Term
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Definition
air supply
alveolar ventialtion = 4.2Lmin-1 |
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Term
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Definition
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Term
| Describe the pressure in pulmonary circulation |
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Definition
|
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Term
| MAP in the pulmonary artery is... |
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Definition
only 15mmHg
pressure drop across the circuit is only 10mmHg |
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Term
| How do pulmonary capillaries compare to systemic capillaries regarding pressure? |
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Definition
pulmonary < capillary pressure
pulmonary are much more susceptible to collapse if external pressures are high |
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Term
| What is the pressure acting on pulmonary capillaries? |
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Definition
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Term
| How does the pulmonary circulation decrease its resistance as pressure increases? |
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Definition
| recruitment and distension |
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Term
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Definition
| as pressure rises, previously 'closed' capillaries open and being to conduct blood (adding resistance units in parallel decreases overall resistance) |
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Term
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Definition
| as pressure rises, capillary lumen radius increases (shape changes from oval to circular), which decreases resistance to flow (Poiseuille's Law) |
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Term
| What is the direction of blood flow in the lungs? |
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Definition
apex (top) to base (bottom)
flow decreases linearly from bottom to top |
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Term
| What does blood flow in the lungs depend on? (3) |
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Definition
1. hydrostatic pressure (blood pressure within the capillary)
2. arteriovenous pressure difference (difference between the blood entering the capillary and the blood leaving the capillary)
3. alveolar pressure (external pressure acting upon the capillary) |
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Term
| What are the zones of the lungs? |
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Definition
| The zones of the lung divide the lung into 3 vertical regions, based upon the relationship between the pressure in the alveoli (PA), in the arteries (Pa) and the in the veins (Pv) |
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Term
|
Definition
air supply
alveolar ventialtion = 4.2Lmin-1 |
|
|
Term
|
Definition
|
|
Term
| Describe the pressure in pulmonary circulation |
|
Definition
|
|
Term
| MAP in the pulmonary artery is... |
|
Definition
only 15mmHg
pressure drop across the circuit is only 10mmHg |
|
|
Term
| How do pulmonary capillaries compare to systemic capillaries regarding pressure? |
|
Definition
pulmonary < capillary pressure
pulmonary are much more susceptible to collapse if external pressures are high |
|
|
Term
| What is the pressure acting on pulmonary capillaries? |
|
Definition
|
|
Term
| How does the pulmonary circulation decrease its resistance as pressure increases? |
|
Definition
| recruitment and distension |
|
|
Term
|
Definition
| as pressure rises, previously 'closed' capillaries open and being to conduct blood (adding resistance units in parallel decreases overall resistance) |
|
|
Term
|
Definition
| as pressure rises, capillary lumen radius increases (shape changes from oval to circular), which decreases resistance to flow (Poiseuille's Law) |
|
|
Term
| What is the direction of blood flow in the lungs? |
|
Definition
| apex (top) to base (bottom) |
|
|
Term
| What does blood flow in the lungs depend on? (3) |
|
Definition
1. hydrostatic pressure
2. arteriovenous pressure difference
3. alveolar pressure |
|
|
Term
| What are the zones of the lungs? |
|
Definition
| The zones of the lung divide the lung into 3 vertical regions, based upon the relationship between the pressure in the alveoli (PA), in the arteries (Pa) and the in the veins (Pv) |
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Term
| How can the inequality of blood flow within the upright human lung be explained? |
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Definition
| by the hydrostatic differences within the blood vessels: a gradient of around 23mmHg exists between apex and base |
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Term
| Where is the most amount of blood flow in the lungs? |
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Definition
| in the capillaries at the base of the lung as the capillaries have higher pressure at the bottom compared to the top (so there will be more capillary recruitment and distension at the base) |
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Term
| How does this change in the supine position? |
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Definition
base to apex differences disappear
apical part of the lung blood flow increases and asal zone remains unchanged |
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Term
| How does this change in exercise? |
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Definition
| blood flow increases throughout the lung and regional variation is reduced |
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Term
|
Definition
apex
PA>pa>Pv
capillaries squashed flat; no flow (alveolar dead space) |
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Term
|
Definition
mid-lung
Pa>pA>Pv
flow determined by the difference between Pa and PA |
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Term
|
Definition
base
Pa>Pv>PA
Flow determined by the arteriovenous pressure difference |
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Term
| Which zone doesn't exist under normal conditions? why? |
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Definition
zone 1
in normal health pulmonary arterial pressure (Pa) exceeds alveolar pressure (PA) in all parts of the lung |
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Term
|
Definition
is arterial pressure is reduced (e.g. during a haemorrhage)
blood vessels can become completely collapsed by alveolar pressure and blood does not flow through these regions.
