Viva F6(i)
What is total (global?) lung perfusion and global ventilation?
- 4-5L/min is the normal average minute volume, which corresponds to a tidal volume of 400ml with a respiratory rate of 10.
- 4-5L/min is also the normal average pulmonary arterial blood flow, split 45%-55% with the right pulmonary artery getting a slightly larger amount of blood.
What are the regional variations in lung ventilation?
- Ventilation is distributed unequally
- The bases get more ventilation, because:
- There is a gravity-related vertical gradient of pleural
- pressure which results in a difference in distending transpulmonary pressure during normal spontaneous ventilation.
- Posture changes the direction of this gradient due to the effects of gravity, because of the weight of the lung, changes in chest wall excursion and the shifting of mediastinal and abdominal contents.
- Bases have more room to expand than apices.
- Compliance differences between lung regions (bases are relatively deflated and therefore more compliant)
- Pattern of breathing (eg. whether it is voluntary or not)
What are the regional variations in lung perfusion?
- Perfusion is also distributed unequally
- The bases get more perfusion in the upright lung, because of:
- Variation in alveolar oxygenation (hypoxic pulmonary vasoconstriction)
- Gravity-related hydrostatic pressure
- Basic architecture of pulmonary vessels: the actual branching and forking pattern of the pulmonary vascular tree has an effect on directing blood flow.
How are ventilation and perfusion related across an upright lung?
- Draw it for me.
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References
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