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Respiratory Phys 7

WVSOM -- Ventilation - Perfusion Relationships

QuestionAnswer
How does ventilation vary within the lung? greater at the base than the apex
How des blood flow vary within the lung? greater at the base than the apex
Do ventilation and blood flow vary by the same amount? NO, blood flow has a greater difference
What 4 processes is arterial PO2 dependent on? ventilation, diffusion, Shunt and Ventilation/Perfusion inequality
What are the 4 causes of hypoxemia? hypoventilation, diffusion impairment, shunting and ventilation/perfusion inequality
What is the A-a gradient? the difference between the Alveolar PO2 and the arterial PaO2
How do you measure the PaO2? arterial blood gas
How do you determine the Alveolar PO2? Ideal alveolar gas equation
What is the ideal alveolar gas equation? PiO2 (149 mmHg at sea level) – (PaCO2/R) (+F) R is around 0.8
How is PaCO2 determined? ABG
What is PIO2? inspired O2. Around 149 mmHg at sea level
What is a normal A-a gradient? 3-4 mmHg
What does hypoventilation decrease? alvolar PO2
What does Hypoventilation do to the A-a gradient? nothing
How do you correct hypoventilation? give oxygen
Why is A-a gradient unaffected in hypoventilation? arterial PO2 decreases as much as alveolar PO2
What what will diffusion impairment do to the A-a gradient? increase it ONLY if it is severe
How do you overcome diffusion impairment? oxygen
What does an increased ventilation-perfusion inequality do to the A-a gradient? increases the A-a gradient
Does ventilation-perfusion inequality reduce arterial PO2 under normal conditions? yes
What is the ideal V/Q ration? 1
What happens in shunting? perfusion without ventilation so unoxygenated blood occurs. The V/Q ratio is < 1
What happens with deadspace? ventilation is greater than perfusion. V/Q is > 1
What is the V/Q ration like in the upright lung? it is high at the apex and decreases as it goes to the base
What is normal shunt? some bronchial artery blood and some coronary venous blood
Can Oxygen treatment fix shunting problems? no because ventilation is not the problem and more O2 isn’t going to help with diffusion
What determines the PAO2 ? V/Q ratio
What is alveolar gas composition dependent on? V/Q ratio. If there is not gas exchange O2 will not enter the capillaries
Alveolar composition = ______________ blood composition
Where does most blood go to in the lung? where PAO2 is low
What is PO2 in the lung with an increased V/Q ratio? 150
What is PO2 in the lung with decreased V/Q ratio? 40
Lung units with high V/Q ratios are effective at removing what? CO2
Why does the lung remove CO2 better at high V/Q ratios? CO2 dissociation curve is steeper
If PaCO2 is elevated, what is the problem? hypoventilation
If there is hypoventilation with an increased A-a gradient what is the diagonosis? hypoventilation plus another mechanism
If there is not an increased A-a gradient and hypoventilation what is the diagnosis? hypoventilation alone
If there is not an increased PaCO2 but an increased A-a gradient what can be the diagnosis? shunting or increased V/Q inequality
If there is not an increased PaCO2 but an increased A-a gradient and it is corrected with pure O2, what is the diagnosis? Increased V/Q inequality
If a patient is hypoxic, but does not have an increased A-a gradient nor an increased PaCO2, what is the diagnosis? decreased inspired PO2
What is the diagnosis if a hypoxic patient does not have an increased PaCO2, has an increased A-a gradient and O2 does not correct the problem? shunting.
Created by: tjamrose