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12 Cards in this Set
- Front
- Back
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What is VA (v dot A)?
What is QC (Q dot C)? |
V-ventillation
q- perfusion |
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Why is it ideal for VA/QC to equal 1?
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Otherwise you have overventillation/underventillation/overperfusion/underperfusion
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What are the PO2 and PCO2 in an alveolus that is ventillated but not perfused?
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PO2 = 150 mmHg
PCO2 = 0 These are atmospheric values. Alveoli that are ventillated but not perfused are called alveolar dead space since its a continuation of the airway. |
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What is the PO2 and PCO2 in an alveolus that is perfused but not ventillated?
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This will have a mixed venous composition in the alveoli. PO2 - 40, PCO2- 45.
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What is the V/q ratio in a state of no ventillation. What is the V/q ratio in a state of no perfusion.
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No ventillation has a v/q = 0
No perfusion has a v/q = infinity |
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What is venous admixture?
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Venous admixture occurs when you have a non ventillated alveolus. This means no gas exchange occurs. This deoxygenated volume is called venous admixture, since it mixes with the rest of the arterial blood.
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How does V/Q ratio differ throughout the lung
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V/Q ratios are highest in the upper lung, and decrease as you move down the lung. The average V/Q ratio is less than one because the lower lung has much more mass and therefore more alveoli. Over a large part of our lungs, we have uniform V/Q ratios that are necessary for ideal gas exchange.
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How does emphysema result in abnormal V/Q ratio in the lungs?
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Airways more readily collapse in emphysema -> not uniform filling/time constants -> abnormal V/Qs.
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What is a shunt?
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Shunt is the passage of deoxygenated blood from the venous circulation to the arterial side without picking up O2. Shunt is a problem in ventillation.
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What are some sources of the shunt?
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2 Normal - thebesian circulation perfusing left ventricle, bronchial circulation emptying into pulmonary veins.
2 abnormal - atelectic/collapsed alveoli, congenital defects. |
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How to calculate the fraction of CO that is shunted?
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Qshunt/Qtotal =
(O2 content end capillary- arterial O2 content)/(O2 content end capillary- venous O2 content) |
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At what point can inspiration no longer compensate for mismatches in Va/Qc
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Once the shunt exceeds 50% of cardiac output.
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