Ventilation And Perfusion COPY Flashcards
What occurs in the conducting zone
Bulk movement of air into the lungs
Does not take part in gas exchange
Anatomical dead space as air breathed out is unchanged
What occurs in the respiratory zone
Gas exchange
What is the serous membrane that lines the lungs
Pleura
Due to gravity there is a pressure gradient within the pleural cavity such as the top cavity has more negative intrapleural pressure compared to the bottom, what effect does this have on alveoli
Alveoli at the apex of the lung tend to larger and smaller at the bottom as they are compressed by the weight of the upper lung
How does ventilation perfusion matching take place
At the top of the lungs there is less blood flow as work needs to be done against gravity and the large alveoli are less likely to stretch during inspiration as they are already stretched so they cannot decrease their intro-alveolar pressure therefore ventilation there is quite low
At the base of the lung we have smaller alveoli which have have greater capacity for stretching and there are more in the base so ventilation and blood flow here is greatest
Why does The base of the lung has the lowest V/Q ration
It receives more blood flow than the rest of the lung
How to calculate V/Q ratio
What is a pulmonary embolism
A blood clot in the lungs
What happens to V/Q during a PE (pulmonary embolism)
The V/Q ration of the embolised area is infinite as there is no blood flow but ventilation is continued
What happens to area proximal to the embolus
There is increased blood flow to the rest of the vascular bed, these areas become hyperaemic so they are receiving too much blood compared to their ventilation so the V/Q ratio ratio decreases as perfusion outmatches ventilation.
O2 levels decrease as there is insufficient ventilation to oxygenate the hyperaemic regions so blood passes through the lungs into the systemic vasculature deoxygenated
When does an anatomical shunt occur
During congenital malformation of the circulatory system which causes blood to bypass the pulmonary circulation, typically due to septal defect
E.g foramen ovale defect, when it doesn’t close during birth the blood can mix between the 2 atria.
When does a physiological shunt occur
A physiological shunt occurs when non-oxygenated blood enters the systemic circulation through non-pathological means.
For example, deoxygenated blood from the coronary veins (those blood vessels that provide blood to the heart muscle) will often drain into the nearest chamber of the heart. This means deoxygenated blood can enter the left ventricle and enter the systemic circulation
What is cyanosis
Cyanosis refers to a bluish-purple hue to the skin. It is most easily seen where the skin is thin, such as the lips, mouth, earlobes and fingernails. Cyanosis indicates there may be decreased oxygen attached to red blood cells in the bloodstream. It may suggest a problem with the lungs or heart.
