Matching lung ventilation and perfusion Flashcards
What is ventilation and how is it measured?
- Movement of gases in and out of the lungs
- Ventilation of the lungs occurs through airways
- Measured as change in volume per unit time
What is perfusion, where does it occur and how is it measured?
- Blood flow through any organ e.g. lungs
- Perfusion occurs through blood vessels
- Measured as flow of blood/unit time e.g. 650 mL/min
What are the regional differences in lung ventilation?
- Apical alveoli are about 4 times larger than basal alveoli in upright posture
- This is due to the effect of the gravity
- Basal alveoli can expand more than apical alveoli
- Basal regions of lungs have better ventilation than apical regions
What is the functional supply for the pulmonary circulation?
Main blood supply to the lungs- RV to pulmonary arteries to lungs to pulmonary veins to body organs to RV
What is structural supply of pulmonary circulation?
Nutrition to the lung tissues. Also called Bronchial circulation Bronchial artery from thoracic aorta Bronchial vein to superior vena cava Only a small amount of blood.
What is the equation for CO?
CO= SV x HR
What is SV?
SV is amount of blood that comes out every ventricle
Which ventricle is thicker and why?
Left ventricle 3 times thicker as pushing against more force- aorta has muscle and elastic tissue. P higher in LV and aorta.
What structures does oxygen travel through to become oxygenated?
Pulmonary artery carry deoxygenated blood from right ventricle; split into right and left branches to supply respective side lung.
Each branch then successively split into smaller branches closely following airway divisions. They are called extra-alveolar vessels while running through lung parenchyma.
What happens to the CO2 exchange when alveoli are damaged?
Can carry out CO2 exchange because it is easier as there are fewer barriers. Since alveoli are very badly damaged, they can’t always carry out oxygen exchange.
Where does blood go when it passes through capillaries?
Beyond terminal bronchioles, blood vessels form capillary beds (starting with smaller arterioles) where gas exchange starts. Blood flowing through rich network of capillaries forms a ‘sheet’ of blood with huge surface area. Very efficient system of gas exchange.
Oxygenated blood flows in to pulmonary venules which unite to form four large veins emptying in to left atrium.
What is emphysema?
– Widespread destruction and dilatation of distal airway (chronic inflammation)
– Regional destruction of vascular beds
– Poor gas exchange and hypoxia
– Chronic inflammation destroys alveoli
Which blood vessel carries deoxygenated blood from heart to lungs?
Pulmonary artery
Where in the pulmonary circulation does gas exchange start?
Small arterioles
Which factor is predominantly responsible for highly efficient gas exchange in the lungs?
Large surface area of exposure between blood and alveolar gases
Regional differences in lung perfusion- where is hydrostatic pressure the highest- top or bottom?
Max hydrostatic pressure at bottom
Hydrostatic pressure definiton
Force exerted by weight of a fluid (blood/ water) due to gravity
What is pulmonary circulation?
A column of blood exerting different hydrostatic pressure in different areas of lungs in relation to the position of the right ventricle – as that is where the blood is coming out of
Higher hydrostatic at the bottom of the lung compared to the top of the lung.
P above ventricle will be less, lower than the ventricle will be more.
What are the extra alveolar vessels?
– Running through lung parenchyma
– Their diameter is affected by the lung volume (via pull of the lung parenchyma)
– When breathing they get bigger and are pulled
Do the alveolar vessels get squashed?
– Diameter dependent
– They get smaller as they squashed
If P upstream is smaller then P out but is larger than P downstream will blood flow through?
No as the alveolar P is greater than the upstream pressure so the capillary will collapse.
If P upstream is larger then P out and is larger than P downstream will blood flow through?
Yes as the upstream P is greater than the alveolar P so capillary will stay open.
What does P upstream, out and downstream relate to?
P us is the pressure in the arterials.
P out is the pressure in the alveoli.
P ds is P in the venous.
What happens to the movement of blood when a patient bleeds?
If patient bleeds they lose blood and drop BP- P out will be more than P us- drop BP upstream P will drop below alveolar P- that zone that was zone of recruitment will turn into a zone where air is still there but no blood passes through.