they become alveolar dead space. |
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Term
| How does ventilation differ in the regions of the lung? |
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Definition
there are regional differences in ventilation
per unit volume, ventilation is greater at the base of the lung than at the apex |
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Term
| What causes the ventilation differences in the upright lung? |
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Definition
the weight of lung and the effects of gravity
intra pleural pressure is increased at the base of the lung compared to the apex |
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Term
| Compare the alveoli at the base to the apex, at rest |
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Definition
| alveoli at the base will be less expanded than the alveoli at the apex |
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Term
| How do the alveoli begin to change upon respiration? |
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Definition
| greater change in volume in the alveoli at the base (partly because it has more scope to expand) |
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Term
| Describe and explain the differences in surfactant in the alveoli and the effects it has |
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Definition
| in an expanded alveolus, the concentration of surfactant is significantly less than in a smaller alveolus. Therefore, less surfactant = increased surface tension = decreased compliance = less of a volume change |
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Term
| What is the ventilation-perfusion ratio? |
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Definition
the ratio between alveolar ventilation (VA) and pulmonary blood flow (Q)
the ratio that o2 is being added to the lung and the rate at which it is diffusing in the blood |
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Term
| Describe the ventilation-perfusion ratio at the base of the lung |
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Definition
pulmonary blood flow > the ratio between alveolar ventilation
Q > VA
ratio is 0.8 |
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Term
| How does the ventilation-perfusion ratio change as you move up the lung? |
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Definition
both Q and VA decrease
Q decreases at a faster rate
ratio increases towards 1 (and exceeds 1 towards the top of the lung) |
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Term
| What is the result of a mismatched ventilation-perfusion ratio? |
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Definition
| impairment of both o2 and co2 transfer |
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Term
| What does VA:Q ratio play a key role in determining? |
|
Definition
|
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Term
| In a normal lung, VA:Q is around 1, under these circumstances, what are PaO2 and PaCO2? |
|
Definition
PaO2: 100mmHg
PaCO2: 40mmHg |
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Term
| What are the effects of decreased ventilation due to airway obstruction? |
|
Definition
VA:Q decreases
decreased PaO2
increased PaCO2 |
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Term
| What are the effects of decreased perfusion due to capillary damage? |
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Definition
VA:Q increases
increased PaO2
decreased PaCO2
however, increased PaO2 doesn't lead to a significant rise in the amount of o2 transported, as haemoglobin is almost fully saturated at normal PaO2 levels |
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Term
| How does the body try to match the VA:Q? |
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Definition
ventilation-perfusion coupling
local auto regulatory mechanisms continuously respond to alveolar conditions |
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Term
| What causes PAO2 to fall and PACO2 to rise? what is the response in pulmonary arterioles? |
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Definition
reduced alveolar ventilation; excessive perfusion
pulmonary arteriolar constriction which reduces perfusion and redirects blood to better ventilated areas |
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Term
| What causes PAO2 to rise and PACO2 to fall? what is the response in pulmonary arterioles? |
|
Definition
inadequate perfusion
pulmonary arterioles dilate which increases capillary blood flow and increase o2 uptake |
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Term
| What is the response in the systemic capillaries? |
|
Definition
the opposite
e.g. increased PAO2 causes systemic arteriole to constrict |
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Term
| What are the effects of high PACO2? |
|
Definition
| bronchodilator to increase elimination of co2 |
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Term
| What are the effects of low PACO2? |
|
Definition
| bronchoconstriction to redirect airflow to better perfused area |
