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Respiratory Phys 7
WVSOM -- Ventilation - Perfusion Relationships
| Question | Answer |
|---|---|
| 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
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