V/Q 1 Flashcards
What is the V/Q ratio?
Ratio of Ventilation to Perfusion
Gas exchange is ideal when there is a uniform distribution of V and Q (0.8 everywhere)
What is the V/Q in lung diseases that restrict or obstruct ventilation?
Low V/Q
These units have lower ventilation due to the obstruction, so perfusion is wasted
Acts somewhat like a shunt
What is the A-a gradient?
The difference between the PAO2 and the PaO2
Ideally the difference is 0 in perfect exchange, normal patient is 5-20
The larger the difference, the poorer the exchange
How does gravity affect the V/Q?
Gravity makes both V and Q unevenly distributed, however the gradient of Q is much greater than that of V
This results in low V/Q at the bottom of the lung and high V/Q at the top
This results in the normal A-a of 5-20mmHg
What is the result of lung transplantation in emphysema patients?
Ventilation continues to mostly go into the emphysematous lung because of hits high compliance
However perfusion will mostly go to the transplanted lung because of the tissue loss associated with emphysema
Causes severe V/Q mismatch
What is the relationship between PACO2 and V/Q ratio?
Inversely proportional
The higher the V/Q, the lower the alveolar PCO2
What is the relationship between PAO2 and the V/Q ratio?
Directly Proportional
High V/Q resluts in high PAO2
What is the relationship between V/Q and arterial PO2 and PCO2?
Directly proportional to PO2
Inversely proportional to PCO2
Same as alveolar relationships
What is a treatment for right heart failure?
Nitric Oxide
Reverses hypoxic pulmonary vasoconstriction
Selectively dilates blood vessels in only those lung segments that are actively participating in gas exchange because it is inhaled
What is an intrapulmonary shunt?
Shunt-like states resulting from V/Q mismatch
What is the PaO2, A-a gradient, and PaCO2 in a low V/Q mismatch (obstructive disease)?
PaO2 - low
A-a gradient - high
PaCO2 - high