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Term
|
Definition
abnormally low level of o2 in the blood
PaO2 is abnormally low (either as a result of a low PAO2 or a normal PAO2 but a significant difference between PAO2 and PaO2) |
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Term
|
Definition
| ventilation is inadequate to perform needed gas exchange -> leads to hypoxaemia |
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Term
| Describe the 'ideal lung' |
|
Definition
no difference between PAO2 and PaO2:
- diffusion across the respiratory membrane proceeds to equilibrium in all lung units
- all the blood passing through the pulmonary circulation is exposed to alveolar air |
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|
Term
| What are the 4 types of hypoxaemia |
|
Definition
1. hypoventilation
2. diffusion limitation
3. shunt
4. ventilation perfusion inequality |
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Term
| What can cause hypoxaemia |
|
Definition
- anything that affects the rate or volume of air entering lungs (ventilation)
-anything that affects the transfer of air from the lungs to the blood (perfusion)
- cardiovascular shunts |
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Term
| What is PAO2 determined by? |
|
Definition
balance between
1. rate of removal of o2 by the blood (set by metabolic demands of respiring tissue)
2. rate of replenishment of o2 by alveolar ventilation |
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Term
| What happens if rate of replenishment of O2 falls and rate of removal stays the same? |
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Definition
PAO2 and PaO2 fall
PACO2 and PaCO2 rise
hypoventilation |
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Term
| What causes hypoventilation? |
|
Definition
- drugs that depress central respiratory drive (e.g. opiates, barbiturates)
- damage to chest wall
- paralysis of respiratory muscles |
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|
Term
| Does diffusion ever achieve equilibrium in a healthy lung? |
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Definition
| no, but very close (very small difference) |
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Term
| When does a larger difference occur? |
|
Definition
1. during exercise (due to reduced time available for diffusion to reach equilibrium)
2. result of thickening of the blood-gas barrier (e.g. asbestosis) |
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Term
| Explain what is meant by a ventilation-perfusion mismatch |
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Definition
| a disruption in the ventilation-perfusion equilibrium |
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Term
| What causes a ventilation-perfusion mismatch |
|
Definition
- oxygen entering the lungs typically diffuses across the alveolar-capillary membrane into blood
- this does not occur when the alveolus is insufficiently ventilated
- blood exiting alveolus is hypoxaemic
- blood mixes with well ventilated alveolus blood and the mix has a lower oxygen partial pressure than alveolar air
- alveolar-arterial difference develops |
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Term
|
Definition
| - shunting refers to blood that bypasses the pulmonary circulation, meaning that the blood does not receive o2 from the alveoli |
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Term
|
Definition
within the heart or lungs
cannot be corrected by administering o2 alone |
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Term
|
Definition
- abnormal vascular connection between a small pulmonary artery and vein (pulmonary arteriovenous fistula)
- cardiac atrial septal defect exists, allowing venous blood to mix with arterial blood |
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|
Term
| What are the effects when the whole lung is exposed to lowered PAO2, like in high altitude? |
|
Definition
|
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Term
| Describe the mechanism of HAPE |
|
Definition
1. uniform constriction of all the pulmonary arterioles = increased pulmonary TPR and rise in pulmonary MAP and increased RV work
2. some arterioles constrict more than others
3. this gives rise to hydrostatic edema |
|
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Term
| What is hydrostatic edema? |
|
Definition
| fluid leaks out into and around the surrounding alveoli |
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|
Term
| What does hydrostatic edema initiate? |
|
Definition
| an inflammatory response which increases pulmonary capillary permeability and makes the situation worse |
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Term
| What is the best treatment for HAPE? |
|
Definition
descent
or supplemental o2 and hyperbaric bag |
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Term
| Which drug can be used to treat HAPE? |
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Definition
nifedipine
blocks Ca2+ channels in vascular smooth muscle
reduces the extent of the pulmonary hypoxic vasoconstrictor response to hypoxia |
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