Pulmonary Circulation, Ventilation-Perfusion Flashcards
What are there variations in, in regards to lungs?
Lung ventilation
Lung perfusion
What needs to occur for effective gas exchange?
Ventilation and perfusion need to be closely matched
What is ventilation?
The change in volume through the respiratory cucle
Is air evenly distributed through the lungs?
No
Where does more gas end up in the lungs?
Base of the lung than the apex
Why does the base of the lung change more in volume than the apex?
The lower ribs are more curved and mobile than the upper
This means the diaphragm extends the lower lobes more and as there is greater compliance
Gravity has a small role as the weight of the lung pulls down on pleura, so the apex has a more negative intrapleural pressure
What two circuits nourish lung tissue?
Pulmonary
Bronchial
What are bronchial arteries a branch of?
Descending aorta
Where does the bronchial circulation join?
Joins with pulmonary veins thus diluting the oxygenated blood with deoxygenated blood
What is the function of the bronchial circulation?
Supply oxygen to lung parenchyma
Airway smooth muscle
Pulmonary arteries and veins
Pleura
Warming inspired air
How much blood enters the pulmonary circulation?
5L every minute
What does one heart beat do?
Replaces entire pulmonary circulation
What are the two keys to pressures in pulmonary circulation?
The pulmonary circulation is a low pressure, low resistance system
Able to recruit more vessels with only a small increase in arterial pulmonary pressure
What is the mean arterial pressure in the pulmonary circulation?
15mmHg
What is blood flow through the pulmonary circulation dependent on?
Balance between alveolar pressure and blood pressure
Called transmural pressure
Slide 10
see if he talks about diagram
Why is blood flow greater at the base than the apex of the lung?
Hydrostatic pressure difference between base and apex of the lung
Around 23mmHg
Or pressure in capillaries is lower at apex than at base of lung
When will blood only flow?
If blood pressure is greater than alveolar pressure
Slide
12
When would there be no oxygen perfusion in the apex?
If the alveo
When would there be no oxygen perfusion in the apex?
If the alveolar pressure is greater than the blood hydrostatic pressure
This forces the capillary to close
Slide 14
lecture
What is flow determined by in zone 2?
Arterial-alveolar pressure difference
This is because alveolar pressure is lower than systolic arterial pressure but may be higher than diastolic AP and venous pressure
What blood flow occurs in zone 3?
Alveolar pressure is lower than both arterial and venous pressure
The capillaries are therefor distended as a consequence of the transmural pressure and there is continuous flow
What is the ventilation and perfusion ratio in the whole lung?
0.85
What is the ventilation and perfusion ratio in the base of lung?
0.6 (more perfusion than ventilation)
What is the ventilation and perfusion ratio in the apex?
About 3
What is the ventilation and perfusion ratio 2/3rds above the base?
1
Describe perfect match between ventilation and perfusion
well ventilated alveoli with a good perfusion of blood
Blood will equilibrate with alveolar air and be rich in oxygen and low in CO2
Describe poor ventilation alveoli with a rich blood supply
Alveolar air will equilibrate with the blood and the blood will tend towards the same composition as venous, as ↓fresh air is being brought in. Low PO2, high PCO2
Describe well ventilated alveoli which are poorly perfused with blood
Blood leaving the alveoli will be low in CO2 (as there is a large concentration gradient, efficiently blown off), but as the haemoglobin is fully saturated, there will not be a significant increase in O2 levels
Can different areas of the lungs compensate for each other?
No
The lowered PO2 of blood leaving poorly ventilated parts of the lung is not compensated for by blood
leaving well ventilated areas, because of the shape of
the oxygen-haemoglobin dissociation curve
What is the effect of low ventilation to perfusion ratios on CO2 concentration?
CO2 diffuses from blood to alveoli but not taken away as rapidly
This CO2 accumulates in alveoli and higher steady rate of PCO2 occurs
PCO2 may be 42mmHg, 40mmHg normally
What is the effect of low ventilation to perfusion ratios on O2 concentration?
O2 diffuses from alveoli into blood but because ventilation is low the oxygen taken up by the blood is not fully replenished by new air entering the lungs
Oxygen is therefore depleted in alveoli and new steady state low PO2 occurs
90mmHg, 100 normally
What is the effect of high ventilation to perfusion ratio on CO2 concentration?
CO2 diffusing from blood is nearly all blown away, thus CO2 in alveoli is depleted until a new lower steady state level occurs
PCO2 may be 28 mmHg (40 normally
What is the effect of high ventilation to perfusion ratio on O2 concentration?
O2 diffusing from alveoli is not taken away by blood as much as normal because relative blood flow is lower. But as O2 is replenished with each breath O2 accumulates, diffusion carries on and a new higher
PO2 level occursPO2 may be 130 mmHg (100 normally)
Example of active control of blood flow to stop mismatching between ventilation and perfusion matching?
Hypoxic vasoconstriction
The result diverts blood away from poorly ventilated areas
When is the hypoxic vasoconstriction action important?
When born
before 1st breath, lungs vasoconstrict and resistance is high, with 1st breath vasoconstriction decreases and so does resistance
