Dasgupta - V/Q Matching Flashcards
Normal V/Q ratio in a normal adult whole lung
O.8
3600/4500
What are the two pumps involved in the pulmonary system?
The heart pumps blood into the lung
The chest wall pumps air into the lung
Areas with blood flow but no ventilation. Pure mixed systemic venous blood
Shunt
Areas with ventilation but no blood flow
Dead space
The more extreme the V/Q mismatch is, the _____ the gas exchange is
Worse
The efficiency in gas exchange is dependent on which 3 things?
High gradient in partial pressure
Low thickness of membrane (~0.5 micron)
High surface area of alveolus
PAO2 =
PO2 in alveolar gas
PaO2 = PO2 in _____
Systemic arterial blood
The bigger the A-a difference is, the _________ the exchange
Poorer
A measure of whether optimal V/Q matching is occurring in the lung
A-a gradient
What causes the normal low V/Q ratio in the bottom of the lung and high V/Q ratio in the top of the lung?
The gradient of Q from gravity is much greater than that of V.
The greater Q is in relation to V, the _____ the PCO2 will be
Higher
V/Q is _______ to PaO2
Directly proportional
The higher the V/Q, the _____ the PaO2
Higher
PCO2 of venous blood = ??
This is what PACO2 of alveoli reaches when it is perfused but not ventilated
46mm Hg
A ____ of the V/Q ration will increase the PO2
Increase
The lung unit with low V/Q will have ____ PO2 and ____ PCO2
Low
High
The lung unit with high V/Q will have ____ PO2 and _____ PCO2
High
Low
Nitric oxide ______ hypoxic pulmonary vasoconstriction
Reverses
Why is inhaled NO more effective at reducing hypoxic pulmonary vasoconstriction than ingested NTG and NTP?
The inhaled NO only goes to the alveoli that are ventilated and dilating the blood vessels there. Instead of going to all lung segments like NTG and NTP would do.
Required concentration of NO for therapy?
20ppm
*NO is very toxic at high concentrations
Shunt-like states are said to be ____ V/Q mismatch
Low
______ are the most dangerous V/Q mismatch
Low V/Q mismatches
Because these units are shunt-like
Low V/Q mismatch results in ______ _
Hypoxemia
High A-a gradient
High PCO2 in arterial blood
Low pCO2 in airways causes the airways to ________
Constrict locally
Paradox of compensation in low V/Q patients
PaCO2 is normal
PaO2 is low
Things that limit ventilation:
Obstructive lung disease (emphysema, bronchitis, asthma)
Shunt (alveoli filled with fluid or foreign material)
Restrictive lung disease (fibrosis)
Pneumonia of the lungs is a classic example of a ______
Shunt
Normal A-a gradients
5-15mmHg
This one is according to dasgupta, BRS has a different number
The fact that there is a normal A-a gradient that is more that 0 is because of ?
V/Q mismatching [due to gravity in normal lungs]
Shunts [all lungs have shunts in the form of venous drainage of parts of the heart and large airways]
The older you are, the _____ your A-a gradient will be.
Larger
Normal range per A-a gradient increases _______ per decade after age 30
3mmHg
Five causes for hypoxemia
Breathing air w/ low pO2
Hypoventilation
Shunts
Low V/Q mismatch
Diffusion problem
Hypoventilation always results in _____ and ______
Hypoxemia
Hypercapnia
(A-a gradient normal)
Patient presents with hypoxemia.
Shows only small increase in PaO2 when 100% O2 is administered.
A-a gradient is large.
Likely diagnosis is?
Shunts
Cause of hypoxemia.
Also associated with hypercapnia.
A-a gradient is normal
Hypoventilation
Pt presents w/ hypoxemia. Shows marked increase in PaO2 when 100% O2 administered.
A-a gradient is large
Low V/Q mismatches
Cause of hypoxemia.
Shows marked increase in PaO2 when 100% O2 administered.
A-a gradient large.
This type is very uncommon and must be differentiated with more diagnostic methods
Diffusion defects
Problems of a pulmonary embolus are initially ______
Cardiovascular.
Right heart has to work harder to move CO thru remaining sections of lungs.
V but no Q
Dead space
Q but no V
Shunt
