Ventilation-Perfusion Relationships Flashcards
What is the definition of a pulmonary shunt?
Results when alveoli are perfused with blood, but ventilation fails to supply the perfused region. This often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused.
This results in blood moving from the right side of the heart to the left side of the heart without being oxygenated
What happens to the concentration of oxygenated blood from better ventilated areas which is downstream from where a pulmonary shunt is occuring?
It becomes diluted with deoxygenated blood
How do the lungs react to pulmonary shunt occuring?
Local mechanisms causes vasoconstriction in arterioles which supply underventilated alveoli, redistributing blood flow to other areas of the lung which are better ventilated.
What happens to the ventilation:perfusion ratio in pulmonary shunt?
Drops to much less than 1
What is the definition of alveolar dead space?
Alveoli become ventilated while the surrounding arterioles are not being adequately perfused. This is regarded as the opposite to pulmonary shunt
What happens in response to alveolar dead space?
PO2 of local tissue increases, which causes vasodilation of vessels. PCO2 also decreases, causing bronchoconstriction. This increase in perfusion and mild decrease in ventilation brings the ventilation/perfusion ratio back towards 1
What is the definition of ventilation?
The amount of air getting to the alveoli in L/min
Where is the perfusion highest in someone at rest?
In the bases of the lungs - due to higher hydrostatic pressure
Where is perfusion lowest in a person at rest?
Apex of the lung - hydrostatic pressure is low
What determines levels of bronchodilation/constriction?
Diameter is mediated by CO2 levels in exhaled air passing through bronchioles.
An increase in PCO2 of exhaled air causes the bronchioles to dilate, and a decrease causes them to constrict.
What is the definition of perfusion?
Local blood flow in L/min
What is unique about capillaries in the lung?
They are collapsible - if the pressure is not high enough, they will shut off and divert blood flow where pressure is higher
Where does the majority of ventilation perfusion mismatch occur?
In the apex of the lung
What is ventilation:perfusion ratio?
A ratio the can be used to determine any mismatches between ventilation and perfusion
What does a V/Q of < 1.0 indicate?
Pulmonary shunting
