ventilation and pulmonary blood flow are increased towards the base of the lungs
Explain the three zones within the lungs, the pressure gradient
Zone 1: PA > Pa> Pv (this zone only happens during hemorrhagic shock = alveolar dead space)
Zone 2: Pa > PA> Pv (equal pressure point situation where at some spot the alveolar pressure will impinge upon blood flow, causing the flow to travel down… “waterfall effect”)
Zone 3: Pa > Pv > PA high intrapleural pressure at the very base crushes the extra-alveolar vessels
Hypoxic Vasoconstriction:
Reduction in _____ reduces blood flow
Explain how this is important at first breath after birth
Hypoxic Vasoconstriction:
Reduction in PAO2 reduces blood flow
There is a reduction in oxygen in your alveoli, the body then reroutes blood away from it by vasoconstriction (aka “hypoxic vasoconstriction)
Important at first breath after birth because there ends up being a dramatic decrease in PVR, and a vast increase in pulmonary blood flow after birth
Fluid Balance:
Fluid leaving the vessels is due to ___ pressure
Fluid entering the vessels is due to ___ pressure
Why does left heart failure increase fluid in the lungs?
Fluid leaves vessels due to hydrostatic pressure
Fluid enters vessels due to oncotic pressure
Left Heart Failure, fluid backs up into pulmonary system, increasing hydrostatic pressure and therefore increasing the amount of fluid entering the lungs
There is no net flow in or out of a blood vessel if what two things are equal?
In a healthy individual ______ pressure is greater than _____
If hydrostatic = oncotic pressure than there is no net flow in or out of the vessel
In a healthy individual, hydrostatic exceeds oncotic (constant flow from lung interstitual fluid into lymph)
Fluid Balance:
If drainage rate from the interstitial space into the lymph is exceeded, what are the next two evens that happen?
If drainiage rate through interstitial space is exceeded
Then fluid will gather in the interstitial space
and then fluid will gather in the alveoli (major issues)
Hypoxic vasoconstriction occurs when ____ is low
Hypoxic vasoconstriction occurs when PAO2 is low
Pressures in the pulmonary circulation ______ systemic circulation
The capillaries are exposed to _____ and _____
Pressures in the pulmonary circulation are a lot less than in the systemic circulation
The capillareis are exposed to both alveolar pressure and intrapleural pressure
Pulmonary Vascular Resistance (PVR) is ___ and falls even more when cardiac output increases (meaning _______). This is due to the mechanisms of ___ and ___.
Hypoxic pulmonary vasoconstriction shifts blood from ________ to _____ and is important at birth.
PVR is already low and falls even more when cardiac output increases (increased arterial pressure). This is due to the mechanisms of recruitment and distension.
Hypoxic Pulmonary Vasoconstriction shifts blood from poorly ventilated areas to well ventilated areas and is important at birth.
Fluid movement across the capillary is governed by balance between _____ forces and ___ forces.
If drainage rate excees maximum lymph flow, ______ develops
Fluid movement across the capillaries is governed by the balance between hydrostatic forces and oncotic forces.
If drainage rate exceeds maximum lymph flow, then edema develops.
What is the ratio of Volumes of Gas: Blood Volume
Ratio of Gas Flow: Blood Flow?
Volumes of gas to blood is 43:1
Flow Rate of Gas to Blood is 1:2
What is the idea PO2 for the “perfect lung”
From the atmospheric air, to the air in the lungs, to the pressure in the tissue
Idea V to Q ratio?
“Ideal Lung”
Atm PO2 is 160 mmHg
Air in the lungs has PO2 of 100 mmHg
Tissues have PO2 of 40 mmHg
Ideal V:Q ratio is 1 to 1
What does it mean when V/Q > 1
When V/Q < 1
What is the normal physiological V/Q ratio?
V/Q > 1 means ventilation exceeds perfusion
V/Q < 1 means perfusion exceeds ventilation
Normal V/Q ratio is approximately 0.8
Explain the two extremes of a V/Q ratio:
The shunt alveolus vs the dead space alveolus
Effect of Altering V/Q
As V/Q goes down, alveolar O2 and CO2 approach ______ (give values)
As V/Q goes up, alveolar O2 and CO2 approach _____ (give values)
As V/Q goes down, alveolar O2 and CO2 approach venous levels (O2= 40mmHg and CO2= 45 mmHg)
As V/Q goes up, alveolar O2 and CO2 approach atmospheric levels (PO2= 150 mmHg and PCO2 = 0)
What is the highest V/Q ratio you can get?
Highest V/Q ratio is dead space alveolus
(blocking perfusion, it’s literally getting ventilated without little if any perfusion)
But yes, the V/Q ratio on the apex is greater than the V/Q ratio on the base, BUT the highest possible V/Q is dead space
Veltilation and perfusion are elevated at the ___ of the lungs relative to the ____
Ventilation and perfusion are elevated at the base of the lungs relative to the apex.
