Ventilation: Perfusion relationship Flashcards
What is ventilation linked with ?
Perfusion (local blood flow L/min)
What is distribution of blood flow in the lung influenced by ?
Hydrostatic pressure and alveolar pressure
What decreases with height across the lung ?
Both blood flow and ventilation
Why is blood flow at the base of the lungs higher than ventilation ?
Arterial pressure exceeds alveolar pressure and vascular resistance, this compresses alveoli
Why is blood flow at the apex of the lungs low ?
Arterial pressure is less than alveolar pressure, this compresses the arterioles and vascular resistance is increased
Both ventilation and perfusion are greater where ?
At the base of the lung than the apex, but blood flow exceeds ventilation at base and ventilation exceeds ventilation at apex
Where is there a ventilation-perfusion mismatch ?
At the base of the lung and the apex of the lung
Where are ventilation and perfusion precisely matched ?
At rib 3
Where is the biggest V/Q mismatch ?
Apex
Over 75% of the height the healthy lung performs quite well in matching blood and air
What is the optimal condition for ventilation ?
Ventilation = perfusion Ratio = 1
What is mismatch 1 (base) ?
Where ventilation < perfusion
ratio < 1
(Under oxygenated blood
What is mismatch 2 (apex) ?
Ventilation > perfusion
ratio >1
( can happen with too much breathing taking place compared to the rate of blood flow)
What happens if ventilation decreases in a group of alveoli ?
PCO2 increases and PO2 decreases. Blood flowing past those alveoli does not get oxygenated
How does blood get oxygenated when ventilation is decreased ?
Oxygenated blood is ‘shunted’ from better ventilated areas to dilute blood
What does shunt mean ?
Passage of blood through areas of the lung that are poorly ventilated (Ventilation
