Ventilation and perfusion Matching Flashcards
What is ventilation?
The change in volume through the respiratory cycle
How is gas distributed in the lung and why?
- More gas goes to the base of the lung than the apex.
- Lower ribs are more curved and mobile than upper, the action of the diaphragm expands the lower lobes more than the upper, partly because upper lobes are attached to main bronchi and upper airways, so less easily stretched than tissue of lower lobes, and compliance alters across lung
What lobes have greater compliance?
The lower lobes
What vein does the conducting portion of the bronchial arteries join?
The pulmonary vein (diluting it and making it slightly deoxygenated)
What do the bronchial arteries supply specifically?
- Lung parenchyma
- Airway smooth muscle
- Pulmonary arteries and veins
- Pleura
What is the volume of blood in the pulmoanry network at rest?
100 ml
What is the stroke volume of the heart?
70 ml
What is the mean pressure within the pulmonary circulation?
15 mmHg - only needs to be sufficient enough to lift blood to apex
What is the transmural pressure? @@@@@@@
The balance between alveolar pressure and blood pressure (blood flow in lungs is dependant on @@@@ @@@@ @@@@ @@@@ @@@ @@
When will blood flow in the lungs?
Only if blood pressure is greater than alveolar pressure
What is the differnce in hydrostatic pressure between the base and apex of te lung?
23 mmHg
What is zone 1?
Apex of lungs if capillaries are closed then they are ventilated but not perfused and are therefore considered alveolar dead space.
Healthy individuals no zone 1
What is zone 2
Alveolar pressure is lower than systolic arterial pressure but may be higher than diastolic arterial presure and venous pressure. Flow is determined by arterial-alveolar pressure difference
What is zone 3
Alveolar pressure is lower than both arterial pressure and venous pressure - the capillaries are distended as a consequence of the transmural pressure and there is continous flow
What is the V/Q ratio for the overall lun?
0.85 (perfect match would be 1)
What is the V/Q at the base?
0.6 there is good perfusion and ventilation
Where is the V/Q 1?
About 2/3 up the lung (rib 3)
What is the V/Q at the apex?
3
What improves more rapidly as you move down the lung blood flow or ventilation?
Blood flow
What is the O2 content like at well ventilated areas of the lung
Normal
- Poorly ventilated areas have low O2 content
Where in the lung is CO2 accumulated more?
Base of the lung because ventilation is low (V/Q low), CO2 not taken away as rapidly and a higher steady state of cO2 occurs
Where is the lowest steady state PO2 ?
At the base of the lung as low V/Q therefore O2 taken up by blood is not fully replenished by new air
How is blood diverted away from poorly ventilated areas?
Hypoxic vasoconstriction intrinsic effect (active control of blood flow)
When is the hypoxic effect important?
At birth,
- When born, before 1st breath, lungs vasoconstricted and resistance is high