What is the V/Q ratio at your apex
What is the V/Q ratio at your base?
V/Q at apex is greater than one (approx 3)
V/Q at base is less than one, roughly 0.6
The V/Q ratio determines the _____ in any single lung unit
The overall V/Q ratio of the normal lung is ___
There are considerable V/Q ratio differences across upright lung. V/Q is high at the ____ and low at the ___
V/Q ratio determines the gas exchange in any single lung unit
The overall V/Q ratio of the normal lung is 0.8
There are considerable V/Q ratio differences across the upright lung. V/Q is high at the apex and low at the base of the lung.
V/Q mismatch and venous drainage (shunting) results in a PaO2 that is _______ than PAO2
Therefore, some level of V/Q mismatch happens in a normal physiological state
V/Q mismatch and venous drainage (“shunting”) results in a PaO2 that is slightly below PAO2
Decrease O2 delivery to the tissue is called ____
Decreased O2 in arterial blood is called ____
Loss of blood flow is called _____
Decreased O2 delivery to the tissues is hypoxia
Decrease O2 in arterial blood is called hypoxemia
(generally PaO2 < 80mmHg is generally called hypoxemia)
Loss of blood flow is ischemia
The clinical measure to diagnose the source of hypoxemia is _______
AaDO2 can help you figure out the source of hypoxemia
Which two sources of hypoxemia have normal AaDO2:
-
-
The two H’s have normal AaDO2’s
- Hypoventilation
- High altitude
This is because the oxygen in the air being inspired is already low, so the O2 in arteries would be even lower, making the difference between the two normal
Hypoxemia sources with increased AaDO2:
-
-
-
Hypoxemia sources with increased AaDO2
- V/Q mismatch
- Diffusion limitation
- Right to left shunt
Normal AaDO2 is _____
How do you determine AaDO2:
Normal AaDO2 at room air is < 15mmHg
Determination of AaDO2:
PAO2 : alveolar gas eqn
PaO2/PaCO2: arterial blood gas analysis
Explain how hypoventilation causes hypoxemia:
Alveolar PO2 depends on
- rate of removal from ____ (metabolic demand)
- Rate of replinishment from ____
If you stop breathing:
____ decreases and ____ increases
Hypoventilation:
Alveolar PO2 depends on rate of removal of oxygen by the blood, and then rate of replinishment from ventilation
If you stop breathing, alveolar PO2 decreases and Co2 will increase
Hypoventilation:
Will the pt have an AaDO2 difference?
What will their PaCO2 and the PaOw look like?
Does additional O2 (increasing PO2 in the air) increase PaO2?
Hypoventilation:
Normal AaDO2
PaCO2 is high
PaO2 is low
this indicates hypoventilation
Additional PO2 will help increase PaO2
Diffusion Limitation and hypoxemia
AaDO2 increased/decreased/or the same?
Reasons for diffusion limitation?
Diffusion Limitation:
Caused by edema, fibrosis, alveolar capillary block
think something is messing up with diffusion
AaDO2 will be increased for diffusion limited
Shunt:
AaDO2 is _____
Additional O2 _______ increased PaO2 to the expected level
What is an anatomic shunt vs a physiological shunt?
Shunt:
AaDO2 is increased
Additional O2 will NOT increase the PaO2
Anatomic shunt: thesbian vessels and bronchial circulation drainage
Physiological shunt: venous mixture
V/Q mismatch:
low V/Q ratio:
AaDO2 will be ______
Additional O2 will _______ PaO2
V/Q inequality:
most frequent reason for hypoexmia in patients in respiratory disorders
AaDO2 is increased
Additional O2 will increase PaO2
Mechanisms for Compensation:
Explain Hypoxic Vasoconstriction and Bronchial Vasoconstriction
Hypoxic Vasoconstriction: instigated by LOW PAO2, the body will redirect the blood/perfusion to an area of higher ventilation
Bronchial Constriction: occurs with high PAO2, the bronchials will constrict in order to send air to places of good perfusion (classic example is a Pulmonary Embolism)
Hypoxemia is abnormally low PO2 in arterial blood ( level is:______)
Causes for hypoxemia are :
Hypoxemia is abnormally low PaO2 (< 80mmHg)
Causes for hypoxemia : Normal AaDO2 will be hypoventilation and high altitidue….. Increased AaDO2 includes diffusion limitation, shunt (anatomical/physiological), and V/q mismatch
______ is the most common cause of hypoxemia
_____ is the only cause of hypoxemia in which arterial PO2 does not rise to the expected level under 100% oxygen
_____ is useful to assess the cause for hypoxemia
V/Q mismatch is most common cause of hypoxemia
Shunt is the only cause of hypoxemia in which PaO2 will not be increased by breathing in 100% O2
AaDO2 is useful to assess the cause for hypoxemia
